,transcriber's ,notes ,texts printed in italics in the source document have been transcribed between underscores2 small capitals have been replaced by ,,all ,,capitals4 ,t represents a superscript ,t1 ,t a ,t-shape part rather than the letter ,t4 ,more ,transcriber's ,notes will be found at the end of this text4 ,,rock ,,blasting4 ,,rock ,,blasting4 ,a ,,practical ,,treatise ,,on ,,the ,,means ,,employed ,,in ,,blasting ,,rocks ,,for ,,industrial ,,purposes4 ,,by ,,geo4 ,g4 ,,andr1 ,f4,g4,s41 ,,assoc4 ,,inst4 ,c4,e41 ,,mining ,,civil ,,engineer2 ,,member ,,of ,,the ,,society ,,of ,,engineers4 ,illustration ,,london3 ,e4 ,f4 ,n4 ,,spon1 #df1 ,,charing ,,cross4 ,,new ,,york3 #ddf1 ,,broome ,,street4 #ahgh4 ,,preface4 ,during the past decade1 numerous and great changes have taken place in the system followed and the methods adopted for blasting rocks in industrial operations4 ,the introduction of the machine drill led naturally to these important changes4 ,the system which was suitable to the operations carried on by hand was inefficient under the requirements of machine labour1 and the methods which had been adopted as the most appropriate in the former case were found to be more or less unsuitable in the latter4 ,moreover1 the conditions involved in machine boring are such as render necessary stronger explosive agents than the common gunpowder hitherto in use1 and a more expeditious and effective means of firing them than that afforded by the ordinary fuse4 ,these stronger agents have been found in the nitro-cotton and the nitro-glycerine compounds1 and in the ordinary black powder improved in constitution and fired by detonation2 and this more expeditious and effective means of firing has been discovered in the convenient application of electricity4 ,hence it is that the changes mentioned have been brought about1 and hence1 also1 has arisen a need for a work like the present1 in which the subjects are treated of in detail under the new aspects due to the altered conditions4 ,,geo4 ,g4 ,,andr4 ,,london1 #ag1 ,,king ,,william ,,street1 ,,strand1 ,january #ast1 #ahgh4 ,,contents4 ,,chapter ,i4 ,,the ,,tools1 ,,machines1 ,,and ,,other ,,appliances ,,used ,,in ,,rock ,,blasting4 ,,page ,section ,i4 ,hand-boring ,tools4--,drills4 ,hammers4 ,auxiliary ,tools4 ,sets of ,blasting ,gear #a ,section ,,ii4 ,machine-boring ,tools4--,machine ,rock-drills4 ,borer- bits4 ,drill ,carriages #bc ,section ,,iii4 ,appliances for firing ,blasting ,charges4--,squibs4 ,safety ,fuse4 ,electric ,fuses4 ,cables4 ,detonators4 ,electric ,firing- ,machines #db ,,chapter ,,ii4 ,,explosive ,,agents ,,used ,,in ,,rock ,,blasting4 ,section ,i4 ,phenomena accompanying an ,explosion4--,nature of an ,explosion4 ,heat liberated by an ,explosion4 ,gases generated by an ,explosion4 ,force developed by an ,explosion #fd ,section ,,ii4 ,nature of ,explosive ,agents4--,mechanical ,mixtures4 ,chemical ,compounds #gf ,section ,,iii4 ,relative ,strength of the common ,explosive ,agents4-- ,force developed by ,gunpowder4 ,relative ,force developed by ,gunpowder1 ,gun-cotton1 and ,nitro-,glycerine #hh ,section ,,iv4 ,means of firing the common ,explosive ,agents4--,action of ,heat4 ,detonation #ib ,section ,v4 ,some ,properties of the common ,explosive ,agents4-- ,gunpowder1 ,gun-cotton1 ,dynamite4 ,firing ,temperatures #ig ,section ,,vi4 ,some ,varieties of the ,nitro-,cellulose and the ,nitro- ,glycerine ,compounds4--,nitrated ,gun-cotton4 ,tonite1 or ,cotton- ,powder4 ,schultze's ,powder4 ,lithofracteur4 ,brain's ,powder4 ,cellulose-,dynamite #ajc ,,chapter ,,iii4 ,,the ,,principles ,,of ,,rock ,,blasting4 ,line of least ,resistance4 ,force required to cause ,disruption4 ,conditions of ,disruption4 ,example of a ,heading4 ,economical ,considerations4 ,tamping #ajf ,,chapter ,,iv4 ,,the ,,operations ,,of ,,rock ,,blasting4 ,hand ,boring4--,boring the ,shot-holes4 ,charging the ,shot-holes4 ,firing the ,charges #abh ,machine ,boring4--,boring the ,shot-holes4 ,charging and ,firing4 ,removing the dislodged ,rock4 ,division of ,labour #adb ,examples of ,drivings4--,the ,st4 ,gothard ,tunnel4 ,the ,hoosac ,tunnel4 ,the ,musconetcong ,tunnel4 ,headings at ,marihaye1 ,anzin1 and ,ronchamp #aeg ,,chapter ,v4 ,,subaqueous ,,blasting4 ,preparation of the ,charge4 ,boring under ,water4 ,submarine ,rocks4 ,obstructions in ,water-courses #afd ,,rock ,,blasting4 ,,chapter ,i4 ,,the ,,tools1 ,,machines1 ,,and ,,other ,,appliances ,,used ,,in ,,blasting ,,rocks4 ,,section ,i4--,,hand ,,boring4 ,drills4--,the operations of blasting consist in boring suitable holes in the rock to be dislodged1 in inserting a charge of some explosive compound into the lower portion of these holes1 in filling up1 sometimes1 the remaining portion of the holes with suitable material1 and in exploding the charge4 ,the subjects which naturally first present themselves for consideration are3 the nature1 form1 and construction of the tools1 machines1 and other appliances used4 ,of these tools1 the 8drill0 or 8borer0 constitutes the chief4 ,to understand clearly the action of the rock drill1 we must consider the nature of the substance which has to be perforated4 ,he who has examined the mineral constitution of rocks will have recognised the impossibility of cutting them1 using that term in its ordinary acceptation1 inasmuch as the rock constituents are frequently harder than the material of the tools employed to penetrate them4 ,as a rock cannot be cut1 the only way of removing portions of it is to fracture or to disintegrate it by a blow delivered through the medium of a suitable instrument4 ,each blow so delivered may be made to chip off a small fragment1 and by this means the rock may be gradually worn away4 ,to effect this chipping1 however1 the instrument used must present only a small surface to the rock1 in order to concentrate the force1 and that surface must be bounded by inclined planes or wedge surfaces1 to cause a lateral pressure upon the particles of rock in contact with them4 ,in other words1 the instrument must be provided with an edge similar to that possessed by an ordinary cutting tool4 ,the conditions under which the instrument is worked are obviously such that this edge will be rapidly worn down by attrition from the hard rock material1 and by fracture4 ,to withstand these destructive actions1 two qualities are requisite in the material of which the instrument is composed1 namely1 hardness and toughness4 ,thus there are three important conditions concurring to determine the nature and the form of a cutting tool to be used in rock boring--#a1 a necessity for a cutting edge2 #b1 a necessity for a frequent renewal of that edge2 and #c1 a necessity for the qualities of hardness and toughness in the material of the tool4 ,in very hard rock1 a few minutes of work suffice to destroy the cutting edge1 and then the tool has to be returned to the smithy to be re-sharpened4 ,hence it is manifest that the form of the edge should not be one that is difficult to produce1 since1 were it so1 much time would be consumed in the labour of re-sharpening4 ,experience has shown that the foregoing conditions are most fully satisfied in the steel rod terminating in a simple chisel edge1 now universally adopted4 ,this form of drill is exhibited in ,fig4 #a1 which represents a common 8jumper0 borer4 ,it consists of a rod terminating at each end in a chisel edge1 and having a swell1 technically described as the 8bead10 between the extremities to give it weight4 ,the bead divides the jumper into two unequal portions1 each of which constitutes a chisel bit1 with its shank or 8stock40 ,the shorter stock is used while the hole is shallow1 and the longer one to continue it to a greater depth4 ,illustration3 ,,fig4 #a4 ,illustration3 ,,fig4 #b4 ,illustration3 ,,fig4 #c4 ,with the jumper1 the blow is obtained from the direct impact of the falling tool4 ,the mode of using the instrument is to lift it with both hands to a height of about a foot1 and then to let it drop4 ,in lifting the jumper1 care is taken to turn it partially round1 that the edge may not fall twice in the same place4 ,by this means1 the edge is made to act most favourably in chipping away the rock1 and the hole is kept fairly circular4 ,so long as the holes are required to be bored vertically downwards1 the jumper is a convenient and very efficient tool1 and hence in open quarrying operations1 it is very commonly employed4 ,but in mining1 the shot-holes are more often required to be bored in some other direction1 or1 as it is termed1 8at an angle20 that is1 at an angle with the vertical4 ,or it may be that a shot-hole is required to be bored vertically upward4 ,it is obvious that in any one of these directions the jumper is useless4 ,to meet the requirements of such cases1 recourse is had to the hammer wherewith to deliver the blow1 and the drill is constructed to be used with the hammer4 ,we have a suitable form of tool for application in this wise when we cut out the bead of the jumper and leave the ends flat for a striking face1 as shown in ,figs4 #b and #c4 ,the form of the two chisels thus obtained is that adopted for the ordinary rock drill4 ,it will be understood from these descriptions that a rock drill consists of the chisel edge or bit1 the stock1 and the striking face4 ,formerly drills were made of wrought iron1 and steeled at each end to form the bit and the striking face4 ,now they are commonly made of cast steel1 which is supplied for that purpose in octagonal bars of the requisite diameter4 ,the advantages offered by steel stocks are numerous4 ,the superior solidity of texture of that material renders it capable of transmitting the force of a blow more effectively than iron4 ,being stronger than the latter material1 a smaller diameter of stock1 and1 consequently1 a less weight1 are sufficient4 ,this circumstance also tends to increase the effect of the blow by diminishing the mass through which it is transmitted4 ,on the other hand1 a steel stock is more easily broken than one of iron4 ,the cutting edge of a drill demands careful consideration4 ,to enable the tool to free itself readily in the bore-hole1 and also to avoid introducing unnecessary weight into the stock1 the bit is made wider than the latter2 the difference in width may be as much as #a inch4 ,it is evident that in hard rock1 the liability of the edge to fracture increases as the difference of width4 ,the edge of the drill may be straight or slightly curved4 ,the straight edge cuts its way somewhat more freely than the curved1 but it is weaker at the corners than the latter1 a circumstance that renders it less suitable for very hard rock4 ,it is also slightly more difficult to forge4 ,the width of the bit varies1 according to the size of the hole required1 from #a inch to #b inches4 ,figs4 #d1 #e1 and #f show the straight and the curved bits1 and the angles of the cutting edges for use in rock4 ,illustration3 ,,fig4 #d4 ,illustration3 ,,fig4 #e4 ,illustration3 ,,fig4 #f4 ,the stock is octagonal in section2 it is made in lengths varying from #bj inches to #db inches4 ,the shorter the stock the more effectively does it transmit the force of the blow1 and therefore it is made as short as possible4 ,for this reason1 several lengths are employed in boring a shot-hole1 the shortest being used at the commencement of the hole1 a longer one to continue the depth1 and a still longer one1 sometimes1 to complete it4 ,to ensure the longer drills working freely in the hole1 the width of the bit should be very slightly reduced in each length4 ,it has already been remarked that the diameter of the stock is less than the width of the bit2 this difference may be greater in coal drills than in rock or 8stone0 drills2 a common difference in the latter is of an inch for the longer4 ,the following proportions may be taken as the average adopted3-- ------------------ ,width of ,diameter the ,bit4 of the ,stock4 ------------------ #a inch inch #a #a #a #a #a #a #b inches#a #b #a #b #a ------------------ ,the striking face of the drill should be flat4 ,the diameter of the face is less than that of the stock in all but the smallest sizes1 the difference being made by drawing in the striking end4 ,the amount of reduction is greater for the largest diameters2 that of the striking face being rarely more than one-eighth of an inch4 ,the making and re-sharpening of rock drills constitute an extremely important part of the labour of the mine smith4 ,the frequent use of the drill1 and its rapid wear1 necessitate a daily amount of work of no trifling proportions1 and the judgment and skill required in proper tempering render some degree of intelligence in the workman indispensable2 indeed1 so much depends upon the smith whose duty it is to repair the miners' tools1 that no pains should be spared to obtain a man capable of fulfilling that duty in the most efficient manner possible4 ,when the borer-steel bars are supplied to the smith1 he cuts them up1 as required1 into the desired lengths4 ,to form the bit1 the end of the bar is heated and flattened out by hammering to a width a little greater than the diameter of the hole to be bored4 ,the cutting edge is then hammered up with a light hammer to the requisite angle1 and the corners beaten in to give the exact diameter of the bore-hole intended4 ,as the drills are made in sets1 the longer stocks will have a bit slightly narrower than the shorter ones1 for reasons already given4 ,the edge is subsequently touched up with a file4 ,in performing these operations1 heavy hammering should be avoided1 as well as high heats1 and care should be taken in making the heat that the steel should be well covered with coal1 and far enough removed from the tuyere to be protected from the 8raw0 air4 ,overheated or 8burned0 steel is liable to fly1 and drills so injured are useless until the burned portion has been cut away4 ,illustration3 ,,fig4 #g4 ,illustration3 ,,fig4 #h4 ,illustration3 ,,fig4 #i4 ,both in making and in re-sharpening drills1 great care is required to form the cutting edge evenly1 and of the full form and dimensions4 ,if the corners get hammered in1 as shown in ,fig4 #g1 they are said to be 8nipped10 and the tool will not free itself in cutting4 ,when a depression of the straight1 or the curved1 line forming the edge occurs1 as shown in ,fig4 #h1 the bit is said to be 8backward10 and when one of the corners is too far back1 as in ,fig4 #i1 it is spoken of as 8odd-cornered40 ,when either of these defects exist--and they are unfortunately common--not only does the bit work less effectively on the rock1 but the force of the blow is thrown upon a portion only of the edge1 which1 being thereby overstrained1 is liable to fracture4 ,the hardening and tempering of steel is a matter requiring careful study and observation4 ,it is a well-known fact that a sudden and great reduction of temperature causes a notable increase of hardness in the metal4 ,the reason of this phenomenon is not understood1 but it is certain that it is in some way dependent upon the presence of carbon4 ,the degree of hardness imparted to steel by this means depends upon the amount of the reduction of the temperature1 and the proportion of carbon present in the metal1 highly carburetted steel being capable of hardening to a higher degree1 under the same conditions1 than steel containing less carbon4 ,thus1 for steel of the same quality1 the wider the range of temperature the higher is the degree of hardness4 ,but here we encounter another condition1 which limits the degree of hardness practically attainable4 ,the change which takes place among the molecules of the metal in consequence of the change of temperature causes internal strains1 and thereby puts portions in a state of unequal tension4 ,this state renders the strained parts liable to yield when an additional strain is thrown upon them while the tool is in use2 in other words1 the brittleness of the steel increases with its hardness4 ,here again the proportion of carbon present comes into play1 and it must be borne in mind that for equal degrees of hardness the steel which contains the least carbon will be the most brittle4 ,in hardening borer-steel1 which has to combine as far as possible the qualities of hardness and toughness1 this matter is one deserving careful attention4 ,it is a remarkable fact1 and one of considerable practical value1 that when oil is employed as the cooling medium instead of water1 the toughness of steel is enormously increased4 ,the tempering of steel1 which is a phenomenon of a similar character to that of hardening1 also claims careful consideration4 ,when a bright surface of steel is subjected to heat1 a series of colours is produced1 which follow each other in a regular order as the temperature increases4 ,this order is as follows3 pale yellow1 straw yellow1 golden yellow1 brown1 brown and purple mingled1 purple1 light blue1 full clear blue1 and dark blue4 ,experience has shown that some one of these colours is more suitable than the rest for certain kinds of tools and certain conditions of working4 ,the selection of the proper colour constitutes a subject for the exercise of judgment and skill on the part of the smith4 ,for rock drills1 straw colour is generally the most suitable when the work is in very hard rock1 and light blue when the rock is only of moderate hardness4 ,the processes of hardening and tempering drills are as follows3 ,when the edge of the bit has been formed in the manner already described1 from #c to #d inches of the end is heated to cherry redness1 and dipped in cold water to a depth of about an inch to harden it4 ,while in the water1 the bit should be moved slightly up and down1 for1 were this neglected1 the hardness would terminate abruptly1 and the bit would be very liable to fracture along the line corresponding with the surface of the water4 ,in cold weather1 the water should be slightly warmed1 by immersing a piece of hot iron in it1 before dipping the steel4 ,when a sufficient degree of hardness has been attained1 the remainder of the hot portion is immersed until the heat is reduced sufficiently for tempering4 ,at this stage it is withdrawn1 and the colours carefully watched for4 ,the heat which is left in the stock will pass down to the edge of the bit1 and as the temperature increases in that part the colours will appear in regular succession upon the filed surface of the edge4 ,when the proper hue appears1 the whole drill is plunged into the water and left there till cold1 when the tempering is complete4 ,when the edge is curved or 8bowed10 the colours will reach the corners sooner than the middle of the bit4 ,this tendency must be checked by dipping the corners in the water1 for otherwise the edge will not be of equal hardness throughout4 ,as the colour can be best observed in the dark1 it is a good plan to darken that portion of the smithy in which tempering is being carried on4 ,the degree of temper required depends upon the quality of the steel and the nature of the work to be performed4 ,the larger the proportion of carbon present in the metal1 the lower must be the temper4 ,also the state of the blunted edges1 whether battered or fractured1 will show what degree of hardness it is desirable to produce4 ,from inattention to these matters1 good steel is not unfrequently condemned as unsuitable4 ,to form the striking face1 the end of the stock is heated to a dull red1 and drawn out by a hammer to form a conical head4 ,the extremity is then flattened to form a face from inch to #a inch in diameter4 ,this head is then annealed to a degree that will combine considerable toughness with hardness4 ,the constant blows to which the head is subjected tend to wear it down very rapidly4 ,there is great difference in the lasting qualities of steel in this respect2 some drills will wear away more quickly at the striking than at the bit end4 ,a smith will1 with the assistance of a striker1 sharpen and temper about thirty single-hand drills of medium size in an hour1 or twenty double-hand drills of medium size in the same time4 ,of course1 much will depend on the degree of bluntness in the cutting edge2 but assuming the drills to be sent up only moderately blunted1 this may be taken as a fair average of the work of two men4 ,it will be evident from the foregoing remarks1 that to enable a drill to stand properly it must be made of good material1 be skilfully tempered in the smithy1 and provided with a cutting edge having an angle and a shape suited to the character of the rock in which it is used4 ,to these conditions1 may be added another1 namely1 proper handling2 for if the drill be carelessly turned in the hole so as to bring all the work upon a portion only of the cutting edge1 or unskilfully struck by the sledge1 fracture or blunting will speedily result4 ,improper handling often destroys the edge in the first five minutes of using4 ,drills1 as before remarked1 are used in sets of different lengths4 ,the sets may be intended for use by one man or by two4 ,in the former case1 the sets are described as 8single-hand0 sets1 and they contain a hammer for striking the drills2 in the latter case1 the sets are spoken of as 8double-handed10 and they contain a sledge instead of a hammer for striking4 ,it may appear at first sight that there is a waste of power in employing two men1 or1 as it is termed1 the double set1 for that two men cannot bore twice as fast as one4 ,this rate of speed can1 however1 be obtained1 and is due less to the greater effectiveness of the stroke than to the fact that two men can1 by repeatedly changing places with each other1 keep up almost without intermission a succession of blows for an indefinite length of time2 whereas1 with the single set1 the man is continually obliged to cease for rest4 ,hammers4--,to deliver the blow upon a rock drill1 hammers and sledges are used4 ,the distinction between a hammer and a sledge is founded on dimensions only3 the hammer being intended for use in one hand1 is made comparatively light and is furnished with a short handle1 while the sledge1 being intended for use in both hands1 is furnished with a much longer handle and is made heavier4 ,the striking face of the blasting sledge should be flat1 to enable the striker to deliver a direct blow with certainty upon the head of the drill2 and to facilitate the directing of the blow1 as well as to increase its effect1 the mass of metal composing the head should be concentrated within a short length4 ,to cause the sledge to fly off from the head of the drill in the case of a false blow being struck1 and thereby to prevent it from striking the hand of the man who holds the drill1 the edges of the striking face should be chamfered or bevelled down till the diameter is reduced by nearly one-half4 ,this requirement is1 however1 but seldom provided for4 ,illustration3 ,,fig4 #aj4 ,illustration3 ,,fig4 #aa4 ,illustration3 ,,fig4 #ab4 ,illustration3 ,,fig4 #ac4 ,the head of a sledge is of iron2 it consists of a pierced central portion called the 8eye10 and two shanks or 8stumps10 the steeled ends of which form the striking faces or 8panes40 ,the form of the head varies in different localities1 but whatever the variations may be1 the form may be classed under one of four types or 8patterns40 ,a very common form is that shown in ,fig4 #aj and known as the 8bully0 pattern4 ,by varying the width1 as shown in ,fig4 #aa1 we obtain the 8broad bully10 the former being called for the sake of distinction the 8narrow0 bully4 ,another common form is the 8pointing0 pattern1 represented in ,fig4 #ab4 ,the form shown in ,fig4 #ac is designated as the 8bloat0 pattern2 and that given in ,fig4 #ad the 8plug0 pattern4 ,each of these forms possesses peculiar merits which renders it more suitable for certain uses than the others4 ,the same forms are used for hammers4 ,the eye is generally made oval in shape1 but sometimes1 especially with the bloat pattern1 it is made circular1 as shown in ,fig4 #ac4 ,the weight of a sledge head may vary from #e lb4 to #aj lb41 but a common and convenient weight is #g lb4 ,the length of the helve varies from #bj inches to #cj inches2 a common length for blasting sledges is #bd inches4 ,the average weight of hammer heads is about #c lb41 and the average length of the helve #aj inches4 ,illustration3 ,,fig4 #ad4 ,illustration3 ,,fig4 #ae4 ,fig4 #ae represents a blasting sledge used in ,south ,wales4 ,the stumps are octagonal in section1 and spring from a square block in the centre4 ,the panes or striking faces1 however1 are circular and flat4 ,the length of the head is #h inches1 and that of the helve #bg inches1 and the weight of the tool complete #g lb4 ,illustration3 ,,fig4 #af4 ,fig4 #af represents a blasting sledge used in ,north ,wales4 ,the central block is an irregular octagon in section1 formed by slightly chamfering the angles of a square section1 and the stumps are chamfered down to form a regular octagon at the panes1 which are flat4 ,the length of the head is #g inches1 and that of the helve #bb inches1 and the weight of the tool complete #f lb4 #g oz4 ,illustration3 ,,fig4 #ag4 ,the sledges used in the north of ,england have shorter heads1 and are lighter than the foregoing4 ,fig4 #ag represents one of these blasting sledges4 ,the head is nearly square in section at the centre1 and the panes are flat4 ,the length of the head is #e inches1 and that of the helve #bd inches1 and the weight of the sledge complete #d lb4 #ad oz4 ,auxiliary ,tools4--,besides the drill and the hammer1 other tools are needed in preparing the hole for the blasting charge4 ,if the bore-hole is inclined downwards1 the dbris or 8bore-meal0 made by the drill remains on the bottom of the hole1 where it is converted into mud or 8sludge0 by the water there present4 ,this sludge has to be removed as the work progresses1 to keep the rock exposed to the action of the drill4 ,the removal of the sludge is effected by a simple tool called a 8scraper40 ,it consists of a rod of iron from inch to inch in diameter1 and of sufficient length to reach the bottom of the bore-hole4 ,one end of the rod is flattened out on the anvil and made circular in form1 and then turned up at right angles to the stem4 ,the disc thus formed must be less in diameter than the bore-hole1 to allow it to pass readily down4 ,when inserted in the hole1 the scraper is turned round while it is being pressed to the bottom2 on withdrawing the instrument1 the sludge is brought up upon the disc4 ,the operation1 two or three times repeated1 is sufficient to clear the bore-hole4 ,the other end of the scraper is sometimes made to terminate in a ring for convenience in handling1 as shown in ,fig4 #ah4 ,instead of the ring1 however1 at one end1 a disc may be made at each end1 as shown in ,fig4 #ai1 the discs in this case being of different diameter1 to render the scraper suitable for different size bore-holes4 ,sometimes the scraper is made to terminate in a spiral hook or 8drag-twist10 as represented in ,fig4 #bj4 ,the use of the drag is to thoroughly cleanse the hole before inserting the charge4 ,a wisp of hay is pushed down the hole1 and the drag end of the scraper introduced after it1 and turned round till it has become firmly entangled4 ,the withdrawal of the hay by the drag wipes the bore-hole clean4 ,instead of the twist drag1 the 8loop0 drag is frequently employed4 ,this consists of a loop or eye1 through which a piece of rag or tow is passed4 ,the rag or tow is used for the same purpose as the hay1 namely1 to thoroughly cleanse and dry the bore-hole previous to the introduction of the charge4 ,very frequently the 8swab-stick0 is used instead of the scraper to clear out the bore-hole4 ,this is simply a deal rod bruised at one end by blows with a hammer until the fibres separate to form a kind of stumpy brush or 8swab40 ,when this is pushed down the hole1 the sludge passes up around and between the fibres1 which are then spread out by being pressed against the bottom of the hole4 ,on withdrawing the swab1 the sludge is brought out with it4 ,illustration3 ,,fig4 #ah4 ,illustration3 ,,fig4 #ai4 ,illustration3 ,,fig4 #bj4 ,when the charge has been placed in the bore-hole1 and the fuse laid to it1 the hole needs to be tamped1 that is1 the portion above the charge has to be filled up with some suitable substance4 ,for this purpose1 a 8rammer10 8stemmer10 or 8tamping iron10 as the instrument is variously called1 is required4 ,this instrument is illustrated in ,fig4 #ba4 ,it consists of a metal bar1 the tamping end of which is grooved to receive the fuse lying against the side of the bore-hole4 ,the other end is flat1 to afford a pressing surface for the hand1 or a striking face for the hammer when the latter is needed4 ,to prevent the danger of accidental ignition from sparks caused by the friction of the metal against silicious substances1 the employment of iron stemmers has been prohibited by law4 ,they are usually made of copper or phosphor-bronze1 the latter substance being more resisting than the former4 ,illustration3 ,,fig4 #ba4 ,illustration3 ,,fig4 #bb4 ,illustration3 ,,fig4 #bc4 ,sometimes in wet ground it becomes necessary to shut back the water from the bore-hole before introducing the charge of gunpowder4 ,this happens very frequently in shaft sinking4 ,the method employed in such cases is to force clay into the interstices through which the water enters4 ,the instrument used for this purpose is the 8claying-iron0 or 8bull10 represented in ,fig4 #bb4 ,it consists of a round bar of iron1 called the stock or shaft1 a little smaller in diameter than the bore-hole1 and a thicker portion1 called the head or poll1 terminating in a striking face4 ,the lower end of the shaft is pointed1 to enable it to penetrate the clay1 and the head is pierced by a hole about an inch in diameter to receive a lever4 ,clay in a plastic state having been put into the bore-hole1 the bull is inserted and driven down by blows with the sledge4 ,as the shaft forces its way down1 the clay is driven into the joints and crevices of the rock on all sides4 ,to withdraw the bull1 a bar of iron is placed in the eye and used as a lever to turn it round to loosen it2 the rod is then taken by both hands and the bull lifted out4 ,to allow the bull to be withdrawn more readily1 the shaft should be made with a slight taper and kept perfectly smooth4 ,as the bull is subjected to a good deal of heavy hammering on the head1 the latter part should be made stout4 ,this tool1 which should be considered as an extra instrument rather than as an essential part of a blasting set1 is a very serviceable one1 and should always be at hand in wet ground when loose gunpowder is employed4 ,another instrument of this auxiliary character is the beche1 ,fig4 #bc1 used for extracting a broken drill4 ,it consists of an iron rod of nearly the diameter of the bore-hole1 and hollow at the lower end4 ,the form of the aperture is slightly conical1 so that the lower end may easily pass over the broken stock of the drill1 and1 on being pressed down with some force1 may grasp the stock in the higher portion of the aperture with sufficient firmness to allow of the two being raised together4 ,when only a portion of the bit remains in the hole1 it may often be extracted by means of the drag-twist end of the scraper1 or the swab-stick may be driven down upon the broken portion1 and latter withdrawn with the swab4 ,sets of ,blasting ,gear4--,on ,plates ,i41 ,,ii41 and ,,iii41 will be found three sets of blasting gear2 a set of coal-blasting gear2 a set of single-hand stone-blasting gear2 and a set of double-hand stone-blasting gear4 ,in the first set1 the drill1 shown in ,fig4 #a1 is #bb inches in length2 the cutting edge is straight and #a inch wide1 and the weight is #b lb4 ,the other drill1 ,fig4 #b1 is #db inches in length2 it has a straight cutting edge #a_/ inch wide1 and weighs #d lb4 #aj oz4 ,the hammer used in this set and shown in ,fig4 #c weighs #b lb4 #ad oz42 the length of the head is #d inches1 and that of the handle #g inches4 ,in the second or single-hand stone set1 the shorter drill1 ,fig4 #f1 ,plate ,,ii41 is #bb inches in length2 the cutting edge is strongly curved1 and is #a inch in width1 and the weight is #c lb4 #aj oz4 ,the longer drill1 ,fig4 #g1 is #cf inches in length2 the width of the cutting edge1 which is curved as in the shorter drill1 is #a_/ inch1 and the weight is #f lb4 #e oz4 ,the hammer used with this set1 and represented in ,fig4 #h1 weighs #c lb4 #f oz42 the length of the head is #e inches1 and that of the handle #aj inches4 ,in the third or double-hand stone set1 ,plate ,,iii41 the first or shortest drill1 ,fig4 #ab1 is #ah inches in length1 #a inch wide on the cutting edge1 and weighs #d lb4 ,the second drill1 ,fig4 #ac1 is #bg inches in length1 #a_/ wide on the cutting edge1 and weighs #f lb4 ,the third or longest drill1 ,fig4 #ad1 is #dj inches in length1 #a inch wide on the cutting edge1 and weighs #i lb4 ,the cutting edges of all these drills are strongly curved as in the preceding set4 ,the sledge used with this set1 and represented in ,fig4 #ae1 weighs about #e lb4 ,,section ,,ii4--,,machine ,,boring4 ,machine ,rock-,drills4--,the most remarkable advance1 which in recent1 or perhaps in any1 times has been made in the practice of mining consists in the substitution of machine for hand labour in rock boring4 ,the importance of this change is obvious1 and very great4 ,not only is the miner relieved thereby of the labour of boring1 but the speed with which the shot-holes may be bored is increased a hundredfold4 ,this gain of speed offers many practical advantages4 ,the ability to sink a shaft or to drive a heading rapidly may ensure the success of an undertaking1 and save indirectly the expenditure of large sums of money2 and1 in all cases1 it allows the time spent in preparatory work to be materially shortened4 ,indeed1 it would be difficult to over-estimate the magnitude of the advantage accruing from the increased rate of progress due to the substitution of machine power for hand labour1 and in the future we may expect to see its application greatly extended4 ,in making this substitution1 numerous difficulties have had to be overcome1 and in encountering these many failures have had to be recorded4 ,but it must now be conceded by the most prejudiced that rock-boring machines have successfully passed through what may be described as the tentative stage of their existence1 and have taken a foremost place among the mechanical appliances which experience has shown to be capable of effectually performing the work required of them4 ,in the author's work on #8,mining ,engineering1' the requirements of a rock drill will be found fully discussed1 and the principles and the construction of the most important machines now in use carefully explained and described4 ,in the present work1 only one example can be given4 ,machine drills penetrate rock in the same way as the ordinary hand drills already described1 namely1 by means of a percussive action4 ,the cutting tool is in most cases attached directly to the piston rod1 with which it consequently reciprocates4 ,thus the piston with its rod is made to constitute a portion of the cutting tool1 and the blow is then given by the direct action of the steam1 or the compressed air1 upon the tool4 ,as no work is done upon the rock by the back stroke of the piston1 the area of the forward side is reduced to the dimensions necessary only to lift the piston1 and to overcome the resistance due to the friction of the tool in the bore-hole4 ,the piston is made to admit steam or air into the cylinder1 and to cut off the supply1 and to open the exhaust1 as required1 by means of tappet valves1 or other suitable devices2 and provision is made to allow1 within certain limits1 a variation in the length of the stroke4 ,during a portion of the stroke1 means are brought into action to cause the piston to rotate to some extent1 for the purposes that have been already explained4 ,to keep the cutting edge of the tool up to its work1 the whole machine is moved forward as the rock is cut away4 ,this forward or 8feed0 motion is usually given by hand1 but in some cases it is communicated automatically4 ,the machine is supported upon a stand or framing which varies in form according to the situation in which it is to be used4 ,this support is in all cases constructed to allow of the feed motion taking place1 and also of the cutting tool being directed at any angle4 ,the support for a rock drill constitutes an indispensable and a very important adjunct to the machine1 for upon the suitability of its form1 material1 and construction1 the efficiency of the machine will largely depend4 ,the foregoing is a general description of the construction and mode of action of percussive rock-drills4 ,the numerous varieties now in use differ from each other rather in the details of their construction than in the principles of their action1 and the importance of the difference is1 of course1 dependent upon that of the details4 ,it is but just to remark here that the first really practical solution of the rock-drilling problem is due to ,m4 ,sommeiller1 whose machine was employed in excavating the ,mont ,cenis tunnel4 ,the ,darlington ,drill4--,the machine which1 in ,england1 has stood the test of experience most satisfactorily1 and which1 consequently1 is surely working itself into general favour in this country1 and also in some of the important mining districts of the ,continent1 is the invention of ,john ,darlington1 and is known as the 8,darlington drill40 ,this drill is remarkable as the attainment of the highest degree of simplicity of parts possible in a machine4 ,the valve gear of a machine drill is especially liable to derangement4 ,it must necessarily consist of several parts1 and these parts must as necessarily be of a somewhat fragile character4 ,besides this1 when actuated by the piston through the intervention of tappets1 the violence of the blow delivered at each stroke is such as to rapidly destroy the parts4 ,in some machines1 the force of these blows and their destructive tendency have been reduced to a minimum2 but when every means of remedying the evil has been employed1 there remains a large amount of inevitable wear and tear1 and a liability to failure from fracture or displacement exists in a greater or less degree4 ,moreover1 as these effects are greatly intensified by increasing the velocity of the piston1 it becomes at least undesirable to use a high piston speed4 ,to remedy these defects1 which are inherent in the system1 ,darlington proposed to remove altogether the necessity for a valve gear by radically changing the mode of admitting the motor fluid to the cylinder4 ,this proposal he has realized in the machine which is illustrated on ,plate ,,iv4 ,the ,darlington rock-drill consists essentially of only two parts3 the cylinder ,a1 ,figs4 #bj and #ba1 with its cover2 and the piston ,b1 with its rod4 ,the cover1 when bolted on1 forms a part of the cylinder2 the piston rod is cast solid with the piston1 and is made sufficiently large at its outer end to receive the tool4 ,these two parts constitute an engine1 and with less than one fixed and one moving part it is obviously impossible to develop power in a machine by the action of an elastic fluid4 ,the piston itself is made to do the work of a valve in the following manner3 ,the annular space affording the area for pressure on the fore part of the piston gives a much smaller extent of surface than that afforded by the diameter of the cylinder1 as shown in the drawing2 and it is obvious that by increasing or diminishing the diameter of the piston rod1 the area for pressure on the one side of the piston may be made to bear any desired proportion to that on the other side4 ,the inlet aperture1 or port ,c1 being in constant communication with the interior of the cylinder1 the pressure of the fluid is always acting upon the front of the piston1 consequently when there is no pressure upon the other side1 the piston will be forced backward in the cylinder4 ,during this backward motion1 the piston first covers the exhaust port ,d1 and then uncovers the equilibrium port ,e1 by means of which communication is established between the front and back ends of the cylinder1 and1 consequently1 the fluid is made to act upon both sides of the piston4 ,the area of the back face of the piston being greater than that of the front face by the extent occupied by the piston rod1 the pressure upon the former first acts to arrest the backward motion of the piston1 which1 by its considerable weight and high velocity1 has acquired a large momentum1 and then to produce a forward motion1 the propelling force being dependent for its amount upon the difference of area on the two sides of the piston4 ,as the piston passes down1 it cuts off the steam from the back part of the cylinder and opens the exhaust4 ,the length or thickness of the piston is such that the exhaust port ,d is never open to its front side1 but1 in the forward stroke1 it is opened almost immediately after the equilibrium port is closed1 and nearly at the time of striking the blow4 ,it will be observed that the quantity of fluid expended is only that which passes over to the back face of the piston1 since that which is used to effect the return stroke is not discharged4 ,the means employed to give a rotary motion to the tool are deserving of special attention1 as being simple in design1 effective in action1 and well situate within the cylinder4 ,these means consist of a spiral or rifled bar ,h1 having three grooves1 and being fitted at its head with a ratchet wheel ,g1 recessed into the cover of the cylinder4 ,two detents ,j1 ,j1 ,fig4 #bb1 also recessed into the cover1 are made to fall into the teeth of the ratchet wheel by spiral springs4 ,these springs may1 in case of breakage1 be immediately renewed without removing the cover4 ,it will be observed that this arrangement of the wheel and the detents allow the spiral bar ,h to turn freely in one direction1 while it prevents it from turning in the contrary direction4 ,the spiral bar drops into a long recess in the piston1 which is fitted with a steel nut made to accurately fit the grooves of the spiral4 ,hence the piston1 during its instroke1 is forced to turn upon the bar2 but1 during its outstroke1 it turns the bar1 the latter being free to move in the direction in which the straight outstroke of the piston tends to rotate it4 ,thus the piston1 and with it the tool1 assumes a new position after each stroke4 ,the mode of fixing the cutting tool to the piston rod is a matter deserving some attention4 ,as the tool has to be changed more than once during the progress of a bore-hole1 it is important that the change should be accomplished in as short a time as possible2 and as the vibration of the machine and the strain upon the tool are necessarily great1 it is equally important that the tool be firmly held4 ,it is also desirable that the mode of fixing the tool shall not require a shoulder upon the latter1 a slot in it1 or any peculiarity of form difficult to be made in the smithy4 ,the ,darlington machine fulfils the requirements of expedition in fixing1 firmness of retention1 and simplicity of form most satisfactorily4 ,the means and the method are the following3 ,the outer end of the rod or holder is first flattened to afford a seat for the nut1 as shown in ,figs4 #ba and #be4 ,the slot is then cut and fitted tightly with a piece of steel ,k forged of the required shape for the clamp1 and the holder is afterwards bored to receive the tool while the clamp is in place4 ,this clamp ,k is then taken out1 its fittings eased a little1 and its end screwed and fitted with a nut4 ,when returned to its place in the holder1 the clamp1 in consequence of the easing1 can be easily drawn tight against the tool1 by which means it is firmly held in position4 ,the shank of the tool is turned to fit the hole easily1 and the end of it is made hemispherical to fit the bottom of the hole1 upon which the force of the reaction of the blow is received4 ,it would seem impossible to attain a higher degree of simplicity of form1 or to construct a machine with fewer parts4 ,the absence of a valve or striking gear of any kind ensures the utmost attainable degree of durability1 and allows a high piston speed to be adopted without risk or injury4 ,as the piston controls its own motion1 there is no liability to strike against the cylinder cover4 ,the stroke may be varied in length from half an inch to four inches1 and as the machine will work effectively with a pressure of #aj lb4 to the inch1 holes may be started with the greatest ease4 ,with a pressure of #dj lb41 the machine makes #ajjj blows a minute1 a speed that may be attained without causing undue strains or vibration4 ,this alone constitutes a very great advantage4 ,it must indeed be conceded that an unprejudiced consideration of the merits of this drill shows it to be admirably adapted to the work required of it4 ,borer-,bits4--,the form and the dimensions of the cutting tools1 variously described as 8drills10 8borers10 and 8bits10 used with machine rock-perforators are matters of great practical importance4 ,the dimensions are determined mainly by two conditions1 namely1 the necessity for sufficient strength in the shank of the tool1 and the necessity for sufficient space between the shank and the sides of the hole to allow the dbris to escape4 ,experience has shown that the latter condition is best fulfilled when the distance between the sides of the hole and the shank of the tool is from _/ inch to inch1 regard being had to the former condition4 ,the form of the cutting edge is determined by several conditions1 some of which have been already discussed in relation to hand drills4 ,the form first adopted was naturally that possessed by the hand drill1 namely1 the chisel edge4 ,to increase the useful effect of the blow1 the cutting edge was subsequently doubled1 the bit being formed of two chisel edges crossing each other at right angles4 ,this bit1 which from its form was called the 8cross0 bit1 was found to penetrate the rock more rapidly than the straight or chisel bit4 ,the gain in speed was very marked at the commencement of the hole2 but it diminished gradually as the hole progressed in depth1 owing to the difficulty with which the dbris escaped4 ,to remedy this defect1 the cutting edges were next made to cross each other obliquely1 so as to form the letter ,x4 ,in this way1 the two chisel edges were retained1 while the breadth of the bit was considerably reduced4 ,this form1 described as the ,x bit1 cleared the hole much more effectively than the cross1 but not in a manner that was altogether satisfactory4 ,another modification of the form was1 therefore1 made1 and this time that of the ,z was adopted1 the upper and the lower portions of which were arcs of circles struck from the centre of the bit in the direction contrary to that of the rotation4 ,this form of tool1 which is known as the ,z bit1 readily cleared itself of the dbris4 ,but besides this advantage1 it was found to possess others of an important character4 ,with the chisel-edge forms1 the corners of the bit were rapidly worn off by friction against the sides of the hole4 ,with the ,z form1 this wearing no longer occurred1 by reason of the large surface exposed to friction4 ,another advantage of the ,z form of bit lies in its tendency to bore the hole truly circular4 ,generally then1 it may be stated that this form satisfies most fully the determining conditions4 ,the form of bit1 however1 that is most suitable in a given case will1 in some degree1 be determined by particular circumstances4 ,of these1 the nature and the character of the rock will operate most strongly to influence the choice4 ,thus the cross bit will generally be found the most suitable in fissured rock1 while the single chisel edge may be used with advantage in rock of a very solid and hard character4 ,indeed1 on the judicious selection of the most suitable form of cutting edge1 the success of machine boring largely depends4 ,the chisel bit1 the cross bit1 the ,x bit1 and the ,z bit1 are shown in ,figs4 #bd to #bg4 ,illustration3 ,,fig4 #bd4 ,illustration3 ,,fig4 #be4 ,illustration3 ,,fig4 #bf4 ,illustration3 ,,fig4 #bg4 ,the sharpening of bits of a form other than that of the chisel is done by means of 8swages40 ,the tempering is effected in the way already described in reference to hand drills4 ,as in the latter case1 the degree of temper must be suited to the hardness of the rocks to be penetrated4 ,generally the straw colour will be found to be the best degree4 ,it is a remarkable fact that the wear of the cutting edge of a machine drill is1 for a given length of boring1 five or six times less than that of a hand drill4 ,steel of the best quality should always be used4 ,as in the case of hand boring1 each successive length of drill must diminish slightly in the width of its cutting edge2 a diminution of about _/ inch may be considered sufficient4 ,care should1 however1 be taken to ensure the proper dimensions being given to the edge1 and it will be found advantageous to have at hand an accurate gauge through which the tool may be passed previously to its being fixed to the machine4 ,it is important that the tool be truly 8centred10 that is1 the centres of the edge of the bit1 of the shank1 and of the piston rod1 should be perfectly coincident4 ,rock-,drill ,supports4--,a machine rock-drill may satisfy every requirement1 and yet1 by reason of the defective character of the support to which it is attached1 it may be unsuitable to the work required of it4 ,hence it becomes desirable to carefully study the design and construction of a drill support1 and to consider the requirements which it is needful to fulfil4 ,assuming the necessity for a high degree of strength and rigidity in the support1 a primary condition is that it shall allow the machine to be readily adjusted to any angle1 so that the holes may be bored in the direction and with the inclination required4 ,when this requirement is not fulfilled1 the machine is placed1 in this respect1 at a great disadvantage with hand labour4 ,if a machine drill were not capable of boring in any position and in any direction1 hand labour would have to be employed in conjunction with it1 and such incompleteness in the work of a machine would constitute a serious objection to its adoption4 ,besides allowing of the desired adjustment of the machine1 the support must be itself adjustable to uneven ground4 ,the bottom of a shaft which is being sunk1 or the sides1 roof1 and floor of a heading which is being driven1 present great irregularities of surface1 and1 as the support must of necessity in most cases be fixed to these1 it is obvious that its design and construction must be such as will allow of its ready adjustment to these irregularities4 ,the means by which the adjustment is effected should be few and simple1 for simplicity of parts is important in the support as well as in the machine1 and for the same reasons4 ,a large proportion of the time during which a machine drill is in use is occupied in shifting it from one position or one situation to another2 this time reduces1 in a proportionate degree1 the superiority of machine over hand labour1 in respect of rapidity of execution1 and it is evidently desirable that it should be shortened as far as possible4 ,hence the necessity for the employment of means of adjustment which shall be few in number1 rapid in action1 and of easy management4 ,for reasons similar to the foregoing1 the drill support must be of small dimensions1 and sufficiently light to allow of its being easily portable4 ,the limited space in which rock drills are used renders this condition1 as in the case of the machine itself1 a very important one4 ,it must be borne in mind that1 after every blast1 the dislodged rock has to be removed1 and rapidity of execution requires that the operations of removal should be carried on without hindrance4 ,a drill support that occupies a large proportion of the free space in a shaft or a heading is thus a cause of inconvenience and a source of serious delay4 ,moreover1 as it has to be continually removed from one situation to another1 it should be of sufficiently light weight to allow of its being lifted or run along without difficulty4 ,in underground workings1 manual power is generally the only power available1 and therefore it is desirable that both the machine and its support should be of such weight that each may be lifted by one man4 ,of course1 when any endeavour is made to reduce the weight of the support1 the necessity for great strength and rigidity must be kept in view4 ,in spacious headings1 such as are driven in railway tunnel work1 supports of a special kind may be used4 ,in these situations1 the conditions of work are different from those which exist in mines4 ,the space is less limited1 the heading is commenced at surface1 and the floor is laid with a tramway and sidings4 ,in such a case1 the support may consist of a more massive structure mounted upon wheels to run upon the rails4 ,this support will carry several machines1 and to remove it out of the way when occasion requires1 it will be run back on to a siding2 but for ordinary mining purposes1 such a support is suitable4 ,the ,stretcher ,bar4--,the simplest kind of support is the 8stretcher bar40 ,this consists essentially of a bar so constructed that it may be lengthened or shortened at pleasure1 by means of a screw4 ,it is fixed in position by screwing the ends into firm contact with the sides1 or with the roof and the floor1 of a heading4 ,the machine is fixed to this bar by means of a clamp1 which1 when loosened1 slides along the bar1 and allows the drill to be placed in the required position1 and to be directed at the required angle4 ,the bar illustrated in ,fig4 #bf1 ,plate ,v41 is that which is used with the ,darlington drill2 in it1 lightness and rigidity are combined in the highest possible degree by the adoption of the hollow section4 ,the mode of setting the bar in a heading is shown in the drawing2 the end claws are set against pieces of wood on the floor and the roof1 and are tightened by turning the screw with a common bar4 ,the simple stretcher bar is frequently used in narrow drivings and in shafts of small diameter4 ,but a more satisfactory support in drivings is afforded by a bar suitably mounted upon a carriage designed to run upon rails4 ,the carriage consists simply of a trolly1 to the fore part of which the bar is fixed usually by some kind of hinge-joint4 ,it is obvious that the details of the construction of this support may be varied greatly1 and numerous designs have been introduced and adopted4 ,in ,figs4 #bg and #bh1 ,plate ,,vi41 is shown a support of this character designed by ,j4 ,darlington4 ,a single vertical bar is carried on the fore part of the trolly1 and fixed1 by the usual means1 against the centre of the roof4 ,this vertical bar carries an arm1 which is capable of turning upon it1 as upon a centre1 and of sliding up and down it4 ,this arm carries the drill4 ,the central bar having been fixed in position1 the arm is slid up to the highest position required1 and fixed against the side of the heading4 ,a row of holes are then bored from this arm4 ,when these are completed1 the arm is lowered the requisite distance1 and another row of holes are bored4 ,this is continued until all the holes are bored over one-half the face4 ,the arm is then swung round1 and fixed against the other side of the heading1 and the holes are bored over that half the face in like manner4 ,in this way1 one-half the heading is kept clear to allow the operations of removing the dislodged rock to be carried on at the same time4 ,if desired1 two arms may be used4 ,this arrangement gives undoubtedly great facilities for working the drill1 and leaves the heading comparatively unencumbered4 ,in shaft sinking1 the same support1 slightly modified1 is used without the trolly4 ,the arrangement adopted in this case is shown in ,fig4 #bi1 ,plate ,,vii4 ,the central bar is held firmly in its position by a cross stretcher bar set against the sides of the shaft4 ,the arms are made to revolve upon this bar to allow the holes to be bored in the positions required4 ,when all the holes have been bored1 the support1 with the machines1 is hauled up1 by means of a chain attached to the central bar1 out of the way of the blast4 ,with this support1 the time of fixing1 raising1 and lowering is reduced to a minimum2 while the facility with which the machines may be slid along and fixed to the arm1 and the positions of the latter changed1 allows the boring to be carried on rapidly4 ,for open work1 as in quarrying1 where the stretcher bar cannot be used1 the tripod stand is adopted4 ,the ,dubois-,franois ,carriage4--,the support commonly used in ,france and in ,belgium consists of a kind of carriage carrying bars upon which the drills are set4 ,this carriage is used in drivings of all kinds2 but it is particularly suitable for tunnelling4 ,it has been adopted1 with but slight modification1 in the ,st4 ,gothard tunnel1 and in several other important works of the like character4 ,a modification of the carriage is shown in ,figs4 #cj and #ca4 ,being designed for ordinary mining operations1 it carries but two machines2 but it will be readily perceived that1 by increasing the number of vertical screws1 the same support may be made to carry a larger number4 ,it consists essentially of a vertical frame of flat bar iron a b c d1 #h feet in length1 and #d feet #i inches in height above the rails1 the hinder portion of which rests upon a cast-iron plate e f g h1 carried upon two wheels2 on this are fixed the two uprights l1 l1 which1 being bound to the upper part by a transverse bar m m1 form a framing to serve as a support to the two vertical screws p1 q4 ,the front framing is formed of two longitudinals b c and b c and the uprights a1 a1 and the vertical screws p1 q1 which are connected to the upper part by the single piece a d4 ,this framing is supported below upon a small trolly with four wheels1 connected to the two longitudinals of the framing by a pivot bolt n of ,t form1 the bar of the ,t being inserted into the elongated openings o cut through the middle of the curved portion of the longitudinals4 ,the cast-iron plate behind1 the use of which is only to give stability to the carriage1 carries above it1 by means of the two curved pieces h1 h1 a wrought-iron plate ,v1 upon which the small tools needed for repairs are kept4 ,two screws1 s1 s1 carried by lugs cast upon the back of the plate1 serve1 by turning them down upon the rails1 to fix the carriage1 the latter being slightly lifted by the screws4 ,each machine is supported at two points4 ,behind1 the point of support is given by a cast-iron bracket t1 having a projecting eye which enters between the two cheeks formed at the back end of the machine by the continuations of the two longitudinals of the framing4 ,a pin bolt1 carried by the machine1 allows the latter to be fixed to the bracket1 while leaving sufficient freedom of motion to allow of its being directed at the required angle4 ,this bracket1 shown in plan in ,fig4 #cc1 is supported by a kind of nut1 ,fig4 #cb1 having two handles whereby it may be easily turned4 ,by raising or lowering this1 the hinder support of the drill may be brought to the requisite height4 ,to prevent it turning upon the screw1 a pin is passed through the hole o1 which pin forms a stop for the handles aforementioned4 ,the rotation of the bracket itself is rendered impossible by the form of the vertical screw upon which it is set1 as shown in ,fig4 #cc4 ,in front1 the support is a fork1 the shank of which slides along in the piece ,u1 ,figs4 #cj and #ca4 ,this support1 which is not screwed on the inside1 rests upon a nut of the same form as that already described1 and the same means are employed to prevent rotation as in the case of the hinder supports4 ,,section ,,iii4--,,appliances ,,for ,,firing ,,blasting ,,charges4 ,in the foregoing sections1 the machines and tools used in rock boring have been treated of4 ,it now remains to describe those which are employed in firing the charges after they have been placed in the bore-holes4 ,in this direction1 too1 great progress has been made in recent times4 ,with the introduction of new explosive agents1 arose the necessity for improved means of firing them4 ,attention being thus directed to the subject1 its requirements were investigated and its conditions observed1 the outcome being some important modifications of the old appliances and the introduction of others altogether new4 ,some of the improvements effected are scarcely less remarkable than the substitution of machine for hand boring4 ,illustration3 ,,fig4 #bh4 ,illustration3 ,,fig4 #bi4 ,the means by which the charge of explosive matter placed in the bore-hole is fired constitute a very important part of the set of appliances used in blasting4 ,the conditions which any such means must fulfil are3 7#a7 that it shall fire the charge with certainty2 7#b7 that it shall allow the person whose duty it is to explode the charge to be at a safe distance away when the explosion takes place2 7#c7 that it shall be practically suitable1 and applicable to all situations2 and 7#d7 that it shall be obtainable at a low cost4 ,to fulfil the second and most essential of these conditions1 the means must be either slow in operation1 or capable of being acted upon at a distance4 ,the only known means possessing the latter quality is electricity4 ,the application of electricity to this purpose is of recent date1 and in consequence of the great advantages which it offers1 its use is rapidly extending4 ,the other means in common use are those which are slow in operation1 and which allow thereby sufficient time to elapse between their ignition and the explosion of the charge for a person to retire to a safe distance4 ,these means consist generally of a train of gunpowder so placed that the ignition of the particles must necessarily be gradual and slow4 ,the old1 and in some parts still employed1 mode of constructing this train was as follows3 ,an iron rod of small diameter and terminating in a point1 called a 8pricker10 was inserted into the charge and left in the bore-hole while the tamping was being rammed down4 ,when this operation was completed1 the pricker was withdrawn1 leaving a hole through the tamping down to the charge4 ,into this hole1 a straw1 rush1 quill1 or some other like hollow substance filled with gunpowder1 was inserted4 ,a piece of slow-match was then attached to the upper end of this train1 and lighted4 ,the combustion of the powder confined in the straw fired the charge1 the time allowed by the slow burning of the match being sufficient to enable the man who ignited it to retire to a place of safety4 ,this method of forming the train does not1 however1 satisfy all the conditions mentioned above4 ,it is not readily applicable to all situations4 ,moreover1 the use of the iron pricker may be a source of danger2 the friction of this instrument against silicious substances in the sides of the bore-hole or in the tamping has in some instances occasioned accidental explosions4 ,this danger is1 however1 very greatly lessened by the employment of copper or phosphor-bronze instead of iron for the prickers4 ,but the method is defective in some other respects4 ,with many kinds of tamping1 there is a difficulty in keeping the hole open after the pricker is withdrawn till the straw can be inserted4 ,when the holes are inclined upwards1 besides this difficulty1 another is occasioned by the liability of the powder constituting the train to run out on being ignited4 ,and in wet situations1 special provision has to be made to protect the trains4 ,moreover1 the manufacture of these trains by the workmen is always a source of danger4 ,many of these defects in the system may1 however1 be removed by the employment of properly constructed trains4 ,one of these trains or 8squibs0 is shown full size in ,fig4 #bh4 ,safety ,fuse4--,many of the defects pertaining to the system were removed by the introduction of the fuse invented by ,w4 ,bickford1 and known as 8safety fuse40 ,the merits of this fuse1 which is shown full size in ,fig4 #bi1 are such as to render it one of the most perfect of the slow-action means that have yet been devised4 ,the train of gunpowder is retained in this fuse1 but the details of its arrangement are changed so as to fairly satisfy the conditions previously laid down as necessary4 ,it consists of a flexible cord composed of a central core of fine gunpowder1 surrounded by hempen yarns twisted up into a tube1 and called the countering4 ,an outer casing is made of different materials1 according to the circumstances under which it is intended to be used4 ,a central touch thread1 or in some cases two threads1 passes through the core of gunpowder4 ,this fuse1 which in external appearance resembles a piece of plain cord1 is tolerably certain in its action2 it may be used with equal facility in holes bored in any direction2 it is capable of resisting considerable pressure without injury2 it may be used without special means of protection in wet ground2 and it may be transported from place to place without risk of damage4 ,in the safety fuse1 the conditions of slow burning are fully satisfied1 and certainty is in some measure provided for by the touch thread through the centre of the core4 ,as the combustion of the core leaves1 in the small space occupied by it1 a carbonaceous residue1 there is little or no passage left through the tamping by which the gases of the exploding charge may escape1 as in the case of the squibs4 ,hence results an economy of force4 ,another advantage offered by the safety fuse is1 that it may be made to carry the fire into the centre of the bursting charge if it be desired to produce rapid ignition4 ,this fuse can be also very conveniently used for firing charges of compounds other than gunpowder1 by fixing a detonating charge at the end of it1 and dropping the latter into the charge of the compound4 ,this means is usually adopted in firing the nitro-glycerine compounds1 the detonating charge in such cases being generally contained within a metallic cap4 ,in using this fuse1 a sufficient length is cut off to reach from the charge to a distance of about an inch1 or farther if necessary1 beyond the mouth of the hole4 ,one end is then untwisted to a height of about a quarter of an inch1 and placed to that depth in the charge4 ,the fuse being placed against the side of the bore-hole with the other end projecting beyond it1 the tamping is put in1 and the projecting end of the fuse slightly untwisted4 ,the match may then be applied directly to this part4 ,the rate of burning is about two and a half feet a minute4 ,safety fuse is sold in coils of #bd feet in length4 ,the price varies according to the quality1 and the degree of protection afforded to the train4 ,electric ,fuses4--,the employment of electricity to fire the charge in blasting rock offers numerous and great advantages4 ,the most important1 perhaps1 is the greatly increased effect of the explosions when the charges are fired simultaneously4 ,but another advantage1 of no small moment1 lies in the security from accident which this means of firing gives4 ,when electricity is used1 not only may the charge be fired at the moment desired1 after the workmen have retired to a place of safety1 but the danger due to a misfire is altogether avoided4 ,further1 the facility afforded by electricity for firing charges under water is a feature in this agent of very great practical importance4 ,it would therefore seem1 when all these advantages are taken into account1 that electricity is destined to become of general application to blasting purposes in this country1 as it is already in ,germany and in ,america4 ,an electric fuse consists of a charge of an explosive compound suitably placed in the circuit of an electric current1 which compound is of a character to be acted upon by the current in a manner and in a degree sufficient to produce explosion4 ,the mode in which the current is made to act depends upon the nature of the source of the electricity4 ,that which is generated by a machine is of high tension1 but small in quantity2 while that which is generated by a battery is1 on the contrary1 of low tension1 but is large in quantity4 ,electricity of high tension is capable of leaping across a narrow break in the circuit1 and advantage is taken of this property to place in the break an explosive compound sufficiently sensitive to be decomposed by the passage of the current4 ,the electricity generated in a battery1 though incapable of leaping across a break in the circuit1 is in sufficient quantity to develop a high degree of heat4 ,advantage is taken of this property to fire an explosive compound by reducing the sectional area of the wire composing a portion of the circuit at a certain point1 and surrounding this wire with the compound4 ,it is obvious that any explosive compound may be fired in this way2 but for the purpose of increasing the efficiency of the battery1 preference is given to those compounds which ignite at a low temperature4 ,hence it will be observed that there are two kinds of electric fuses1 namely1 those which may be fired by means of a machine1 and which are called 8tension0 fuses1 and those which require a battery1 and which are known as 8quantity0 fuses4 ,in the tension1 or machine fuses1 the circuit is interrupted within the fuse case1 and the priming1 as before remarked1 is interposed in the break2 the current1 in leaping across the interval1 passes through the priming4 ,in the quantity or battery fuses1 the reduction of the sectional area is effected by severing the conducting wire within the fuse case1 and again joining the severed ends of the wire by soldering to them a short piece of very fine wire4 ,platinum wire1 on account of its high resistance and low specific heat1 is usually employed for this purpose4 ,the priming composition is placed around this fine wire1 which is heated to redness by the current as soon as the circuit is closed4 ,the advantages of high tension lie chiefly in the convenient form and ready action of the machines employed to excite the electricity4 ,being of small dimensions and weight1 simple in construction1 and not liable to get quickly out of order1 these sources of electricity are particularly suitable for use in mining operations1 especially when these operations are entrusted1 as they usually are1 to men of no scientific knowledge4 ,another advantage of high tension is the small effect of line resistance upon the current1 a consequence of which is that mines may be fired at long distances from the machine1 and through iron wire of very small section4 ,a disadvantage of high tension is the necessity for a perfect insulation of the wires4 ,when electricity of low tension is employed1 the insulation of the wires needs not to be perfect1 so that leakages arising from injury to the coating of the wire are not of great importance4 ,in many cases1 bare wires may be used4 ,other advantages of low tension are the ability to test the fuse at any moment by means of a weak current1 and an almost absolute certainty of action4 ,for this reason1 it is usually preferred for torpedoes and important submarine work4 ,on the other hand1 the copper wires used must be of comparatively large section1 and the influence of line resistance is so considerable that only a small number of shots can be fired simultaneously when the distance is great4 ,illustration3 ,,fig4 #cj4 ,illustration3 ,,fig4 #ca4 ,illustration3 ,,fig4 #cb4 ,in ,fig4 #cj is shown an external view of an electric tension fuse4 ,it consists of a metal cap containing a detonating composition1 upon the top of which is placed the priming to be ignited by the electric spark4 ,the ends of two insulated wires project into this priming1 which is fired by the passage of the spark from one of these wires to the other4 ,the insulated wires are sufficiently long to reach a few inches beyond the bore-hole4 ,sometimes the fuse is attached to the end of a stick1 and the wires are affixed to the latter in the manner shown in ,fig4 #ca4 ,the rigidity of the stick allows the fuse to be readily pushed into the bore-hole4 ,when the ground is not very wet1 bare wires are1 for cheapness1 used1 and the stick is in that case covered with oiled paper1 or some other substance capable of resisting moisture4 ,these 8blasting sticks10 as they are called1 are extensively used in ,germany4 ,when heavy tamping is employed1 the stick is not suitable1 by reason of the space which it occupies in the bore-hole4 ,a mode of insulating the wires1 less expensive than the guttapercha shown in ,fig4 #cj1 is illustrated in ,fig4 #cb4 ,in this case1 the wires are cemented between strips of paper1 and the whole is dipped into some resinous substance to protect it from water4 ,these 8ribbon0 wires may be used in ground that is not very wet4 ,they occupy little or no space in the bore-hole1 and therefore are suitable for use with tamping4 ,to connect the fuses with the machine or the battery1 two sets of wires are required when a single shot is fired1 and three sets may be needed when two or more shots are fired simultaneously4 ,of these several sets of wires1 the first consists of those which are attached to the fuses1 and which1 by reason of their being placed in the shot-hole1 are called the 8shot-hole wires40 ,two shot-hole wires must be attached to each fuse1 and they must be of such a length that1 when the fuse has been placed in its proper position in the charge1 the ends may project a few inches from the hole4 ,these wires must also be 8insulated10 that is1 covered with a substance capable of preventing the escape of electricity4 ,the second set of wires consists of those which are employed to connect the charges one with another1 and which1 for this reason1 are called 8connecting wires40 ,in connecting the charges in single circuit1 the end of one of the shot-hole wires of the first charge is left free1 and the other wire is connected1 by means of a piece of this connecting wire1 to one of the shot-hole wires in the second hole2 the other wire in this second hole is then connected1 in the same manner1 to one of the wires in the third hole2 and so on till the last hole is reached1 one shot-hole wire of which is left free1 as in the first4 ,whenever the connecting wires can be kept from touching the rock1 and also from coming into contact one with another--and in most cases this may be done--bare wire may be used1 the cost of which is very little4 ,but when this condition cannot be complied with1 and1 of course1 when blasting in water1 the connecting wires1 like the shot-hole wires1 must be insulated4 ,when guttapercha shot-hole wires are used1 it is best to have them sufficiently long to allow the ends projecting from one hole to reach those projecting from the next hole4 ,this renders connecting wire unnecessary1 and moreover saves one joint for each shot4 ,illustration3 ,,fig4 #cc4 ,illustration3 ,,fig4 #cd4 ,cables4--,the third set of wires required consists of those used to connect the charges with the machine or the battery4 ,these wires1 which are called the 8cables10 consist each of three or more strands of copper wire well insulated with guttapercha1 or better1 indiarubber1 the coating of these materials being protected from injury by a sheathing of tape or of galvanized iron wire underlaid with hemp4 ,two cables are needed to complete the circuit2 the one which is attached to the positive pole of the machine1 that is1 the pole through which the electric current passes out1 is distinguished as the 8leading cable10 and the other1 which is attached to the negative pole1 that is1 the pole through which the current returns to the machine1 is described as the return cable4 ,sometimes both the leading and the return cables are contained within one covering4 ,when a cable having a metallic sheathing is used1 the sheathing may be made to serve as a return cable1 care being taken to make good metallic contact with the wires that connect the sheathing to the fuses and to the terminal of the machine4 ,the best kind of unprotected cable consists of a three-strand tinned copper wire1 each #jjce inch in diameter1 insulated with three layers of indiarubber to #jbb inch diameter1 and taped with indiarubber-saturated cotton to #jbd inch diameter1 as shown in ,fig4 #cc4 ,the best protected cable consists of a similar strand of copper wire1 covered with guttapercha and tarred jute1 and sheathed with fifteen galvanized iron wires of #jjh inch diameter each1 to a total diameter of #jdh inch1 as shown in ,fig4 #cd4 ,detonators4--,the new explosives of the nitro-cotton and nitro-glycerine class cannot be effectively fired by means of safety or other fuse alone4 ,to bring about their instantaneous decomposition1 it is necessary to produce in their midst the explosion of some other substance4 ,the force of this initial explosion causes the charge of gun-cotton1 or dynamite1 as the case may be1 to detonate4 ,it has been found that the explosion of the fulminate of mercury brings about this result most effectively and with the greatest certainty2 and this substance is therefore generally used for the purpose4 ,the charge of fulminate is contained in a copper capsule about a quarter of an inch in diameter1 and from #a inch to #a inch in length4 ,these caps1 with their charge of fulminate1 which are now well known to users of the nitro-compounds1 are called 8detonators40 ,it is of the highest importance that these detonators should contain a sufficiently strong charge to produce detonation1 for if too weak1 not only is the whole force of the explosive not developed1 but a large quantity of noxious gas is generated4 ,gun-cotton requires a much stronger charge of fulminate than dynamite4 ,illustration3 ,,fig4 #ce4 ,in the electric fuses illustrated1 the metal case shown is the detonator1 the fuse being placed inside above the fulminate4 ,when safety fuse is used1 the end is cut off clean and inserted into the cap1 which is then pressed tightly upon the fuse by means of a pair of nippers1 as shown in ,fig4 #ce4 ,when water tamping is used1 and when1 with ordinary tamping1 the hole is very wet1 a little white-lead or grease must be put round the edge of the cap as a protection4 ,the electric fuses are always made waterproof2 consequently1 they are ready for use under all circumstances4 ,when the safety fuse burns down into the cap1 or when1 in the other case1 the priming of the electric fuse is fired1 the fulminate explodes and causes the detonation of the charge in which it is placed4 ,firing ,machines and ,batteries4--,the electrical machines used for firing tension fuses are of two kinds4 ,in one kind1 the electricity is excited by friction1 and stored in a condenser to be afterwards discharged by suitable means provided for the purpose4 ,in the other kind1 the electricity is excited by the motion of an armature before the poles of a magnet4 ,the former kind are called 8frictional electric0 exploders2 the latter kind are known as 8magneto-electric0 exploders4 ,when a magneto-electric machine contains an electro-magnet instead of a permanent magnet1 it is described as a 8dynamo-electric exploder40 ,frictional machines act very well as exploders so long as they are kept in a proper state4 ,but as they are injuriously affected by a moist atmosphere1 and weaken rapidly with use by reason of the wearing away of the rubbers1 it is necessary to take care that they be in good electrical condition before using them for firing4 ,unless this care be taken1 the quantity of electricity excited by a given number of revolutions of the plate will be very variable1 and vexatious failures will ensue4 ,if1 however1 the proper precautions be observed1 very certain and satisfactory results may be obtained4 ,in ,germany and in ,america1 frictional exploders are generally used4 ,magneto-electric machines possess the very valuable quality of constancy4 ,they are unaffected1 in any appreciable degree1 by atmospheric changes1 and they are not subject to wear4 ,these qualities are of inestimable worth in an exploder used for ordinary blasting operations4 ,moreover1 as they give electricity of a lower tension than the frictional machines1 defects of insulation are less important4 ,of these machines1 only the dynamo variety are suitable for industrial blasting4 ,it is of primary importance that an exploder should possess great power4 ,the mistake of using weak machines has done more than anything else to hinder the adoption of electrical firing in this country4 ,illustration3 ,,fig4 #cf4 ,the machine most used in ,germany is ,bornhardt's frictional exploder1 shown in ,fig4 #cf4 ,this machine is contained in a wooden case #bj inches in length1 #g inches in breadth1 and #ad inches in depth1 outside measurement4 ,the weight is about #bj lb4 ,to fire the charges by means of this exploder1 the leading wire is attached to the upper terminal ,b1 and the return to the lower terminal ,c1 the other ends of these wires being connected to the fuses4 ,the handle is then turned briskly from fifteen to thirty times1 according to the number of the fuses and the state of the machine1 to excite the electricity4 ,the knob ,a is then pressed suddenly in1 and the discharge takes place4 ,to ascertain the condition of the machine1 a scale of fifteen brass-headed nails is provided on the outside1 which scale may be put in communication with the poles ,b and ,c by means of brass chains1 as shown in the drawing4 ,if after twelve or fourteen turns1 the spark leaps the scale when the knob is pushed in1 the machine is in a sufficiently good working condition4 ,to give security to the men engaged1 the handle is designed to be taken off when the machine is not in actual use2 and the end of the machine into which the cable wires are led is made to close with a lid and lock1 the key of which should be always in the possession of the man in charge of the firing operations4 ,illustration3 ,,fig4 #cg4 ,illustration3 ,,fig4 #ch4 ,in ,america1 there are two frictional exploders in common use4 ,one1 shown in ,fig4 #cg1 is the invention of ,h4 ,julian ,smith4 ,the apparatus is enclosed in a wooden case about #a foot square and #f inches in depth4 ,the handle is on the top of the case1 and is turned horizontally4 ,this handle is removable1 as in ,bornhardt's machine4 ,the cable wires having been attached to the terminals1 the handle is turned forward a certain number of times to excite the electricity1 and then turned a quarter of a revolution backward to discharge the condenser and to fire the blast4 ,by this device1 the necessity for a second aperture of communication with the inside is avoided1 an important point in frictional machines1 which are so readily affected by moisture4 ,the aperture through which the axis of the plate passes1 upon which axis the handle is fixed1 is tightly closed by a stuffing-box4 ,a leathern strap on one end of the case allows the machine to be easily carried4 ,the weight of this exploder is under #aj lb4 ,the other exploder used is that designed by ,g4 ,mowbray4 ,this machine1 which is shown in ,fig4 #ch1 is contained in a wooden barrel-shaped case1 and is known as the 8powder-keg0 exploder1 the form and dimensions of the case being those of a powder-keg4 ,the action is similar to that of the machine last described4 ,the cable wires having been attached to the terminals at one end of the keg1 the handle at the other end is turned forward to excite the electricity1 and the condenser is discharged by making a quarter turn backward1 as in ,smith's machine4 ,the handle is in this case also removable4 ,the weight of the powder-keg exploder is about #bf lb4 ,both of these machines are very extensively used1 and good results are obtained from them4 ,they stand well in a damp atmosphere1 and do not quickly get out of order from the wearing of the rubbers4 ,they are also1 especially the former1 very easily portable4 ,illustration3 ,,fig4 #ci4 ,the machine commonly used in ,england is the dynamo-electric exploder of the ,messrs4 ,siemens4 ,this machine1 which is the best of its kind yet introduced for blasting purposes1 is not more than half the size of ,bornhardt's frictional exploder2 but it greatly exceeds the latter in weight1 that of ,siemens' being about #ee lb4 ,the apparatus1 which is contained within the casing shown in ,fig4 #ci1 consists of an ordinary ,siemens' armature1 which is made1 by turning the handle1 to revolve between the poles of an electro-magnet4 ,the coils of the electro-magnet are in circuit with the wire of the armature2 the residual magnetism of the electro-magnet cores excites1 at first1 weak currents2 these pass into the coils1 thereby increasing the magnetism of the cores1 and inducing still stronger currents in the armature wire1 to the limit of magnetic saturation of the iron cores of the electro-magnets4 ,by the automatic action of the machine1 this powerful current is1 at every second turn of the handle1 sent into the cables leading to the fuses4 ,to fire this machine1 the handle is turned gently till a click is heard from the inside1 indicating that the handle is in the right position to start from4 ,the cable wires are then attached to the terminals1 and the handle is turned quickly1 but steadily4 ,at the completion of the second revolution1 the current is sent off into line1 as it is termed1 that is1 the current passes out through the cables and the fuses4 ,as in the case of the frictional machines1 the handle is1 for safety1 made removable4 ,this exploder is practically unaffected by moisture1 and it is not liable to get out of order from wear4 ,induction coils have been used to fire tension fuses2 but it is surprising that they have not been more extensively applied to that purpose4 ,a coil designed for the work required of it is a very effective instrument4 ,if constructed to give a spark not exceeding three inches in length1 with comparatively thick wire for quantity1 it makes a very powerful exploder4 ,an objection to its use is the necessity for a battery4 ,but a few bichromate of potash cells1 provided with spiral springs to hold the zincs out of the liquid1 and designed to be set in action by simply pressing down the zincs1 give but little trouble1 so that the objection is not a serious one4 ,the writer has used an induction exploder in ordinary mining operations without experiencing any difficulty or inconvenience4 ,it is cheap1 easily portable1 and constant in its action4 ,batteries are used to fire what are known as 8quantity0 or 8low tension0 fuses4 ,any cells may be applied to this purpose2 but they are not all equally suitable4 ,a firing battery should require but little attention1 and should remain in working order for a long time4 ,these conditions are satisfactorily fulfilled by only two cells1 namely1 the ,lclanch and the ,bichromate of ,potash4 ,the latter is the more powerful1 and generally the more suitable4 ,the ,lclanch is much used in this country for firing purposes1 under the form known as the 8,silvertown ,firing ,battery40 ,this battery consists of a rectangular teak box1 containing ten cells4 ,two1 or more1 of these may be joined up together when great power is required4 ,in ,france1 the battery used generally for firing is the ,bichromate4 ,this battery is much more powerful than the ,lclanch1 and as no action goes on when the zincs are lifted out of the liquid1 it is equally durable4 ,it is moreover much cheaper4 ,at the suggestion of the writer1 ,mr4 ,apps1 of the ,strand1 ,london1 has constructed a bichromate firing battery of very great power4 ,it is contained in a box of smaller dimension than the #aj-;cell ,silvertown4 ,the firing is effected by simply lowering the zincs1 which rise again automatically out of the liquid1 so that there is no danger of the battery exhausting itself by continuous action in case of neglect4 ,externally1 this battery1 like the ,silvertown1 appears a simple rectangular box1 so that no illustration is needed4 ,with either of these1 the usual objections urged against the employment of batteries1 on the ground of the trouble involved in keeping them in order1 and their liability to be injured by ignorant or careless handling1 do not apply1 or at least apply in only a very unimportant degree4 ,to guard against misfires1 the machine or the battery used should be constructed to give a very powerful current4 ,if this precaution be observed1 and the number of fuses in circuit be limited to one-half that which the machine is capable of firing with a fair degree of certainty1 perfectly satisfactory results may be obtained4 ,the employment of weak machines and batteries leads inevitably to failure4 ,in the minds of those who have hitherto tried electrical blasting in this country1 there seems to be no notion of any relation existing between the work to be done and the force employed to do it4 ,the electrical exploder is regarded as a sort of magic box that needs only to be set in action to produce any required result4 ,whenever failure ensues1 the cause is unhesitatingly attributed to the fuses4 ,,chapter ,,ii4 ,,explosive ,,agents ,,used ,,in ,,blasting ,,rocks4 ,,section ,i4--,,phenomena ,,accompanying ,,an ,,explosion4 ,nature of an ,explosion4--,the combination of oxygen with other substances for which it has affinity is called generally 8oxidation40 ,the result of this combination is a new substance1 and the process of change is accompanied by the liberation of heat4 ,the quantity of heat set free when two substances combine chemically is constant1 that is1 it is the same under all conditions4 ,if the change takes place within a short space of time1 the heat becomes sensible2 but if the change proceeds very slowly1 the heat cannot be felt4 ,the same quantity1 however1 is liberated in both cases4 ,thus1 though the quantity of heat set free by a chemical combination is under all conditions the same1 the degree or intensity of the heat is determined by the rapidity with which the change is effected4 ,when oxidation is sufficiently rapid to cause a sensible degree of heat1 the process is described as 8combustion40 ,the oxidation of a lump of coke in the furnace1 for example1 is effected within a short space of time1 and1 as the quantity of heat liberated by the oxidation of that weight of carbon is great1 a high degree results4 ,and it is well known and obvious that as combustion is quickened1 or1 in other words1 as the time of change is shortened1 the intensity of the heat is proportionally increased4 ,so in the case of common illuminating gas1 the oxidation of the hydrogen is rapidly effected1 and1 consequently1 a high degree of heat ensues4 ,when oxidation takes place within a space of time so short as to be inappreciable to the senses1 the process is described as 8explosion40 ,the combustion of a charge of gunpowder1 for example1 proceeds with such rapidity that no interval can be perceived to intervene between the commencement and the termination of the process4 ,oxidation is in this case1 therefore1 correctly described as an explosion2 but the combustion of a train of gunpowder1 or of a piece of quick-match1 though exceedingly rapid1 yet1 as it extends over an appreciable space of time1 is not to be so described4 ,by analogy1 the sudden change of state which takes place when water is 8flashed0 into steam1 is called an explosion4 ,it may be remarked here that the application of this expression to the bursting of a steam boiler is an abuse of language2 as well may we speak of an 8explosion0 of rock4 ,from a consideration of the facts stated in the foregoing paragraphs1 it will be observed that oxidation by explosion gives the maximum intensity of heat4 ,measure of ,heat1 and specific ,heat4--,it is known that if a certain quantity of heat will raise the temperature of a body one degree1 twice that quantity will raise its temperature two degrees1 three times the quantity1 three degrees1 and so on4 ,thus we may obtain a measure of heat by which to determine1 either the temperature to which a given quantity of heat is capable of raising a given body1 or the quantity of heat which is contained in a given body at a given temperature4 ,the quantity of heat requisite to produce a change of one degree in temperature is different for different bodies1 but is practically constant for the same body1 and this quantity is called the 8specific heat0 of the body4 ,the standard which has been adopted whereby to measure the specific heat of bodies is that of water1 the unit being the quantity of heat required to raise the temperature of #a lb4 of water through #a ,fahr41 say from #cb to #cc4 ,the quantity of heat required to produce this change of temperature in #a lb4 of water is called the 8unit of heat10 or the 8thermal unit40 ,having determined the specific heat of water1 that of air may in like manner be ascertained1 and expressed in terms of the former4 ,it has been proved by experiments that if air be heated at constant pressure through #a ,fahr41 the quantity of heat absorbed is #jbcge thermal units1 whatever the pressure or the temperature of the air may be4 ,similarly it has been shown that the specific heat of air at constant volume is1 in thermal units1 #jafhg2 that is1 if the air be confined so that no expansion can take place1 #jafhg of a thermal unit will be required to increase its temperature one degree4 ,heat liberated by an ,explosion4--,in the oxidation of carbon1 one atom of oxygen may enter into combination with one atom of that substance2 the resulting body is a gas known as 8carbonic oxide40 ,as the weight of carbon is to that of oxygen as #ab is to #af1 #a lb4 of the former substance will require for its oxidation #a lb4 of the latter2 and since the two enter into combination1 the product1 carbonic oxide1 will weigh #a #a #b lb4 ,the combining of one atom of oxygen with one of carbon throughout this quantity1 that is1 #a lb4 of oxygen1 with #a lb4 of carbon1 generates #aj1ajj units of heat4 ,of this quantity1 #egjj units are absorbed in changing the carbon from the solid into the gaseous state1 and #ddjj are set free4 ,the quantity of heat liberated1 namely1 the #ddjj units1 will be expended in raising the temperature of the gas from #cb ,fahr41 which we will assume to be that of the carbon and the oxygen previous to combustion1 to a much higher degree1 the value of which may be easily determined4 ,the #ddjj units would raise #a lb4 of water from #cb to #cb #ddjj #ddcb2 and as the specific heat of carbonic oxide is #jag when there is no increase of volume1 the same quantity of heat will raise #a lb4 of that gas from #cb to #ddjj #cb ---- #be1iad4 #jag ,but in the case under consideration1 we have #b lb4 of the gas1 the resulting temperature of which will be #be1iad ------ #igah4 #b ,in the oxidation of carbonic oxide1 one atom of oxygen combines with one atom of the gaseous carbon2 the resulting body is a gas known as 8carbonic acid40 ,since #b lb4 of carbonic oxide contains #a lb4 of carbon1 that quantity of the oxide will require #a lb4 of oxygen to convert it into the acid1 that is1 to completely oxidize the original pound of solid carbon4 ,by this combination1 #aj1ajj units of heat are generated1 as already stated1 and since the carbon is now in the gaseous state1 the whole of that quantity will be set free4 ,hence the temperature of the resulting #c lb4 of carbonic acid will be #ddjj #aj1ajj #cb ------------- #bc1eaf4 #jag #cffg ,it will be seen from the foregoing considerations that if #a lb4 of pure carbon be burned in #b lb4 of pure oxygen1 #c lb4 of carbonic acid is produced1 and #ad1ejj units of heat are liberated2 and further1 that if the gas be confined within the space occupied by the carbon and the oxygen previously to their combination1 the temperature of the product may reach #bc1eaf ,fahr4 ,in the oxidation of hydrogen1 one atom of oxygen combines with two atoms of the former substance2 the resulting body is water4 ,as the weight of hydrogen is to that of oxygen as #a is to #af1 #a lb4 of the former gas will require for its oxidation #h lb4 of the latter2 and since the two substances enter into combination1 the product1 water1 will weigh #a #h #i lb4 ,by this union1 #fb1jcb units of heat are generated4 ,of this quantity1 #hfid are absorbed in converting the water into steam1 and #ec1cch are set free4 ,the specific heat of steam at constant volume being #jcg1 the temperature of the product of combustion1 estimated as before1 will be #ec1cch #cb -------- #af1jdi4 #jcg #i ,hence it will be observed that if #a lb4 of hydrogen be burned in #h lb4 of oxygen1 #i lb4 of steam will be produced1 and #ec1cch units of heat will be liberated2 and further1 that the temperature of the product may reach #af1jdi4 ,gases generated by an ,explosion4--,it was shown in the preceding paragraph that in the combustion of carbon1 one atom of oxygen may unite with one atom of carbon to form carbonic oxide1 or two atoms of oxygen may unite with one atom of carbon to form carbonic acid4 ,when the combination takes place according to the former proportions1 the reaction is described as 8imperfect combustion10 because the carbon is not fully oxidized2 but when the combination is effected in the latter proportions1 the combustion is said to be 8perfect10 because no more oxygen can be taken up4 ,the products of combustion are in both cases gaseous4 ,carbonic oxide1 the product of imperfect combustion1 is an extremely poisonous gas2 it is this gas which is so noisome in close headings1 and in all ill-ventilated places1 after a blast has been fired4 ,a cubic foot of carbonic oxide1 the specific gravity of which is #jige1 weighs1 at the mean atmospheric pressure1 #jjge lb41 so that #a lb4 will occupy a space of #ace cubic feet4 ,thus #a lb4 of carbon imperfectly oxidized will give #b lb4 of carbonic oxide1 which1 at the mean atmospheric pressure of #cj inches and the mean temperature of #fb ,fahr41 will occupy a space of #ace #b #cae cubic feet4 ,the product of perfect combustion1 carbonic acid1 is a far less noxious gas than the oxide1 and it is much more easily expelled from confined places1 because water possesses the property of absorbing large quantities of it4 ,in an ill-ventilated but wet heading1 the gas from a blast is soon taken up4 ,carbonic acid is a comparatively heavy gas1 its specific gravity relatively to that of common air being #aebd4 ,hence a cubic foot at the ordinary pressure and temperature will weigh #jaaf lb41 and #a lb4 of the gas under the same conditions will occupy a space of #hf cubic feet4 ,thus if #a lb4 of carbon be completely oxidized1 there will result #c lb4 of carbonic acid1 which will fill a space of #hf #c #cae cubic feet4 ,it will be observed that1 though an additional pound of oxygen has been taken up during this reaction1 the product occupies the same volume as the oxide4 ,in complete combustion1 therefore1 a contraction takes place4 ,in the oxidation of hydrogen1 as already pointed out1 one atom of oxygen combines with two atoms of the former substance to form water4 ,in this case1 the product is liquid4 ,but the heat generated by the combustion converts the water into steam1 so that we have to deal with this product also in the gaseous state1 in all considerations relating to the effects of an explosion4 ,a cubic foot of steam1 at atmospheric pressure and a temperature of #bab ,fahr41 weighs #jjdg lb42 #a lb4 of steam under these conditions will1 therefore1 occupy a space of #baad cubic feet4 ,thus the combustion of #a lb4 of hydrogen will produce #i lb4 of steam1 which1 under the conditions mentioned1 will fill a space of #baad #i #aijbf cubic feet4 ,usually in an explosion a large quantity of nitrogen gas is liberated4 ,this gas1 which is not in itself noxious1 has a specific gravity of #jiga1 so that practically a cubic foot will weigh #jjge lb41 and #a lb4 will occupy a space of #ace cubic feet1 which are the weight and the volume of carbonic oxide4 ,other gases are often formed as products of combustion2 but the foregoing are the chief1 viewed as the results of an explosion1 since upon these the force developed almost wholly depends4 ,force developed by an ,explosion4--,a consideration of the facts enunciated in the foregoing paragraphs will show to what the tremendous energy developed by an explosion is due4 ,it was pointed out that the combustion of #a lb4 of carbon gives rise to #cae cubic feet of gas4 ,if this volume of gas be compressed within the space of #a cubic foot it will obviously have a tension of #cae atmospheres2 that is1 it will exert upon the walls of the containing vessel a pressure of #dgb lb4 to the square inch4 ,if the same volume be compressed into a space one-eighth of a cubic foot in extent1 say a vessel of cubical form and #f inches side1 the tension will be #cae #h #beb atmospheres1 and the pressure #dgb #h #cggf lb4 to the square inch4 ,assuming now the oxygen to exist in the solid state1 and the two bodies carbon and oxygen to occupy together a space of one-eighth of a cubic foot1 the combustion of the carbon will develop upon the walls of an unyielding containing vessel of that capacity a pressure of #beb atmospheres4 ,also the combustion of #a lb4 of hydrogen gives rise1 as already remarked1 to #aijbf cubic feet of steam2 and if combustion take place under similar conditions with respect to space1 the pressure exerted upon the containing vessel will be #bb1hcj lb41 or nearly #aje tons1 to the square inch1 the tension being #aijbf #h #aebb atmospheres4 ,the force thus developed is due wholly to the volume of the gas generated1 and by no means represents the total amount developed by the explosion4 ,the volume of the gases evolved by an explosion is estimated for a temperature of #fb2 but it was shown in a former paragraph that the temperature of the products of combustion at the moment of their generation is far above this4 ,now it is a well-known law of thermo-dynamics that1 the volume remaining the same1 the pressure of a gas will vary directly as the temperature2 that is1 when the temperature is doubled1 the pressure is also doubled4 ,by temperature is understood the number of degrees measured by ,fahrenheit's scale on a perfect gas thermometer1 from a zero #dfab below the zero of ,fahrenheit's scale1 that is1 #dicb below the freezing point of water4 ,thus the temperature of #fb for which the volume has been estimated is equal to #dfab #fb #ebcb absolute4 ,it was shown that the temperature of the product of combustion when carbon is burned to carbonic oxide is #igah ,fahr41 which is equivalent to #ajagib absolute4 ,hence it will be observed that the temperature has been increased #ajagib -------- #aide times4 #ebcb ,according to the law above enunciated1 therefore1 the pressure will be increased in a like ratio1 that is1 it will be1 for the volume and the space already given1 #cggf #aide #gc1ddc lb4 #cbh tons to the square inch4 ,when carbon is burned to carbonic acid1 the temperature of the product was shown to be #bc1eaf ,fahr41 which is equivalent to #bciggb absolute4 ,in this case1 it will be observed that the temperature has been increased #bciggb ------- #dehc times4 #ebcb ,hence the resulting pressure will be #cggf #dehc #agc1aed lb4 #ggc tons to the square inch4 ,it will be seen from these pressures that when combustion is complete1 the force developed is #bcf greater than when combustion is incomplete2 and also that the increase of force is due to the larger quantity of heat liberated1 since the volume of the gases is the same in both cases4 ,if we suppose the carbon burned to carbonic oxide in the presence of a sufficient quantity of oxygen to make carbonic acid1 we shall have #cae cubic feet of the oxide #aeg cubic feet of free oxygen1 or a total volume of #dbg cubic feet of gases4 ,if this volume be compressed within the space of one-eighth of a cubic foot1 it will have a tension of #dbg #h #cdaf atmospheres1 and will exert upon the walls of the containing vessel a pressure of #eabd lb4 to the square inch4 ,the temperature of the gases will be #ddjj #cb ------------- #fcdg ,fahr4 #fhjhb absolute1 #jaij #cffg the mean specific heat of the gases being #jaij2 whence it will be seen that the temperature has been increased #fhjhb ------- #acja times4 #ebcb ,according to the law of thermo-dynamics1 therefore1 the pressure under the foregoing conditions will be #eabd #acja #ff1ffc lb4 #bih tons to square inch4 ,so that1 under the conditions assumed in this case1 the pressures developed by incomplete and by complete combustion are as #bih to #ggc1 or as #a to #bei4 ,similarly1 when hydrogen is burned to water1 the temperature of the product will be1 as shown in a former paragraph1 #af1jdi ,fahr4 #afeajb absolute2 and the pressure will be #afeajb #bb1hcj ------- #gbj1bhf lb4 #cbaa tons to the square inch4 #ebcb ,it will be observed1 from a consideration of the foregoing facts1 that a very large proportion of the force developed by an explosion is due to the heat liberated by the chemical reactions which take place4 ,and hence it will plainly appear that1 in the practical application of explosive agents to rock blasting1 care should be taken to avoid a loss of the heat upon which the effects of the explosion manifestly so largely depend4 ,,section ,,ii4--,,nature ,,of ,,explosive ,,agents4 ,mechanical ,mixtures4--,in the preceding section1 it was shown that an explosion is simply the rapid oxidation of carbon and hydrogen4 ,to form an explosive agent1 the problem is1 how to bring together in a convenient form the combustible1 carbon or hydrogen1 and the oxygen required to oxidize it4 ,carbon may be obtained pure1 or nearly pure1 in the solid form4 ,as wood charcoal1 for example1 that substance may be readily procured in any needful abundance2 but pure oxygen does not exist in that state1 and it is hardly necessary to point out that only the solid form is available in the composition of an explosive agent4 ,in nature1 however1 oxygen exists in the solid state in very great abundance in combination with other substances4 ,silica1 for example1 which is the chief rock constituent1 is a compound of silicon and oxygen1 and the common ores of iron are made up chiefly of that metal and oxygen4 ,the elementary constituents of cellulose1 or wood fibre1 are carbon1 hydrogen1 and oxygen2 and the body known as saltpetre1 or nitrate of potash1 is compounded of potassium1 nitrogen1 and oxygen4 ,but though oxygen is thus found in combination with many different substances1 it has not the same affinity for all4 ,when it is combined with a substance for which its affinity is strong1 as in the silica and the iron oxide1 it cannot be separated from that substance without difficulty2 but if the affinity be weak1 dissociation may be more easily effected4 ,the former combination is said to be 8stable10 and the latter is1 in contradistinction1 described as 8unstable40 ,it will be evident on reflection that only those compounds in which the oxygen exists in unstable combination can be made use of as a constituent part of an explosive agent1 since it is necessary that1 when required1 the oxygen shall be readily given up4 ,moreover1 it will also appear that when one of these unstable oxygen compounds and carbon are brought together the mixture will constitute an explosive agent1 since the oxygen which is liberated by the dissociation of the unstable compound will be taken up by the carbon for which it has a stronger affinity4 ,saltpetre is one of those compounds1 and a mixture of this body with charcoal constitutes gunpowder4 ,the means employed to dissociate the elements of saltpetre is heat4 ,it is obvious that other compounds of oxygen might be substituted for the saltpetre1 but this body being easily procurable is always employed4 ,the chlorate of potash1 for example1 is less stable than the nitrate1 and therefore an explosive mixture containing the former substance will be more violent than another containing the latter4 ,for the violence of an explosion is in a great measure determined by the readiness with which the oxygen is given up to the combustible4 ,but the chlorate is much more costly than the nitrate4 ,as1 however1 the force developed is greater1 the extra cost would perhaps be compensated by the increased effect of the explosion4 ,but the instability of the chlorate is such that friction or a moderately light blow will produce explosion in a mixture containing that substance1 a circumstance that renders it unfit to be the oxidizer in an explosive agent in common use4 ,the nitrate is therefore preferred on the ground of safety4 ,saltpetre1 or nitrate of potash1 consists1 as already pointed out1 of the metal potassium in combination with the substances nitrogen and oxygen4 ,of these1 the last only is directly concerned in the explosion2 but the two former1 and especially the nitrogen1 act indirectly to intensify its effects in a manner that will be explained hereafter4 ,the chemical formula for nitrate of potash is ,,kno1 which signifies that three atoms of oxygen exist in this body in combination with one atom of nitrogen and one atom of kalium or potassium4 ,as the atomic weights of these substances are #af1 #ad1 and #ci respectively1 the weight of the molecule is #aja1 that is1 in #aja lb4 of nitrate of potash there are #ci lb4 of potassium1 #ad lb4 of nitrogen1 and 7#af #c7 #dh lb4 of oxygen4 ,hence the proportion of oxygen in nitrate of potash is by weight #dge per cent4 ,it will be seen from this proportion that to obtain #a lb4 of oxygen1 #ba lb4 of the nitrate must be decomposed4 ,the carbon of gunpowder is obtained from wood charcoal1 the light woods1 such as alder1 being preferred for that purpose4 ,the composition of the charcoal varies somewhat according to the degree to which the burning has been carried1 the effect of the burning being to drive out the hydrogen and the oxygen4 ,but1 generally1 the composition of gunpowder charcoal is about #hj per cent4 carbon1 #cbe per cent4 hydrogen1 #ae per cent4 oxygen1 and #age per cent4 ash4 ,knowing the composition of the charcoal1 it is easy to calculate the proportion of saltpetre required in the explosive mixture4 ,thus far we have considered gunpowder as composed of charcoal and saltpetre only4 ,but in this compound1 combustion proceeds too slowly to give explosive effects4 ,were the chlorate of potash used instead of the nitrate1 the binary compound would be sufficient4 ,the slowness of combustion in the nitrate mixture is due to the comparatively stable character of that body4 ,to accelerate the breaking up of the nitrate1 a quantity of sulphur is mixed up with it in the compound4 ,this substance possesses the property of burning at a low temperature4 ,the proportion of sulphur added varies from #aj per cent4 in powder used in fire-arms1 to #bj per cent4 in that employed for blasting purposes4 ,the larger the proportion of sulphur1 the more rapid1 within certain limits1 is the combustion4 ,thus ordinary gunpowder is a ternary compound1 consisting of charcoal1 saltpetre1 and sulphur4 ,as the composition of charcoal varies1 it is not practicable to determine with rigorous accuracy the proportion of saltpetre required in every case2 a mean value is therefore assumed1 the proportions adopted being about-- ,charcoal #ae ,saltpetre #ge ,sulphur #aj --- #ajj --- ,with these proportions1 the carbon should be burned to carbonic acid1 and the sulphur should be all taken up by the potassium4 ,powder of this composition is used for fire-arms4 ,for blasting purposes1 as before remarked1 the proportion of sulphur is increased at the expense of the saltpetre1 in order to quicken combustion and to lessen the cost1 to #bj per cent4 as a maximum4 ,with such proportions1 some of the carbon is burned to carbonic oxide only1 and some of the sulphur goes to form sulphurous acid1 gases that are particularly noisome to the miner4 ,it is essential to the regular burning of the mixture that the ingredients be finely pulverized and intimately mixed4 ,the manufacture of gunpowder consists of operations for bringing about these results4 ,the several substances are broken up by mechanical means1 and reduced to an impalpable powder4 ,these are then mixed in a revolving drum1 and afterwards kneaded into a paste by the addition of a small quantity of water4 ,this paste is subjected to pressure1 dried1 broken up1 and granulated2 thus1 the mixing being effected by mechanical means1 the compound is called a mechanical mixture4 ,it will be observed that in a mechanical mixture the several ingredients are merely in contact1 and are not chemically united4 ,they may therefore be separated if need be1 or the proportions may be altered in any degree4 ,mechanical mixtures1 provided the bodies in contact have no chemical action one upon another1 are stable1 that is1 they are not liable1 being made up of simple bodies1 to decompose spontaneously4 ,chemical ,compounds4--,in a mechanical mixture1 as we have seen1 the elements which are to react one upon another are brought together in separate bodies4 ,in gunpowder1 for example1 the carbon is contained in the charcoal1 and the oxygen in the saltpetre4 ,but in a chemical compound1 these elements are brought together in the same body4 ,in a mechanical mixture1 we may put what proportion of oxygen we please4 ,but elements combine chemically only in certain definite proportions1 so that in the chemical compound we can introduce only a certain definite proportion of oxygen4 ,the oxygen in saltpetre is in chemical combination with the potassium and the nitrogen1 and1 as we have already seen1 these three substances hold certain definite proportions one to another4 ,that is1 to every atom of potassium1 there are one atom of nitrogen and three atoms of oxygen4 ,or1 which amounts to the same thing1 in #a lb4 of saltpetre1 there are #jchf lb4 of potassium1 #jaci lb4 of nitrogen1 and #jdge lb4 of oxygen4 ,moreover1 these elements occupy definite relative positions in the molecule of saltpetre4 ,but in the mechanical mixture1 the molecules of which it is made up have no definite relative positions4 ,even if the three substances--charcoal1 saltpetre1 and sulphur--of which gunpowder is composed1 could be so finely divided as to be reduced to their constituent molecules1 the relative position of these would be determined by the mixing1 and it would be impossible so to distribute them that each should find itself in immediate proximity to those with which it was to combine4 ,but so far are we from being able to divide substances into their constituent molecules1 that when we have reduced them to an impalpable powder1 each particle of that powder contains a large number of molecules4 ,thus1 in a mechanical mixture1 we have groups of molecules of one substance mingled irregularly with groups of molecules of another substance1 so that the atoms which are to combine are not in close proximity one to another1 but1 on the contrary1 are1 many of them1 separated by wide intervals4 ,in the chemical compound1 however1 the atoms are regularly distributed throughout the whole mass of the substance1 and are1 relatively to one another1 in the most favourable position for combining4 ,viewed from this point1 the chemical compound may be regarded as a perfect mixture1 the mechanical mixture being a very imperfect one4 ,this difference has an important influence on the effect of an explosion4 ,all the atoms in a chemical compound enter at once into their proper combinations1 and these combinations take place in an inconceivably short space of time1 while1 in a mechanical mixture1 the combinations are less direct1 and are much less rapidly effected4 ,this is the reason why the former is more violent in its action than the latter4 ,the one is crushing and shattering in its effects1 the other rending and projecting4 ,the compound gives a sudden blow2 the mixture applies a gradually increasing pressure4 ,it is this sudden action of the compound that allows it to be used effectively without tamping4 ,the air1 which rests upon the charge1 and which offers an enormous resistance to motion at such inconceivably high velocities1 serves as a sufficient tamping4 ,gun-cotton may be taken as an example of a chemical compound4 ,the woody or fibrous part of plants is called 8cellulose40 ,its chemical formula is ,c,h,o1 that is1 the molecule of cellulose consists of six atoms of carbon in combination with ten atoms of hydrogen and five atoms of oxygen4 ,if this substance be dipped into concentrated nitric acid1 some of the hydrogen is displaced and peroxide of nitrogen is substituted for it4 ,the product is nitro-cellulose1 the formula of which is ,c,h7,,no7,o4 ,if this formula be compared with the last1 it will be seen that three atoms of hydrogen have been eliminated and their place taken by three molecules of the peroxide of nitrogen ,,no2 so that we now have a compound molecule1 which is naturally unstable4 ,the molecules of the peroxide of nitrogen are introduced into the molecule of cellulose for the purpose of supplying the oxygen needed for the combustion of the carbon and the hydrogen1 just as the groups of molecules of saltpetre were introduced into the charcoal of the gunpowder for the combustion of the carbon and the hydrogen of that substance4 ,only1 in the former case1 the molecules of the peroxide are in chemical combination1 not merely mixed by mechanical means as in the latter4 ,the compound molecule of nitro-cellulose may be written ,c,h,n,o1 that is1 in #big lb4 of the substance1 there are 7#f #ab7 #gb lb4 of carbon1 7#g #a7 #g lb4 of hydrogen1 7#c #ad7 #db lb4 of nitrogen1 and 7#aa #af7 #agf lb4 of oxygen2 or #bdb per cent4 carbon1 #bc per cent4 hydrogen1 #ada per cent4 nitrogen1 and #eid per cent4 oxygen4 ,when the molecule is broken up by the action of heat1 the oxygen combines with the carbon and the hydrogen1 and sets the nitrogen free4 ,but it will be observed that the quantity of oxygen present is insufficient to completely oxidize the carbon and the hydrogen4 ,this defect1 though it does not much affect the volume of gas generated1 renders the heat developed1 as shown in a former section1 considerably less than it would be were the combustion complete1 and gives rise to the noxious gas carbonic oxide4 ,cotton is one of the purest forms of cellulose1 and1 as it may be obtained at a cheap rate1 it has been adopted for the manufacture of explosives4 ,this variety of nitro-cellulose is known as 8gun-cotton40 ,the raw cotton made use of is waste from the cotton mills1 which waste1 after being used for cleaning the machinery1 is swept from the floors and sent to the bleachers to be cleaned4 ,this is done by boiling in strong alkali and lime4 ,after being picked over by hand to remove all foreign substances1 it is torn to pieces in a 8teasing0 machine1 cut up into short lengths1 and dried in an atmosphere of #aij ,f4 ,it is then dipped into a mixture of one part of strong nitric acid and three parts of strong sulphuric acid4 ,the use of the sulphuric acid is1 first1 to abstract water from the nitric acid1 and so to make it stronger2 and1 second1 to take up the water which is formed during the reaction4 ,after the dipping1 it is placed in earthenware pots to digest for twenty-four hours1 in order to ensure the conversion of the whole of the cotton into gun-cotton4 ,to remove the acid1 the gun-cotton is passed through a centrifugal machine1 and subsequently washed and boiled4 ,it is then pulped1 and again washed with water containing ammonia to neutralize any remaining trace of acid4 ,when rendered perfectly pure1 it is compressed into discs and slabs of convenient dimensions for use4 ,another important chemical compound is nitro-glycerine4 ,glycerine is a well-known1 sweet1 viscous liquid that is separated from oils and fats in the processes of candle-making4 ,its chemical formula is3 ,c,h,o2 that is1 the molecule is composed of three atoms of carbon1 in combination with eight atoms of hydrogen1 and three atoms of oxygen4 ,in other words1 glycerine consists of carbon #cia per cent41 hydrogen #hg per cent41 and oxygen #ebb per cent4 ,when this substance is treated1 like cellulose1 with strong nitric acid1 a portion of the hydrogen is displaced1 and peroxide of nitrogen is substituted for it2 thus the product is3 ,c,h7,,no7,o1 similar1 it will be observed1 to nitro-cellulose4 ,this product is known as nitro-glycerine4 ,the formula may be written ,c,h,n,o4 ,hence1 in #bbg lb4 of nitro-glycerine1 there are 7#c #ab7 #cf lb4 of carbon2 7#e #a7 #e lb4 of hydrogen2 7#c #ad7 #db lb4 of nitrogen2 and 7#i #af7 #add lb4 of oxygen2 or #aeh per cent4 is carbon1 #bb per cent4 hydrogen1 #ahe per cent4 nitrogen1 and #fce per cent4 oxygen4 ,when the molecule is broken up by the action of heat1 the oxygen combines with the carbon and the hydrogen1 and sets the nitrogen free4 ,and it will be seen that the quantity of oxygen present is more than sufficient to completely oxidize the carbon and the hydrogen4 ,in this1 the nitro-glycerine is superior to the nitro-cotton4 ,in both of these compounds1 the products of combustion are wholly gaseous1 that is1 they give off no smoke1 and leave no solid residue4 ,in the manufacture of nitro-glycerine1 the acids1 consisting of one part of strong nitric acid and two parts of strong sulphuric acid1 are mixed together in an earthenware vessel4 ,when quite cold1 the glycerine is run slowly into this mixture1 which1 during the process1 is kept in a state of agitation1 as heat is developed in the process2 and1 as the temperature must not rise above #dh ,f41 the vessels are surrounded with iced water1 which is kept in circulation4 ,when a sufficient quantity of glycerine has been run into the mixture1 the latter is poured into a tub of water4 ,the nitro-glycerine being much heavier than the dilute acid mixture1 sinks to the bottom2 the acid liquid is then poured off1 and more water added1 this process being repeated until the nitro-glycerine is quite free from acid4 ,nitro-glycerine is1 at ordinary temperatures1 a clear1 nearly colourless1 oily liquid1 having a specific gravity of about #af4 ,it has a sweet1 pungent taste1 and if placed upon the tongue1 or even if allowed to touch the skin in any part1 it causes a violent headache4 ,below #dj ,f4 it solidifies in crystals4 ,dynamite is nitro-glycerine absorbed in a silicious earth called kieselguhr4 ,usually it consists of about #ge per cent4 nitro-glycerine and #be per cent4 kieselguhr4 ,the use of the absorbent is to remove the difficulties and dangers attending the handling of a liquid4 ,dynamite is a pasty substance of the consistence of putty1 and is1 for that reason1 very safe to handle4 ,it is made up into cartridges1 and supplied for use always in that form4 ,,section ,,iii4--,,relative ,,strength ,,of ,,the ,,common ,,explosive ,,agents4 ,force developed by ,gunpowder4--,in the combustion of gunpowder1 the elements of which it is composed1 which elements1 as we have seen1 are carbon1 hydrogen1 nitrogen1 oxygen1 potassium1 and sulphur1 combine to form1 as gaseous products1 carbonic acid1 carbonic oxide1 nitrogen1 sulphuretted hydrogen1 and marsh gas or carburetted hydrogen1 and1 as solid products1 sulphate1 hyposulphite1 sulphide1 and carbonate of potassium4 ,theoretically1 some of these compounds should not be produced2 but experiment has shown that they are4 ,it has also been ascertained that the greater the pressure1 the higher is the proportion of carbonic acid produced1 so that the more work the powder has to do1 the more perfect will be the combustion1 and1 consequently1 the greater will be the force developed4 ,this fact shows that overcharging is not only very wasteful of the explosive1 but that the atmosphere is more noxiously fouled thereby4 ,the same remark applies even more strongly to gun-cotton and the nitro-glycerine compounds4 ,the careful experiments of ,messrs4 ,noble and ,abel have shown that the explosion of gunpowder produces about #eg per cent4 by weight of solid matters1 and #dc per cent4 of permanent gases4 ,the solid matters are1 at the moment of explosion1 in a fluid state4 ,when in this state1 they occupy #jf of the space originally filled by the gunpowder1 consequently the gases occupy only #jd of that space4 ,these gases would1 at atmospheric pressure and #cb ,f4 temperature1 occupy a space #bhj times that filled by the powder4 ,hence1 as they are compressed into #jd of that space1 they would give a pressure of #bhj --- #ae #aj1ejj lb41 #jd or about #dfh tons to the square inch4 ,but a great quantity of heat is liberated in the reaction1 and1 as it was shown in a former section1 this heat will enormously increase the tension of the gases4 ,the experiments of ,noble and ,abel showed that the temperature of the gases at the instant of explosion is about #djjj ,f4 ,thus the temperature of #cb #dfab #dicb absolute1 has been raised #djjj ------ #haa times1 #dicb so that the total pressure of the gases will be #dfh #haa #dbf tons to the square inch4 ,and this pressure was1 in the experiments referred to1 indicated by the crusher-gauge4 ,when1 therefore1 gunpowder is exploded in a space which it completely fills1 the force developed may be estimated as giving a pressure of about #db tons to the square inch4 ,relative ,force developed by ,gunpowder1 ,gun-cotton1 and ,nitro-glycerine4--,unfortunately no complete experiments have hitherto been made to determine the absolute force developed by gun-cotton and nitro-glycerine4 ,we are1 therefore1 unable to estimate the pressure produced by the explosion of those substances1 or to make an accurate evaluation of their strength relatively to that of gunpowder4 ,it should1 however1 be borne in mind that a correct estimate of the pressure produced to the square inch would not enable us to make a full comparison of the effects they were capable of causing4 ,for though1 by ascertaining that one explosive gives twice the pressure of another1 we learn that one will produce twice the effect of another2 yet it by no means follows from that fact that the stronger will produce no more than twice the effect of the weaker4 ,the rending effect of an explosive depends1 in a great measure1 on the rapidity with which combustion takes place4 ,the force suddenly developed by the decomposition of the chemical compounds acts like a blow1 and it is a well-known fact that the same force1 when applied in this way1 will produce a greater effect than when it is applied as a gradually increasing pressure4 ,but some calculations have been made1 and some experiments carried out1 which enable us to form an approximate estimate of the relative strength of these explosive substances4 ,messrs4 ,roux and ,sarrau give the following as the result of their investigations1 derived from a consideration of the weight of the gases generated and of the heat liberated4 ,the substances are simply exploded1 and the strength of gunpowder is taken as unity4 ---------------------------------------- ------ ,relative ,heat in ,units ,substance4 ,weight liberated ,relative of ,gases4 from #a lb4 ,strength4 ---------------------------------------- ------ ,gunpowder #jdad #acaf #ajj ,gun-cotton #jhej #aijb #cjj ,nitro-glycerine #jhjj #cjig #dhj ---------------------------------------- ------ ,the relative strength is that due to the volume of the gases and the heat1 no account being taken of the increased effect due to the rapidity of the explosion4 ,alfred ,noble has essayed to appreciate the effects of these different explosives by means of a mortar loaded with a #cb-lb4 shot and set at an angle of #aj1 the distances traversed by the shot being taken as the results to be compared4 ,considered1 weight for weight1 he estimates as follows the relative strengths of the substances compared1 gunpowder being again taken as unity3-- ,gunpowder #ajj ,gun-cotton #bhd ,dynamite #bhi ,nitro-glycerine #djj ,the relative strength1 bulk for bulk1 is1 however1 of greater importance in rock blasting4 ,this is easily computed from the foregoing table and the specific gravity of the substances1 which is #ajj for gunpowder and compressed gun-cotton1 #afj for nitro-glycerine1 and #afe for dynamite4 ,compared in this way1 bulk for bulk1 these explosives range as follows3-- ,gunpowder #ajj ,gun-cotton #beg ,dynamite #dbc ,nitro-glycerine #ega ,hence1 for a given height of charge in a bore-hole1 gun-cotton exerts about #b times the force of gunpowder1 and dynamite about #d times that force4 ,,section ,,iv4--,,means ,,of ,,firing ,,the ,,common ,,explosive ,,agents4 ,action of ,heat4--,we have seen that the oxygen required for the combustion of the carbon in gunpowder is stored up in the saltpetre4 ,so long as the saltpetre remains below a certain temperature1 it will retain its oxygen2 but when that temperature is reached1 it will part with that element4 ,to fire gunpowder1 heat is therefore made use of to liberate the oxygen1 which at once seizes upon the carbon with which it is in presence4 ,the means employed to convey heat to an explosive have been described in the preceding chapter4 ,it is necessary to apply heat to one point only of the explosive2 it is sufficient if it be applied to only one grain4 ,that portion of the grain which is thus raised in temperature begins to 8burn10 as it is commonly expressed1 that is1 this portion enters at once into a state of combustion1 the saltpetre giving up its oxygen1 and the liberated oxygen entering into combination with the carbon4 ,the setting up of this action is called 8ignition40 ,the hot gases generated by the combustion set up ignite other grains surrounding the one first ignited2 the gases resulting from the combustion of these ignite other grains2 and1 in this way1 ignition is conveyed throughout the mass4 ,thus the progress of ignition is gradual4 ,but though it takes place1 in every case1 gradually1 if the gases are confined within the space occupied by the powder1 it may be extremely rapid4 ,it is easy to see that the gases evolved from a very small number of grains are sufficient to fill all the interstices1 and to surround every individual grain of which the charge is composed4 ,but besides this ignition from grain to grain1 the same thing goes on from the outside to the inside of each individual grain1 the grain burning gradually from the outside to the inside in concentric layers4 ,the successive ignitions in this direction1 however1 of layer after layer1 is usually described as the progress of combustion4 ,thus the time of an explosion is made up of that necessary for the ignition of all the grains1 and of that required for their complete combustion4 ,the time of ignition is determined in a great measure by the proportion which the interstices1 or empty spaces between the grains1 bear to the whole space occupied by the powder4 ,if the latter be in the form of an impalpable dust1 ignition cannot extend throughout the mass in the manner we have described2 but we shall have merely combustion proceeding from grain to grain4 ,if1 on the contrary1 the powder be in large spherical grains or pellets1 the interstices will be large1 and the first gases formed will flash through these1 and ignite all the grains one after another with such rapidity that ignition may be regarded as simultaneous4 ,thus the time of ignition is shortened by increasing the size of the grains and approximating the latter to the spherical form4 ,but the time of combustion is determined by conditions contrary to these4 ,as combustion proceeds gradually from the outside to the inside of a grain1 it is obvious that the larger the grain is1 the longer will be the time required to burn it in4 ,also it is evident that if the grain be in the form of a thin flake1 it will be burned in a much shorter time than if it be in the spherical form4 ,thus the conditions of rapid ignition and rapid combustion are antagonistic4 ,the minimum time of explosion is obtained when the grains are irregular in shape and only sufficiently large to allow a fairly free passage to the hot gases4 ,there are other conditions which influence the time of combustion2 among them is the density of the grain4 ,this is obvious1 since the denser the grain1 the greater is the quantity of material to be consumed4 ,but besides this1 combustion proceeds more slowly through a dense grain than through an open one4 ,the presence of moisture also tends to retard combustion4 ,the progress both of ignition and of combustion is accelerated1 not uniform4 ,in proportion as the grains are ignited1 the gases evolved increase in volume1 and as the progress of combustion continues to generate gases1 the tension of these increases1 until1 as we have seen1 the pressure rises as high as #db tons to the square inch4 ,as the pressure increases1 the hot gases are forced more and more deeply into the grains1 and combustion1 consequently1 proceeds more and more rapidly4 ,detonation4--,by detonation is meant the simultaneous breaking up of all the molecules of which the explosive substance is composed4 ,properly the term is applicable to the chemical compounds only4 ,but it is applied to gunpowder to denote the simultaneous ignition of all the grains4 ,the mode of firing by detonation is obviously very favourable to the rending effect required of blasting powder1 since it reduces to a minimum the time of explosion4 ,it is brought about1 in all cases1 by means of an initial explosion4 ,the detonator1 which produces this initial explosion1 consists of an explosive compound1 preferably one that is quick in its action1 contained within a case sufficiently strong to retain the gases until they have acquired a considerable tension4 ,when the case bursts1 this tension forces them instantaneously through the interstices of the powder1 and so produces simultaneous ignition4 ,a pellet of gun-cotton1 or a cartridge of dynamite1 the latter especially1 makes a good detonator for gunpowder4 ,fired in this way1 very much better effects may be obtained from gunpowder than when fired in the usual manner4 ,indeed1 in many kinds of rock1 more work may be done with it than with gun-cotton or with dynamite4 ,the action of a detonator upon a chemical compound is different4 ,in this case1 the explosion seems to be due more to the vibration caused by the blow than by the heat of the gases from the detonator4 ,probably both of these causes operate in producing the effect4 ,however this may be1 the fact is certain that under the influence of the explosion of the detonator1 the molecules of a chemical compound1 like nitro-glycerine1 are broken up simultaneously1 or at least1 so nearly simultaneously1 that no tamping is needed to obtain the full effect of the explosion4 ,dynamite is always1 and gun-cotton is usually1 fired by means of a detonator4 ,a much larger quantity of explosive is needed to detonate gunpowder than is required for dynamite1 or gun-cotton1 since1 for the former explosive1 a large volume of gases is requisite4 ,dynamite detonators usually consist of from six to nine grains of fulminate of mercury contained in a copper cap1 as described in the preceding chapter4 ,gun-cotton detonators are similar1 but have a charge of from ten to fifteen grains of the fulminate4 ,an insufficient charge will only scatter the explosive instead of firing it1 if it be unconfined1 and only explode it without detonation1 if it be in a confined space4 ,,section ,v4--,,some ,,properties ,,of ,,the ,,common ,,explosive ,,agents4 ,gunpowder4--,the combustion of gunpowder1 as we have seen1 is gradual and comparatively slow4 ,hence its action is rending and projecting rather than shattering4 ,this constitutes one of its chief merits for certain purposes4 ,in many quarrying operations1 for instance1 the shattering action of the chemical compounds would be very destructive to the produce4 ,in freeing blocks of slate1 or of building stone1 a comparatively gentle lifting action is required1 and such an action is exerted by gunpowder4 ,moreover1 this action may be modified by using light tamping1 or by using no tamping1 a mode of employing gunpowder often adopted in slate quarries4 ,the effect of the violent explosives cannot be modified in this way4 ,gunpowder is injured by moisture4 ,a high degree of moisture will destroy its explosive properties altogether1 so that it cannot be used in water without some protective covering4 ,even a slight degree of moisture1 as little as one per cent4 of its weight1 materially diminishes its strength4 ,for this reason1 it should be used1 in damp ground1 only in cartridges4 ,this is1 indeed1 the most convenient and the most economical way of using gunpowder in all circumstances4 ,it is true that there is a slight loss of force occasioned by the empty space around the cartridge1 in holes that are far from circular in shape4 ,but at least as much will be lost without the cartridge from the moisture derived from the rock1 even if the hole be not wet4 ,but in all downward holes1 the empty spaces may be more or less completely filled up with dry loose sand4 ,the products of the explosion of gunpowder are partly gaseous1 partly solid4 ,of the former1 the most important are carbonic acid1 carbonic oxide1 and nitrogen4 ,the sulphuretted and the carburetted hydrogen are formed in only small quantities4 ,the carbonic oxide is a very noxious gas2 but it is not formed in any considerable quantity1 except in cases of overcharging4 ,the solid products are compounds of potassium and sulphur1 and potassium and carbon4 ,these constitute the smoke1 the dense volumes of which characterize the explosion of gunpowder4 ,this smoke prevents the immediate return of the miner to the working face after the blast has taken place4 ,gun-cotton4--,the combustion of gun-cotton takes place with extreme rapidity1 in consequence of which its action is very violent4 ,its effect is rather to shatter the rock than to lift it out in large blocks4 ,this quality renders it unsuitable to many quarrying operations4 ,in certain kinds of weak rock1 its disruptive effects are inferior to those produced by gunpowder4 ,but in ordinary mining operations1 where strong tough rock has to be dealt with1 its superior strength and quickness of action1 particularly the latter quality1 produce much greater disruptive effect than can be obtained from gunpowder4 ,moreover1 its shattering action tends to break up into small pieces the rock dislodged1 whereby its removal is greatly facilitated4 ,gun-cotton may be detonated when in a wet state by means of a small quantity of the dry material4 ,this is a very important quality1 inasmuch as it allows the substance to be used in a wet hole without protection1 and conduces greatly to the security of those who handle it4 ,when in the wet state1 it is uninflammable1 and cannot be exploded by the heaviest blows4 ,only a powerful detonation will bring about an explosion in it when in the wet state4 ,it is1 therefore1 for safety1 kept and used in that state4 ,since it is insensible to blows1 it may be rammed tightly into the bore-hole1 so as to fill up all empty spaces4 ,the primer of dry gun-cotton1 however1 which is to detonate it1 must be kept perfectly dry1 and handled with caution1 as it readily detonates from a blow4 ,gun-cotton1 when ignited in small quantities in an unconfined space1 burns fiercely1 but does not explode4 ,the products of the combustion of gun-cotton are3--carbonic acid1 carbonic oxide1 water1 and a little carburetted hydrogen or marsh-gas4 ,on account of the insufficiency of oxygen1 already pointed out1 a considerable proportion of carbonic oxide is formed1 which vitiates the atmosphere into which it is discharged4 ,overcharging1 as in the case of gunpowder1 causes an abnormal quantity of the oxide to be formed4 ,dynamite4--,as combustion takes place more rapidly in nitro-glycerine than in gun-cotton1 the effects of dynamite are more shattering than those of the latter substance4 ,gun-cotton holds1 indeed1 a mean position in this respect between dynamite1 on the one hand1 and gunpowder on the other4 ,dynamite is1 therefore1 even less suitable than gun-cotton for those uses which are required to give the produce in large blocks4 ,but in very hard and tough rock1 it is considerably more effective than gun-cotton1 and1 under some conditions1 it will bring out rock which gun-cotton fails to loosen4 ,dynamite is unaffected by water1 so that it may be used in wet holes2 indeed1 water is commonly used as tamping1 with this explosive4 ,in upward holes1 where water cannot1 of course1 be used1 dynamite is generally fired without tamping1 its quick action rendering tamping unnecessary4 ,the pasty form of dynamite constitutes a great practical advantage1 inasmuch as it allows the explosive to be rammed tightly into the bore-hole so as to fill up all empty spaces and crevices4 ,this is important1 for it is obvious that the more compactly the charge is placed in the hole1 the greater will be the effect of the explosion4 ,moreover1 this plastic character renders it very safe to handle1 as blows can hardly produce sufficient heat in it to cause explosion4 ,if a small quantity of dynamite be placed upon an anvil and struck with a hammer1 it explodes readily2 but a larger quantity so struck does not explode1 because the blow is cushioned by the kieselguhr4 ,if ignited in small quantities in an unconfined space1 it burns quietly without explosion4 ,if dynamite be much handled out of the cartridges1 it causes violent headaches2 and the same effect is produced by being in a close room in which there is dynamite in the unfrozen state4 ,dynamite possesses one quality which places it at a disadvantage with respect to other explosives1 namely1 that of freezing at a comparatively high temperature4 ,at about #dj ,f4 the nitro-glycerine solidifies1 and the dynamite becomes chalky in appearance4 ,in this state1 it is exploded with difficulty1 and1 consequently1 it has to be thawed before being used4 ,this may be safely done with hot water2 performed in any other way the operation is dangerous4 ,the products of the combustion of dynamite are carbonic acid1 carbonic oxide1 water1 and nitrogen4 ,as1 however1 there is more than a sufficiency of oxygen in the compound1 but little of the oxide is formed when the charge is not excessive4 ,if1 therefore1 dynamite be properly detonated1 and overcharging be avoided1 its explosion will not greatly vitiate the atmosphere4 ,but if it be only partially detonated hypo-nitric fumes are given off1 which have a very deleterious effect upon the health4 ,it is1 thus1 of the highest importance that complete detonation should be effected1 not merely to obtain the full effect of the explosive1 but to avoid the formation of this noxious gas4 ,this may be done by using a detonator of sufficient strength1 and placing it well into the primer4 ,firing ,points of the ,common ,explosive ,compounds4--,the following table shows the temperatures at which the commonly used compounds explode3-- ---------------------------------------- ------- ,when slowly ,when suddenly ,heated4 ,heated4 ---------------------------- ,gunpowder 44 from #ejj to #edj ,gun-cotton #cfj #dhb ,kieselguhr dynamite #cef #ddf ,cellulose dynamite #cdb #ddf ---------------------------------------- ------- ,cotton powder explodes at the same temperatures as gun-cotton1 and lithofracteur at the same temperature as kieselguhr dynamite4 ,,section ,,vi4--,,some ,,varieties ,,of ,,the ,,nitro-,,cellulose ,,and ,,the ,,nitro-,,glycerine ,,compounds4 ,nitrated ,gun-cotton4--,it has been shown that gun-cotton contains an insufficient quantity of oxygen for its complete combustion4 ,to furnish that which is wanting1 gun-cotton has sometimes incorporated with it a certain proportion of nitrate of potash1 or of nitrate of baryta4 ,this compound1 which1 it will be observed1 is at once a chemical compound and a mechanical mixture1 is known as 8nitrated gun-cotton40 ,cotton ,powder1 or ,tonite4--,the explosive which is now well known as 8tonite0 or 8cotton powder10 is essentially nitrated gun-cotton4 ,it is produced in a granulated form1 and is compressed into cartridges of various dimensions to suit the requirements of practice4 ,the convenient form in which tonite is made up1 ready to the miner's hand1 has greatly contributed towards bringing it into favour4 ,but irrespective of this1 the fact of its being so highly compressed as to give it a density equal1 or nearly equal1 to dynamite gives it a decided advantage over the other nitro-cotton compounds as they are at present used4 ,schultze's ,powder4--,in ,schultze's powder1 the cellulose is obtained from wood4 ,the wood is first sawn into sheets1 about _/ inch thick1 and then passed through a machine1 which punches it up into grains of a uniform size4 ,these are deprived of their resinous matters by a process of boiling in carbonate of soda1 and are further cleansed by washing in water1 steaming1 and bleaching by chloride of lime4 ,the grains1 which are then pure cellulose1 are converted into nitro-cellulose in the same way as cotton1 namely1 by being treated with a mixture of nitric and sulphuric acids4 ,the nitro-cellulose thus produced is subsequently steeped in a solution of nitrate of potash4 ,thus the finished compound is similar in character to nitrated gun-cotton4 ,lithofracteur4--,lithofracteur is a nitro-glycerine compound in which a portion of the base is made explosive4 ,in dynamite1 the base1 or absorbent material1 is1 as we have said1 a silicious earth1 called 8kieselguhr40 ,in lithofracteur1 the same substance is used2 but in addition1 a mixture of nitrate of baryta and charcoal1 a kind of gunpowder1 is introduced4 ,the object of employing this explosive mixture is to increase the force of the explosion1 the kieselguhr being an inert substance4 ,obviously this object would be attained if the explosive mixture possessed the same absorbent power as the kieselguhr4 ,but unfortunately it does not1 and1 as a consequence1 less nitro-glycerine is used4 ,thus what is gained in the absorbent is lost in the substance absorbed4 ,the composition of lithofracteur varies somewhat2 but its average proportion of ingredients are the following3-- ,nitro-glycerine #ebej ,nitrate of baryta #afdj ,charcoal #bhe ,sulphur #bege ,kieselguhr #bbej ------ #ajjjj ------ ,brain's ,powder4--,brain's powder is a nitro-glycerine compound1 similar in character to lithofracteur4 ,the exact composition of the base has never been published1 so far as relates to the proportions of the ingredients4 ,but it is composed of chlorate of potash1 charcoal1 and nitrated sawdust4 ,the proportion of nitro-glycerine never exceeds #dj per cent4 ,horseley's powder contains about the same proportion of nitro-glycerine in a base of chlorate of potash and nut-galls4 ,cellulose ,dynamite4--,in ,germany1 gun-cotton is used as an absorbent for nitro-glycerine1 the compound being known as 8,cellulose dynamite40 ,it is chiefly used for primers to explode frozen dynamite4 ,it is more sensitive to blows than the kieselguhr dynamite4 ,,chapter ,,iii4 ,,the ,,principles ,,of ,,rock ,,blasting4 ,line of ,least ,resistance4--,the pressure of a fluid is exerted equally in all directions2 consequently the surrounding mass subjected to the force will yield1 if it yield at all1 in its weakest part1 that is1 the part which offers least resistance4 ,the line along which the mass yields1 or line of rupture1 is called the 8line of least resistance40 ,if the surrounding mass were perfectly homogeneous1 it would always be a straight line1 and it would be the shortest distance from the centre of the charge to the surface4 ,such1 however1 is never the case1 and the line of rupture is1 therefore1 always a more or less irregular line1 and often much longer than that from the centre direct to the surface4 ,it will be obvious1 on reflection1 that the line of least resistance will be greatly dependent upon 7#a7 the texture of the rock1 which may vary from one point to another2 7#b7 its structure1 which renders it more easily cleavable in one direction than in another2 7#c7 the position1 direction1 and number of the joints1 which separate the rock into more or less detached portions2 and 7#d7 the number and relative position of the unsupported faces of the rock4 ,all these circumstances must be ascertained1 and the position and the direction of the bore-hole determined in accordance with them1 in order to obtain the maximum effect from a given quantity of explosive4 ,it must not be supposed1 however1 that this is a labour involving minute examination and long consideration4 ,on the contrary1 a glance is generally sufficient to enable the trained eye to estimate the value of those circumstances1 and to determine accordingly the most effective position for the shot4 ,in practice1 the line of least resistance is taken as the shortest distance from the centre of the charge to the surface of the rock1 unless the existence of joint planes1 a difference of texture1 or some other circumstance1 shows it to lie in some other direction4 ,force required to cause ,disruption4--,when the line of least resistance is known1 it remains to determine the quantity of the explosive compound required to overcome the resistance along that line4 ,this matter is one of great importance1 for not only is all excess waste1 but this waste will be expended in doing mischief4 ,in mining operations1 the dislodged rock is violently projected1 and the air is vitiated in an unnecessary degree2 and in quarrying1 stones are shattered which it is desirable to extract in a sound state4 ,the evil effects of overcharging1 in occasioning the formation of noxious gases1 was pointed out in the last chapter4 ,of course it is not possible so to proportion a charge to the resistance that the rock shall be just lifted out1 and no more2 because neither the force developed by the charge1 nor the value of the resistance can be known with precision4 ,but a sufficient approximation may be easily arrived at to enable us to avoid the loud report that is indicative of wasted force4 ,charges of an explosive compound of uniform strength produce effects that vary as the weight of those charges1 that is1 a double charge will move a double mass4 ,and1 as homogeneous masses vary as the cube of any similar line within them1 the general rule is established that charges of powder capable of producing the same effects are to each other as the cubes of the lines of least resistance4 ,generally1 the quantity of black blasting powder requisite to overcome the resistance will vary from _/ to _/ of the cube of the line of least resistance1 the latter being measured in feet and the former in pounds4 ,thus1 if the rock to be blasted be moderately strong limestone1 for example1 and the shortest distance from the centre of the charge to the surface of the rock be #c feet1 we shall have #c #c #c #bg1 the cube of the line1 and _/ lb4 #a_/ lb41 or about #a lb4 #a oz41 as the weight of the powder required4 ,if dynamite be used1 and we assume it to be four times as strong as common black powder1 of course1 only one-fourth of this quantity will be required4 ,also if gun-cotton1 or cotton-powder1 be used1 and we assume its strength to be three times that of black powder1 one-third only will be needed4 ,again1 if ,curtis's and ,harvey's new extra-strong mining powder fired by a detonator be employed1 we may assume it to be twice as strong as common black powder fired by the ordinary means1 and consequently we shall need only one-half the quantity indicated by the formula4 ,it is neither practicable nor desirable that such calculations and measurements as these should be made for every blast2 their practical value lies in this1 namely1 that if the principles involved in them be clearly understood1 the blaster is enabled to proportion his charges by sight to the resistance to be overcome1 with a sufficient degree of precision4 ,a few experiments in various kinds of rock1 followed by some practice1 will enable a man to acquire this power4 ,as it is a common and a convenient practice to make use of the bore-hole as a measure of the quantity of explosive to be employed1 we have calculated the following table3-- ---------------------------------------- --- ,diameter ,dynamite 7or of ,black ,powder,gun-cotton ,tonite7 the ,hole4 in #a inch4 in #a inch4 in #a inch4 ---------------------------------------- --- ins4 ozs4 ozs4 ozs4 #a #jdai #jdai #jfgj #a #jfed #jfed #ajdf #a #jidb #jidb #aejg #a #abhc #abhc #bjec #b #afge #afge #bfhj #b #babj #babj #ccib #b #bfah #bfah #dahi #b #caff #caff #ejff #c #cgfi #cgfi #fjcj ---------------------------------------- --- ,illustration3 ,,fig4 #dj4 ,illustration3 ,,fig4 #da4 ,illustration3 ,,fig4 #db4 ,illustration3 ,,fig4 #dc4 ,conditions of ,disruption4--,having explained the law according to which the elastic gases evolved by an explosion act upon the surrounding rock1 and shown how the force required to cause disruption may be calculated1 it now remains to consider the conditions under which disruption may take place4 ,suppose a block of unfissured rock detached on all sides1 as shown in plan1 in ,fig4 #dj1 and a bore-hole placed in the centre of this block4 ,if a charge be fired in this position1 the lines of rupture will radiate from the centre towards any two1 or towards all four of the unsupported faces of the block1 because the forces developed will act equally in all directions1 and the lines of rupture will be those of least resistance4 ,evidently this is the most favourable condition possible for the charge1 since the rock offers an unsupported face on every side2 and it is evident that the line of rupture must reach an unsupported face to allow of dislodgement taking place4 ,suppose1 again1 as shown in ,fig4 #da1 the block to be unsupported on three sides only1 and the charge placed at h4 ,in this case1 the lines of rupture may run to any two1 or to all three1 of the unsupported faces2 and hence this will be the next most favourable condition for the action of the charge4 ,the greatest useful effect1 however1 will be obtained in this case by placing the charge farther back at h1 when the lines of rupture must necessarily run to the opposite faces b c1 and1 consequently1 the whole of the block will be dislodged4 ,assume another case1 in which the rock is unsupported upon only two sides1 as shown in ,fig4 #db1 and the charge placed at h4 ,in this case1 the lines of rupture must run to each of the unsupported faces a b4 ,thus1 it is evident that this condition1 though still a favourable one for the good effect of the charge1 is inferior to the preceding4 ,as rock is never homogeneous in composition nor uniform in texture1 the lines of rupture1 which1 as before remarked1 will be those of least resistance1 may reach the faces at any point1 as at m n1 m n1 or any point intermediate between these4 ,but it will be seen that the useful effect will be greatest when these lines1 radiating from the charge1 make an angle of #ahj1 or1 in other words1 run in directly contrary directions1 and that the useful effect diminishes with the angle made by these lines of rupture4 ,suppose1 again1 the rock to be unsupported upon one side only1 as shown in ,fig4 #dc1 and the charge placed at h4 ,in this case1 the lines of rupture must run to the face a1 and the condition must therefore be considered as less favourable than the preceding4 ,as in those cases1 the useful effect will depend upon the angle made by the lines of rupture h m and h n1 which angle may be very small1 and which must necessarily be much less than #ahj4 ,a greater effect may be obtained1 under this condition1 by firing several charges simultaneously4 ,if1 for example1 we have two charges placed1 one at h1 and the other at h1 and fired successively1 the lines of rupture will run in or near the directions h m1 h n1 h m1 h n1 and the portion of rock dislodged will be m h n h n4 ,but if these two charges be fired simultaneously1 the lines of rupture will be h m1 h o1 h o1 h n1 and the mass of rock dislodged will be m h h n4 ,simultaneous firing is in this way productive of a greatly increased useful effect in numerous cases1 and the mining engineer1 and the quarryman especially1 will do well to direct their attention to this source of economy4 ,there is yet another case to be considered1 in which the conditions are still less favourable4 ,suppose two unsupported faces at right angles to each other1 and the charge placed at h1 as shown in ,fig4 #dd4 ,in this case1 the lines of rupture will run to each of the two unsupported faces2 but as these lines must necessarily make a very small angle with each other--for the length of the lines increases rapidly with the angle--the useful effect will be less than in the last case4 ,it follows1 therefore1 that this is the most unfavourable condition possible1 and as such it should be avoided in practice4 ,illustration3 ,,fig4 #dd4 ,illustration3 ,,fig4 #de4 ,illustration3 ,,fig4 #df4 ,in the foregoing considerations1 the holes have been assumed to be vertical1 and for this reason the unsupported face which is perpendicular to the hole1 that is1 the face into which the hole is bored1 has been neglected4 ,for it is evident that1 under the conditions assumed1 the lines of rupture cannot reach this face1 which1 therefore1 has practically no existence4 ,suppose1 for example1 a bore-hole placed at h1 in ,fig4 #de1 and the rock to be supported upon every side except that at right angles to the hole4 ,the forces acting perpendicularly to the direction of the bore-hole are opposed on all sides by an infinite resistance4 ,hence1 in this case1 either the tamping will be blown out1 or1 if the forces developed are unequal to the work1 no effect will be produced beyond a slight enlargement of the hole at the base4 ,this1 however1 is a case of frequent occurrence in practice1 and it becomes necessary to adopt measures for making this unsupported face available4 ,evidently this object can be attained only by so directing the bore-hole that a line perpendicular to it may reach the face2 that is1 the line of the bore-hole must make with the unsupported face an angle less than #ij4 ,this direction of the bore-hole is shown in ,fig4 #df1 which may be regarded as a sectional elevation of ,fig4 #de4 ,in this case1 the lines of rupture1 which will run similarly to those produced in the case shown in ,fig4 #dc1 will reach the unsupported face at b1 and the length of these lines1 and consequently the depth of the excavation1 for a given length of bore-hole1 will depend upon the angle which the latter makes with the face4 ,this mode of rendering a single exposed surface available is called 8angling the holes10 and it is generally resorted to in shaft sinking and in driving headings4 ,the conditions involved in 8angling0 are favourable to the action of strong explosives4 ,example of a ,heading4--,to show how these principles are applied in practice1 we will take a typical case of a heading1 #g feet by #i feet1 as shown in ,fig4 #dg4 ,in this case1 we have at starting only one exposed face1 which is perpendicular to the direction of the driving4 ,hence it is evident that we shall have to proceed by angling the holes4 ,we might begin in any part of the exposed face2 but1 as it will hereafter appear1 the most favourable position is the centre4 ,we therefore begin at this point by boring a series of holes1 numbered #a on the drawing4 ,these holes are angled towards each other2 that is1 the two sets of three holes vertically above each other converge in the direction of their lower ends1 as shown in the sectional plan1 ,fig4 #dh4 ,in this instance1 we have assumed six holes as necessary and sufficient4 ,but it is obvious that the number of holes1 as well as their distance apart horizontally1 will be determined by their depth1 the tenacity of the rock1 and the strength of the explosive used4 ,when these holes are fired1 a wedge-shaped portion of the rock will be forced out1 and this result will be more effectually and certainly obtained if the charges be fired simultaneously4 ,the removal of this portion of the rock is called 8taking out the key40 ,the effect of removing this key is to leave the surrounding rock unsupported on the side towards the centre2 that is1 another face is formed perpendicular to the first4 ,illustration3 ,,fig4 #dg4 ,illustration3 ,,fig4 #dh4 ,illustration3 ,,fig4 #di4 ,having thus unkeyed the rock by the removal of this portion from the centre1 it will evidently be unnecessary1 except for convenience or increased effect1 to angle any more of the shot-holes4 ,the second series therefore1 numbered #b in the drawing1 may be bored perpendicularly to the face of the heading4 ,when this series is fired1 the lines of rupture will all run to the unsupported face in the centre--and from hole to hole1 if the shots be fired simultaneously--and the annular portion of rock included between the dotted lines #a and #b will be removed4 ,if the shots be fired successively1 the first will act under the condition of one unsupported face1 as illustrated in ,fig4 #dc2 but as another unsupported face will be formed by the removal of the rock in front of this charge1 the succeeding shots will be subject to the more favourable condition represented in ,fig4 #db4 ,the firing of this second series of shots still leaves the surrounding rock unsupported towards the centre1 and consequently the same conditions will exist for the third series1 numbered #c on the drawing1 the firing of which series will complete the excavation4 ,fig4 #di shows the appearance of ,fig4 #dh after the firing of the central holes4 ,it may be remarked here that1 owing to the want of homogeneity in the rock1 and to the existence of joints and fissures1 the outer line of rupture will not1 in practice1 run so regularly as indicated1 in this assumed case1 by the dotted lines4 ,this circumstance will influence the position of the holes1 or the quantity of explosive1 in the next series1 and furnish an opportunity for the exercise of judgment on the part of the blaster4 ,there exist also other circumstances which will influence the position and the number of the holes in a very important degree1 and which therefore must be taken fully into account at every advance4 ,one of these is the irregularity of the face of the excavation4 ,instead of forming an unbroken plane at right angles to the direction of the heading1 or of the shaft1 this face is broken up by projecting bosses and more or less deep depressions4 ,obviously these protuberances and cavities will influence1 in no inconsiderable degree1 the lines of least resistance2 the latter being lengthened or shortened1 or changed in direction1 by the presence of the former1 which give existence to unsupported faces to which the lines may radiate4 ,these conditions must1 in every case1 be taken into account when determining the best position for the bore-hole4 ,of yet greater importance1 is the existence of joint planes and bedding planes4 ,a bed of rock may be1 and frequently is1 cut up by these planes into detached blocks of greater or less dimensions1 according to the more or less perfect development of the different sets4 ,hence it becomes necessary1 in determining a suitable position for blasting the charge1 to consider such planes as unsupported faces1 and to ascertain the direction and length of the lines of resistance under such conditions4 ,if a charge be placed in close proximity to one of these planes1 not only may the lines of rupture run in unforeseen directions1 but the greater part of the force of the explosion will be lost by the escape of the gases along the plane4 ,the same loss of force may be occasioned by the presence of a cavity1 such as are of frequent occurrence in cellular or vughy rock4 ,when the joint planes are fully developed1 their existence can be ascertained by inspection2 but when their development is imperfect1 there may be considerable difficulty in discovering them4 ,in such cases1 the rock should be carefully inspected1 and sounded with a hammer or pick4 ,when a cavity is bored into1 it may be rammed full of clay1 and the boring continued through the clay2 or if sufficient depth has been obtained1 the charge may be placed upon the clay1 which will prevent the wasteful dissipation of the gases4 ,as none of the aforementioned circumstances occur under precisely similar conditions1 no general rule of much service can be laid down2 they are matters upon which the blaster must be left to use his own judgment1 and to do this effectively1 it is necessary that he possess some knowledge of the materials with which he deals4 ,economical ,considerations4--,besides the important economical considerations involved in the foregoing1 there are others which claim attention4 ,foremost among these is the question whether1 for a given effect1 it be better to augment or to diminish the individual importance of the shots2 that is1 whether it be better to diminish the number of the holes and to increase their diameter1 or to diminish their diameter and increase their number2 or1 again1 to diminish their diameter and to increase their depth1 or to increase their diameter and to diminish their number and their depth4 ,it may be readily shown mathematically1 and the results are confirmed by experience1 that there is an important gain in reducing the diameter of the shot-holes to the lowest limit allowed by the strength and the gravimetric density of the explosive1 and increasing their depth4 ,the gain is mainly in the direction of a saving of labour1 and it is especially remarkable in the case of machine boring4 ,here again we perceive the advantage of strength in the explosive agent employed4 ,the simultaneous firing of the shots offers several important advantages4 ,it has already been shown how one charge aids another1 under such a condition1 and in what way the line of rupture is affected by it4 ,when the shots are fired successively1 each one has to tear out the portion of rock allotted to it2 but when they are fired simultaneously1 their collective force is brought to bear upon the whole mass to be dislodged4 ,this is seen in the diagram1 ,fig4 #dc4 ,when deep holes are used1 the greater useful effect caused by simultaneous firing becomes very marked4 ,hence electricity associates itself naturally with machine drills and strong explosives4 ,tamping4--,to 8tamp0 a shot-hole is to fill it up above the charge of explosive with some material1 which1 when so applied1 is called the 8tamping40 ,the object of tamping is to oppose a resistance to the escape of the gases in the direction of the bore-hole4 ,hence a primary condition is that the materials used shall be of a strongly resisting character4 ,a second determining condition is that these materials shall be of easy application4 ,this condition precludes the use of all such devices as plugs1 wedges1 and forms of a similar character1 which have been from time to time proposed4 ,the only material that1 in practice1 has been found to satisfactorily fulfil the requirements1 is rock in a broken1 pulverulent1 or plastic state4 ,as1 however1 all rock is not equally suitable1 either from the point of view of its resisting character1 or from that of convenience of handling1 it becomes necessary to consider which satisfies the two conditions in the most complete manner4 ,though it is not easy to assign a perfectly satisfactory reason why one kind of rock substance opposes a greater resistance to motion in a bore-hole than another1 yet it is certain that this resistance is mainly due to the friction among the particles of that substance4 ,if a column of solid1 hard rock1 of the same diameter as the bore-hole1 be driven down upon the charge1 the resistance opposed by the column to the imprisoned gases will be1 neglecting the weight of the former1 that of the friction between the sides of the column and those of the hole4 ,but if disintegrated rock be used1 not only is an absolute motion imparted to the particles1 but1 on account of the varying resistances1 a relative motion also4 ,consequently1 friction occurs amongst the particles1 and as the number of these is immense1 the sum of the slight friction of one particle against another1 and of the great friction of the outside particles against the sides of the hole1 amounts to a much greater value than that of the outside particles of the solid column against the sides of the bore-hole4 ,if this view of the facts alone be taken1 it follows that dry sand is the most resistant material1 and that the finer the grains1 the greater will be the resistance which it offers4 ,in practice1 however1 it has been found that though the resistance offered by sand tamping is very great1 and though also the foregoing inference is true when the tamping is lifted by the pressure of a solid against it from below1 this substance is notably inferior to some others when acted upon by an explosion of gases4 ,the explanation of this apparent anomaly is that the gases1 under the enormous tension to which they are subjected in the bore-hole1 insinuate themselves between the particles1 and so prevent the friction which would otherwise take place4 ,when the readiness with which water1 through the influence of gravity alone1 permeates even closely compacted sand1 is borne in mind1 there will be no difficulty in conceiving a similar action on the part of more subtile gases in a state of extreme tension4 ,under such conditions as these1 there is no resistance whatever due to friction1 and the only resistance opposed to the escape of the gases is that proceeding from the inertia of the mass4 ,how this resistance may be very great1 we have shown in the case of air tamping4 ,hence1 it becomes necessary to have recourse to some other material of a composition less liable to be thus acted upon1 or to seek means of remedying the defect which renders such action possible4 ,clay1 dried either in the sun1 or1 preferably1 by a fire1 appears to fulfil the requirements of a tamping material in the fullest degree4 ,this substance is composed of exceedingly minute grains of silicious matters1 bound together by an aluminous and calcareous or ferruginous cement4 ,thus constituted1 there are no voids between the particles1 as in porous substances1 and1 consequently1 there is no passage for the gases1 the substance being impervious alike to water and gas4 ,hence1 when this material is employed as tamping1 the forces act only upon the lower surface1 friction takes place among the particles1 and the requisite degree of resistance is produced4 ,by reason of its possession of this property1 clay is generally used as the tamping material4 ,in rock blasting1 it is usual to prepare the clay beforehand1 and this practice is conducive both to effective results and to rapidity of tamping4 ,the latter consideration is an important one1 inasmuch as the operation1 as commonly performed1 requires a good deal of time4 ,to prepare the pellets of clay1 a lump is taken and rolled between the palms of the hands until it has assumed the form of a sausage1 from three to four inches in length1 and of the diameter of the bore-hole4 ,these pellets are then baked until they are thoroughly dry1 when they are ready for use4 ,in making them up to the requisite diameter1 a little excess should be allowed for shrinkage1 since it is essential that they fit tightly into the hole4 ,when the charge has been put in1 and covered with a wad of hay1 or a handful of sand or rubbish1 one of these pellets is inserted and pushed home with a wooden rammer4 ,considerable pressure should be applied to make the clay fill the hole completely1 but blows should be avoided4 ,a second pellet is then pushed down in the same way1 and the operations are repeated until the whole of the hole is tamped4 ,to consolidate the whole1 light blows may be applied to the outer pellet4 ,it will be found advantageous to place an undried pellet immediately above the charge1 because the plasticity of such a pellet enables it to fill all the irregularities of the sides of the hole1 and to securely seal the passage between the sides and the tamping1 along which the gases might otherwise force their way4 ,in coal blasting1 soft shale is always used for tamping1 because it is ready at hand1 and heavy shots are not required4 ,broken brick constitutes a fairly good tamping material1 especially when tempered with a little moisture2 but as it is not readily procurable1 its application is necessarily limited4 ,the dust and chippings of the excavated rock are largely employed as tamping in quarries4 ,this material1 however1 has but little to recommend it for the purpose beyond its readiness to hand4 ,it now remains to consider what means are available for remedying the defect inherent in sand as a tamping material4 ,this constitutes a very important practical question1 because if the defect can be removed1 sand will constitute by far the most suitable material whenever the bore-hole has a downward direction4 ,it can be everywhere obtained at a low cost2 it may be poured into the hole as readily as water2 and its application gives rise to no danger4 ,obviously the difficulty will be overcome if we can find suitable means for preventing the gases from penetrating the sand4 ,the end proposed may be successfully attained by means of the plastic clay pellet applied in the following manner4 ,immediately above the charge1 place a handful of perfectly dry and very fine sand4 ,this may be obtained by sifting1 if not otherwise procurable4 ,upon this sand1 force firmly down with a wooden rammer1 so as to fill every irregularity1 a plastic clay pellet1 about four inches in length1 and of the same diameter as the bore-hole1 prepared by rolling between the hands in the manner already described4 ,above this pellet1 fill the hole with dry sand4 ,the impervious nature of the clay prevents the gases from reaching the sand1 except along the line of junction of the clay with the sides of the hole4 ,tamped in this way1 a resistance is obtained scarcely1 if at all1 inferior to that opposed by the most carefully placed dried clay4 ,by the employment of a detonator1 the defect due to the porous character of sand is not removed1 but its influence is greatly diminished4 ,when detonation is produced in an explosive compound1 the full force of the elastic gases is developed instantaneously2 and it has already been shown that1 under such conditions1 the resistance occasioned by the presence of any substance in the bore-hole1 even the air alone1 in the case of nitro-glycerine1 is sufficient to throw the chief portion of the force upon the sides of the hole4 ,loose sand1 therefore1 may be successfully employed as tamping under these conditions1 since its inertia will oppose a sufficient resistance to the escape of the gases4 ,but though the rock may be dislodged when light tampings are used with detonation1 there can be no doubt that a considerable proportion of the force of the explosion is lost2 and hence it will always be advantageous to tamp securely by means of the clay pellet1 as already described4 ,the highest degree of economy is to be obtained by detonating the charge1 and tamping in this manner4 ,,chapter ,,iv4 ,,the ,,operations ,,of ,,rock ,,blasting4 ,hand ,boring4--,when the positions and the directions of the shot-holes have been determined1 the operations of blasting are begun by striking a few blows with the hammer upon the spot from which the hole is to start1 for the purpose of preparing the surface to receive the drill4 ,in some cases1 this preliminary operation will not be needed2 but generally some preparation is desirable1 especially if the surface be smooth1 and the hole be to be bored at an angle with it4 ,for the purpose of illustration1 we will take the case of a hole bored vertically downwards1 and will suppose the boring to be carried on by double-hand4 ,boring the ,shot-holes4--,the surface of the rock having been prepared to receive the drill1 one man sits down1 and placing the shortest drill between his knees1 holds it vertically1 with both hands4 ,the other man1 who stands opposite1 if possible1 then strikes the drill upon the head with the sledge1 lightly at first1 but more heavily when the tool has fairly entered the rock4 ,the man who holds the drill raises it a little after each blow1 and turns it partly round1 the degree of turn usually given being about one-eighth of a revolution4 ,by this means1 the hole is kept circular1 and the cutting edge of the drill is prevented from falling twice in the same place4 ,to keep the tool cool1 and to convert the dust and chippings into sludge1 the hole is kept partially filled with water1 whenever it is inclined downwards4 ,for this reason1 downward holes are sometimes described as 8wet0 holes1 and upward holes as 8dry0 holes4 ,the presence of water greatly facilitates the work of boring4 ,it has been found by experience that the rate of boring in a dry and in a wet hole varies as #a 3 #ae2 that is1 it takes one and a half times as long to bore a dry hole as to bore a wet hole4 ,thus1 by using water1 the time may be reduced by one-third4 ,to prevent the water from spurting out at each stroke and splashing the man who holds the drill1 a kind of leathern washer is placed upon the drill immediately above the hole1 or a band of straw is tied round it4 ,when the hole has become too deep for the short drill1 the next length is substituted for it1 which is in its turn replaced by the third or longest drill as the depth becomes greater4 ,each drill1 on the completion of the length of hole for which it is intended1 is sent away to the smithy to be re-sharpened4 ,in very hard rock1 the drills may have to be frequently changed1 a circumstance that renders it necessary to have several of the same length at hand4 ,the depth of shot-holes varies from #a foot to #aj feet1 according to the nature of the rock1 the character of the excavation1 and the strength of the explosive to be used4 ,in shafts and in headings1 the depth varies generally between #b feet #f inches and #d feet1 a common depth being #c feet4 ,the dbris which accumulates at the bottom of the hole must be removed from time to time to keep the rock exposed to the edge of the drill4 ,the removal of this sludge is effected by means of the tool called a 8scraper40 ,if the sludge is in too liquid a state to allow of its ready removal by this means1 a few handfuls of dust are thrown in to render the mass more viscous4 ,the importance of keeping the bore-hole clear of sludge1 and of shortening the time expended in using the scraper1 has led1 in some localities1 to the adoption of means for rendering the sludge sufficiently viscous to adhere to the drill4 ,when in this state1 the sludge accumulates around the tool rather than beneath it1 the fresh portion formed pushing the mass upward till it forms a thick coating upon the drill throughout a length of several inches4 ,when the tool is withdrawn from the hole1 this mass of dbris is withdrawn with it2 in this way1 the employment of a scraper is rendered unnecessary4 ,this mode of clearing the bore-hole is commonly adopted by the ,hartz miners1 who use slaked lime for the purpose4 ,this lime they reduce to the consistency of thick paste by the addition of water1 and they store it1 covered with water1 in a small tin box1 which they carry with them to their work4 ,to use this paste1 they take a piece about the size of a walnut1 dilute it with water1 and pour it into the bore-hole4 ,this lime paste is1 for the purpose intended1 very effective in friable rock1 especially if it be of a granular structure1 as sandstone4 ,as the grains of sand resulting from the trituration of such rocks have no more tendency to adhere to each other than to the drill1 each of them becomes covered with a coating of lime1 which causes them to agglutinate into a viscous mass possessing sufficient adhesiveness to enable it to cling to the tool in the manner described4 ,when the hole has been bored to the required depth1 it is prepared for the reception of the charge4 ,the sludge is all carefully scraped out to clear the hole1 and to render it as dry as possible4 ,this is necessary in all cases2 but the subsequent operations will be determined by the nature of the explosive1 and the manner in which it is to be used4 ,if black powder be employed in a loose state1 the hole must be dried4 ,this is done by passing a piece of rag1 tow1 or a wisp of hay1 through the eye of the scraper and forcing it slowly up and down the hole1 to absorb the moisture4 ,if water is likely to flow into the hole from the top1 a little dam of clay is made round the hole to keep it back4 ,when water finds its way into the hole through crevices1 claying by means of the 8bull0 must be resorted to4 ,in such cases1 however1 it is far more economical of time and powder to employ the latter in waterproof cartridges4 ,indeed1 excepting a few cases that occur in quarrying1 gunpowder should always be applied in this way4 ,for not only is a notable saving of time effected by avoiding the operations of drying the hole1 but the weakening of the charge occasioned by a large proportion of the grains being in contact with moist rock is prevented4 ,but besides these advantages1 the cartridge offers security from accident1 prevents waste1 and affords a convenient means of handling the explosive4 ,it may be inserted as easily into upward as into downward holes1 and it allows none of the powder to be lost against the sides of the hole1 or by spilling outside4 ,these numerous and great advantages are leading to the general adoption of the cartridge4 ,charging the ,shot-holes4--,when the hole is ready to receive the explosive1 the operations of charging are commenced4 ,if the powder be used loose1 the required quantity is poured down the hole1 care being taken to prevent the grains from touching and sticking to the sides of the hole4 ,this precaution is important1 since not only is the force of the grains so lodged lost1 but they might be the cause of a premature explosion4 ,as it is difficult to prevent contact with the sides when the hole is vertical1 and impossible when it is inclined1 recourse is had to a tin or a copper tube4 ,this tube is rested upon the bottom of the hole1 and the powder is poured in at the upper end2 when the tube is raised1 the powder is left at the bottom of the hole4 ,in horizontal holes1 the powder is put in by means of a kind of spoon4 ,in holes that are inclined upwards1 loose powder cannot be used4 ,when the powder is used in cartridges1 the cartridge is inserted into the hole and pushed to the bottom with a wooden rammer4 ,if the charge is to be fired by means of a squib1 a pointed metal rod1 preferably of bronze1 of small diameter1 called a 8pricker10 is placed against the side of the bore-hole1 with its lower pointed end in the charge4 ,the tamping is then put in1 in small portions at a time1 and firmly pressed down with the tamping iron1 the latter being so held that the pricker lies in the groove4 ,the nature of tamping has been already fully described4 ,when the tamping is completed1 the pricker is withdrawn1 leaving a small circular passage through the tamping down to the charge4 ,care must be taken in withdrawing the pricker not to loosen the tamping1 so as to close up this passage4 ,a squib is then placed in the hole thus left1 and the charge is ready for firing4 ,if the charge is to be fired by means of safety fuse1 a piece sufficiently long to project a few inches from the hole is cut off and placed in the hole in the same position as the pricker4 ,when the powder is in cartridges1 the end of the fuse is inserted into the cartridge before the latter is pushed into the bore-hole4 ,the fuse is held in its position during the operation of tamping by a lump of clay placed upon the end which projects from the hole1 this end being turned over upon the rock4 ,the tamping is effected in precisely the same manner as when the pricker is used4 ,if the charge is to be fired by electricity1 the fuse is inserted into the charge1 and the wires are treated in the same way as the safety fuse4 ,when the tamping is completed1 the wires are connected for firing in the manner described in a former chapter4 ,in all cases1 before tamping a gunpowder charge placed loose in the hole1 a wad of tow1 hay1 turf1 or paper is placed over the powder previously to putting in the tamping4 ,if the powder is in cartridges1 a pellet of plastic clay is gently forced down upon the charge4 ,heavy blows of the tamping iron are to be avoided until five or six inches of tamping have been put in4 ,when gun-cotton is the explosive agent employed1 the wet material which constitutes the charge is put into the shot-hole in cartridges1 one after another1 until a sufficient quantity has been introduced4 ,each cartridge must be rammed down tightly with a wooden rammer to rupture the case and to make the cotton fill the hole completely4 ,a length of safety fuse is then cut off1 and one end of it is inserted into a detonator cap4 ,this cap is fixed to the fuse by pressing the open end into firm contact with the latter by means of a pair of nippers constructed for the purpose4 ,the cap1 with the fuse attached1 is then placed into the central hole of a dry 8primer10 which should be well protected from moisture4 ,when an electric fuse is used1 the cap of the fuse is inserted in the same way into the primer4 ,the primer is put into the shot-hole and pushed gently down upon the charge4 ,as both the dry gun-cotton and the detonator may be exploded by a blow1 this operation must be performed with caution4 ,cotton-powder or tonite requires a somewhat different mode of handling4 ,it is made up in a highly compressed state into cartridges1 having a small central hole for the reception of the detonator cap4 ,this cap1 with the safety fuse attached in the way described1 or the cap of the electric fuse1 is inserted into the hole1 and fixed there by tying up the neck of the cartridge with a piece of copper wire placed round the neck for that purpose4 ,the cartridge is then pushed gently down the shot-hole1 or1 if a heavier charge is required1 a cartridge without a detonator is first pushed down1 and the 8primed0 cartridge put in upon it4 ,no ramming may be resorted to1 as the substance is in the dry state4 ,when dynamite is the explosive agent used1 a sufficient number of cartridges is inserted into the shot-hole to make up the charge required4 ,each cartridge should be rammed home with a moderate degree of force to make it fill the hole completely4 ,provided a wooden rammer be employed1 there is no danger to be feared from explosion4 ,a detonator cap is fixed to the end of a piece of safety fuse1 and1 if water tamping is to be used1 grease1 or white-lead1 is applied to the junction of the cap with the fuse4 ,a 8primer10 that is1 a small cartridge designed to explode the charge1 is then opened at one end1 and the detonator cap1 or the cap of the electric fuse1 is pushed into the dynamite to a depth equal to about two-thirds of its length1 and the paper covering of the primer is firmly tied to the cap with a string4 ,if the cap be pushed too far into the dynamite1 the latter may be fired by the safety fuse1 in which case the substance is only burned1 not detonated4 ,with an electric fuse this cannot occur4 ,the same result ensues if the cap be not in contact with the dynamite4 ,the object of tying in the cap is to prevent its being pulled out4 ,the primer thus attached to the fuse is then pushed gently down upon the charge in the shot-hole4 ,it should be constantly borne in mind that no ramming may take place after the detonator is inserted4 ,gun-cotton and tonite require a light tamping4 ,this should consist of plastic clay2 or sand may be used in downward holes4 ,the tamping should be merely pushed in1 blows being dangerous4 ,a better effect is obtained from dynamite when tamped in this way than when no tamping is used4 ,in downward holes1 water is commonly employed as tamping for a dynamite charge1 especially in shaft sinking1 when the holes usually tamp themselves4 ,but in other cases1 it is a common practice to omit the tamping altogether to save time4 ,firing the ,charges4--,when all the holes bored have been charged1 or as many of them as it is desirable to fire at one time1 preparation is made for firing them4 ,the charge-men retire1 taking with them the tools they have used1 and leaving only him of their number who is to fire the shots1 in the case of squibs or safety fuse being employed4 ,when this man has clearly ascertained that all are under shelter1 he assures himself that his own way of retreat is open4 ,if1 for example1 he is at the bottom of a shaft1 he calls to those above1 in order to learn whether they be ready to raise him1 and waits till he receives a reply4 ,when this reply has been given1 he lights the matches of the squibs or the ends of the safety fuse1 and shouts to be hauled up2 or if in any other situation than a shaft1 he retires to a place of safety4 ,here he awaits the explosion1 and carefully counts the reports as they occur4 ,after all the shots have exploded1 a short time is allowed for the fumes and the smoke to clear away1 and then the workmen return to remove the dislodged rock4 ,if one of the shots has failed to explode1 fifteen or twenty minutes must be allowed to elapse before returning to the place4 ,nine out of ten of the accidents that occur are due to these delayed shots4 ,some defect in the fuse1 or some injury done to it1 may cause it to smoulder for a long time1 and the blaster1 thinking the shot has missed1 approaches the fuse to see the effects produced by the shots that have fired4 ,the defective portion of the fuse having burned through1 the train again starts1 and the explosion takes place1 probably with fatal consequences4 ,thus missed shots are not only a cause of long delays1 but are sources of great danger4 ,accidents may occur also from premature explosion4 ,in this case1 the fuse is said to 8run10 that is1 burn so rapidly that there is not sufficient time for retreat4 ,illustration3 ,,fig4 #ej4 ,when the firing is to take place by means of electricity1 the man to whom the duty is entrusted connects the wires of the fuses in the manner described in a former chapter1 and as shown in ,fig4 #ej4 ,he then connects the two outer wires to the cables1 and retires from the place4 ,premature explosion is1 in this case1 impossible4 ,when he has ascertained that all are under shelter1 he goes to the firing machine1 and1 having attached the cables to the terminals1 excites and sends off the electric current4 ,the shots explode simultaneously1 so that only one report is heard4 ,but there is no danger to be feared from a misfire1 since there can be no smouldering in an electric fuse4 ,the face may1 therefore1 be approached immediately1 so that no delay occurs1 and there is no risk of accident4 ,moreover1 as all the holes can be fired at the moment when all is in readiness1 a considerable saving of time is effected4 ,it is essential to the success of a blast fired by this means that a sufficient charge of electricity be generated to allow for a considerable loss by leakage4 ,if ,siemens' large dynamo-machine be used1 the handle should be turned slowly till a click is heard inside1 and then1 not before1 the cable wires should be attached to the terminals4 ,to fire1 the handle must be turned as rapidly as possible1 a jerky motion being avoided4 ,as considerable force is required1 the machine must be firmly fixed4 ,if a frictional machine be used1 care must be had to give a sufficient number of turns4 ,as this kind of machine varies greatly1 according to the state of the rubbing surfaces and the degree of moisture in the atmosphere1 it should always be tested for a spark before firing a blast4 ,in this way only1 can the number of turns required be ascertained4 ,it is important that the discharging knob should be pushed in1 or1 as the case may be1 the handle turned backward1 suddenly4 ,a slow motion may be fatal to the success of a blast4 ,in testing ,bornhardt's machine1 the handle should always be turned forwards2 but in firing1 half the number of turns should be given in one direction and half in the other4 ,the following table shows the number of turns required for a given number of ,andr's fuses with ,bornhardt's machine4 ,the first column1 containing the least number of turns1 may be taken also for ,julian ,smith's machine as manufactured by the ,silvertown ,company with the modifications suggested by ,w4 ,b4 ,brain4 ,,firing ,,table ,,for ,,frictional ,,machine4 ---------------------------------------- ------------------------- ,when the ,when the ,when the ,machine sparks ,machine sparks ,machine sparks with #aj ,turns4 with #ab ,turns4 with #ad ,turns4 ---------------------------------------- ------------------------- ,fuses in ,circuit4,number of ,turns4,number of ,turns4,number of ,turns4 ---------------------------------------- ------------------------- #d #ab #ae #ag #e #ab #ae #ag #f #ad #ag #bj #g #af #ai #bb #h #ah #bb #be #i #bj #bd #bh #aj #bb #bf #ca #aa #bd #bh #cd #ab #be #cj #ce #ac #bf #ca #cf #ad #bg #cc #ch #ae #bh #cd #ci ---------------------------------------- ------------------------- ,,note4--,if the machine does not spark with #ad turns1 the rubber should be taken out and brushed4 ,places of refuge1 called man-holes1 are often provided in headings for the blaster to retire into2 these man-holes are small excavations made in the sides of the heading4 ,sometimes it is necessary to erect a shield of timbers in the heading for the protection of the men2 such a shield is frequently needed to protect machine drills from the effects of a blast4 ,in ,belgium1 it is a common practice to provide man-holes in the sides of a shaft as places of retreat for the men2 these holes are called caponnires4 ,instead of caponnires1 a hollow iron cylinder is sometimes used as a protection to the men4 ,this cylinder is suspended in the shaft at a height of a few yards from the bottom1 and is lowered as the sinking progresses4 ,the men climb into this cylinder to await the explosion of the shots beneath them4 ,the workmen1 on returning to the working face1 remove the dislodged rock1 and break down every block that has been sufficiently loosened4 ,for this purpose1 they use wedges and sledges1 picks1 and crowbars4 ,and not until every such block has been removed1 do they resume the boring for the second blast4 ,sometimes1 to facilitate the removal of the rock dislodged by the shots1 iron plates are laid in front of the face in a heading4 ,the rock falling upon these plates is removed as quickly as possible1 to allow the boring for the succeeding blast to commence4 ,it is important1 in the organization of work of this character1 that one gang of men be not kept waiting for the completion of the labour of another4 ,,machine ,,boring4--,in machine drilling1 the operations necessarily differ somewhat in their details from those of hand boring1 and1 in some cases1 other methods of procedure will be adopted more suitable to the requirements of machine labour4 ,it may even be1 and in most cases indeed is1 inexpedient to follow closely the principles which lead to economy of the explosive substance employed1 since the more restricted conditions under which machine power may be applied may point to more important gains in other directions4 ,thus it may be found more conducive to rapidity of execution to determine the position and the direction of the shot-holes rather to satisfy the requirements of the machine than those of the lines of least resistance2 or1 at least1 these requirements must be allowed to have a modifying influence in determining those positions and directions4 ,for it is obvious that holes cannot be angled with the same ease when a machine drill is used1 as they can when the boring is executed by hand4 ,boring the ,shot-holes4--,it has already been remarked that the exigencies of machine labour render it impracticable to follow closely the principles which lead to economy of labour and material in blasting4 ,in hand boring1 economy is gained by reducing to a minimum the number of holes and the quantity of explosive substance required4 ,but in machine boring1 economy is to be sought mainly in the reduction of the time needed to accomplish the driving4 ,attempts have been made to assimilate the methods of machine boring to those adopted for hand labour1 but the results have not been satisfactory4 ,on the contrary1 the conditions determining the position and the direction of the holes relatively to the production of the greatest useful effect have been wholly ignored in favour of those which determine the most rapid boring4 ,this system has been attended with more satisfactory results4 ,another system1 partaking of both the preceding1 is widely adopted1 and hitherto the best results have been obtained from this1 which may be regarded as a compromise between conflicting conditions4 ,thus we have three systems of executing machine boring3 one in which a single machine is used upon a support capable of holding it in any position1 so as to be able to bore at any angle1 and in which the holes are placed according to the lines of least resistance1 as in hand boring4 ,a second1 in which several machines are fixed upon a heavy support1 allowing but little lateral or angular motion1 and in which the holes are placed at regular intervals apart1 and bored parallel1 or nearly parallel1 with the axis of the excavation1 irrespective of the varying nature of the rock1 and the lines of least resistance4 ,and a third1 in which it is sought1 by the employment of one1 two1 or at the most three machines1 upon a simple and light support allowing the position and direction of the machine to be readily changed1 to satisfy in some degree the two sets of conditions determining the two former systems1 by placing the shot-holes as far in accordance with the lines of resistance as the exigencies of a fairly rapid handling of the machine will allow4 ,in the first of these systems1 the necessity for extreme lightness in the machine is unfavourable to its efficient action1 and the great length of time consumed in changing the position of the machine1 so as to comply with the conditions of resistance in the rock1 render it impossible to attain a much higher rate of progress than is reached by a well-regulated system of hand boring4 ,with such a result1 there is nothing to compensate the first cost of the machinery1 or in any way to justify its adoption4 ,in the second system1 the time consumed in removing and fixing the machines is reduced to a minimum1 and the chief portion of the time during which the machines are at the working face is1 consequently1 occupied in actual boring1 a circumstance that is highly favourable to machine labour4 ,hence the rate of progress attained by this system is greatly in excess of that accomplished by hand labour2 and this superiority has led to the adoption of the system in several important cases1 and has also led many to regard it as the most favourable to the exigencies of machine drilling4 ,but as the holes are bored to suit the requirements of the machine1 quite irrespectively of the resistance of the rock1 their positions and directions are very unfavourable to the action of the explosive4 ,this circumstance necessitates a much greater number of holes to ensure the fracture of the rock around each charge1 and hence the time saved in shifting the machines is in part lost in extra boring2 besides which1 the consumption of powder is enormously increased4 ,it would1 therefore1 appear that the full advantages of machine boring are to be obtained from the intermediate system1 if carried out in accordance with all the conditions of the case4 ,assuming that we have a machine and a support of such dimensions1 weight1 and construction as to be capable of being readily placed in position1 it is evident that we shall still require a much larger number of holes than would be needed if the boring were performed by hand1 because they are not placed wholly in accordance with the lines of least resistance4 ,in some parts of the heading1 indeed1 these lines will have to be wholly neglected1 in order to avoid the loss of time involved in shifting the supports2 for the principle upon which an intermediate system is based is to fulfil the requirements of the lines of least resistance1 when that can be conveniently done1 and to neglect them1 when such fulfilment would involve a considerable expenditure of labour and time4 ,in this way1 the time both for fixing and removing the machines and of boring is reduced to a minimum1 and thus two conditions favourable to rapid and economical progress is ensured4 ,it is evident that when this system is followed1 the face will not require the same number of holes at each blast4 ,another circumstance operating to increase the number of shot-holes is the desirability of bringing down the face in fragments small enough to be lifted without great difficulty4 ,when the rock is completely broken up1 the labour1 and1 consequently1 the time of removing it after each blast1 are lessened in an important degree4 ,hence there will be an advantage in placing the shot-holes sufficiently close together to ensure the fracture of the mass between each4 ,these circumstances render it necessary to bore a large number of holes when the work is done by mechanical means4 ,the boring of the additional holes reduces the superiority of machine over hand labour1 and the additional quantity of the explosive required augments the cost of the work4 ,to counterbalance these disadvantages1 the shot-holes should be bored deep4 ,it has already been pointed out that when a hole is once started with a machine1 the rate of progress is immensely superior to that attained in hand boring1 and to profit by this advantage1 the hole should be continued to as great a depth as practicable4 ,this is sufficiently obvious1 since it amounts to increasing the proportion of the whole time consumed that is occupied in actual boring2 for as it is in the rapidity of the operation of boring alone that the superiority of machine labour exists1 it is plain that the longer the proportion of the time so occupied1 the more marked that superiority will be4 ,thus1 by increasing the depth of the holes to the farthest practicable limit1 we approximate as much as possible to the condition most favourable to machine boring4 ,the intermediate system1 therefore1 which takes full advantage of this means1 will lead to the best results4 ,to recapitulate the main points of such a system2 it should follow the lines of least resistance when that can be conveniently done1 and neglect them when the fulfilment of their requirements would occasion a considerable expenditure of time2 and to counterbalance the disadvantages of machine boring1 it should employ shot-holes of as great a depth as is practicable4 ,supposing such a system in use1 it now remains to consider the operations of boring1 and the subsequent operations of charging1 firing1 and removing the rock dislodged by the blast4 ,of the method of executing the boring1 little remains to be said4 ,it may1 however1 be well to direct attention to the necessity of keeping the holes clear of the dbris4 ,to ensure this1 the bits should be chosen of a form suitable to the nature and the structure of the rock1 and the hole kept well supplied with water4 ,when the hole becomes deep1 it should be cleared out with a scraper during the time of changing the bit1 and in very argillaceous rock it may become necessary sometimes to withdraw the tool1 and to remove the accumulation with the scraper4 ,when the dbris does not work out freely1 its escape may be facilitated by giving a slow motion to the tool1 and then suddenly changing to a rapid motion4 ,when several machines are employed1 the maximum number that can be applied with advantage is one to the square yard of working face4 ,the absolute number of holes required in any case1 will1 of course1 depend upon the tenacity of the rock and the development of the joint planes1 and also1 in some degree1 by the lines of fracture due to the preceding blast4 ,the same circumstance will determine the distribution of the holes4 ,leaving minor variations out of account1 however1 the same distribution will be adhered to throughout the driving4 ,the manner of distributing the holes over the face of the heading may be varied according to the judgment of the engineer in charge2 that is1 the general features of the distribution to be adopted may be chosen to suit the requirements of the machines and their supports4 ,also1 it should be noted that one method of distributing the shot-holes will require a less number of them than another4 ,some examples will be found on ,plate ,,ix41 where there are represented the ,gschenen end of the ,st4 ,gothard tunnel2 the ,airolo end of the same tunnel2 the face of a stone drift driven at ,marihaye2 that of a similar drift at ,anzin2 and that of a drift of the same character at ,ronchamp2 the latter three examples being typical of the distribution adopted in the ,french collieries4 ,the same mode of unkeying the face is adopted with machine as with hand boring4 ,generally1 two parallel rows of holes1 from two to five in a row1 are bored in the middle of the face or fore-breast1 the rows being from #ah inches to #cj inches1 according to the strength of the rock1 apart on the surface1 and angled so as to be from #i inches to #ae inches apart at the bottom4 ,these shots unkey the fore-breast2 and it is greatly conducive to a successful accomplishment of the operation1 to fire these shots simultaneously4 ,sometimes1 when dynamite is used1 another method is adopted4 ,a hole is bored horizontally in the centre2 at about three inches distant1 are bored three other holes at an equal distance apart4 ,these latter are heavily charged with dynamite1 the centre hole being left empty4 ,when these charges are fired1 the rock between them is crushed1 and a large hole made4 ,the lines of fracture of the subsequent shots run into this hole4 ,in this case1 it is even more desirable than in the preceding to fire the central shots simultaneously4 ,in shaft sinking1 if the strata are horizontal or nearly so1 it is usual to unkey from the centre1 as in the heading4 ,but if they be highly inclined1 it will be better to unkey from one side of the excavation4 ,the water which flows into the workings must be collected into one place1 both for convenience in raising it1 and for the purpose of keeping the surface of the rock clear for the sinkers4 ,the depression caused by the removal of the key serves to collect the water1 and1 on that account1 it is called 8the sump40 ,into this sump1 the tub dips1 or1 when pumps are used1 the suction pipe drops4 ,when the strata are highly inclined1 the water gravitates towards the dip side of the excavation1 and it becomes1 therefore1 necessary to place the sump in that situation4 ,the unkeying of the rock from this direction is1 moreover1 favourable to the effect of the shots4 ,in putting in the shot-holes1 it is well to avoid1 as far as possible1 terminating them in1 or nearly in1 a bedding plane1 because when so terminated1 the force of the charge expends itself along this plane4 ,the position and the direction of the holes will1 however1 be determined in some degree by the character of the support used for the drills1 and by other conditions of convenience4 ,charging and ,firing4--,the operations of charging the holes and firing the shots demand particular attention when machine labour is employed4 ,it has been pointed out in the foregoing paragraphs that holes bored by machine drills cannot be placed or directed strictly in accordance with the requirements of the lines of least resistance2 but that1 on the contrary1 these requirements can only be approximately complied with1 and in some cases must be wholly neglected4 ,to compensate in some degree this defect of machine labour1 the strength of the charges should be varied according to the resistance which they will be required to overcome4 ,that is1 the principles of blasting described in a former chapter1 which cannot be complied with by the borer1 should be strictly followed by the blaster in apportioning his charges4 ,by this means1 a great saving of the explosive compound may be effected1 and that without difficulty or loss of time1 if the blaster be intelligent and understand his work4 ,a glance will be sufficient to show what charge a given hole of a known depth will require1 and as cartridges of different sizes are ready at hand1 no delay is occasioned in making up the charge4 ,the holes in the centre1 which are intended to unkey the face1 require1 of course1 the heaviest charge1 since the conditions are there most unfavourable to the effects of the explosion4 ,and the more complete is the unkeying resulting from this first explosion1 and the more fractured and jointed is the rock surrounding the cavity thus formed1 the more may the charges placed behind these unsupported faces be reduced4 ,as economy of time is1 in machine boring1 the chief end to be attained1 the tamping should be done with dried clay pellets previously prepared4 ,this material gives the greatest resistance1 and thereby ensures the maximum of useful effect2 and if prepared beforehand1 in the manner described in the preceding chapter1 the time consumed in tamping will be reduced to a minimum4 ,an abundant supply of such pellets should always be ready at hand4 ,in downward holes1 such as are used in shaft sinking1 the plastic clay pellet and sand may be employed4 ,this tamping may be put in very rapidly1 and1 in all but very shallow holes1 it is very effective4 ,when it is desired to use sand tamping in horizontal holes1 and holes bored in an ascending direction1 the sand should be made up in paper cartridges4 ,the tamping employed in the ,st4 ,gothard tunnel consisted of sand prepared in this manner4 ,at the ,mont ,cenis tunnel1 an argillaceous earth was similarly prepared in paper cartridges for tamping4 ,firing the charges also affords an occasion for the exercise of knowledge and judgment4 ,a skilful determination of the order in which the charges are to be fired will in a great measure compensate the ill effects of badly-placed holes4 ,the firing of a shot leaves the surrounding rock more or less unsupported on certain sides2 and it is evident that to profit fully by the existence of these unsupported faces1 the succession of explosions must be regulated so that each shall have the advantage of those formed by the preceding shots4 ,this condition can be wholly fulfilled only by simultaneous firing2 but when the firing is to take place successively1 the condition may be approximated to by regulating the succession according to the indications observed on a careful inspection of the rock4 ,before firing the charges1 the blaster should consider the relative positions of the holes1 the stratification and jointing of the rock1 the fissures caused by the preceding blast1 and any other circumstances that may influence the results4 ,the charges intended to unkey the face will be fired first1 and those in the concentric series will be then fired1 in the order determined upon1 by means of different lengths of fuse4 ,the series will follow each other from the centre outwards4 ,when a large number of shots regularly placed in series have to be fired1 a convenient practical means of ensuring the successive explosion of the series1 in the case of the whole being lighted simultaneously1 consists in bringing the fuses from all the shot-holes together to one point at the centre4 ,this method of regulating the length of the fuses was adopted at the ,st4 ,gothard tunnel4 ,it is obvious that the acceleration of the labour of excavation1 which has been effected in so remarkable a degree by the introduction of machine drills and strong explosives1 may be still further promoted by the adoption of electricity as the firing agent4 ,the advantages of firing a number of shots simultaneously1 some of which have already been pointed out1 are great and manifest4 ,in the case of a driving1 for example1 when all the holes have been bored and charged1 and the machines withdrawn1 it is clearly desirable to blast down the face as quickly and as effectively as possible4 ,if the whole of the shots can be fired at once1 the time is reduced to a minimum1 and1 consequently1 the maximum of progress in a given time is ensured4 ,electricity affords1 indeed1 the most convenient1 the most effective1 and the most safe means of firing blasts4 ,hofrath ,ritter von ,pischof1 the ,austrian ,chief ,inspector of ,railways1 in one of his reports1 says3--8,a greatly increased amount of work and a notable saving of cost are effected when the shots can be so disposed and fired as to mutually aid one another4 ,these results are obtained by employing electricity as the firing agent4 ,the experience which has been gained at the ,bchenberg cutting1 where electrical firing has been extensively adopted1 has shown that1 when properly employed1 this means allows1 in comparison with the ordinary methods1 twice the amount of work to be performed in a given time4 ,it is therefore highly desirable to adopt electrical blasting whenever it is a question of economy of time and money40 ,removing the dislodged ,rock4--,as the removal of the rock brought down by the blast consumes a large proportion of the time saved by machine boring1 it becomes necessary to provide means for reducing this loss to a minimum4 ,the most important of these means is a suitable provision for the rapid removal of the machine to a place of safety1 and a conveniently designed and well-laid tramway1 upon which the rock may be quickly run out without confusion and its consequent delay4 ,the number of wagons required to remove a given cube of rock may be readily ascertained1 and sufficient provision should be made for the transport of these to 8day0 in the most rapid succession4 ,the wagons should be of such dimensions as to be capable of being handled without great difficulty2 the importance of this condition will be understood when the frequency of derailments is borne in mind4 ,the shovelling up of the rubbish is greatly facilitated by laying iron plates in front of the face to be brought down previously to the firing of the blast4 ,this expedient is often adopted in important drivings4 ,it has also been remarked that the dislodged rock can be more rapidly removed when it exists in small blocks4 ,thus there will be an advantage in placing the charges and in regulating their strength so as to completely break up the rock4 ,another matter of importance in the arrangements for the rapid removal of the rock brought down by the blast1 is the proportioning of the number of hands employed to the requirements of the case4 ,this number will increase with the size of the blocks to be lifted1 the distance to be run over1 and the want of suitability in the matriel employed4 ,division of ,labour4--,a proper division of labour is greatly conducive to rapid and economical progress4 ,the operations may be divided into three series1 namely3 boring the shot-holes1 charging and firing1 and removing the rock dislodged4 ,each of these series of operations may be performed by different sets of men1 and in several instances this division of labour has been adopted4 ,but it does not appear that such a division leads to the most satisfactory results4 ,the work of boring occupies a much longer time than either of the other two series of operations1 and hence the distribution of the time is unequal4 ,it has been found that1 generally1 where all the arrangements have been well considered1 the labour of charging the shot-holes1 firing the blast1 and removing the rock brought down1 can be performed in about the same time as that of boring4 ,thus it would seem to be more conducive to economy of time to divide the men employed into only two sets3 one set to bore the holes1 the other to perform all the subsequent operations4 ,this division has been adopted in numerous instances with favourable results4 ,sometimes the whole of the operations have been performed by the same set2 but such an arrangement is not to be recommended4 ,the labour of directing the machines is of too distinct and skilled a character to be confounded with that of removing the dbris1 without a strong reason for such a proceeding1 which does not appear to exist4 ,besides reserving a set of men specially for this portion of the work1 it is desirable to keep the same men to the same machine1 for in such a case each man gets accustomed to the peculiarities of the machine entrusted to him1 and besides conceives a kind of affection for it that leads to careful handling and watchful attention4 ,in addition to the men required for the operations referred to above1 smiths will be needed to re-sharpen the bits and to repair the machines4 ,the amount of this labour will obviously depend upon the number of machines employed1 and the hardness of the rock to be passed through4 ,,examples ,,of ,,drivings4 ,the ,st4 ,gothard ,tunnel4--,the ,st4 ,gothard tunnel is driven in five sections4 ,first1 the 8heading0 is driven at the roof level #f feet #f inches wide1 and #g feet high4 ,the position of the holes is shown in the drawings on ,plate ,,ix4 ,the number of holes at the ,gschenen end is #bh1 and the depth about #dj inches4 ,the shots are fired by means of safety fuse1 the ends of the fuse being brought together at the centre4 ,this arrangement causes the shots to explode in the proper order of succession4 ,at a certain distance back from the face1 is the 8right enlargement20 this is a widening of the heading to the limits of the tunnel in that direction4 ,farther back is the 8left enlargement10 by which the heading is widened to the full width of the tunnel4 ,still farther back is the first 8bench cut10 in which one half of the floor is blasted out to the full depth of the tunnel1 and behind this again is the second bench cut1 in which the remaining half is removed4 ,the boring machines employed are the ,dubois-,franois1 the ,mc,kean1 and the ,ferroux4 ,the explosive agent used is dynamite4 ,the rock is a tough granite4 ,the ,hoosac ,tunnel4--,at the west end of the ,hoosac tunnel1 the system adopted was the following4 ,first1 a centre cut was made by drilling two rows of five or six holes each1 about #i feet apart on the face1 and converging to about #c feet at their lower ends4 ,the depth of these holes was from #i to #ab feet1 according to the hardness of the rock4 ,these holes are numbered from #a to #aa on ,plate ,x4 ,they were charged with nitro-glycerine1 and fired by electricity1 ,mowbray's frictional machine being used4 ,as soon as the rock had been removed1 the next series of fourteen holes1 numbered from #ab to #be1 were drilled4 ,these holes were then charged and fired simultaneously like those of the first series4 ,when the rock dislodged had been removed1 the third series of holes1 numbered from #bf to #da1 were bored4 ,this series1 like the other two1 were charged1 and fired by electricity4 ,the effect of these three blasts1 which were fired within twenty-four hours1 was to advance the heading1 #i feet in height by the full width of #bd feet1 to the extent of #g feet #f inches4 ,the drawings on ,plate ,,xi4 are3 an elevation of the fore-breast1 which shows the positions of the shot-holes2 a sectional plan1 which shows the directions of the first series of holes2 a similar plan1 showing the directions of the second series of holes1 and the centre cut removed2 and a sectional plan of the heading after the second series have been fired1 showing the direction of the third series of holes4 ,the operations of taking out the 8bench0 were carried on at a distance of about #agj yards back from the fore-breast4 ,this was effected by first drilling six holes #g feet deep2 two of these were each about #d feet from the face of the bench and close to the side of the tunnel1 whilst two others were each #d feet behind these first holes1 and the remaining two holes were #h feet from the face1 #h feet from the sides of the tunnel1 and #h feet from each other4 ,these were fired simultaneously1 the result being to lower the bench about #g feet throughout the full width of the tunnel4 ,at a safe distance beyond this first bench cut1 the same operations were carried on by another gang of men1 whereby the bench was lowered to the floor of the tunnel1 the full area of #bd feet in width by #bb in height being thus completed4 ,the rock was a moderately tough granite4 ,the ,musconetcong ,tunnel4--,the heading of the tunnel1 shown on ,plate ,,xii41 like that of the ,hoosac1 was driven to the full width of the tunnel4 ,it is clear from theoretical considerations1 and experience has confirmed the conclusions1 that the method of taking1 with machine drills1 the whole width of the excavation at once conduces to rapidity of advance1 and to economy of explosive4 ,in the example under consideration1 three tram lines were laid up to the face4 ,the carriages carrying the drills were run upon the two outside lines4 ,these carriages were simply stout frameworks of oak1 each having in front three horizontal iron bars1 on which the drills were clamped in a way that ensured easy lateral and vertical motion4 ,after the firing of a blast1 all hands were set to shovel the dislodged rock into the middle between the machine lines for the purpose of clearing the latter as soon as possible to make way for the machines to be brought up for the next boring4 ,the lines being thus cleared1 drilling was recommenced1 and the broken rock removed in wagons upon the centre line of rails4 ,the heading being #bf feet wide1 there was ample room1 and1 a convenient system of switching having been adopted1 no delay was occasioned by a want of wagons4 ,the system followed was that of centre cuts1 and subsequent squaring up4 ,it consists in first blasting out an entering wedge or 8key10 about #aj feet deep in this case1 in the centre1 and afterwards squaring up the sides by several blasts4 ,in the ,musconetcong heading1 twelve holes were first drilled1 as shown in the drawing1 and marked ,c1 ,a being the floor of the heading4 ,these holes were drilled with from #a-;inch to #b-;inch 8bits10 in two rows of six1 #i feet apart on the face1 and angled to meet at the bottom4 ,they were charged with #be lb4 of ,no4 #a and #ej lb4 of ,no4 #b dynamite1 and fired simultaneously by electricity4 ,the ,no4 #a dynamite was used in the bottom of these centre holes2 in all the subsequent blasts in squaring up1 ,no4 #b only was used4 ,as soon as the cut was out1 a second round of holes was started for the first squaring up1 as shown in the drawings1 where they are numbered #a1 #a1 #a1 #a1 c4 ,in these and in the subsequent rounds1 numbered #b1 #b1 #b1 #b1 c41 and #c1 #c1 #c1 #c1 c41 the resistance to be overcome is1 of course1 not so great as in the cut4 ,in the first and the second squaring-up rounds1 from #ej lb4 to #fj lb4 of dynamite was used1 and1 in the third round1 this quantity was increased to #hj lb4 or #ij lb41 the resistance becoming greater as the roof arch falls at the sides4 ,in this third round1 there were generally one or two additional roof holes2 these are not shown in the drawing1 as their position varied1 according to the lay of the rock4 ,the top holes in the first round are also intended to bring down any roof not shaken by the cut1 and these are therefore angled sharply towards the centre1 and bored from #ab feet to #ad feet deep4 ,in the plan1 ,plate ,,xii41 the number #c indicates the cut holes1 and #d1 #e1 and #f1 the squaring-up rounds4 ,the holes of the first squaring round were always drilled about a foot deeper than the cut holes2 when blasted1 these generally brought out an additional foot of shaken rock at the apex of the cut4 ,the following table shows approximately the number and the depth of the holes required1 and the quantity of dynamite used for a linear advance of #aj feet4 ---------------------------------------- -------------- ,total ,no4 of ,depth ,depth ,holes4of ,holes4 of ,no4 #a4,no4 #b4 ,holes4 --------------------------------- ft4 in4 ft4 lb4 lb4 ,cut #ab #aj #f #abf #be #ej #ast square up #h #ab #j #if 44 #ee #bnd #h #ab #j #if 44 #ee #crd #f #ab #j #gb 44 #he ,additional roof holes #b #aj #j #ah 44 44 #h #j --------------------------------- #cf 44 #djh #be #bde ---------------------------------------- -------------- ,the cut holes being #aj feet #f inches deep1 the blast usually brought out about #i feet full1 which1 as explained above1 was increased to #aj feet in the subsequent rounds4 ,the cross section being about #age square feet1 in an advance of #aj linear feet1 there are about #fe cubic yards of rock to be broken2 this gives on an average #jd lb4 of ,no4 #a and #d lb4 of ,no4 #b dynamite1 and a little over #f feet of drilling per cubic yard4 ,the 8bench0 was kept from #aej yards to #bjj yards back from the face of the heading1 to avoid interruptions from the heading blasts1 and to allow plenty of room for handling the wagons1 and for running back the machines to a safe distance1 previously to firing4 ,the system adopted in removing the bench is shown on ,plate ,,xii4 ,first1 six top holes1 from #ab feet to #ac feet deep1 were drilled and blasted2 their relative positions are shown in the drawings1 ,a being the centre line1 ,b1 the sides in the enlargement1 ,b1 the sides of the heading1 ,c1 the face of the bench1 and #a1 #b1 #c1 #d1 #e1 #f1 the holes4 ,these six holes lifted the greater portion of the rock2 what was left was broken by several horizontal holes4 ,these two sets of holes1 at the top and at the bottom1 gave an average advance of about #i feet4 ,the following table shows1 for that advance1 the number of feet drilled1 and the quantity of dynamite burned4 ---------------------------------------- -- ,depth ,total ,no4 of of ,depth ,no4 #b ,holes4,holes4of ,holes4,dynamite4 ------------------------------ ft4 ft4 lb4 ,top holes #f #ab #gb #fb ,bottom holes #d #aj #dj #de ------------------------------ ,totals #aj #bb #aab #ajg ---------------------------------------- -- ,the sectional area of the bench being about #cjf square feet1 an advance of #i linear feet gives about #ajb cubic yards of rock to be removed4 ,the quantity of dynamite used was therefore #aje lb41 and the depth of boring #aa foot1 per cubic yard of rock broken4 ,three machines were used at this bench1 two on the top and one below4 ,the holes were commenced with #b-;inch bits1 and terminated by #a-;inch bits4 ,the rock was a tough syenite4 ,,chapter ,,vi4 ,,subaqueous ,,blasting4 ,preparation of the ,charge4--,it is essential to the success of subaqueous blasting operations1 that the explosive substance used should be suitable to the conditions under which it is to be applied4 ,this is true of all blasting1 but the requirement is frequently overlooked in some of the operations that have to be performed under water4 ,in clearing a wreck for salvage purposes1 gunpowder will in most cases act more effectually than either gun-cotton or dynamite4 ,also1 in many cases1 this compound will prove more suitable than the stronger substances in removing obstructions in water-courses4 ,examples of this will be given hereafter4 ,but when a wreck has to be broken up1 when piles1 or objects of a similar character1 have to be removed1 or when rocks have to be blasted1 the more violent compounds will be found to accomplish the purpose much more effectively4 ,generally1 it may be stated that when it is required merely to remove objects1 gunpowder is the most suitable explosive agent to employ2 and that when it is required to break objects1 the nitro-cotton and the nitro-glycerine compounds are the agents whose application is likely to be attended with the greatest degree of success4 ,when gunpowder is used1 means must be adopted to protect it from the water1 since a small proportion of moisture is sufficient to lessen1 in a very important degree1 the force developed1 while a large proportion of moisture will destroy altogether its explosive properties4 ,it is no easy matter1 under the most favourable circumstances1 to keep the water from the charge2 but when the depth of water is considerable1 it becomes very difficult to attain that object4 ,the pressure of a considerable 8head0 will force the water through substances that1 without a pressure1 are sufficiently impervious4 ,at ordinary depths1 metal canisters are usually employed to contain gunpowder4 ,old oil-cans are as good as anything for this purpose4 ,the fuse1 whether safety or electric1 is passed through the cork1 and the latter is luted with some waterproofing composition4 ,the best consists of3 ,tallow #a part4 ,rosin #c parts4 ,guttapercha #d parts4 ,swedish pitch #ab parts4 ,instead of metal canisters1 indiarubber bags are sometimes used4 ,these are1 however1 more expensive than the oil-cans1 and1 in many cases1 they are scarcely more efficient or suitable4 ,small charges of gunpowder may be put into short lengths of indiarubber tubing1 so as to form a kind of cartridge4 ,but care must be taken to close the ends securely4 ,the best way is to insert a cork1 or if that cannot be obtained1 a cylindrical piece of wood1 and to tie the tubing to this very tightly with twine4 ,the ends should then be dipped into the luting composition described above4 ,tubing suitable for this purpose is sold under the designation of 8blasting tubes40 ,for large blasts1 wooden casks are the most suitable receptacle for the charge4 ,the casks should be well tarred1 or1 if the depth of water be great1 laid over with pitch applied very hot4 ,great care must be taken to protect the aperture through which the safety fuse1 or the wire of the electric fuse1 passes4 ,in blasting under water with gunpowder1 only the best and strongest qualities of that compound should be used4 ,the extra strong mining powder of the ,messrs4 ,curtis's and ,harvey's1 commercially known as the ,e4,s4,m4 powder1 is1 of all1 the most suitable4 ,it is also highly conducive to success to detonate the charge4 ,if the charge be not detonated1 the enclosing vessel is ruptured when only a small proportion of the number of grains have been ignited1 and1 consequently1 a large proportion of the charge is blown away into the water unburned4 ,were gunpowder in blasting charges always fired by a detonation1 it would compare in its effects far more favourably with the nitro-cotton and the nitro-glycerine compounds than it does under the circumstances attending the common method of firing it4 ,when gun-cotton is used1 the difficulty of waterproofing is much lessened1 but not wholly removed4 ,inasmuch as this compound may be detonated in the wet state1 it is not required to take those precautions which are necessary in the case of gunpowder4 ,but1 as we have pointed out in a former chapter1 the detonation of wet gun-cotton is effected by means of that of a small quantity of the dry substance4 ,this quantity1 which is generally employed in the form of a cylinder1 and is called the 8priming10 must be thoroughly protected from the water4 ,for this purpose1 indiarubber tubing may be used1 or1 if the primer be large1 indiarubber bags4 ,when the pressure of the water is not great1 a very efficient protective covering is obtained by dipping the primer into melted paraffine4 ,care should be taken to avoid raising the temperature of the paraffine above the degree required to melt it completely4 ,the primer should be placed in contact with the charge1 and it is desirable that the latter1 when it can be conveniently made to do so1 should surround the former4 ,charges of gun-cotton for subaqueous blasts are usually made up of discs of a large diameter1 or of slabs of a rectangular form4 ,when1 however1 the charge has to be put into a bore-hole in rock1 the common cartridge is employed4 ,tonite1 or cotton powder1 is largely used in subaqueous blasting operations4 ,this substance is always applied in a dry state1 and requires1 therefore1 to be protected from the water4 ,this protection it is however1 not difficult to give4 ,being prepared for use in a very highly compressed state1 it does not readily absorb moisture4 ,in this state1 it is enclosed in cartridges1 which are subsequently dipped into melted paraffine4 ,this is the form and preparation adopted for ordinary use4 ,for application under water1 especially when the depth is considerable1 additional protection is given4 ,for wreckage purposes1 tonite may be obtained in convenient charges1 made up in suitable forms1 and sufficiently protected4 ,when dynamite is used1 the conditions are similar to those prevailing in the case of gun-cotton4 ,since nitro-glycerine is unaffected by water1 no necessity exists for protecting it from moisture4 ,but when a charge of dynamite is immersed in water1 and not contained in a bore-hole1 the nitro-glycerine rapidly exudes4 ,the writer once made several ineffectual attempts to explode a charge of dynamite at a depth of #gj fathoms beneath the surface4 ,the cause of failure was found to be this exudation2 for subsequent experiments showed that1 though the dynamite was in the form of the ordinary parchment paper cartridges1 and was contained in a stout canvas bag1 the kieselguhr retained hardly a trace of nitro-glycerine when the charge reached the surface from that depth1 after being rapidly lowered and raised4 ,hence it becomes necessary to enclose dynamite within some fairly impervious substance1 to prevent the exudation of the nitro-glycerine4 ,waxed linen1 or fine canvas overlaid with the composition already described1 may be used as a protective covering2 for blasts in deep water1 indiarubber bags and tubing are employed4 ,when the charge is contained in a bore-hole in rock1 exudation can hardly occur1 and therefore in such cases waterproofing is unnecessary4 ,for firing subaqueous blasts with safety fuse1 only the guttapercha covered kinds are suitable4 ,great care must be taken to render the junction of the fuse and the detonator water-tight4 ,a stronger detonator is required under water than in dry ground4 ,electric fuses offer not only a cheaper1 but a far more certain and suitable means of firing in water4 ,this means is now very generally employed4 ,when tension currents are used1 the insulation must be very good4 ,in all cases1 ample power should be possessed by the firing machine or battery4 ,the shattering class of explosives are very suitable for subaqueous-rock blasting4 ,in many cases1 their employment renders the boring of shot-holes unnecessary1 an advantage of obviously great importance4 ,when detached or projecting masses of rock have to be broken up1 it is sufficient to place the charges upon them4 ,of course1 when so applied1 larger quantities of the explosive are required2 but though the method is wasteful of explosive1 it is very economical of labour and time4 ,even when large undetached masses of rock have to be removed1 the same method may often be successfully followed4 ,suppose a level surface of rock1 for example4 ,a few heavy charges judiciously distributed over this surface will blow out craters of a considerable radius1 and more or less fracture the rock in their immediate neighbourhood4 ,a few other blasts then fired between these shattered points will break up the intervening solid portions4 ,sometimes the rock will be disintegrated to a considerable depth1 and so broken up generally that it may be removed by dredging4 ,by proceeding in this way1 the whole of the rock may often be removed without any labour of boring4 ,but when the rock is too tough to be removed in this way1 recourse must be had to boring1 though even when boring is necessary1 an occasional 8loose0 shot may be found to be very efficacious4 ,boring under ,water4--,the percussive drills1 one of which1 the ,darlington1 was described in a former chapter1 may be used effectively under water4 ,compressed air is used as the motor fluid4 ,the tripod stand1 having its legs weighted to give it stability1 is generally the most suitable support4 ,these drills need the immediate attention of a diver4 ,sometimes the boring is carried on by hand from the deck of a vessel or from a raft provided for the purpose4 ,the following description will give a general notion of the operations involved in subaqueous boring3-- ,the working vessel having been moored over the rock by means of mooring-lines attached to buoys placed about #ej yards from each quarter of the vessel1 the diver descends and selects the most suitable position for the blast2 he then signals1 by a certain number of pulls upon his signal line1 to have the drill and stand lowered to him4 ,this being quickly done by means of a steam derrick1 he guides the drill-stand to its place1 and finally fixes it in position by means of its adjustable legs4 ,this being done1 he signals for air to commence drilling4 ,it has been found that the drill can be worked in a rapid current as well as in slack water4 ,this allows the operations of drilling and blasting1 by a proper division of time and labour1 to be conducted in an extremely rapid tidal current1 so that the principal work of the diver1 in inserting charges for blasting and slinging stone1 may be done near the periods of slack water1 while the drilling may be advantageously continued during the period of rapid flow4 ,in a rapid current1 the stoppage of the drill for the purpose of 8spooning out0 the hole becomes unnecessary1 as the motion of the drill works up the dbris to the mouth of the hole1 whence it is sucked out and carried off by the current in a dark stream1 like the smoke from the funnel of a locomotive4 ,in a sluggish current1 or during slack water1 the hose of the air-pump is sometimes introduced1 and air forced into the bore-hole to create a current of water1 by which means the hole is cleared more thoroughly than by the most careful 8spooning out40 ,as soon as the hole is drilled to the required depth1 the drill is stopped2 the diver then fastens the derrick chain1 which is lowered to him for the purpose1 to the drill-stand1 and signals to hoist away1 whereupon the machine is quickly hoisted on deck4 ,after having examined the hole and cleared away any dbris remaining at the bottom1 the diver comes to the surface1 and taking in his hand the charge contained in a water-tight cartridge1 and provided with its electric fuse to which a sufficient length of insulated wire is attached1 returns with it1 and inserts it into the drill hole1 carefully pressing it to the bottom with a rod4 ,the tamping1 if any is used1 is then inserted above the cartridge1 and the diver comes up4 ,the working vessel having been quickly hauled by the mooring-lines to a safe distance by means of capstans worked1 whenever practicable1 by the steam-engine1 the wires are attached to the machine1 and at the signal 8all ready0 the charge is fired4 ,the working vessel is then hauled back to her position1 and as soon as the water becomes sufficiently cleared of the dark muddy matter stirred up by the blast1 to enable the diver to see in it1 he descends and examines the result4 ,if the blast has been effective1 he signals for the stone chains to be lowered to him2 which being done1 he proceeds to sling the large pieces of broken rock1 one after another1 as they are hoisted up and deposited on deck4 ,all the pieces large enough to sling having been thus removed1 he signals for the tub and shovel1 and upon their being lowered to him1 proceeds to shovel into the tub the small fragments1 and to have them hoisted up and piled on deck1 until the surface of the rock is sufficiently cleared to place the drill for a new blast4 ,submarine ,rocks4--,the following brief account of the removal of the 8,tower0 and the 8,corwin0 ,rocks from the ,narrows1 at the entrance of ,boston ,harbour1 ,u4,s41 from the pen of ,j4 ,g4 ,foster1 is instructive as illustrating the method of procedure in submarine blasting1 and as showing the unfitness1 for work of that character1 of the slow-burning explosives3-- 8,tower ,rock10 being the smaller of the two1 was selected as the one to be first removed4 ,its horizontal dimensions being only #ej by #bf feet1 it was estimated that one large central charge surrounded by five or six others1 all in large and deep drill-holes1 would be able to rend the rock into pieces4 ,the working vessel1 the sloop 8,hamilton10 of #gj tons1 was moored over this rock on the #cjth of ,july1 #ahfg1 and the new submarine drilling machine1 designed for this work1 by ,mr4 ,townsend1 the contractor1 was placed in position and tried4 ,several imperfections were found at the first trial1 which prevented its efficient working4 ,while these were being remedied1 a trial was made of surface blasts1 placed in and around the rock in the positions most favourable to their action4 ,these proved to be entirely without effect4 ,no seams or breaks were made by them in the smooth surface of the rock4 ,as soon as the submarine drilling machine was perfected1 it was put in operation1 and successfully worked4 ,the central and the surrounding holes were drilled to depths varying from #b to #h feet1 each hole being #c inches in diameter4 ,these were well charged with black blasting powder1 and tamped with sand4 ,in some holes1 the charges produced no visible effect1 the tamping being blown out like the charge from a cannon4 ,in others1 a crater was formed1 but with a radius only about one-half the line of least resistance4 ,the holes that were intact were then deepened1 and new ones drilled2 these were charged with ,dupont's sporting powder4 ,the result was much better1 but not what was desired4 ,the pressure of the water1 from #bc to #cc feet in depth1 seemed to diminish largely the ordinary explosive effect of gunpowder upon rock1 as seen in blasts in the open air4 ,trial was then made of the patent safety blasting powder1 manufactured by the ,oriental ,company of ,boston1 the proportions of the ingredients having been modified to increase its strength for this especial use4 ,this produced the desired effect4 ,the rock was rent in pieces2 and by drilling additional holes and continuing large charges of the powder1 the rock was finally reduced to the required depth4 ,to smooth off its upper surface and break down the sharp projecting points1 large surface charges of sporting powder were employed4 ,these accomplished the result to a limited extent1 but not completely4 ,a large #ae-;inch shell was then placed in a crevice near the centre of the rock and fired4 ,its explosion swept the rock completely1 breaking down and levelling the projecting points4 ,the work upon this rock occupied eight weeks4 ,in that time1 #hj tons of stone had been blasted out1 hoisted up1 and deposited on shore1 attaining the required depth of #bc feet at mean low water4 ,about #gj tons of small fragments were suffered to remain on the bottom around the rock1 where they had been thrown by the blasts1 and where they could do no harm4 ,the cost per ton of the quantity hoisted up and deposited on shore was #fdic dollars1 no account being taken of the quantity blown1 in small fragments1 into deep water4 8,tower ,rock0 having been entirely removed to the required depth1 the moorings of the working vessel were at once removed to 8,corwin ,rock10 and work commenced upon it on the #ast of ,october1 #ahfg4 ,this rock was found to be much more difficult to blast1 on account of its extremely tortuous lamination1 its great toughness1 and the presence of a great number of iron pyrites4 ,surface blasts were also tried upon this rock at the outset1 in hopes that1 by being placed in the most favourable positions between the sharp ridges of the rock1 they might break them down4 ,these1 however1 like those upon ,tower ,rock1 entirely failed to produce any noticeable effect1 even when they contained four and five hundred pounds of the best sporting powder4 ,the drilling machine was therefore called into requisition as before1 and used continuously till the completion of the work4 ,on account of the extent of this rock1 a different plan of operations for its removal was adopted4 ,one side of the rock most favourable for blasting was selected1 and a row of holes drilled parallel to the edge1 and at a distance from it equal to the depth of the holes1 which was taken to extend #a foot below the required level1 #bc feet at mean low tide4 ,after blasting out these holes1 a new line of holes was drilled parallel to the former line1 or to the 8face0 left by the blasts1 and these also were blasted out2 then a third line1 and so on1 progressing regularly across the rock1 continually blasting it off in parallel blocks1 extending downward a little below the depth required4 ,the advantages of this mode of operation were that it enabled the blasts to act laterally1 in which direction they were the most powerful2 and the rock was left1 after each series of blasts1 with a nearly vertical side1 or 8face10 in which the presence of seams could be more readily detected1 and the character of the strata observed1 so that the most favourable positions could be selected for the next blasts4 ,sometimes the craters1 following the strata1 ran under1 or left an overhanging 8face10 in which case a large charge placed under its projecting edge1 usually had the effect of throwing off the overhanging portion1 and sometimes of dislodging large masses4 ,after the rock had been in this way blasted entirely across1 and to the general depth required1 a careful survey was made1 the soundings being taken in lines from #e to #aj feet apart1 and at right angles to each other1 the lower end of the sounding pole being placed by the diver alternately upon the highest and the lowest points4 ,this survey showed that although more than the required depth had been generally attained1 yet many points projected above this level by distances varying from #b to #ad inches4 ,to remove these1 large surface charges were again tried1 but with the same ineffective result4 ,their only effect was to pile up the sand and small fragments of stone into irregular windrows on the surface of the rock4 ,small holes had1 therefore1 to be drilled at each of these points to blast them off4 ,this occupied much more time than could reasonably have been expected2 so that it was not until two months' labour had been expended1 that all the points were finally reduced to the required level4 ,obstructions in ,water-courses4--,the removal of obstructions from water-courses often leads to much subaqueous blasting4 ,trees that have fallen into the stream are most effectively broken up by charges of gunpowder fired by a detonation4 ,the success of the operation will1 however1 be greatly dependent upon the judicious placing of the charges4 ,brickwork may also be very effectively dealt with by charges of gunpowder4 ,but stone masonry and blocks of rock may be more effectively broken up by gun-cotton1 tonite1 or dynamite4 ,for work of this character1 electrical firing offers great advantages1 for1 besides its convenience1 it allows of several charges being exploded simultaneously1 a condition that is always favourable1 and in many cases essential1 to success4 ,the following highly interesting and instructive account of the removal by blasting of some obstructions in certain rivers in ,india is given by ,lieut4 ,a4 ,o4 ,green1 ,r4,e4 ,illustration3 ,,fig4 #ea4 ,illustration3 ,,fig4 #eb4 ,he1 in company with some assistants1 left ,calcutta for ,maldah on the #hth of ,april1 #ahgd1 where they commenced work on the following day upon the wreck of a large county boat1 which lay on the top of a tree in mid-stream1 as shown in ,fig4 #ea4 ,soundings were taken over and around this tree1 which was found to be about #c feet #f inches in diameter at its base4 ,the gunpowder intended to be used in these operations not having arrived1 three #e-lb4 charges of gun-cotton were made up2 it was thought that under the #ae-;feet head of water1 these would have been sufficient to break the tree in half4 ,the gun-cotton was in the form of compressed discs1 #b inches in diameter1 and #b inches thick1 each disc weighing about #e ounces4 ,these discs were filled into a tin cylinder to within about #d inches of the top4 ,an electric fuse1 with wires attached1 having been securely pushed into the hole in the centre of the top disc1 the empty space above was filled up1 with first a layer of sawdust1 and then a layer of plastic clay1 well rammed4 ,the whole was then painted over1 and the upper end tied up in a covering of waxed cloth1 the holes through which the fuse wires passed being carefully luted4 ,the charge1 thus made up1 is shown in section in ,fig4 #eb4 ,it was fired by means of a dynamo-electric machine4 ,the first charge produced but little effect2 a second failed from the case not being water-tight2 a third charge was more effective1 as it lifted the tree and the boat partially out of the water4 ,the positions of these gun-cotton charges are indicated by circles on the figure4 ,the next day1 two charges of gunpowder1 of about #gj lb4 each1 were placed under the boat1 these charges being lashed on to the snag by the divers4 ,these charges consisted simply of common oil-tins1 carefully cleaned and painted over with red-lead paint4 ,the bunghole was closed by a wooden plug1 bored through to allow the fuse wires to pass4 ,this plug1 after being inserted1 was coated over with a waterproofing compound4 ,the effect of the two charges was to completely demolish the boat4 ,another charge of #ej lb4 removed the tree underneath4 ,the positions of these gunpowder charges are indicated by squares in ,fig4 #ea4 ,the next obstruction met with was a sand bank caused by a boat which had broken in half and then sunk4 ,the sand nearly covered the boat1 so that there was little else to operate upon4 ,a charge of #hj lb4 7one large charge being considered preferable to two or three small ones in getting rid of the sand71 placed close to the part of the boat that was visible1 made a considerable crater1 and a second charge of #hj lb4 was placed in a much more favourable position1 as nearly all the boat was removed except portions of the bow and stern1 which required two separate charges of #ej lb4 each before they disappeared4 ,in half an hour1 the whole of the sand bank had been washed away by the stream1 and there was from #c to #d feet of water over the spot where before the sand was high and dry out of the water4 ,the removal of this obstruction was dangerous1 owing to the nearness of the boat to the surface1 the consequent small resistance offered to the projection of its pieces through the air1 and the largeness of the charges used4 ,had1 however1 small charges been used1 it is more than probable that the small craters made by them would have become too quickly filled up again to have been of any good in facilitating the placing in position of subsequent ones4 ,the following day1 a large mango tree1 about #d feet #f inches in diameter1 was destroyed by two #ej-lb4 charges1 which broke it up into three pieces1 easily removable ashore4 ,a few days later1 a large trunk of a tree1 about #c feet in diameter1 was removed with two #ej-lb4 charges2 but the depth of water over it was so small that a large portion of the trunk was thrown a considerable distance on shore4 ,the next day a large tree which had formed a sand bank was very successfully removed by a charge of #ej lb4 placed among the roots1 it being considered that a smaller charge than #ej lb4 would not have effected the purpose4 ,opposite to ,ksimpore1 a boat was removed with a charge of #ej lb4 placed in the centre up-stream1 which entirely demolished it1 the pieces being all dragged ashore4 ,at ,mooty1 a large cotton tree1 the wood of which is extremely tough1 was found with many large branches projecting out of the water4 ,a charge of #gj lb4 tied under the tree at the springing of the branches effectually broke it up1 and the pieces were all hauled to land4 ,three miles farther down the river1 an attempt was made to destroy another large cotton tree with a similar charge1 but it only broke it into three pieces1 and two more charges of #ej lb4 each were necessary to clear it away effectually4 ,this tree was1 if anything1 slightly larger than the last1 i4 e4 from #c to #d feet in diameter1 and there was less water over it4 ,farther on1 the party came across a collection of three or four trees1 with their branches interlaced1 lying on a sand bank near ,alumpore ,dldah2 these were sufficiently broken up by a #gj-lb4 charge to make them easy of removal by coolie labour4 ,opposite to the village1 another awkward snag1 in the shape of a large tree sticking up in #cj feet of water1 was destroyed by tying a #gj-lb4 charge at its base4 ,a charge of #ej lb4 of powder under this head of water1 or even a smaller amount1 might have been sufficient1 but as the work had to be done quickly1 not much account was taken of a few pounds of powder more or less1 provided the object was attained4 ,at ,gomashtapore1 a large tree1 branches and all1 was found in #be feet of water1 lying in the channel under the bank4 ,the current here was considerable1 and some difficulty was experienced in placing the charges4 ,one charge of #gj lb4 broke the tree in half2 another of #ej lb4 at the springing of the branches broke them up2 and another of the same weight got rid of the roots4 ,below ,gomashtapore1 a large mango tree was demolished with #fj lb4 of powder4 ,a short distance farther on1 a bad bamboo snag was met with4 ,these bamboo snags1 which were merely the roots of the bamboos with perhaps a dozen or so whole ones left1 gave much trouble4 ,fig4 #ec gives an idea of what these snags are like4 ,it was found impossible to place a charge underneath this one1 so an opening was prized between the bamboos1 and a charge of #gj lb4 rammed down pretty well into the middle4 ,this cleared the whole of it away and opened the channel4 ,illustration3 ,,fig4 #ec4 ,at ,chandpore1 at a re-entering angle of the river and in a place peculiarly dangerous to navigation during the rains1 was an enormous banyan tree 7,ficus ,indica71 the main trunk of which1 to judge from the branches1 must have been at least from #ab to #ae feet in diameter4 ,an approximate measurement was made with a pole1 but any such measurement can only have been a very rough one4 ,illustration3 ,,fig4 #ed4 ,illustration3 ,,fig4 #ee4 ,the trunk was lying in deep water1 but the branches1 more like an accumulation of large trees1 were lying stretched out for a considerable distance over the bank1 covering an area of more than #hj square feet4 ,a charge of #bjj lb4 of powder was made up in an indiarubber bag1 and placed by the divers in about #bh feet of water1 well under the trunk of the tree4 ,the effect of this was to split the trunk up into several pieces1 each of which subsequently required separate removal4 ,a #gj-lb4 charge was next fired under two of the largest pieces in #ah feet of water1 and this broke them up completely4 ,having now run out of all the cases for powder1 three charges of gun-cotton1 similar to the first1 were made up1 and fired separately1 each placed under a good thick branch1 about #h feet in girth4 ,the effect of all three was prodigious2 seemingly greater than that of the #gj lb4 of gunpowder4 ,as there were no more cases left1 and time was precious1 some common earthenware ghurrahs were obtained from the village as a makeshift4 ,these held about #bj lb4 of powder2 the fuse was placed in the centre in a disc of gun-cotton1 and the neck was closed up with damp earth1 white-lead paint1 c41 just in the same way as the gun-cotton charges had been4 ,a rope for lashing them to the obstacle was securely fastened round the neck1 and the fuse wires were tied under1 this lashing1 leaving a small loop towards the fuse free1 so as to avoid any chance of a strain being brought on the fuse in lowering the charge4 ,figs4 #ed and #ee show the arrangement of this charge4 ,the first one tried had but little effect when placed under a branch of the tree in deep water1 and it was accordingly determined to wait for cases from ,calcutta2 but after waiting five days without their appearing1 three more of these charges were tried1 and this time with very excellent results4 ,they were indeed so satisfactory1 that the same evening four more were made up and fired4 ,the first under a mango tree a little farther down the river4 ,this broke it in half1 throwing one part high and dry on shore1 and the other into deep water4 ,the other three were fired under the remaining branches of the banyan tree with very good effect1 cutting them away4 ,it is more than probable1 observes ,lieut4 ,green1 that the good results obtained with all these ghurrah charges were entirely due to the gun-cotton disc inside causing the gunpowder itself to detonate1 so that the thinness of the envelope was of little moment in determining the force of the explosion4 ,the tin cases having arrived1 the rest of the powder was made up into five charges of #dh lb4 and three ghurrah charges of #bj lb each4 ,about four miles farther down the river1 there was an old peepul tree lying in mid-channel1 with several of the branches above water4 ,two tins1 one placed under the springing of the branches and the other under the roots1 blew away the lower branches on which the tree was resting1 and it sank slightly in the water4 ,a ghurrah was next fired under the trunk with splendid results1 the tree disappearing entirely except one branch1 which required another small charge to remove it4 ,the trunk of this tree was nearly #h feet in diameter1 but of soft stringy wood4 ,on returning to camp1 a small charge of #b lb4 of gun-cotton was made up in a section of bamboo1 and used against the banyan tree with very good effect1 and a ghurrah charge demolished the last branch but one4 ,the next day #a lb4 of gun-cotton in a piece of bamboo finished the last of this enormous tree4 ,after clearing away several more trees1 the foundations of an old factory1 which had slipped into the stream1 were removed by introducing two charges of #a lb4 of gun-cotton1 in the ends of two bamboos1 well into the crevices of the masonry under the water4 ,another obstruction consisted of a row of old piles1 about #ae inches square1 stretching across the river below the surface of the water4 ,six of the most dangerous of these were removed from the dry season channel with ghurrah charges tied to the foot of the piles4 ,an old well that had fallen bodily into the water was afterwards met with4 ,the position of this well is shown in ,fig4 #ef4 ,a charge of #d lb4 of gun-cotton completely destroyed it4 ,near ,azimgunge1 the trunk of a very large peepul tree was found sunk in deep water4 ,it was so large that it was thought necessary to place a #ajj-lb4 charge underneath it2 this charge broke it up completely1 but two small charges of #bj lb4 each were subsequently required to remove the pieces4 ,illustration3 ,,fig4 #ef4 ,later on1 a well1 similar to the one previously destroyed1 was met with4 ,the brickwork was remarkably good and about #c feet thick1 and the mortar was excellent4 ,one charge of #d lb4 of gun-cotton broke it up into large pieces2 but it took another similar charge1 and two charges of #bj lb4 of gunpowder to destroy it completely4 ,on the same day1 two trees were removed with ghurrah charges1 which had been used throughout1 for small charges1 with unvarying success4 ,at a place called ,farrashdangah1 there was a very bad obstruction in the river1 caused by the remains of an old bathing ghat and bridge having been cut out from the bank by the water getting underneath the masonry4 ,both were projecting about #c feet above the water1 and in the rainy season they formed the centre of a very nasty and dangerous whirlpool1 in which many boats had1 according to the ,executive ,engineer of the ,nuddea ,rivers ,division1 been lost4 ,there was an immense mass of masonry1 but no means of getting a charge placed underneath it2 so a charge of #ajj lb4 of powder was placed close alongside it in about #ae feet of water4 ,this shunted the mass bodily over and underneath the water4 ,two #ej-lb4 charges were next placed underneath the mass1 and these shattered it all up1 except one piece1 which was got rid of with a fourth charge of #bj lb4 placed well underneath it4 ,the ,executive ,engineer wishing that the wing-wall of the bridge1 which was on dry land during the dry season1 might be removed as well1 a small hole was made at the foot of the visible portion of the brickwork1 and a charge of #b lb4 of gun-cotton was introduced into this1 and fired with only a tolerable effect1 the brickwork being cracked for a distance of #c or #d feet from the centre of the charge4 ,a hole was next dug down about #e feet at one side of the wing-wall1 and a charge of #d lb4 of gun-cotton well tamped was fired4 ,the tamping was blown out1 and the wall foundations cracked a good deal4 ,the excavation was now deepened to #f feet1 and a hole made under the brickwork big enough to contain a #ajj-lb4 charge4 ,it was then well tamped up and fired4 ,its effect was excellent4 ,all the brickwork of the wing-wall was got rid of1 and a crater about #cj feet in width at the top blown out in the point of the bank that was required to be removed1 and which was one of the chief causes of the whirlpool1 so that the next rise of the river was sure to carry it all away4 ,the following day an old pucka ghat opposite to ,berhampore was entirely broken up with three #bj-lb4 charges1 and an enormous quantity of old bricks were thrown into the river4 ,the last operation undertaken consisted in the blowing up of a very large ghat opposite to the ,nawb of ,moorshedabd's palaces4 ,the river during successive rains had cut into and underneath the steps of the ghat1 bringing down large masses of it into the river1 where they formed most dangerous obstacles to navigation4 ,the work was necessarily carried out in a very rough way1 for want of the proper tools4 ,deep excavations were made under the three largest masses of masonry1 at about #be feet apart1 and into these were introduced three #ej-lb4 and one #bj-lb4 charges of powder4 ,these charges were well tamped1 connected up in divided circuit1 and fired simultaneously4 ,all the masonry was broken up completely1 so as to be easily removable afterwards by coolie labour1 which was all that was required4 ,the conclusions to be drawn from the foregoing notes are1 that large trees lying in shallow water require charges of #ej lb4 of gunpowder and upwards for their effectual removal2 but that where there is plenty of water1 and the trees are not very large1 #bj lb4 is sufficient4 ,for these small charges1 it has been seen that the common earthenware ghurrah answers admirably1 and under similar circumstances it would undoubtedly be advantageous to use them1 as they are inexpensive1 and obtainable in nearly every ,indian village4 ,the charges used might1 in many cases1 at first have been no doubt made smaller with advantage1 both for safety and economy2 but as speed was the great object1 these were not so much thought of4 ,for the removal of masonry under water1 it is not necessary to place the charge underneath the mass1 which is often impossible2 a large charge alongside it being generally quite sufficient to break it up pretty effectually where there is sufficient head of water4 ,smaller charges can of course be easily used afterwards1 whenever required1 and for these small charges1 gun-cotton is very effective1 as it can be easily introduced1 in the end of a bamboo1 into holes and crevices where it would be impossible to get any but the smallest charges of gunpowder4 ,,index4 ,appliances for firing blasting charges1 #db ,auxiliary tools1 #ag ,batteries1 firing1 #fb ,beche1 #ba ,bichromate firing battery1 #fb ,bits1 borer1 #ca ,blasting gear1 sets of1 #bb ---- sticks1 #ea ---- subaqueous1 #afd ,borer-bits1 #ca ,boring under water1 #agj ---- the shot-holes1 #abh1 #adb ,bornhardt's firing machine1 #eg ,brain's powder1 #aje ,bull1 #bj ,cables1 #ec ,cellulose dynamite1 #aje ,charging and firing1 #aej ---- the shot-holes1 #acb ,chemical compounds1 #ha ,claying iron1 #bj ,conditions of disruption1 #aaj ,connecting wires1 #eb ,cotton powder1 #ajc ,darlington drill1 #bf ,detonation1 #ie ,detonators1 #ed ,dislodged rock1 removal of1 #aed ,disruption1 conditions of1 #aaj ---- force required to cause1 #ajg ,division of labour1 #aee ,drills1 dimension of1 #f ---- form of1 #d ---- hand1 #a ---- hardening and tempering1 #aj ---- making and sharpening1 #g ---- sets of1 #ac ,drivings1 examples of1 #aeg ,dubois-,franois carriage1 #ci ,dynamite1 #ajj ---- composition of1 #hg ,electrical firing1 advantage of1 #aec ,electric fuses1 #dg ---- tension fuse1 #ej ,example of a heading1 #aae ,examples of drivings1 #aeg ,explosion1 force developed by1 #gb ---- heat liberated by1 #fg ---- gases generated by1 #fi ---- nature of1 #fd ,explosive agents1 nature of1 #gf ,firing batteries1 #fb ---- blasting charges1 appliances for1 #db ---- by electricity1 #ach ---- machines1 #ee ---- machine1 ,bornhardt's1 #eg ---- ---- induction coil1 #fa ---- ---- ,mowbray's1 #ei ---- ---- ,siemens'1 #fj ---- ---- ,smith's1 #eh ---- points of the common explosive agents1 #ajb ---- table for frictional electric machine1 #adj ---- the charges1 #acg ,force developed by an explosion1 #gb ---- developed by gunpowder1 #hh ---- required to cause disruption1 #ajg ,fuse1 safety1 #de ,fuses1 electric1 #dg ,gases generated by an explosion1 #fi ,gun-cotton1 #ii ---- constitution of1 #ha ,gunpowder1 #ig ---- composition of1 #hj ---- force developed by1 #hh ,hammers1 #ad ---- patterns of1 #ae ,hand boring1 #abh ,heading1 example of1 #aae ,heat1 action of1 in firing1 #ib ---- liberated by an explosion1 #fg ---- measure of1 #ff ---- specific1 #ff ,hoosac ,tunnel1 #aeh ,induction firing coils1 #fa ,joint and bedding planes1 #aah ,jumper1 #c ,labour1 division of1 #aee ,line of least resistance1 #ajf ,lithofracteur1 #ajd ,machine boring1 #adb ---- rock-drills1 #bc ,machines1 firing1 #ee ,means of firing the common explosive agents1 #ib ,measure of heat1 #ff ,mechanical mixture1 #gf ,mowbray's firing machine1 #ei ,musconetcong ,tunnel1 #aei ,nature of an explosion1 #fd ,nitrated gun-cotton1 #ajc ,nitro-glycerine1 constitution of1 #hf ,obstructions in water-courses1 #agh ,operations of rock blasting1 #abh ,preparation of subaqueous charges1 #afd ,principles of blasting1 #ajf ,rammer1 #bj ,relative strength of gunpowder1 gun-cotton1 and dynamite1 #ia ---- ---- of the common explosive agents1 #hh ,removing dislodged rock1 #aed ,rock-drill supports1 #cd ,safety ,fuse1 #de ,st4 ,gothard ,tunnel1 #aeg ,schultze's powder1 #ajd ,scraper1 #ah ,shot-holes1 boring1 #abh1 #adb ---- charging1 #acb ,siemens' firing machine1 #fj ,silvertown firing battery1 #fb ,sledges1 #ad ---- ,north of ,england1 #ag ---- ,north ,wales1 #ag ---- ,south ,wales1 #af ,smith's firing machine1 #eh ,some properties of the common explosive agents1 #ig ,some varieties of the nitro-cellulose and the nitro-glycerine compounds1 #ajc ,squibs1 #dd ,steel1 hardening and tempering1 #i ,stemmer1 #bj ,sticks1 blasting1 #ea ,stretcher bar1 #cg ,subaqueous blasting1 #afd ---- charges1 preparation of1 #afd ,submarine rocks1 removal of1 #agc ,swab-stick1 #ai ,tamping1 #aba ,tonite1 #ajc ,water1 boring under1 #agj ,water-courses1 obstructions in1 #agh ,waterproofing composition1 #afe ,weight of explosive in bore-hole1 table of1 #aji ,wires1 connecting1 #eb ,,london3 ,,printed ,,by ,,wm4 ,,clowes ,,and ,,sons1 ,,stamford ,,street ,,and ,,charing ,,cross4 ,illustration3 ,plate ,i4 ,,set ,,of ,,coal ,,blasting ,,gear4 ,fig4 #a4 ,fig4 #b4 ,fig4 #d4 ,fig4 #e4 ,fig4 #c4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,ii4 ,,set ,,of ,,single ,,hand ,,stone ,,blasting ,,gear4 ,fig4 #f4 ,fig4 #g4 ,fig4 #h4 ,fig4 #i4 ,fig4 #aj4 ,fig4 #aa4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,iii4 ,,set ,,of ,,double ,,hand ,,stone ,,breaking ,,gear4 ,fig4 #ab4 ,fig4 #ae4 ,fig4 #ac4 ,fig4 #ad4 ,fig4 #af4 ,fig4 #ag4 ,fig4 #ah4 ,fig4 #ai4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,iv4 ,,the ,,darlington ,,machine ,,drill4 ,fig4 #bj4 ,fig4 #bb4 ,fig4 #ba4 ,fig4 #bc4 ,fig4 #bd4 ,fig4 #be4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,v4 ,,stretcher ,,bar4 ,fig4 #bf4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,vi4 ,,machine ,,drill ,,supports4 ,fig4 #bg4 ,fig4 #bh4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,vii4 ,,machine ,,drill ,,support4 ,fig4 #bi4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,viii4 ,,dubois-,,fran,,ois ,,machine ,,drill ,,carriage4 ,fig4 #cj4 ,elevation4 ,fig4 #ca4 ,plan4 ,fig4 #cb4 ,raising and lowering ,screw4 ,fig4 #cc4 ,back support for the ,drill4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,ix4 ,s,t4 ,,gothard ,,tunnel4 ,gschenen ,end4 ,airolo ,end4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,x4 ,,examples ,,of ,,headings4 ,heading1 ,marihaye4 ,heading1 ,anzin4 ,heading1 ,ronchamp4 ,,hoosac ,,tunnel--,west ,end4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,xi4 ,,hoosac ,,tunnel4 ,centre ,cut4 ,side ,cuts4 ,squaring the ,heading4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,illustration3 ,plate ,,xii4 ,,musconetcong ,,tunnel4 ,the ,heading2 ,plan4 ,the ,bench4 ,sectional ,elevation4 ,the ,bench1 ,plan4 ,the ,heading1 ,elevation4 ,e ,f4 ,n4 ,spon4 ,london ,new ,york4 ,transcriber' ,notes ,inconsistent and unusual spelling1 hyphenation1 use of accents and lay-out have been retained1 except as mentioned below4 ,there are two sets of numbered illustrations3 numbered illustrations in the text1 and numbered illustrations in the plates in the back of the book4 ,calculations and tables have been copied verbatim although some contain calculation errors4 ,some reference letters in the text are missing from the illustrations4 ,changes made3 ,tables and illustrations have been moved to between paragraphs4 ,some minor typographic errors have been corrected and some missing punctuation has been added silently4 ,page #dj3 plate ,v changed to plate ,v4 ,page #aji3 ,curtiss' and ,harvey's changed to ,curtis's and ,harvey's4 ,page #aff3 ,curtis's and ,harvey changed to ,curtis's and ,harvey's4