,this file was produced from images generously made available by ,the ,internet ,archive4 ,,liquid ,,drops ,,and ,,globules ,,by ,,the ,,same ,,author4 -------------------------------- 99,,pyrometry99 ,a ,practical ,treatise on the ,measurement of ,high ,temperatures4 ,with #fj ,illustrations1 xii #bjj pp4 ,crown #hvo1 cloth 7#aiaa74 ,price 99#e_/-99 net4 ---------------- 99,,heat ,,for ,,engineers99 ,a ,treatise on ,heat1 with special regard to its ,practical ,applications4 ,second ,edition ,revised1 with #aaj ,illustrations1 xiv #dcj pp4 ,demy #hvo1 cloth 7#aiab74 ,price 99#ab_/f99 net4 -------------------------------- ,e4 ,f4 ,n4 ,,spon1 ,ltd41 #eg ,haymarket1 ,london1 ,s4,w4 ,,liquid ,,drops ,,and ,,globules ,their ,formation and ,movements ,,three ,,lectures ,,delivered ,,to ,,popular ,,audiences ,,by ,,chas4 ,r4 ,,darling ,,associate ,,of ,,the ,,royal ,,college ,,of ,,science1 ,,ireland2 ,,fellow ,,of ,,the ,,institute ,,of ,,chemistry2 ,,fellow ,,of ,,the ,,physical ,,society1 ,,etc42 ,,lecturer ,,in ,,physics ,,at ,,the ,,city ,,and ,,guilds ,,of ,,london ,,technical ,,college1 ,,finsbury ,,with #dc ,,illustrations ,london ,e4 ,f4 ,n4 ,,spon1 ,,limited1 #eg ,,haymarket ,,new ,,york ,,spon ,,chamberlain1 #abc ,,liberty ,,street #aiad ,,contents ,,page ,list of ,illustrations 4 4 4 4 4 4 4 vii ,preface 4 4 4 4 4 4 4 4 4 ix ,lecture ,i4 ,introduction 4 4 4 4 4 4 4 4 4 #a ,general ,properties of ,liquids 4 4 4 4 4 4 #b ,properties of the ,surface ,skin of ,water 4 4 4 4 #c ,elastic ,skin of other ,liquids-,minimum ,thermometer 4 4 4 #e ,boundary ,surface of two ,liquids 4 4 4 4 4 4 #f ,area of ,stretched ,surface 4 4 4 4 4 4 4 #g ,shape of detached ,masses of ,liquid 4 4 4 4 4 #h ,production of ,true ,spheres of ,liquids 4 4 4 4 4 #aj ,the ,centrifugoscope 4 4 4 4 4 4 4 4 #ad ,effect of ,temperature on ,sphere of ,orthotoluidine 4 4 4 #ae ,other ,examples of ,equi-,density 4 4 4 4 4 4 #ag ,aniline ,films or ,skins 4 4 4 4 4 4 4 #ai ,surface ,tension 4 4 4 4 4 4 4 4 #ba ,the ,diving ,drop 4 4 4 4 4 4 4 4 #bb ,formation of ,falling ,drops of ,liquid 4 4 4 4 4 #bd ,ascending or ,inverted ,drops 4 4 4 4 4 4 #ca ,lecture ,,ii4 ,automatic ,aniline ,drops 4 4 4 4 4 4 4 #cc ,automatic ,drops of other ,liquids4 4 4 4 4 4 #cg ,liquid ,jets 4 4 4 4 4 4 4 4 4 #ch ,liquid ,columns 4 4 4 4 4 4 4 4 #dj ,communicating ,drops 4 4 4 4 4 4 4 4 #dd ,combined ,vapour and ,liquid ,drops 4 4 4 4 4 #dg ,condensation of ,drops from ,vapour 4 4 4 4 4 #di ,liquid ,clouds in ,liquid ,media 4 4 4 4 4 4 #ed ,overheated ,drops 4 4 4 4 4 4 4 4 #ee ,floating ,drops on ,hot ,surfaces 4 4 4 4 4 4 #eg ,lecture ,,iii4 ,spreading of ,oil on the ,surface of ,water 4 4 4 4 #fj ,movements due to ,solubility 4 4 4 4 4 4 #fc ,movements of ,aniline ,globules on a ,water ,surface 4 4 4 #fc ,movements of ,orthotoluidine and ,xylidine #a-c-d on a ,water ,surface #ff ,production of ,globules from ,films 4 4 4 4 4 #fh ,network formed from a ,film 4 4 4 4 4 4 #gj ,quinoline ,rings 4 4 4 4 4 4 4 4 #ga ,expanding ,globules 4 4 4 4 4 4 4 4 #ga ,attraction between ,floating ,globules 4 4 4 4 4 #gc ,analogies of ,surface ,tension ,phenomena with ,life 4 4 4 #ge ,conclusion 4 4 4 4 4 4 4 4 4 #gf ,appendix ,apparatus and ,materials required for ,experiments on ,drops and ,globules 4 4 4 4 4 4 4 4 #gh ,index 4 4 4 4 4 4 4 4 4 4 #ha ,,list ,,of ,,illustrations ,,fig4 ,,page #a4 ,silver sheet floating on water 4 4 4 4 4 #d #b4 ,column and index of minimum thermometer 4 4 4 #f #c4 ,thread of golden syrup rising and forming a drop 4 4 #h #d4 ,drops of different sizes resting on flat plate 4 4 #aj #e4 ,formation of a sphere of orthotoluidine 4 4 4 #ab #f4 ,detached sphere floating under water 4 4 4 4 #ac #g4 ,the centrifugoscope 4 4 4 4 4 4 4 #ad #h4 ,aniline drops falling through cold water and ascending through hot water 4 4 4 4 4 4 #ag #i4 ,aniline skins enveloping water 4 4 4 4 4 #bj #aj1 #aa1 #ab4 ,the diving drop4 ,three stages 4 4 4 4 #bc #ac4 ,apparatus for forming ascending or descending drops of liquids #bg #ad-bj4 ,formation of a drop of orthotoluidine1 showing the droplet4 ,seven stages 4 4 4 4 4 #bi-ca #ba1 #bb4 ,automatically formed aniline drops1 showing the formation of droplets from the neck 4 4 4 #cd1 #ce #bc-be4 ,jets of orthotoluidine discharged under water 4 4 #ci #bf4 ,water stretched between a tube and a plate 4 4 4 #dj #bg-cj4 ,a liquid column stretched upwards by addition of water until broken4 ,four stages 4 4 4 #dc #ca4 ,a column of aceto-acetic ether in water 4 4 4 #dd #cb4 ,apparatus for communicating drops 4 4 4 4 #de #cc4 ,combined vapour and liquid drops 4 4 4 4 #di #cd4 ,spheroid of water on a hot plate 4 4 4 4 #eh #ce4 ,forces acting on a floating globule 4 4 4 4 #fa #cf4 ,aniline globules on a water surface 4 4 4 4 #fd #cg4 ,orthotoluidine globules on a water surface 4 4 4 #ff #ch4 ,resolution of a floating skin into globules 4 4 4 #fh #ci4 ,network formed from a film of tar-oil 4 4 4 4 #gj #dj4 ,quinoline rings and perforated plates 4 4 4 4 #ga #da4 ,the expanding globule 4 4 4 4 4 4 #gb #db4 ,the devouring globule4 ,five stages 4 4 4 #gd #dc4 ,photograph of one globule absorbing another 4 4 4 #ge ,,preface ,the object of the present little volume is to reproduce in connected form1 an account of the many interesting phenomena associated with liquid drops and globules4 ,much of the matter relates to experiments devised by the author during the past four years1 descriptions of which have appeared in the ,proceedings of the ,physical ,society2 in the columns of ,nature and ,knowledge2 and elsewhere4 ,the exhibition of these experiments at the conversazioni of the ,royal ,society and the ,royal ,institution1 and in the author's lectures1 has evoked such interest as to suggest the present publication4 ,it may be added that all the experiments described may be repeated by any intelligent reader at a trifling cost1 no special manipulative skill being required4 ,the context maintains the form of the lectures delivered on this subject by the author at various places1 and the method of presentation is such as may be followed by those who have not received a training in this branch of science4 ,it is hoped1 in addition1 that the book may prove of some service to teachers of science and others interested in the properties of liquids4 ,a number of the illustrations used have appeared in the pages of ,knowledge in connexion with the author's articles1 and are here reproduced by courtesy of the ,editor4 ,other drawings have been provided by ,mr4 ,w4 ,narbeth1 to whom the author expresses his thanks4 ,,chas4 ,r4 ,,darling4 ,city and ,guilds ,technical ,college1 ,finsbury1 #aiad4 ,,liquid ,,drops ,,and ,,globules ,,lecture ,i 99,introduction499--,in choosing a subject for a scientific discourse1 it would be difficult to find anything more familiar than a drop of liquid4 ,it might even appear1 at first sight1 that such a subject in itself would be quite inadequate to furnish sufficient material for extended observation4 ,we shall find1 however1 that the closer study of a drop of liquid brings into view many interesting phenomena1 and provides problems of great profundity4 ,a drop of liquid is one of the commonest things in nature2 yet it is one of the most wonderful4 ,apart from the liquids associated with animal or vegetable life1 water and petroleum are the only two which are found in abundance on the earth2 and it is highly probable that petroleum has been derived from the remains of vegetable life4 ,many liquids are fabricated by living organisms1 such as turpentine1 alcohol1 olive oil1 castor oil1 and all the numerous vegetable oils with which we are all familiar4 ,but in addition to these1 there are many liquids produced in the laboratory of the chemist1 many of which are of great importance2 for example1 nitric acid1 sulphuric acid1 and aniline4 ,the progress of chemical science has greatly enlarged the number of liquids available1 and in our experiments we shall frequently utilize these products of the chemist's skill1 for they often possess properties not usually associated with the commoner liquids4 99,general ,properties of ,liquids499--,no scientific study can be pursued to advantage unless the underlying principles be understood2 and hence it will be necessary1 in the beginning1 to refer to certain properties possessed by all liquids1 whatever their origin4 ,the most prominent characteristic of a liquid is mobility1 or freedom of movement of its parts4 ,it is owing to this property that a liquid1 when placed in a vessel1 flows in all directions until it reaches the sides2 and it is this same freedom of movement which enables water1 gathering on the hills1 to flow under the pull of gravitation into the lowlands1 and finally to the sea4 ,if we drop a small quantity of a strongly-coloured fluid--such as ink--into a large volume of water1 and stir the mixture for a short time1 the colour is evenly distributed throughout the whole mass of water1 because the freedom of movement of the particles enables the different portions to intermingle readily4 ,this property of mobility distinguishes a liquid from a solid2 for a solid maintains its own shape1 and its separate parts cannot be made to mix freely4 ,mobility1 however1 is not possessed in equal degree by all liquids4 ,petrol1 for example1 flows more freely than water1 which in turn is more mobile than glycerine or treacle4 ,sometimes a substance exhibits properties intermediate between those of a solid and a liquid1 as1 for instance1 butter in hot weather4 ,we shall not be concerned1 however1 with these border-line substances1 but shall confine our attention to well-defined liquids4 ,there is another feature1 however1 common to all liquids1 which has a most important bearing on our subject4 ,every liquid is capable of forming a boundary surface of its own2 and this surface has the properties of a stretched1 elastic membrane4 ,herein a liquid differs from a gas or vapour1 either of which always completely fills the containing vessel4 ,you cannot have a bottle half full of a vapour or gas only2 if one-half of that already present be withdrawn1 the remaining half immediately expands and distributes itself evenly throughout the bottle1 which is thus always filled4 ,but a liquid may be poured to any height in a vessel1 because it forms its own boundary at the top4 ,let us now take a dish containing the commonest of all liquids1 and in many ways the most remarkable--water--and examine some of the properties of the upper surface4 99,properties of the ,surface ,skin of ,water499--,here is a flat piece of thin sheet silver1 which1 volume for volume1 is #aj #a_/b times as heavy as water1 in which it might therefore be expected to sink if placed upon the surface4 ,i lower it gently1 by means of a piece of cotton1 until it just reaches the top1 and then let go the cotton4 ,instead of sinking1 the piece of silver floats on the surface2 and moreover1 a certain amount of pressure may be applied to it without causing it to fall to the bottom of the water4 ,by alternately applying and relaxing the pressure we are able1 within small limits1 to make the sheet of silver bob up and down as if it were a piece of cork4 ,if we look closely1 we notice that the water beneath the silver is at a lower level than the rest of the surface1 the dimple thus formed being visible at the edge of the floating sheet 7,fig4 #a74 ,if now ,i apply a greater pressure1 the piece of silver breaks through the surface and sinks rapidly to the bottom of the vessel4 ,or1 if instead ,i place a thick piece of silver1 such as a shilling1 on the surface of the water1 we find that this will not float1 but sinks immediately4 ,all these results are in agreement with the supposition that the surface layer of water possesses the properties of a very thin elastic sheet4 ,if we could obtain an extremely fine sheet of stretched rubber1 which would merely form a depression under the weight of the thin piece of silver1 but would break under the application of a further pressure or the weight of a heavier sheet1 the condition of the water surface would then be realized4 ,we may note in passing that a sheet of metal resting on the surface of water is a phenomenon quite distinct from the floating of an iron ship1 or hollow metal vessel1 which sinks until it has displaced an amount of water equal in weight to itself4 ,illustration3 ,fig4 #a4--,silver sheet floating on water4 ,we can now understand why a water-beetle is able to run across the surface of a pond1 without wetting its legs or running any risk of sinking4 ,each of its legs produces a dimple in the surface1 but the pressure on any one leg is not sufficient to break through the skin4 ,we can imitate this by bringing the point of a lead pencil gently to the surface of water1 when a dimple is produced1 but the skin is not actually penetrated4 ,on removing the pencil1 the dimple immediately disappears1 just as the depression caused by pushing the finger into a stretched sheet of indiarubber becomes straight immediately the finger is removed4 99,elastic ,skin of other ,liquids--,minimum ,thermometer499--,the possession of an elastic skin at the surface is not confined to water1 but is common to all liquids4 ,the strength of the skin varies with different liquids1 most of which are inferior to water in this respect4 ,the surface of petroleum1 for example1 is ruptured by a weight which a water surface can readily sustain4 ,but wherever we have a free liquid surface1 we shall always find this elastic layer at the boundary1 and ,i will now show1 by the aid of lantern projection1 an example in which the presence of this layer is utilized4 ,on the screen is shown the stem of a minimum thermometer--that is1 a thermometer intended to indicate the lowest temperature reached during a given period4 ,the liquid used in this instrument is alcohol1 and you will observe that the termination of the column is curved 7,fig4 #b74 ,in contact with the end of the column is a thin piece of coloured glass1 with rounded ends1 which fits loosely in the stem1 and serves as an index4 ,when ,i warm the bulb of the thermometer1 you notice that the end of the column moves forward1 but the index1 round which the alcohol can flow freely1 does not change its position4 ,on inclining the stem1 the index slides to the end of the column1 but its rounded end does not penetrate the elastic skin at the surface4 ,i now pour cold water over the bulb1 which causes the alcohol to contract1 and consequently the end of the column moves towards the bulb4 ,in doing so1 it encounters the opposition of the index1 which endeavours to penetrate the surface2 but we see that the elastic skin1 although somewhat flattened1 is not pierced1 but is strong enough to push the index in front of it4 ,and so the index is carried towards the bulb1 and its position indicates the lowest point attained by the end of the column--that is1 the minimum temperature4 ,obviously1 a thermometer of this kind must be mounted horizontally1 to prevent the index falling by its own weight4 ,illustration3 ,fig4 #b4--;,column and index of minimum thermometer4 99,boundary ,surface of two ,liquids499--,so far we have been considering surfaces bounded by air1 or--in the case of the alcohol thermometer--by vapour4 ,it is possible1 however1 for the surface of one liquid to be bounded by a second liquid1 provided the two do not mix4 ,we may1 for example1 pour petroleum on to water1 when the top of the water will be in contact with the floating oil4 ,if now we lower our piece of silver foil through the petroleum1 and allow it to reach the surface of the water1 we find that the elastic skin is still capable of sustaining the weight2 and thus we see that the elastic layer is present at the junction of the two liquids4 ,what is true of water and oil in this respect also holds good for the boundary or interface of any two liquids which do not mix4 ,evidently1 if the two liquids intermingled1 there would be no definite boundary between them2 and this would be the case with water and alcohol1 for example4 99,area of ,stretched ,surface499--,we will not at present discuss the nature of the forces which give rise to this remarkable property of a liquid surface1 but will consider one of the effects4 ,the tendency1 as in the case of all stretched membranes1 will be to reduce the area of the surface to a minimum4 ,if we take a disc of stretched indiarubber and place a weight upon it1 we cause a depression which increases the area of the surface4 ,but on removing the weight1 the disc immediately flattens out1 and the surface is restored to its original smallest dimension4 ,now1 in practice1 the surface of a liquid is frequently prevented from attaining the smallest possible area1 owing to the contrary action of superior forces2 but the tendency is always manifest1 and when the opposing forces are absent or balanced the surface always possesses the minimum size4 ,a simple experiment will serve to illustrate this point4 ,i dip a glass rod into treacle or golden syrup1 and withdraw it with a small quantity of the syrup adhering to the end4 ,i then hold the rod with the smeared end downwards1 and the syrup falls from it slowly in the form of a long1 tapered column4 ,when the column has become very thin1 however1 owing to the diminished supply of syrup from the rod1 we notice that it breaks across1 and the upper portion then shrinks upwards and remains attached to the rod in the form of a small drop 7,fig4 #c74 ,so long as the column was thick1 the tendency of the surface layer to reduce its area to the smallest dimensions was overpowered by gravity2 but when the column became thin1 and consequently less in weight1 the elastic force of the outer surface was strong enough to overcome gravitation1 and the column was therefore lifted1 its area of surface growing less and less as it rose1 until the smallest area possible under the conditions was attained4 ,illustration3 ,fig4 #c4--,thread of golden syrup rising and forming a drop4 99,shape of ,detached ,masses of ,liquid499--,let us now pay a little attention to the small drop of syrup which remains hanging from the rod4 ,it is in contact with the glass at the top part only1 and the lower portion is only prevented from falling by the elastic skin around it1 which sustains the weight4 ,we may compare it to a bladder full of liquid1 in which case also the weight is borne by the containing skin4 ,now suppose we could separate the drop of syrup entirely from the rod2 what shape would it take8 ,we know that its surface1 if not prevented by outside forces from doing so1 would become of minimum area4 ,assuming such extraneous forces to be absent or counterbalanced1 what would then be the shape of the drop8 ,it would be an exact sphere4 ,for a sphere has a less surface-area in proportion to its volume than any other shape2 and hence a free drop of liquid1 if its outline were determined solely by its elastic skin1 would be spherical4 ,a numerical example will serve to illustrate this property of a sphere4 ,supposing we construct three closed vessels1 each to contain #a cubic foot1 the first being a cube1 the second a cylinder of length equal to its diameter1 and the third a sphere4 ,the areas of the surfaces would then be3-- ,cube 4 4 4 4 #f square feet4 ,cylinder 4 4 4 4 #e4hf 11 11 ,sphere 4 4 4 4 #d4i 11 11 ---------------------------------------- -------------- ,and whatever shape we make the vessel1 it will always be found that the spherical form possesses the least surface4 ,illustration3 ,fig4 #d4--;,drops of different sizes resting on flat plate4 ,now let us examine some of the shapes which drops actually assume4 ,i take a glass plate covered with a thin layer of grease1 which prevents adhesion of water to the glass1 and form upon it drops of water of various sizes by the aid of a pipette4 ,you see them projected on the screen 7,fig4 #d74 ,the larger drops are flattened above and below1 but possess rounded sides and resemble a teacake in shape4 ,those of intermediate size are more globular1 but still show signs of flattening2 whilst the very small ones1 so far as the eye can judge1 are spherical4 ,evidently1 the shape depends upon the size2 and this calls for some explanation4 ,if we take a balloon of indiarubber filled with water1 and rest it on a table1 the weight of the enclosed water will naturally tend to stretch the balloon sideways1 and so to flatten it4 ,a smaller balloon1 made of rubber of the same strength1 will not be stretched so much1 as the weight of the enclosed water would be less2 and if the balloon were very small1 but still had walls of the same strength1 the weight of the enclosed water would be incompetent to produce any visible distortion4 ,it is evident1 however1 that so long as it is under the influence of gravitation1 even the smallest drop cannot be truly spherical1 but will be slightly flattened4 ,the tendency of drops to become spherical1 however1 is always present4 ,illustration3 ,fig4 #e4--;,formation of a sphere of orthotoluidine4 99,production of ,true ,spheres of ,liquids499--,now it is quite possible to produce true spheres of liquid1 even of large size1 if we cancel the effect of gravity2 and we may obtain a hint as to how this may be accomplished by considering the case of a soap-bubble1 which1 when floating in air1 is spherical in shape4 ,such a bubble is merely a skin of liquid enclosing air2 but being surrounded by air of the same density1 there is no tendency for the bubble to distort1 nor would it fall to the ground were it not for the weight of the extremely thin skin4 ,the downward pull of gravity on the air inside the bubble is balanced by the buoyancy of the outside air2 and hence the skin1 unhampered by any extraneous force1 assumes and retains the spherical form4 ,and similarly1 if we can arrange to surround a drop of liquid by a medium of the same density1 it will in turn become a sphere4 ,evidently the medium used must not mix with the liquid composing the drop1 as it would then be impossible to establish a boundary surface between the two4 ,plateau1 many years ago1 produced liquid spheres in this manner4 ,he prepared a mixture of alcohol and water exactly equal in density to olive oil1 and discharged the oil into the mixture1 the buoyancy of which exactly counteracted the effect of gravity on the oil1 and hence spheres were formed4 ,the preparation of an alcohol-water mixture of exactly correct density is a tedious process1 and we are now able to dispense with it and form true spheres in a more convenient way4 ,there is a liquid known as orthotoluidine1 which possesses a beautiful red colour1 does not mix with water1 and which has exactly the same density as water when the temperature of both is #ge deg4 ,f4 or #bd deg4 ,c4 ,at this temperature1 therefore1 if orthotoluidine be run into water1 spheres should be formed2 and there is no reason why we should not be able to make one as large as a cricket-ball1 or even larger4 ,i take a flat-sided vessel for this experiment1 in order that the appearance of the drop will not be distorted as it would be in a beaker1 and pour into it water at #ge deg4 ,f4 until it is about two-thirds full4 ,i now take a pipette containing a #c per cent4 solution of common salt1 and discharge it at the bottom of the water4 ,being heavier1 the salt solution will remain below the water1 and will serve as a resting-place for the drop4 ,the orthotoluidine is contained in a vessel provided with a tap and wide stem1 which is now inserted in the water so that the end of the stem is about #a inch above the top of the salty layer4 ,i now open the tap so as to allow the orthotoluidine to flow out gradually2 and we then see the ball of liquid growing at the end of the stem 7,fig4 #e74 ,by using a graduated vessel1 we can read off the quantity of orthotoluidine which runs out1 and thus measure the volume of the sphere formed4 ,when the lower part reaches the layer of salt solution1 we raise the delivery tube gently1 and repeat this as needed during the growth of the sphere4 ,we have now run out #ajj cubic centimetres1 or about one-sixth of a pint1 and our sphere consequently has a diameter of #e #c_/d centimetres1 or #b #a_/d inches4 ,to set it free in the water we lift the delivery tube rapidly--and there is the sphere floating in the water 7,fig4 #f74 ,we could have made it as much larger as we pleased1 but the present sphere will serve all our requirements4 ,illustration3 ,fig4 #f4--,the detached sphere floating under water4 ,illustration3 ,fig4 #g4--,the ,centrifugoscope4 99,the ,centrifugoscope499--,i have here a toy1 which we may suitably call the centrifugoscope1 which shows in a simple way the formation of spheres of liquid in a medium of practically equal density4 ,it consists of a large glass bulb attached to a stem1 about three-quarters full of water1 the remaining quarter being occupied by orthotoluidine4 ,this liquid1 being slightly denser than water at the temperature of the room1 rests on the bottom of the bulb4 ,when ,i hold the stem horizontally1 and rotate it--suddenly at first1 and steadily afterwards--a number of fragments are detached from the orthotoluidine1 which immediately become spherical1 and rotate near the outer side of the bulb4 ,the main mass of the red liquid rises to the centre of the bulb1 and rotates on its axis 7,fig4 #g71 and we thus get an imitation of the solar system1 with the planets of various sizes revolving round the central mass2 and even the asteroids are represented by the numerous tiny spheres which are always torn off from the main body of liquid along with the larger ones4 ,when the rotation ceases1 the detached spheres sink1 and after a short time join the parent mass of orthotoluidine4 ,we can therefore take this simple apparatus at any time1 and use it to show that a mass of liquid1 possessing a free surface all round1 and unaffected by gravity1 automatically becomes a sphere4 ,after all1 this is only what we should expect of an elastic skin filled with a free-flowing medium4 99,effect of ,temperature on ,sphere of ,orthotoluidine499--,i will now return to the large sphere formed under water in the flat-sided vessel1 and direct your attention to an experiment which teaches an important lesson4 ,by placing a little ice on the top of the water1 we are enabled to cool the contents of the vessel1 and we soon notice that the red-coloured sphere becomes flattened on the top and below1 and sinks a short distance into the saline layer4 ,evidently the cooling action1 which has affected both liquids1 has caused the orthotoluidine to become denser than water4 ,i now surround the vessel with warm water1 and allow the contents gradually to attain a temperature higher than #ge deg4 ,f4 ,you observe that the flattened drop changes in shape until it is again spherical2 and as the heating is continued elongates in a vertical direction1 and then rises to the surface1 being now less dense than water4 ,so sensitive are these temperature effects that a difference of #a degree on either side of #ge deg4 ,f4 causes a perceptible departure from the spherical shape in the case of a large drop4 ,it therefore follows that orthotoluidine may be either heavier or lighter than water1 according to temperature1 and this fact admits of a simple explanation4 ,orthotoluidine expands more than water on heating1 and contracts more on cooling4 ,the effect of expansion is to decrease the density1 and of contraction to increase it2 hence the reason why warm air rises through cold air1 and vice versa4 ,now if orthotoluidine and water1 which are equal in density at #ge deg4 ,f41 expanded or contracted equally on heating above or cooling below this temperature1 their densities would always be identical4 ,but inasmuch as orthotoluidine increases in volume to a greater extent than water on heating1 and shrinks more on cooling1 it becomes lighter than water when both are hotter than #ge deg4 ,f41 and heavier when both are colder4 ,we call the temperature when both are equal in density the equi-density temperature4 ,here are some figures which show how the densities of these two liquids diverge from a common value on heating or cooling1 and which establish the conclusions we have drawn3-- ---------------------------------------- --------------------------- ,temperature4 ,density4 ,deg4 ,f4 ,deg4 ,c4 ,water4 ,orthotoluidine4 ---------------------------------------- --------------------------- #ej #aj #j4iiig #a4jji #ei #ae #j4iiia #a4jje #fh #bj #j4iihb #a4jja ,equal3 #ge #bd #j4iigc #j4iig #hf #cj #j4iieg #j4iib #ie #ce #j4iidj #j4ihh #ajd #dj #j4iibc #j4ihc ---------------------------------------- --------------------------- ,illustration3 ,fig4 #h4--;,aniline drops falling through cold water and ascending through hot water4 99,other ,examples of ,equi-,density499--,there are many other liquids which1 like orthotoluidine1 may be heavier or lighter than water1 according to temperature1 and ,i now wish to bring to your notice the remarkable liquid aniline1 which falls under this head4 ,aniline is an oily liquid1 which1 unless specially purified1 has a deep red colour4 ,it forms the basis of the beautiful and varied colouring materials known as the aniline dyes1 which we owe to the skill of the chemist4 ,the equi-density temperature of water and aniline is #adg deg4 ,f4 or #fd deg4 ,c42 that is1 aniline will sink in water if both be colder than #adg deg4 ,f41 and rise to the surface if this temperature be exceeded4 ,we may illustrate this fact by a simple but striking experiment4 ,here are two tall beakers side by side1 and above them a cistern containing aniline 7,fig4 #h74 ,the stem of the cistern communicates with the two branches of a horizontal tube1 the termination of one branch being near the top of one of the beakers1 whilst the other branch is prolonged to the bottom of the second beaker1 and is curved upwards at the end4 ,both branches are provided with taps to regulate the flow of liquid1 and to commence with are full of aniline4 ,cold water is poured into the beaker containing the shorter branch until the end is submerged2 and water nearly boiling is placed in the second beaker to an equal height4 ,i now open the taps1 so that the aniline may flow gradually into each beaker2 and you notice that the drops of aniline sink through the cold water and rise through the hot4 ,we have thus the same liquid descending and ascending simultaneously in water1 the only difference being that the water is cold on the one side and hot on the other4 ,prolonging the delivery-tube to the bottom of the beaker containing the hot water enables the rising drops to be observed throughout the length of the column of water2 and in addition enables the cold aniline from the cistern to be warmed up on its way to the outlet1 so that by the time it escapes its temperature is practically the same as that of the water4 ,if this temperature exceed #adg deg4 ,f41 the drops will rise4 ,we might1 in this experiment1 have used orthotoluidine instead of aniline2 or1 indeed1 any other liquid equal in density to water at some temperature intermediate between those of the hot and cold water--always provided that the liquid chosen did not mix with water4 ,amongst such other liquids may be mentioned anisol2 butyl benzoate2 and aceto-acctic ether2 but none of these possess the fine colour of aniline or its chemical relative orthotoluidine1 and in addition are more costly liquids4 ,besides these are a number of other liquids rarer still1 practically only known to the chemist1 which behave in the same way4 ,these liquids are all carbon compounds1 and more or less oily in character4 ,there is a simple rule which may be used to predict whether any organic liquid will be both lighter and heavier than water1 according to temperature4 ,here it is3 ,if the density of the liquid at #cb deg4 ,f4 or #j deg4 ,c4 be not greater than #a4ab1 the liquid will become less dense than water below #bab deg4 ,f4 or #ajj deg4 ,c41 at which temperature water boils4 ,this rule is derived from a knowledge of the extent to which the expansion of organic liquids in general exceeds that of water4 ,i have considered it necessary to enter at some length into this subject of equi-density1 as much that will follow involves a knowledge of this physical relation between liquids4 99,aniline ,films or ,skins499--,we have previously concluded1 largely from circumstantial evidence1 that a liquid drop is encased in a skin or what is equivalent to a skin1 and ,i propose now to show by experiments with aniline how we can construct a drop1 commencing with a skin of liquid4 ,here is some aniline in a vessel1 covered by water4 ,i lower into the aniline a circular frame of wire1 which ,i then raise slowly into the overlying water2 and you observe that a film of aniline remains stretched across the frame4 ,by lifting the frame up and down in the water the skin is stretched1 forming a drop which is constricted near the frame 7,fig4 #i74 ,on lifting the wire more suddenly1 the skin of aniline closes in completely at the narrow part1 and a sphere of water1 encased in an aniline skin1 then falls through the water in the beaker1 and comes to rest on the aniline below--into which1 however1 it soon merges4 ,you were previously asked to regard a drop of liquid as being similar to a filled soap-bubble2 and this experiment realizes the terms of the definition4 ,and it requires only a little imagination to picture a drop surrounded by its own skin instead of that of another liquid4 ,it is easy to make one of these enclosed water-drops by imitating the blowing of a soap-bubble--using1 however1 water instead of air4 ,in order to do this ,i take a piece of glass tubing1 open at both ends1 and pass it down the vessel1 until it reaches the aniline4 ,water1 in the meantime1 has entered the tube1 to the same height as that at which it stands in the vessel4 ,on raising the tube gently1 a skin of aniline adheres to the end2 and as we raise it still further1 the water in the tube1 sinking so as to remain at the level in the vessel1 expands the skin into a sphere 7,fig4 #i7--the equivalent of a filled soap-bubble4 ,on withdrawing the tube gradually1 the composite sphere is left hanging from the surface of the water4 ,illustration3 ,fig4 #i4--;,aniline skins enveloping water4 99,surface ,tension499--,before proceeding further1 it will be advisable to introduce and explain the term surface tension4 ,we frequently use it1 without attaching to it any numerical value1 to express the fact that the free surface of a liquid is subjected to stretching forces1 or is in a state of tension2 and thus we say that certain phenomena are due to surface tension4 ,but the physicist does not content himself with merely observing occurrences2 he tries also to measure1 in definite units1 the quantities involved in the phenomena4 ,and hence surface tension is defined as the force tending to pull apart the two portions of the surface on either side of a line #a centimetre in length4 ,that is1 we imagine a line #a centimetre long on the surface of the liquid1 dividing the surface into two portions on opposite sides of the line1 and we call the force tending to pull these two portions away from each other the surface tension4 ,experiments show that this force1 in the case of cold water1 is equal to about #ge dynes1 or nearly #h_/ajj of a gramme4 ,if we choose a line #a inch long on the surface of water1 the surface tension is represented by about #c #a_/f grains4 ,it is always necessary to specify the length when assigning a value to the surface tension2 and unless otherwise stated a length of #a centimetre is implied4 ,the values for different liquids vary considerably2 and it is also necessary to note that the figure for a given liquid depends upon the nature of the medium by which it is bounded--whether1 for example1 the surface is in contact with air or another liquid4 ,the following table gives the values for several liquids when the surfaces are in contact with air3-- ---------------------------------------- -------------------------- ,liquid4 ,tension at #ae deg4 ,c4 7#ei deg4 ,f471 dynes per cm4 ---------------------------------------- -------------------------- ,water #ge ,aniline #dc ,olive ,oil #cb ,chloroform #bg ,alcohol #be ---------------------------------------- -------------------------- ,when one liquid is bounded by another1 the interfacial tension1 as it is called1 is generally less than when in contact with air4 ,thus the value for water and olive oil is about #ba dynes per centimetre at #ae deg4 ,c4 ,we are now in a position to speak of surface tension quantitatively1 and shall frequently find it necessary to do so in order to explain matters which will come under our notice later4 ,illustration3 ,figs4 #aj1 #aa and #ab4--,the ,diving ,drop4 ,three stages4 99,the ,diving ,drop499--,in order to illustrate the tension at the boundary surface of two liquids1 ,i now show an experiment in which a drop is forcibly projected downwards by the operation of this tension4 ,i pour some water into a narrow glass vessel1 and float upon it a liquid called dimethyl-aniline1 so as to form a layer about #a inch in depth4 ,a glass tube1 open at both ends1 is now passed down the floating liquid into the water1 and then raised gradually1 with the result that a skin of water adheres to the end1 and is inflated by the upper liquid1 forming a sphere on the end of the tube 7,fig4 #aj74 ,on withdrawing the tube from the upper surface1 the sphere is detached and falls to the boundary surface1 where it rests for a few seconds1 and is then suddenly shot downwards into the water 7,figs4 #aa and #ab74 ,it then rises to the interface2 breaks through1 and mingles with the floating liquid1 thereby losing its identity4 ,why should the drop1 which is less dense than water1 dive below in this manner8 ,the explanation is that the drop 7which consists of a skin of water filled with dimethyl-aniline71 after resting for a time on the joining surface1 loses the under part of its skin1 which merges into the water below4 ,the shape of the boundary of the two liquids is thereby altered1 the sides now being continuous with the skin forming the upper part of the drop4 ,this is an unstable shape2 and accordingly the boundary surface flattens to its normal condition1 and with such force as to cause the drop beneath it to dive into the water1 although the liquid is lighter than water and tends to float4 ,the result is the same as that which would occur if a marble were pressed on to a stretched disc of rubber1 and then released1 when it would be projected upwards owing to the straightening of the disc4 ,i now repeat the experiment1 using paraffin oil instead of dimethyl-aniline2 but in this case the drop is only projected to a small depth1 and the effect is not so marked4 ,the experiment furnishes conclusive evidence of the existence of the interfacial tension4 99,formation of ,falling ,drops of ,liquid499--,we will now direct our attention to one of the most beautiful of natural phenomena--the growth and partition of a drop of liquid4 ,let us observe1 by the aid of the lantern1 this process in the case of water1 falling in drops from the end of a glass tube4 ,the flow of water is controlled by a tap1 and you observe that the drop on the end gradually grows in size1 then becomes narrower near the end of the tube1 and breaks across at this narrow part1 the separated drop falling to the ground4 ,another drop then grows and breaks away2 but the process is so rapid that the details cannot be observed4 ,none of you saw1 for example1 that each large drop after severance was followed by a small droplet1 formed from the narrowed portion from which the main drop parted4 ,but the small1 secondary drop is always present1 and is called1 in honour of its discoverer1 ,plateau's spherule4 ,nor did any of you observe that the large drop1 immediately after separation1 became flattened at the top1 nor were you able to notice the changing shape of the narrow portion4 ,to show all these things it will be necessary to modify the experimental conditions4 ,mr4 ,h4 ,g4 ,wells1 in one of his short stories1 describes the wonderful effects of a dose of a peculiarly potent drug1 called by him the ,accelerator4 ,while its influence lasted1 all the perceptions were speeded up to a remarkable degree1 so that occurrences which normally appeared to be rapid seemed absurdly slow4 ,a cyclist1 for example1 although travelling at his best pace1 scarcely appeared to be making any movement2 and a falling body looked as if it were stationary4 ,now if we could come into possession of some of this marvellous compound1 and take the prescribed quantity1 we should then be able to examine all that happens when a drop forms and falls at our leisure4 ,but it is not necessary to resort to such means as this to render the process visible to the eye4 ,we could1 for example1 take a number of photographs succeeding each other by very minute intervals of time--a kind of moving picture--from which the details might be gleaned by examining the individual photographs4 ,this procedure1 however1 would be troublesome2 and evidently the simplest plan1 if it could be accomplished1 would be to draw out the time taken by a drop in forming and falling4 ,and our previous experiments indicate how this may be done1 as we shall see when we have considered the forces at work on the escaping liquid4 ,a liquid issuing from a tube is pulled downwards by the force of gravitation1 and therefore is always tending to fall4 ,at first1 when the drop is small1 the action of gravity is overcome by the surface tension of the liquid2 but as the drop grows in size and increases in weight1 a point arrives at which the surface tension is overpowered4 ,then commences the formation of a neck1 which grows narrower under the stretching force exerted by the weight of the drop1 until rupture takes place4 ,now if we wish to make the process more gradual1 it will be necessary to reduce the effect of gravity1 as we cannot increase the surface tension4 ,we have already seen how this may be done in connexion with liquid spheres--indeed1 we were able to cancel the influence of gravity entirely1 by surrounding the working liquid by a second liquid of exactly equal density4 ,we require now1 however1 to allow the downward pull of the drop ultimately to overcome the surface tension1 and we must therefore form the drop in a less dense liquid4 ,if this surrounding liquid be only slightly less dense1 we should be able to produce a very large drop2 and if we make its growth slow we may observe the whole process of formation and separation with the unaided eye4 ,illustration3 ,fig4 #ac4--;,apparatus for forming ascending or descending drops of liquids4 ,now it so happens that we have to hand two liquids which1 without any preparation1 fulfil our requirements4 ,orthotoluidine1 at temperatures below #ge deg4 ,f4 or #bd deg4 ,c41 is denser than water of equal temperature4 ,at #ge deg4 ,f4 their densities are identical2 and as the ordinary temperature of a room lies between #fj deg4 and #gj deg4 ,f41 water1 under the prevailing conditions1 will be slightly the less dense of the two1 and will therefore form a suitable medium in which to form a large drop of orthotoluidine4 ,i therefore run this red-coloured liquid into water from a funnel controlled by a tap 7,fig4 #ac71 and in order to make a large drop the end of the stem is widened to a diameter of #a #a_/b inches4 ,it is best1 when starting1 to place the end of the stem in contact with the surface of the water1 as the first quantity of orthotoluidine which runs down then spreads over the surface and attaches itself to the rim of the widened end of the stem4 ,the tap is regulated so that the liquid flows out slowly1 and we may now watch the formation of the drop4 ,at first it is nearly hemispherical in shape2 gradually1 as you see1 it becomes more elongated2 now the part near the top commences to narrow1 forming a neck1 which1 under the growing weight of the lower portion1 is stretched until it breaks1 setting the large drop free 7,figs4 #ad to #ah74 ,and then follows the droplet2 very small by comparison with the big drop1 but plainly visible 7,figs4 #ai and #bj74 ,the graceful outline of the drop at all stages of the formation must appeal to all who possess an eye for beauty in form2 free-flowing curves that no artist could surpass1 changing continuously until the process is complete4 ,slow as was the formation of this drop1 it was still too rapid to enable you to trace the origin of the droplet4 ,it came1 as it always does come1 from the drawn-out neck4 ,when the large drop is severed1 the mass of liquid clinging to the delivery-tube shrinks upwards1 as the downward pull upon it is now relieved4 ,the result of this shrinkage--which1 as usual1 reduces the area of surface to the minimum possible--is to cut off the elongated neck1 at its upper part1 thus leaving free a spindle-shaped column of liquid4 ,this column immediately contracts1 owing to its surface tension1 until its surface is a minimum--that is1 it becomes practically a sphere2 and this constitutes the droplet4 ,in a later experiment1 in which the formation is slower still1 and the liquid more viscous1 the origin of the droplet will be plainly seen1 and the correctness of the description verified4 ,the recoil due to the liberation of the stretching force after rupture of the neck was visible on the top of the large drop1 and also on the bottom of the portion of liquid which remained attached to the tube1 both of which were momentarily flattened 7,figs4 #ai and #bj7 before assuming their final rounded shape4 ,this is exactly what we should expect to happen if a filled skin of indiarubber were stretched until it gave way at the narrowest part4 ,illustration3 ,fig4 #ad4 ,as a variation on the two liquids just used1 ,i now take the yellow liquid nitrobenzene1 and run it into nitric acid 7or other suitable medium7 of specific gravity #a4b1 and you observe the same sequence of events as in the previous experiment1 even to the details4 ,very rapid photography shows that the breaking away of a drop of water from the end of a tube in air is in all respects identical with what we have just seen on a large scale4 ,illustration3 ,figs4 #ad to #bj4--;,formation of a drop of orthotoluidine1 showing the droplet4 ,seven stages4 99,ascending or ,inverted ,drops499--,if we discharge orthotoluidine into water when both are hotter than #ge deg4 ,f41 the former liquid will rise1 as its density is now less than that of water4 ,if1 therefore1 ,i take a funnel with the stem bent into a parallel branch1 so as to discharge upwards 7,a1 ,fig4 #ac7 and raise the temperature of both liquids above #ge deg4 ,f41 we see that the drop gradually grows towards the top of the water1 finally breaking away and giving rise to the droplet4 ,everything1 in fact1 was the same as in the case of a falling drop1 except that the direction was reversed4 ,a slight rise in temperature has thus turned the whole process topsy-turvy1 but the action is really the same in both cases4 ,when1 on heating1 the water acquired the greater density1 its buoyancy overcame the pull of gravitation on the orthotoluidine1 and accordingly the drop was pushed upwards1 the result being the same as when it was pulled downwards4 ,an inverted drop may always be obtained by discharging a light liquid into a heavier one1 e4g4 olive oil into water1 or water into any of the liquids mentioned on p4 #ai1 below the equi-density temperature4 ,,lecture ,,ii 99,automatic ,aniline ,drops499--,in the foregoing experiments the drop was enlarged until it broke away by feeding it with liquid2 but it is possible to arrange that the formation shall be quite automatic4 ,the experiment1 as we shall see1 is extremely simple1 and yet it contains an element of surprise4 ,into a beaker containing water nearly boiling ,i pour a considerable quantity of aniline1 which at first breaks up into a large number of drops4 ,after a short time1 however1 all the aniline floats to the surface1 having been warmed by contact with the water to a temperature higher than that of equi-density 7#adg deg4 ,f41 or #fd deg4 ,c47--which is exactly what we should expect to happen4 ,there it remains for a brief period in the form of a large mass with the lower portion curved in outline4 ,soon1 however1 we observe the centre of the mass sinking in the water1 and taking on the now familiar outline of a falling drop4 ,gradually1 it narrows at the neck and breaks away2 but as aniline is a viscous liquid1 the neck in this case is long and therefore easily seen4 ,the large drop breaks away and falls to the bottom of the beaker1 its upper surface rising and falling for some time owing to the recoil of its skin after separation1 finally becoming permanently convex4 ,immediately after the large drop has parted1 the upper mass shrinks upwards1 spreading out further on the surface of the water1 with the result that the long neck is severed at the top1 its own weight assisting the breakage4 ,now follows the resolution of the detached neck into two or more spheres1 usually a large and a small 7,fig4 #bb74 ,and now1 to those who view the experiment for the first time1 comes the surprise4 ,the large drop1 which was more or less flattened when it came to rest at the bottom of the beaker1 becomes more and more rounded1 and finally spherical4 ,then1 unaided1 it rises to the top and mingles itself with the aniline which remained on the surface4 ,after a brief interval a second drop falls1 imitating the performance of the first one2 and1 like its predecessor1 rises to the surface1 after remaining for a short time at the bottom of the vessel4 ,and so long as we keep the temperature a few degrees above that of equi-density1 the process of partition and reunion goes on indefinitely4 ,the action is automatic and continuous1 and the large size of the drop and of the neck1 and the slowness of the procedure1 enables us to follow with ease every stage in the formation of a parting drop4 ,illustration3 ,fig4 #ba4 ,illustration3 ,figs4 #ba and #bb4--;,automatically formed aniline drops1 showing the formation of droplets from the neck4 ,and now as to the explanation of this curious performance4 ,when the aniline reaches the surface1 and spreads out1 it cools by contact with the air more rapidly than the water below4 ,as it cools1 its density increases1 and soon becomes greater than that of the water1 in which it then attempts to sink4 ,the forces of surface tension prevent the whole of the aniline from falling--the water surface can sustain a certain weight of the liquid--but the surplus weight cannot be held1 and therefore breaks away4 ,but when the detached drop reaches the bottom of the vessel1 it is warmed up again2 and when its temperature rises above that of equi-density it floats up to the top4 ,and so the cycle of operations becomes continuous1 owing to cooling taking place at the top and heating at the bottom4 ,perpetual motion1 you might suggest4 ,nothing of the kind4 ,perpetual motion means the continuous performance of work without any supply of energy2 it does not mean merely continuous movement4 ,a steam-engine works so long as it is provided with steam1 and an electric motor so long as it is fed with electricity2 but both stop when the supply of energy is withdrawn4 ,so with our aniline drop1 which derives its energy from the heat of the water1 and which comes to rest immediately the temperature falls below #adg deg4 ,f4 or #fd deg4 ,c4 ,but in order that the process of separation and reunion may continue1 the cooling at the top is quite as necessary as the heating at the bottom4 ,our aniline drop is in essence a heat-engine--although it does no external work--and like all heat-engines possesses a source from which heat is derived1 and a sink into which heat at a lower temperature is rejected4 ,we might1 with certain stipulations1 work out an indicator diagram for our liquid engine1 but that would be straying too far from our present subject4 99,automatic ,drops of other ,liquids499--,liquids which possess a low equi-density temperature with water do not form automatic drops like aniline1 as the rate of cooling at the surface is too slow1 and hence the floating mass of liquid does not attain a density in excess of that of the water beneath4 ,aceto-acetic ether1 however1 behaves like aniline1 if the temperature of the water be maintained at about #agj deg4 ,f4 7#gg deg4 ,c471 but as this liquid is fairly soluble in hot water further quantities must be added during the progress of the experiment4 ,results equal to those obtained with aniline1 however1 may be secured by using nitrobenzene in nitric acid of specific gravity #a4b at #ei deg4 ,f4 7#ae deg4 ,c471 the acid being heated to #ahe deg4 ,f4 7#he deg4 ,c472 and here you see the yellow drop performing its alternate ascents and descents exactly as in the case of aniline and water4 ,other examples might be given2 but we may take it as a general rule that when the equi-density temperature of the liquid and medium is above #abe deg4 ,f4 7#eb deg4 ,c471 the phenomenon of the automatic drop may usually be observed when the temperature is raised by #cj deg4 ,f4 7#ag deg4 ,c471 above this point4 99,liquid ,jets499--,so far we have been observing the formation of single drops1 growing slowly at the end of a tube1 or breaking away from a large mass of the floating liquid4 ,if1 however1 we accelerate the speed at which the liquid escapes1 the drop has no time to form at the outlet1 and a jet is then formed4 ,we are all familiar with a jet of water escaping from a tap2 it consists of an unbroken column of the liquid up to a certain distance1 depending upon the pressure1 but the lower part is broken up into a large number of drops1 which break away from the column at a definite distance from the tap4 ,there are many remarkable features about jets which ,i do not intend to discuss here1 as it is only intended to consider the manner in which the drops at the end are formed4 ,to observe this procedure1 it is necessary again to resort to our method of slowing down the rate of formation1 by allowing the liquid to flow into a medium only slightly inferior in density4 ,for this purpose1 orthotoluidine falling into water at the ordinary room temperature is eminently satisfactory2 and we see on the screen the projection of a pipe1 with its end under water1 placed so that a jet of orthotoluidine may be discharged vertically downwards from a stoppered funnel4 ,i open the tap slightly at first1 and we then merely form a single drop at the end4 ,now it is opened more widely1 and you observe that the drop breaks away some distance below the outlet1 being rapidly succeeded by another and another 7,fig4 #bc74 ,on still further opening the tap the drops form at a still greater distance from the end of the pipe1 and succeed each other more rapidly1 so that quite a number appear in view at any given moment 7,figs4 #bd and #be74 ,notice how the drop is distorted by breaking away from the stream of liquid1 and how it gradually recovers its spherical shape during its fall through the water4 ,finally1 ,i increase the discharge to such an extent that the formation of the terminal drops is so rapid as to be no longer visible to the eye1 but appears like the turmoil observed at the end of a jet of water escaping into air4 ,illustration3 ,figs4 #bc1 #bd1 #be4--;,jets of ,orthotoluidine1 discharged under water4 ,illustration3 ,fig4 #bf4--,water stretched between a tube and a plate4 99,liquid ,columns499--,a simple experiment will suffice to illustrate what is meant by a liquid column4 ,here is a drop of water hanging from the end of a glass tube4 ,i place it in the lantern and obtain a magnified image on the screen1 and then bring up a flat plate of glass until it just touches the suspended drop4 ,as soon as contact is established1 the water spreads outwards over the plate1 causing the drop to contract in diameter at or near its middle part1 so that its outline resembles that of a capstan 7,fig4 #bf74 ,the end of the glass tube is now connected to the plate by a column of water of curved outline1 which is quite stable if undisturbed4 ,if1 however1 ,i gradually raise the tube1 or lower the plate1 the narrow part of the column becomes still narrower1 and finally breaks across4 ,in the same way we may produce columns of other liquids2 those obtained with viscous liquids such as glycerine being capable of stretching to a greater extent than water1 but showing the same general characteristics4 ,a liquid column1 then1 is in reality a supported drop1 and the severance effected by lowering the support is similar to that which occurs when a pendent drop breaks away owing to its weight4 ,in our previous experiments we have seen that in order to produce large drops of a given liquid1 the surroundings should be of nearly the same density1 so as largely to diminish the effective weight of the suspended mass4 ,we might therefore expect that large columns of liquid could be produced under similar conditions2 and our conjecture is correct4 ,we may1 for example1 use the apparatus by means of which large drops of orthotoluidine were formed 7,fig4 #ac71 using a shallow layer of water1 so that the lower end of the drop would come into contact with the bottom of the vessel before the breaking stage was reached1 and thus produce1 on a large scale1 the same result as that we have just achieved by allowing a hanging drop of water to touch a glass plate4 ,this method1 however1 restricts the diameter of the top of the column to that of the delivery tube1 and in this respect the shape is strained4 ,the remedy for this is to hang the drop from the surface of the water1 when a degree of freedom is conferred upon the upper part1 which enables the column to assume a greater variety of shapes4 ,in order to show how this may be accomplished1 ,i pour a small quantity of water into the rounded end of a wide test-tube1 which is now seen projected on the screen1 and then pour gently down the side a quantity of ethyl benzoate1 a liquid slightly denser than water4 ,you observe that the liquid spreads out on the surface of the water1 forming a hanging drop which at first is nearly hemispherical in shape2 but as ,i continue to add the liquid the drop grows in size downwards1 and finally reaches the bottom of the tube4 ,there is our liquid column 7,fig4 #bg71 which has formed itself in its own way1 free from the restriction imposed by a delivery tube4 ,notice the graceful curved outline1 produced by a beautiful balance between the forces of surface tension and gravitation2 and notice also how the outline may be varied by the gradual addition of water1 which causes the upper surface to rise1 and thus stretches the column 7,fig4 #bh74 ,the middle becomes more and more narrow 7,fig4 #bi71 and finally breaks across1 leaving a portion of the former column hanging from the surface1 and the remainder1 in rounded form 7,fig4 #cj71 at the bottom of the tube4 ,and1 as usual1 the partition was accompanied by the formation of a small droplet4 ,illustration3 ,figs4 #bg1 #bh1 #bi1 #cj4--;,a liquid column stretched upwards until broken by addition of water4 ,four stages4 ,it is possible1 by using other liquids1 and different diameters of vessels1 to produce columns of a large variety of outlines4 ,some liquids spread over a greater area on the surface of water than others1 and therefore produce columns with wider tops4 ,here we see a column of orthotoluidine1 which has a top diameter of #b inches2 and here again1 in contrast1 is a column of aceto-acetic ether1 the surface diameter of which is only #a_/b inch 7,fig4 #ca74 ,other liquids1 such as aniline1 give an intermediate result4 ,the lower diameter is determined by the width of the vessel2 and hence we are able to produce an almost endless number of shapes4 ,it is interesting to note how workers in glass and pottery have unconsciously imitated these shapes2 and ,i have here a variety of articles which simulate the outlines of one or other of the liquid columns you have just seen4 ,it is possible that designers in these branches of industry might obtain useful ideas from a study of liquid columns1 which present an almost limitless field for the practical observation of curved forms4 ,illustration3 ,fig4 #ca4--;,a column of aceto-acetic ether in water4 99,communicating ,drops499--,there is a well-known experiment1 which some of you may have seen1 in which two soap-bubbles are blown on separate tubes1 and are then placed in communication internally4 ,if the bubbles are exactly equal in size1 no alteration takes place in either2 but if unequal1 the smaller bubble shrinks1 and forces the air in its interior into the larger one1 which therefore increases in size4 ,finally1 the small bubble is resolved into a slightly-curved skin which covers the end of the tube on which it was originally blown4 ,it is evident from this experiment that the pressure per unit area exerted by the surface of a bubble on the air inside is greater in a small than in a large bubble4 ,the internal pressure may be proved to vary inversely as the radius of the bubble2 thus by halving the radius we double the pressure due to the elastic surface1 and so on4 ,the reciprocal of the radius of a sphere is called its curvature1 and we may therefore state that the pressure exerted by the walls of the bubble on the interior vary directly as the curvature4 ,illustration3 ,fig4 #cb4--;,apparatus for communicating drops1 with extensions of unequal length attached4 ,we have already seen that a drop of liquid possesses an elastic surface1 and is practically the same thing as a soap-bubble filled with liquid instead of air4 ,we might therefore expect the same results if two suspended drops of liquid were placed in communication as those observed in the case of soap-bubbles4 ,and our reasoning is correct1 as we may now demonstrate4 ,the apparatus consists 7,fig4 #cb7 of two parallel tubes1 each provided with a tap1 and communicating with a cross-branch at the top1 which contains a reservoir to hold the liquid used4 ,about half-way down the parallel tubes a cross-piece1 provided with a tap1 is placed4 ,we commence by filling the whole of the system with the liquid under trial1 and the parallel tubes equal in length4 ,drops are then formed at the ends of each vertical tube by opening the taps on these in turn1 and closing after suitable drops have been formed4 ,then1 by opening the tap on the horizontal cross-piece1 we place the drops in communication and watch the result4 ,i have chosen orthotoluidine as the liquid1 and by placing the ends of the vertical tubes under water--which at the temperature of the room is slightly less dense than orthotoluidine--,i am able to form much larger drops than would be possible in air4 ,you now see a small and a large drop projected on the screen2 and ,i now open the cross-tap1 so that they may communicate4 ,notice how the little drop shrinks until it forms merely a slightly-curved prominence at the end of its tube4 ,it attains a position of rest when the curvature of this prominence is equal to that of the now enlarged drop which has swallowed up the contents of the smaller one4 ,so far the result is identical with that obtained with soap-bubbles2 but we can extend the experiment in such a way as to reverse the process1 and make the little drop absorb the big one4 ,in order to do this ,i fasten an extension to one of the tubes1 and form a small drop deep down in the water1 and a larger one on the unextended branch near the top4 ,when ,i open the communicating top1 the system becomes a kind of siphon1 the orthotoluidine tending to flow out of the end of the longer tube4 ,the tendency of the large drop to siphon over is opposed by the superior pressure exerted by the skin of the smaller drop2 but the former now prevails1 and the big drop gradually shrinks and the little one is observed to grow larger4 ,it is possible by regulating the depth at which the smaller drop is placed1 to balance the two tendencies1 so that the superior pressure due to the lesser drop is equalled by the extra downward pressure due to the greater length of the column of which it forms the terminus4 ,both pressures are numerically very small1 but are still of sufficient magnitude to cause a flow of liquid in one or other direction when not exactly in equilibrium4 ,in the case of communicating soap-bubbles1 containing air and surrounded by air1 locating the small bubble at a lower level would not reverse the direction of flow1 which we succeeded in accomplishing with liquid drops formed in a medium of slightly inferior density4 ,illustration3 ,fig4 #cc4--;,combined drops of vapour and liquid4 99,combined ,vapour and ,liquid ,drops499--,all liquids when heated give off vapour1 the amount increasing as the temperature rises4 ,the vapour formed in the lower part of the vessel in which the liquid is heated rises in the form of bubbles1 which may condense again if the upper part of the liquid be cold4 ,when the liquid becomes hot throughout1 however1 the vapour bubbles reach the surface and break1 allowing the contents to escape into the air above4 ,everyone who has watched a liquid boiling will be familiar with this process1 but it should be remembered that a liquid may give off large quantities of vapour without actually boiling4 ,a dish of cold water1 if exposed to the air1 will gradually evaporate away2 whilst other liquids1 such as petrol and alcohol1 will disappear rapidly under the same circumstances--and hence are called volatile liquids4 ,the formation of vapour and its subsequent escape at the surface of the liquid1 enable us to produce a very novel kind of drop2 if1 instead of allowing the bubbles to escape into air1 we cause them to enter a second liquid4 ,here1 for example1 is a coloured layer of chloroform#a at the bottom of a beaker1 with a column of water above4 ,i project the image of the beaker on the screen1 and then heat it below4 ,the chloroform vapour escapes in bubbles2 but notice that each bubble carries with it a quantity of liquid1 torn off1 as it were1 at the moment of separation4 ,the vapour bubbles and their liquid appendages vary in size1 but some of them1 you observe1 have an average density about equal to that of the water1 and float about like weighted balloons4 ,some rise nearly to the surface1 where the water is coldest2 and then the vapour partially condenses1 with the result that its lifting power is diminished1 and hence the drops sink into the lower part of the beaker4 ,but the water is warmer in this region1 and consequently the vapour bubble increases in size and lifting power until again able to lift its load to the surface4 ,so the composite drops go up and down1 until finally they reach the surface1 when the vapour passes into the air1 and the suspended liquid falls back to the mass at the bottom of the beaker4 ,notice that the drop of liquid attached to each bubble is elongated vertically4 ,this is because chloroform is a much denser liquid than water 7,fig4 #cc74 ,there is a practical lesson to be drawn from this experiment4 ,whenever a bubble of vapour breaks through the surface of a liquid1 it tends to carry with it some of the liquid1 which is dragged mechanically into the space above4 ,in our experiment the space was occupied by water1 which enabled the bubble to detach a much greater weight than would be possible if the surface of escape had been covered by air1 which is far less buoyant than water4 ,but even when the bubbles escape into air1 tiny quantities of liquid are detached2 so that steam from boiling water1 for example1 is never entirely free from liquid4 ,all users of steam are well acquainted with this fact4 #a ,mono-brom-benzene is better than chloroform for this experiment1 but is more costly4 ,it may be coloured with indigo4 ,chloroform may be coloured with iodine4 99,condensation of ,drops from ,vapour1--,mists1 ,fogs and ,raindrops499--,the atmosphere is the great laboratory for the manufacture of drops4 ,it is continually receiving water in the form of vapour from the surface of the sea1 from lakes1 from running water1 and even from snow and ice4 ,all this vapour is ultimately turned into drops1 and returned again to the surface1 and to this never-ceasing exchange all the phenomena connected with the precipitation of moisture are due4 ,the atmosphere is only capable of holding a certain quantity of water in the form of vapour1 and the lower the temperature the less the capacity for invisible moisture4 ,when fully charged1 the atmosphere is said to be saturated--a condition realized on the small scale by air in a corked bottle containing some water1 which evaporates until the air can hold no more4 ,the maximum weight of vapour that can be held by #a cubic metre of air at different temperatures is shown in the table3-- ---------------------------------------- -------------------------- ,temperature4 ,weight of water vapour 7grammes7 required to ,deg4 ,c4 ,deg4 ,f4 saturate #a cubic metre4 ---------------------------------------- -------------------------- #j #cb #d4h #e #da #f4h #aj #ej #i4c #ae #ei #ab4g #bj #fh #ag4a #be #gg #bb4h #cj #hf #cj4j #ce #ie #ci4b #dj #ajd #ej4f ---------------------------------------- -------------------------- ,it will be seen from the table that air on a warm day in summer1 with a temperature of #gg deg4 ,f41 can hold nearly five times as much moisture as air at the freezing point1 or #cb deg4 ,f4 ,the amount actually present1 however1 is usually below the maximum1 and is recorded for meteorological purposes as a percentage of the maximum4 ,thus if the relative humidity at #gg deg4 ,f4 were #gj per cent41 it would imply that the weight of moisture in #a cubic metre was #gj per cent4 of #bb4h grammes2 that is1 nearly #af grammes4 ,if #a cubic metre of air at #gg deg4 ,f41 containing #af grammes of moisture1 were cooled to #ej deg4 ,f41 a quantity of water equal to 7#af-i4c7 #f4g grammes would separate out1 as the maximum content at the lower temperature is #i4c grammes4 ,precipitation would commence at #ff deg4 ,f41 at which temperature #a cubic metre is saturated by #af grammes4 ,and similarly for all states of the atmosphere with respect to moisture1 cooling to a sufficient extent causes deposition of water to commence immediately below the saturation temperature1 and the colder the air becomes afterwards the greater the amount which settles out4 ,the temperature at which deposition commences is called the dew point4 ,whenever atmospheric moisture assumes the liquid form1 drops are invariably formed4 ,these may vary in size1 from the tiny spheres which form a mist to the large raindrops which accompany a thunderstorm4 ,but in every instance it is necessary that the air shall be cooled below its saturation point before the separation can commence2 and keeping this fact in mind we can now proceed to demonstrate the production of mists and fogs4 ,here is a large flask containing some water1 fitted with a cork through which is passed a glass tube provided with a tap4 ,i pump some air into it with a bicycle pump1 and then close the tap4 ,as excess of water is present1 the enclosed air will be saturated4 ,now a compressed gas1 on expanding into the atmosphere1 does work1 and is therefore cooled2 and consequently if ,i open the tap the air in the flask will be cooled1 and as it was already saturated the result of cooling will be to cause some of the moisture to liquefy4 ,accordingly1 when ,i open the tap1 the interior of the flask immediately becomes filled with mist4 ,if we examine the mist in a strong light by the aid of a magnifying glass1 we observe that it consists of myriads of tiny spheres of water1 which float in the air1 and only subside very gradually1 owing to the friction between their surfaces and the surrounding air preventing a rapid fall4 ,the smaller the sphere1 the greater the area of surface in proportion to mass1 and therefore the slower its fall4 ,and so in nature1 the mists are formed by the cooling of the atmosphere by contact with the surface1 until1 after the saturation point is reached1 the surplus moisture settles out in the form of tiny spheres1 which float near the surface1 and are dissipated when the sun warms up the ground and the misty air1 and thus enables the water again to be held as vapour4 ,fogs1 like mists1 are composed of small spheres of water condensed from the atmosphere by cooling2 but in these unwelcome visitors the region of cooling extends to a higher level1 and the lowering of temperature is due to other causes than contact with the cold surface of the earth4 ,in our populous cities1 the density of the fogs is accentuated by the presence of large quantities of solid particles in the atmosphere1 which arise from the smoke from coal fires1 and the abrasion of the roads by traffic4 ,we can make a city fog in our flask4 ,i blow in some tobacco smoke1 and then pump in air as before4 ,you will notice that the smoke1 which is now disseminated through the air in the flask1 is scarcely visible2 but now1 on opening the tap1 the interior becomes much darker than was the case in our previous experiment4 ,we have produced a genuine yellow fog1 that is1 a dense mist coloured by smoke4 ,when we have learned how to abolish smoke1 and how to prevent dust arising from the streets1 our worst fogs will be reduced to dense mists1 such as are now met with on the sea or on land remote from large centres of habitation4 ,there is one feature common to the spheres which compose a mist or fog1 or indeed to any kind of drop resulting from the condensation of moisture in the atmosphere4 ,as shown by the deeply interesting researches of ,aitken and others1 each separate sphere forms round a core or nucleus1 which is usually a small speck of dust1 and hence an atmosphere charged with solid particles lends itself to the formation of dense fogs immediately the temperature falls below the dew-point4 ,but dust particles are not indispensable to the production of condensed spheres1 for it has been shown that the extremely small bodies we call ions1 which are electrically charged atoms1 can act as centres round which the water will collect2 and much atmospheric condensation at high elevations is probably due to the aid of ions4#b ,near the surface1 however1 where dust is ever present1 condensation round the innumerable specks or motes is the rule4 ,here1 for example1 is a jet of steam escaping into air1 forming a white cloud composed of a multitude of small spheres of condensed water4 ,if now ,i allow the steam to enter a large flask containing air from which the dust has been removed by filtration through cotton wool1 no cloud is formed in the interior1 but instead condensation takes place at the end of the jet1 from which large drops fall1 and on the cold sides of the flask4 ,the cloud we see in dusty air is entirely absent1 and the effect of solid particles in the process of condensation is thus shown in a striking manner4 ,clouds are masses of thick mist floating at varying heights in the atmosphere4 ,on sinking into a warmer layer of dry air the particles of which clouds are composed will evaporate and vanish from sight4 ,if the condensation continue1 however1 the spheres will grow in size until the friction of the atmosphere is unable to arrest their fall2 and then we have rain4 ,and whether the precipitation be very gentle1 and composed of small drops falling slowly1 as in a ,scotch mist1 or in the form of rapid-falling large drops such as accompany a thunderstorm1 the processes at work are identical4 ,every particle of a mist or cloud1 and every raindrop1 is formed round a nucleus1 and owes its spherical shape to the tension at the surface4 #b ,mr4 ,c4 ,t4 ,r4 ,wilson has recently devised an apparatus for making visible the tracks of ionizing rays1 by the condensation of water vapour round the freshly liberated ions4 99,liquid ,clouds in ,liquid ,media499--,just as the excess of moisture is precipitated from saturated air when the temperature falls1 so is the excess of one liquid dissolved in another thrown down by cooling below the saturation temperature4 ,moreover1 a liquid when precipitated in a second liquid appears in the form of myriads of small spheres1 which have the appearance of a dense cloud4 ,here is some boiling water to which an excess of aniline has been added1 so that the water has dissolved as much aniline as it can hold4 ,aniline dissolves more freely in hot water than in cold1 so that if ,i remove the flame1 and allow the beaker to cool1 the surplus of dissolved aniline will settle out4 ,cooling takes place most rapidly at the surface1 and you observe white streaks falling from the top into the interior1 where they are warmed up and disappear4 ,soon1 however1 the cooling spreads throughout2 and now the streaks become permanent1 and the water becomes opaque1 owing to the thick white cloud of precipitated aniline4 ,the absence of the red colour characteristic of aniline is due to the extremely fine state of division assumed in the process4 ,if left for some hours1 the white cloud sinks through the water to the bottom of the beaker1 where the small particles coalesce and form large drops1 leaving the overlying water quite transparent4 ,the process is quite analogous to the precipitation of moisture from the atmosphere in the form of small spheres1 which1 if undisturbed1 would gradually sink to the ground and leave the air clear4 99,overheated ,drops499--,the temperature at which a liquid boils1 under normal conditions1 depends only upon the pressure on its surface4 ,thus water boiling in air1 when the pressure is #gf centimetres or #bi4ib inches of mercury1 corresponding to #ad4g pounds per square inch1 possesses a temperature of #ajj deg4 ,c4 or #bab deg4 ,f4 ,at higher elevations1 where the pressure is less1 the boiling point is lower2 thus ,tyndall observed that on the summit of the ,finsteraarhorn 7#ad1jjj feet7 water boiled at #hf deg4 ,c4 or #ahg deg4 ,f4 ,conversely1 under increased pressure1 the boiling point rises2 so that at a pressure of #ce pounds per square inch water does not boil until the temperature reaches #abe deg4 ,c4 or #beg deg4 ,f4 ,there are certain abnormal conditions1 however1 under which the boiling point of a liquid may be raised considerably without any increase in the pressure at the surface2 and it is then said to be over-heated4 ,dufour showed that when drops of water are floating in another liquid of the same density1 they may become greatly overheated1 and if very small in size may attain a temperature of #aej deg4 ,c4 or #cjb deg4 ,f41 or even higher1 before bursting into steam4 ,in order to provide a medium in which water drops would float at these temperatures1 ,dufour made a mixture of linseed oil and oil of cloves1 which possessed the necessary equi-density temperature with water4 ,to demonstrate this curious phenomenon1 ,i take a mixture of #d volumes of ethyl benzoate and #a volume of aniline1 which at #abe deg4 ,c4 or #beg deg4 ,f4 is exactly equal in density to water at the same temperature4 ,i add to the mixture two or three cubic centimetres of freshly-boiled water1 the temperature being maintained at #abe deg4 ,c4 by surrounding the vessel with glycerine heated by a flame4 ,at first the water sinks1 but on attaining the temperature of the mixture it breaks up with some violence1 forming spheres of various sizes which remain suspended in the mixture4 ,any portion of the water which has reached the surface boils vigorously1 and escapes in the form of steam2 and some of the larger spheres may be observed to be giving off steam1 which rises to the surface4 ,most of the spheres1 however1 remain perfectly tranquil1 in spite of the fact that the water of which they are composed is many degrees above its normal boiling point4 ,if ,i penetrate one of these spheres with a wire1 you notice that it breaks up immediately1 with a rapid generation of steam4 ,a complete explanation of this abnormal condition of water is difficult to follow1 as a number of factors are involved4 ,one of the contributory causes--though possibly a minor one--is the opposition offered to the liberation of steam by the tension at the surface of the spheres4 ,illustration3 ,fig4 #cd4--,spheroid of water on a hot plate4 99,floating ,drops on ,hot ,surfaces499--,if a liquid be allowed to fall in small quantity on to a very hot solid1 it does not spread out over the surface1 but forms into drops which run about and gradually evaporate4 ,by careful procedure1 we may form a very large1 flattened drop on a hot surface1 and on investigation we shall notice some remarkable facts4 ,i take a plate of aluminium1 with a dimple in the centre1 and make it very hot by means of a burner4 ,you see the upper surface of this plate projected on the screen4 ,i now allow water to fall on the plate drop by drop1 and you hear a hissing noise produced when each drop strikes the plate4 ,the separate drops gather together in the depression at the centre of the plate1 forming a very large flattened globule4 ,you might have expected the water to boil vigorously1 but no signs of ebullition are visible2 and what is more remarkable1 the temperature of the drop1 in spite of its surroundings1 is actually less than the ordinary boiling point4 ,notice now how the drop has commenced to rotate1 and has been set into vibration1 causing the edges to become scalloped 7,fig4 #cd74 ,the drop1 although not actually boiling1 is giving off vapour rapidly1 and therefore gradually diminishes in size4 ,and now ,i want to prove that the drop is not really touching the plate1 but floating above it4 ,to do this ,i make an electric circuit containing a cell and galvanometer1 and connect one terminal to the plate and place the other in the drop4 ,no movement is shown on the galvanometer1 as would be the case if the drop touched the plate and thus completed the electric circuit4 ,and at close range we can actually see a gap between the drop and the plate1 so that the evidence is conclusive4 ,if now ,i remove the flame--leaving the electric circuit intact--and allow the plate to cool1 we notice after a time that the globule flattens out suddenly and touches the plate1 as shown by the deflection of the galvanometer2 and simultaneously a large cloud of steam arises1 due to the rapid boiling which occurs immediately contact is made4 ,what we have seen in the case of water is shown by most liquids when presented to a surface possessing a temperature much higher than the boiling point of the liquid4 ,a liquid held up in this manner above a hot surface is said to be in the spheroidal state1 to distinguish it from the flat state usually assumed by spreading when contact occurs between the liquid and the surface4 ,it is doubtful whether any satisfactory explanation of the spheroidal state has ever been given4 ,evidently1 the layer of vapour between the plate and the drop must exert a considerable upward pressure in order to sustain the drop1 but the exact origin of this pressure is difficult to trace4 ,,lecture ,,iii 99,spreading of ,oil on the ,surface of ,water499--,if a small drop of oil be placed on the surface of water it will be observed to spread immediately until it forms a thin layer covering the surface4 ,if a further addition of the oil be made1 globules will be formed1 which1 as you now see upon the screen1 remain floating on the surface4 ,the spreading of the oil in all directions from the place on which the small quantity of oil was dropped is due to the superior surface tension of water1 which pulls the oil outwards4 ,the surface tension of the oil opposes that of the water1 and would prevent the drop from spreading were it not overcome by a greater force4 ,the result is the same as would be observed if the centre or any other part of a stretched rubber disc were weakened2 the weak part would be stretched in all directions1 and the rest of the disc would shrink towards the sides4 ,when the oil has spread out1 however1 and contaminated1 as it were1 the surface of the water1 the surface tension is reduced1 and is not sufficiently strong to stretch out a further quantity of oil1 which1 if added1 remains in the form of a floating globule4 ,illustration3 ,fig4 #ce4--;,forces acting on a floating globule4 ,let us study the forces at work on the floating globule a little more closely4 ,its upper surface is in contact with air1 and the surface tension tends1 as usual1 to reduce the area to a minimum4 ,the top of the globule is not flat1 but curved 7,fig4 #ce71 and its surface meets that of the water at an angle2 and the counter-pull exerted against the stretching-pull of the water surface is not horizontal1 but inclined in the direction of the angle of contact1 as shown by the line ,b4 ,the under part of the globule is also curved1 and meets the water surface from below at an angle2 and here also is exerted a pull in opposition to that of the water surface1 different in magnitude to the force at the upper surface1 but also directed at the angle of contact as shown by the line ,c4 ,this tension at the joining surface of two liquids is called the interfacial tension1 to distinguish it from that of a surface in contact with air4 ,acting against these two tensions is that of the water1 which is directed horizontally along the surface1 as shown by the line ,a4 ,the lines ,a1 ,b1 and ,c indicate the forces acting at a single point2 but the same forces are at work at every point round the circle of contact of the globule and the surface of the water4 ,and therefore the tendency on the part of the water tension is to cause the globule to spread out in all directions1 whereas the other two tensions tend to prevent any enlargement of its surface4 ,the result depends upon the magnitudes and directions of the conflicting forces4 ,we can imagine a kind of tug-of-war taking place1 in which one contestant1 ,a1 is opposed to two others1 ,b and ,c1 all pulling in the directions indicated in ,fig4 #ce4 ,although ,a is single-handed1 he has the advantage of a straight pull1 whereas ,b and ,c can only exert their strength at an angle1 and the larger the angle the more they are handicapped4 ,if ,a be more powerful than ,b and ,c1 the globule will spread2 but the result of the spreading is to diminish the angles at which the pulls of ,b and ,c are inclined to the surface1 and hence their effective opposition to ,a will be increased4 ,moreover1 the spreading of the liquid diminishes the surface tension of the water--that is1 weakens ,a--and hence it becomes possible for ,b and ,c to prevail and draw back the surface of the globule which ,a had previously stretched4 ,if1 in spite of these disabilities1 ,a should still be the stronger1 the globule will be stretched until it covers the whole surface2 whereas if ,b and ,c overcome ,a1 the globule will shrink1 increasing the angles at which ,b and ,c operate1 and therefore reducing their effective pulls1 until their combined strength is equal to that of ,a1 when the globule will remain at rest4 ,bearing these facts in mind1 we can understand why a small drop of oil placed on a clean water surface spreads across2 for in this case ,a is stronger than ,b and ,c combined4 ,but when the surface of the water is covered with a layer of oil1 ,a is weakened1 and can no longer overcome the opposing pulls of ,b and ,c4 ,hence a further drop of oil poured on to the surface remains in the form of a globule4 99,movements due to ,solubility499--,when small fragments of camphor are placed on the surface of water some remarkable movements are seen4#c ,the bits of camphor move about with great rapidity over the surface1 and generally1 in addition1 show a rapid rotary motion4 ,the explanation usually given is that the camphor dissolves in the water at the points of contact forming a solution which possesses a less surface tension than pure water4 ,this solution is in consequence stretched by the tension of the rest of the surface1 and the camphor floating on its solution is therefore made to move in the direction of the line along which the stretching force happens to be the greatest4 ,but the camphor continues to dissolve wherever it goes1 and is therefore continuously pulled about as a result of this interplay of tensions4 ,touching the surface with a wire which has been dipped in oil immediately arrests the movements1 owing to the tension of the water being diminished to such an extent by the skin of oil that it is no longer competent to stretch the part on which the camphor floats4 ,no doubt this explanation is correct so far as it goes1 but it is highly probable that when the floating substance dissolves1 other forces are called into action in addition to the tensions4 #c ,these movements were first recorded by ,romieu in #agdh and were ascribed by him to electricity4 ,illustration3 ,fig4 #cf4--;,aniline globules on a water surface4 99,movements of ,aniline ,globules on a ,water ,surface499--,if we allow a small quantity of aniline to run on to the surface of water1 it forms itself into a number of floating globules4 ,i now project on the screen a water surface on which a little aniline has been poured1 and we are thus enabled to watch the movements which occur4 ,all the globules appear to be twitching or shuddering2 and if you observe closely you will notice the surface of each globule stretching and recoiling alternately4 ,the recoil is accompanied by the projection of tiny globules from the rim1 which becomes scalloped when the globule is stretched4 ,the small globules thrown off appear to be formed from the protuberances at the edge 7,fig4 #cf71 and after leaving the main globule they spread out over the surface1 or dissolve4 ,this process continues for a long time1 gradually diminishing in vigour1 until small stationary globules are left floating on the surface1 which is now covered with a skin of aniline4 ,this action is in striking contrast to the tranquil formation of floating globules of oil1 and calls for some special comment4 ,let us recall again the three forces at work at the edge of a floating globule 7,fig4 #ce74 ,the surface tension of the water1 acting horizontally1 tends to stretch the globule1 and is successful momentarily in overcoming the opposing tensions1 each of which pulls at an angle to the surface4 ,enlargement of the upper surface of the globule1 however1 reduces the angles at which the tensions ,b and ,c act1 and in consequence their effective strength is increased4 ,the spreading of the aniline over the water surface diminishes the pull ,a1 which ,b and ,c combined now overcome1 and hence the surface of the globule shrinks again4 ,for some unexplained reason both the stretching and recoil of the globule occur suddenly1 there being an interval of repose between each1 and these jerky movements result in small portions of the rim being detached1 each of which forms a separate small globule4 ,the aniline which spreads over the surface of the water dissolves1 and the water tension ,a1 which had been enfeebled by the presence of the aniline skin1 recovers its former strength1 and again stretches the globule2 and so the whole process is repeated4 ,when the surface of the water becomes permanently covered with a skin1 which occurs when the top layer is saturated with aniline1 the globule remains at rest1 and has such a shape that the tensions ,b and ,c act at angles which enable them just to balance the weakened pull of ,a4 ,why the edge of the globule becomes indented during the movements1 and why these movements are spasmodic instead of gradual1 has not been clearly made out4 ,it is interesting to recall that a spheroid of liquid on a hot plate also possesses a scalloped edge1 and it may be that the two phenomena have something in common4 ,illustration3 ,fig4 #cg4--,orthotoluidine globules on a water surface4 99,movements of ,orthotoluidine and ,xylidine #a-c-d on a ,water ,surface499--,we will now observe1 by the aid of the lantern1 movements of globules more striking1 and certainly more puzzling1 than those of aniline4 ,i place on the surface of the water a quantity of a special sample of orthotoluidine1 and you see that immediately a number of globules are formed which are endowed with remarkable activity4 ,they become indented at one side1 and then dart across the surface at a great speed1 usually breaking into two as a result of the violent action 7,fig4 #cg74 ,then follows a short period of rest1 when suddenly1 as if in response to a signal1 all the larger globules again become indented1 forming shapes like kidneys1 and again shoot across the surface1 breaking up into smaller globules4 ,notice that the very small globules remain at rest2 it is only those above a certain size that display this remarkable activity4 ,a film of the liquid forms on the water1 and the action gradually becomes more intermittent1 ceasing altogether when a skin is well established1 and the large globules have sub-divided into very small ones4 ,my sample of orthotoluidine is somewhat unique1 as other specimens of the liquid1 obtained from the same and other sources1 do not show the same lively characteristics4 ,as in the case of camphor1 touching the surface with a drop of oil arrests the movements immediately4 ,the organic liquid xylidine #a-c-d1 however1 exhibits the same movements1 as you now see on the screen2 and1 if anything1 is even more active than the orthotoluidine previously shown4 ,it may be added that occasional samples of aniline show similar movements1 but of less intensity4 ,now if ,i am asked to explain these extraordinary movements1 ,i am bound to confess my inability to do so at present4 ,why should the globules become indented on one side only8 ,the two tensions acting at the edge in opposition to the water tension are at work all round the globule1 and it is not easy to see why they should prevail to such a marked degree at one spot only4 ,the movement across the surface1 if we followed our previous explanations1 would be due to the superior pull of the water tension behind the globule1 opposite the indented part2 although to look at it would seem as if some single force produced the indentation and pushed the globule along bodily4 ,are there local weaknesses in the tension of the water1 and1 if so1 why should such weak spots form simultaneously near each globule1 causing each to move at the same moment8 ,any explanation we may give as to the origin of the cavity in the side of the globule does not suffice to account for the intermittent character of the movement1 and its simultaneous occurrence over the whole surface4 ,we must therefore leave the problem at present1 and trust to future investigation to provide a solution4 ,illustration3 ,,fig4 #ch4--,resolution of a floating skin into globules4 99,production of ,globules from ,films499--,when a film of oil spreads over a water surface it sometimes remains as such indefinitely4 ,certain other liquids1 however1 form films which after a short interval break up into globules1 and the process of transition is at once striking and beautiful4 ,in order to show it1 ,i project a water surface on the screen1 and pour on to it a very small quantity of dimethyl-aniline--an oily liquid related to but distinct from ordinary aniline4 ,it spreads out into a film of irregular outline1 which floats quietly for a short time4 ,soon1 however1 indentations are formed at the edges1 which penetrate the film1 and from the sides of the indentations branches spread which in turn become branched2 and shortly the whole film becomes ramified1 resembling a mass of coral1 or1 to use a more homely illustration1 a jig-saw puzzle 7,fig4 #ch74 ,the various branches join in numerous places1 cutting off small islands from the film2 and immediately each island becomes circular in outline--and the resolution into globules is complete4 ,we have witnessed one of the beauty-sights of ,nature4 ,the same method of globule formation is shown by nitro-benzol and quinoline1 and as the action is more gradual in the case of the latter substance1 ,i show it in order that we may study the process in greater detail4 ,notice the formation of the indentations and their subsequent branching2 and also that holes form in the skin from which branchings also proceed4 ,in this instance the film is broken up in sections1 but the action continues until nothing but globules remain on the surface4#d ,it is not easy to see why the canals of water penetrate the film and split it up into small sections1 nor why entry takes place at certain points on the edge in preference to others4 ,some orderly interplay of forces1 not yet properly understood1 gives rise to the action2 and a satisfactory explanation has yet to be given4 #d ,the breaking-up of films on the surface of water was first noticed by ,tomlinson about #ej years ago4 ,he used essential oils1 and called the patterns cohesion figures4 99,network formed from a ,film499--,a further example of the breaking up of a film is furnished by certain oils derived from coal-tar1 the result in this case being the formation of a network or cellular structure4 ,i place on the surface of water in a glass dish a small quantity of tar-oil1 and project it on the screen4 ,it spreads out at first into a thin film1 which1 by reflected light1 shows a gorgeous display of colours4 ,after a short time1 little holes make an appearance in the film1 and these holes gradually increase in size until the whole of the film is honeycombed 7,fig4 #ci71 the oil having been heaped up into the walls which divide the separate compartments4 ,here again the accepted views on surface tension do not appear competent to explain the action4 ,it appears to be the case that most films on the surface of water show this tendency to perforation1 which may be due to inequalities in the thickness of the film1 or in the distribution of the strain to which it is subjected4#e #e ,an interesting discussion on cellular structures of this type may be found in ,nature1 ,april #af to ,june #aa1 #aiad4 ,illustration3 ,fig4 #ci4--,network formed from a film of tar-oil on the surface of water4 ,illustration3 ,fig4 #dj4--,quinoline rings and perforated plates4 99,quinoline ,rings499--,reference has already been made to the breaking-up of a quinoline film into globules4 ,but if we examine the surface about half an hour after the formation of these globules1 we find that each has been perforated in the centre1 forming a ring or annulus 7,fig4 #dj74 ,some of the larger globules have undergone perforation in several places1 forming honeycombed plates4 ,these rings and plates1 which you now see projected on the screen1 remain unchanged1 and apparently represent the final stage of equilibrium under the action of the various forces4 ,quinoline1 so far as observations have been made1 appears to be unique in respect to the formation of stable rings from globules4 ,illustration3 ,fig4 #da4--,the expanding globule4 99,expanding ,globules499--,i now wish to show1 by an experiment1 how sensitive a floating globule is to disturbances in the existing tensions1 which maintain it at rest4 ,on the screen is projected a globule of dimethyl-aniline1 floating tranquilly on the surface of water4 ,i now allow a small drop of quinoline to fall upon it1 and immediately it spreads out over the surface1 forming a hole in its centre 7,fig4 #da71 after which it gradually resumes its former shape4 ,sometimes the action is so violent that the globule is split up into several portions1 which1 however1 join together again after a short time4 ,in order to explain this action1 we must again refer to the three tensions operating on the globule 7,fig4 #ce74 ,when in equilibrium1 ,a is balanced by the joint pull of ,b and ,c2 and hence if either of the latter be weakened1 ,a will predominate and stretch the globule4 ,in our experiment it is the interfacial tension1 ,c1 which has been diminished in strength1 as we may now prove by a second experiment4 ,in this instance ,i float on the water surface a globule of lubricating oil1 with which quinoline does not readily mix1 and which does not act so immediately as dimethyl-aniline4 ,on allowing the drop of quinoline to fall into it1 no action is observed until the drop has rested on the junction of the oil and water for a short time2 but when it has penetrated the interface the oil globule suddenly spreads over the water surface1 and with such violence as to detach several portions from the main globule4 ,merely touching the upper surface of the oil with a rod moistened with quinoline has no effect1 and hence the result is due to the weakening of the interfacial tension4 ,a similar effect is obtained when quinoline is dropped into a globule of aniline1 and may be obtained with various other liquids4 99,attraction between ,floating ,globules4--,the ,devouring ,globule499 ,when globules of different liquids are floating on the same water surface1 a tendency to coalesce is sometimes noticed1 but is by no means general4 ,i will show one example which possesses striking features1 showing as it does the remarkable results which may be brought about by surface forces4 ,first of all1 we form a number of active orthotoluidine globules on the surface of a dish of water1 which you see wriggling about in their characteristic fashion4 ,after their activity has subsided somewhat1 ,i float on to the surface a large globule of dimethyl-aniline4 ,attraction of some kind is at once apparent1 for the nearest globule of orthotoluidine immediately approaches the intruder4 ,and now comes the process of absorption4 ,the large globule of dimethyl-aniline develops a protuberance in the direction of its victim 7,figs4 #db and #dc71 and the small globule of orthotoluidine coalesces with this feeler1 which then shrinks back into the large globule1 conveying with it the entangled orthotoluidine4 ,this1 however1 by no means satisfies the devouring globule1 as a second victim is at once appropriated in the same manner2 and you will notice a nibbling process at work round the edges continuously1 which is due to the absorption of the smaller globules of orthotoluidine4 ,the action continues until the whole of the surface has been cleared of orthotoluidine1 after which the large globule floats tranquilly in the centre of the vessel1 apparently resting after its heavy meal4 ,the interaction of the forces which gives rise to this phenomenon is difficult to fathom2 there are no doubt several tensions1 constantly changing in magnitude1 which in the result cause the liquids of the large and small globules to intermingle4 ,separate globules of a single liquid sometimes unite in this manner1 but this is not common1 it being more usual for the scattered units to remain apart4 ,illustration3 ,fig4 #db4--,the devouring globule4 ,five stages4 ,illustration3 ,fig4 #dc4--,photograph of one globule absorbing another4 99,analogies of ,surface ,tension ,phenomena with ,life499--,when we watch the movements of globules on the surface of water1 the resemblance to the antics of the lower forms of life immediately occurs to our minds4 ,now ,i do not intend here to intrude any opinion on the much-discussed subject of the ,origin of ,life1 but merely to point out that certain phenomena1 usually supposed to be associated only with living things1 may result from the interplay of surface tensions4 ,in our experiments we have witnessed expansive and contractile motion 7aniline globules on water72 movement of translation1 of a very vigorous kind 7xylidine and orthotoluidine globules72 incorporation of external matter1 or feeding 7dimethyl-aniline absorbing orthotoluidine7--we are getting quite familiar with these long names now--1 splitting up of masses1 or division 7skins of quinoline1 etc41 breaking up into branched portions1 and sub-division of large globules72 and formation of cellular structure 7tar-oil on water74 ,and the conclusion we may legitimately draw is this3 that mechanical forces may account for many observed phenomena in connexion with life which formerly were attributed to the action of vital forces4 ,modern biological research all points in the same direction1 and it seems probable that the operations of the animate and inanimate are controlled by the same forces4 ,but the mystery of ,life still remains4 99,conclusion499--,i have endeavoured in these lectures to bring to your notice some of the remarkable results which may be produced by the use of water and a few other liquids1 and the scientific conclusions which may be drawn from them4 ,it may be that the phenomena we have considered have little or no commercial application2 but science has other uses in addition to its fruitful alliance with commerce4 ,the study of the methods by which ,nature achieves her ends stimulates the imagination and quickens the perceptions1 and is therefore of the highest educational value4 ,it is a great scientific achievement to run a railway to the summit of the ,jungfrau1 but we should not envy the mental condition of the individual to whom that glorious mountain appealed only through the railway dividends4 ,and ,i trust that we shall never become so imbued with the industrial aspects of science1 as to lessen our appreciation of the works of ,nature1 whether manifested in the snow-clad peak or the equally wonderful drop of water4 ,,appendix ,apparatus and ,materials required for ,experiments on ,drops and ,globules4 99,vessels499--,for direct observation of liquid spheres1 large drops1 etc41 beakers about #f inches in height and #d inches in diameter are suitable4 ,it must be remembered1 however1 that a beaker containing water behaves like a cylindrical lens1 and hence objects in the interior appear distorted in shape4 ,in order to observe the true dimensions1 flat-sided vessels must be used1 in which the faces are of uniform thickness4 ,glass battery-vessels1 which are made of a single piece of glass1 have sides of irregular thickness1 and are not to be recommended4 ,a useful form of vessel is one in which the bottom and edges are made of copper1 the sides being formed of windows of plate glass cemented to the copper framework4 ,water may be boiled in such a vessel without danger to the glass1 starting with cold water2 it is not advisable to pour hot water into the cold vessel1 however1 as the glass may crack4 ,suitable dimensions for a vessel of this kind are #f inches high1 and #d inches in width and thickness4 ,a beaker containing water1 in which drops are formed may be placed in this square vessel1 and surrounded by water1 when distortion will be absent2 and the whole of the contents may be kept hot--as required1 for example1 with the automatic aniline drop4 ,it is best to conduct the experiments in beakers immersed as described1 as the materials used may then be easily recovered without having to clean out the flat vessel4 ,for the formation of liquid columns1 test-tubes1 of diameter #a to #b inches1 or small beakers1 may be used4 ,test-tubes provided with a foot1 which will stand upright1 are most satisfactory2 and the true shape may be seen by immersing the test-tube or beaker in water in a flat-sided vessel of the form described above4 ,the effect of heat on the shape of the column may be observed by warming the water in the vessel4 ,the centrifugoscope 7,fig4 #g7 and the apparatus depicted in ,figs4 #h1 #ac1 and #cb1 may be procured from the makers1 ,messrs4 ,a4 ,gallenkamp ,co41 ,sun ,street1 ,e4,c4 ,experiments with skins and globules may be conducted in beakers of about #d inches diameter1 or in small porcelain photographic dishes4 ,if intended for lantern projection shallow cells1 with a bottom of plate glass1 are necessary1 and may be obtained from dealers in scientific apparatus4 99,materials499--,sufficient quantities of the various liquids used may be procured from dealers in chemicals at a small cost4 ,aniline and orthotoluidine1 which figure largely in the experiments1 should be obtained in the commercial form1 which is the cheapest and most suitable4 ,the remaining liquids should be of the variety described as pure in the catalogues4 ,when used for the formation of films1 they should be kept in bottles in which the glass stopper is prolonged into a tapered rod1 which dips into the liquid1 and which1 on removal1 carries a convenient quantity of liquid to drop on to the water surface4 ,accessories such as glass rods1 plates1 tubing of various diameters1 thin copper wire1 and an aluminium plate for the spheroidal state1 can be obtained from any dealer in apparatus2 and the same applies to clamp-stands for holding funnels1 etc4 99,water499--,ordinary tap-water suffices for all the experiments described1 and for work with films and globules is superior to distilled water1 which often possesses a surface so greasy as to retard or even entirely prevent the desired result4 ,all experiments conducted on the surface of water should be performed in a clean vessel which has been rinsed out several times with tap-water before filling4 99,lantern ,projection499--,in demonstrating the phenomena to an audience1 a lantern may be used to advantage4 ,it should be of the type now procurable1 which is arranged for the projection of experiments conducted either in a horizontal or vertical position1 by the use of the electric arc or other suitable source of light4 ,flat-sided vessels are essential for the successful projection of views of objects in a vertical position2 and for showing globules1 etc41 on the surface of water1 better definition is secured if cells with plate-glass bottoms are used instead of vessels made of a single piece of glass4 ,the author has generally used a ,kershaw lantern for lecture purposes1 with quite satisfactory results4 ,this lantern may also be adapted for projecting solid objects by reflected light--as1 for example1 a hot plate on which a spheroid of water is floating 7,fig4 #cd74 ,the contrivance known as the ,mirrorscope may also be used1 with slight modification1 for producing a magnified image of solid objects on the screen4 ,,index ,a ,,page ,aceto-acetic ether1 automatic drops of1 4 4 4 #cg columns of1 4 4 4 4 4 4 #dd ,aniline1 automatic drops of1 4 4 4 4 #cc equi-density temperature of1 4 4 4 #ag films or skins1 4 4 4 4 4 #ai globules1 movements of1 4 4 4 #fc ,anisol1 4 4 4 4 4 4 4 4 #ai ,area of stretched surfaces1 4 4 4 4 4 #g ,b ,boundary surface of two liquids1 4 4 4 4 #f ,butyl benzoate1 4 4 4 4 4 4 4 #ai ,c ,camphor1 movements of on the surface of water1 4 #fc ,centrifugoscope1 4 4 4 4 4 4 #ad ,chloroform1 composite drops of1 4 4 4 4 #dh ,d ,dimethyl-aniline1 skin of on water1 4 4 4 #fh ,diving drop1 4 4 4 4 4 4 4 #bb ,droplet1 formation of1 4 4 4 4 #bh1 #cd ,drops of liquid1 apparatus for1 4 4 4 4 #bg automatic1 4 4 4 #cc1 #cg combined with vapour1 4 4 #dg communicating1 4 4 4 #dd condensation of from vapour1 4 #di floating on hot surface1 4 4 #eg formation of1 4 4 #bd1 #cc1 #cg overheated1 4 4 4 4 #ee shapes of1 4 4 #aj1 #bi1 #cj1 #ca ,e ,elastic skin of liquids1 4 4 4 4 4 #e ,equi-density temperatures1 4 4 4 #af1 #ag1 #ai ,ethyl benzoate1 columns of1 4 4 4 4 #db ,f ,fogs1 4 4 4 4 4 4 4 4 #eb ,g ,globule1 forces acting on1 4 4 4 4 4 #fa the devouring1 4 4 4 4 4 #gd ,globules1 attraction between1 4 4 4 4 #gc expanding1 4 4 4 4 4 4 #gb production from films1 4 4 4 4 #fi surface movements on water1 4 4 #fc1 #ff ,golden syrup1 experiment with1 4 4 4 4 #h ,i ,interfacial tension1 4 4 4 4 4 #bb1 #fa ,ions1 condensation on1 4 4 4 4 4 #ec ,j ,jets of liquid1 4 4 4 4 4 4 4 #ch ,l ,liquid clouds in liquid media1 4 4 4 4 #ed columns1 4 4 4 4 4 4 #dj jets1 4 4 4 4 4 4 #ch ,liquids1 general properties of1 4 4 4 4 #b origin of1 4 4 4 4 4 4 #a properties of surface of1 4 4 4 #c ,m ,minimum thermometer1 4 4 4 4 4 4 #f ,mists1 4 4 4 4 4 4 4 4 #di ,mono-brom-benzene1 4 4 4 4 4 4 #dh ,n ,network formed from film1 4 4 4 4 4 #gj ,nitrobenzene1 drops of1 4 4 4 4 #bi1 #cg films1 4 4 4 4 4 4 #fi ,o ,orthotoluidine columns1 4 4 4 4 4 #db drops1 4 4 4 4 4 4 #bg equi-density temperature of1 4 4 4 #af globules1 movements of1 4 4 4 4 #ff jets1 4 4 4 4 4 4 4 #ci spheres1 4 4 4 4 4 #aa1 #ad ,p ,petroleum1 boundary surface with water1 4 4 4 #f ,plateau's spherule1 4 4 4 4 4 4 #be ,q ,quinoline1 formation of globules of1 4 4 4 #fi rings of1 4 4 4 4 4 4 #ga ,r ,raindrops1 4 4 4 4 4 4 4 #ed ,s ,shape of detached masses of liquid1 4 4 4 #h ,silver floating on water1 4 4 4 4 4 #d ,solubility1 movements due to1 4 4 4 4 #fc ,spheres of liquids1 effect of temperature on1 4 #ae production of1 4 4 #aj ,spheroidal state of liquids1 4 4 4 4 #ei ,spreading of oil on water1 4 4 4 4 4 #fj ,surface skin of water1 properties of1 4 4 4 #c tension1 definition of1 4 4 4 4 #ba phenomena1 analogies to life1 4 #ge value for various liquids1 4 4 #bb ,w ,water1 column of1 4 4 4 4 4 4 #dj surface tension of1 4 4 4 4 #ba beetle1 4 4 4 4 4 4 #d ,x ,xylidine #a-c-d1 movements of globules of1 4 4 #ff 7,pr #abff7 -------- ,butler ,tanner ,frome and ,london ,transcription note ,the following minor typographical flaws have been corrected3 - ,fig4 #g3 missing period at the end of the caption - feeler1' unnecessary additional closing quote - 99,index399 ,drops of liquid1 shapes of1 #aj1 #bi1 #cj1 #ca missing commas - 99,index399 ,mono-brom-benzene added hyphen to conform with reference in text ,footnotes have been renumbered progressively throughout the book4