,an ,examination of some ,methods ,employed in ,determining the ,atomic ,weight of ,cadmium4 ,a ,thesis ,presented to the ,board of ,university ,studies of the ,johns ,hopkins ,university for the ,degree of ,doctor of ,philosophy4 by ,john ,e4 ,bucher4 #ahid ,contents4 ,i4 ,introduction and ,historical ,statement #a ,,ii4 ,the ,oxalate ,method #c ,preparation of ,pure ,cadmium #c ,preparation of ,nitric ,acid #d ,purification of ,water #d ,purification of ,oxalic ,acid #e ,preparation of ,cadmium ,oxalate #g ,procedure #h ,results #ac ,,iii4 ,the ,sulphide ,method #af ,preparation of ,hydrogen ,sulphide #af ,preparation of ,nitrogen #ag ,mode of ,procedure #ah ,results #bd ,discussion of the ,results #bd ,discussion of the ,method #bf ,,iv4 ,the ,chloride ,method #cc ,preparation of ,cadmium ,chloride #ce ,the ,filters #dh ,analytical ,process #eb ,results #eg ,discussion of the ,results #eh ,v4 ,the ,bromide ,method #fi ,preparation of ,cadmium ,bromide and ,hydrobromic ,acid #gj ,method of ,analysis #gh ,results #hj ,discussion of the ,results #hj ,,vi4 ,syntheses of ,cadmium ,sulphate #hb ,results #ij ,discussion of the ,results #ia ,,vii4 ,the ,oxide ,method #id ,results #if ,discussion of the ,results #ig ,determination of ,error #ajd ,discussion of the ,oxalate ,method #aad ,,viii4 ,other ,methods #aai ,,ix4 ,conclusion #abb ,acknowledgement4 ,the author wishes to acknowledge his indebtedness for advice and instruction to ,professor ,morse at whose suggestion and under whose guidance this work has been carried on4 ,he also wishes to express his thanks for instruction to ,professor ,remsen in ,chemistry1 ,professor ,williams in ,mineralogy1 ,dr4 ,ames in ,physics and ,mr4 ,hulburt in ,mathematics4 ,introduction and ,historical ,statement4 ,the atomic weight of cadmium has been investigated by a number of chemists but the results obtained vary between wide limits4 ,the work described in this paper was undertaken with the object of finding the cause of the discrepancy in some of the methods employed4 ,a complete historical statement has been given by ,morse and ,jones1 7,amer4 ,chem4 ,jour41 #ad4 #bfa47 and it is only necessary1 here1 to give a summary for the purpose of reference3 ,ratio4 ,at4 ,wt4 ,cd4 #ahah1 ,stromeyer1 ,cd 3 ,cd,o #aaa4dhc 7,schweiggers ,jour4 #bb1 #ccf47 #aheg1 ,von ,hauer1 ,cd,s,o#d 3 ,cd,s #aaa4ice 7,jour4 f4 ,prakt4 ,chemie #gb1 #cch47 #ahei1 ,dumas1 #ast series4 ,cd,cl#b 3 ,ag #aab4daf #b;d ,cd,cl#b 3 ,ag #aab4jjg 7,ann4 ,chim4 ,phys4 #c1 #ee1 #aeh47 #ahfj1 ,lenssen1 ,cd,c#b,o#d 3 ,cd,o #aab4jdc 7,jour4 f4 ,prakt4 ,chem4 #gi1 #bha7 #ahhb1 ,huntington and ,cooke1 ,cd,br#b 3 ,ag,br #aab4bci ,cd,br#b 3 ,ag #aab4bde 7,proceedings ,amer4 ,acad4 #ag1 #bh7 #ahij1 ,partridge1 #ast ,series ,cd,c#b,o#d 3 ,cd,o #aaa4haf #b;d ,cd,s,o#d 3 ,cd,s #aaa4gbg #c;d ,cd,c#b,o#d 3 ,cd,s #aaa4faf 7,amer4 ,jour4 ,sci4#c1 #dj1 #cgg7 #ahib1 ,morse and ,jones1 #ast ,method1 ,cd 3 ,cd,o #aab4jgff #b;d ,cd,c#b,o#d 3 ,cd,o #aab4fcb #ahib1 ,torimer and ,smithy ,cd,o 3 ,cd #aab4jee 7,zeit4 f4 ,anorg4 ,chem4 ,i4 #cfd7 ,in this summary as well as in the rest of this paper the following atomic weights are used3 ,oxygen #af4jj ,sulphur #cb4jei ,carbon #ab4jjc ,chlorine #ce4de ,bromine #gi4ie ,silver #ajg4ic ,the ,oxalate ,method ,preparation of ,pure ,cadmium4 8,cadmium met4 puriss4 galv4 reduc01 obtained from ,schuchardt1 was used for preparing pure cadmium4 ,it was heated to redness in a current of hydrogen which had been purified by washing with both acid and alkaline solutions of potassium permanganate4 ,this treatment converted the metallic powder into a bar which could be distilled in a vacuum4 ,the metal was then distilled nine times in the same manner that ,morse and ,burton1 ,amer4 ,chem4 ,jour4 #ab1 #bai1 had distilled zinc4 ,all distillations were made slowly except the last one1 which was made quite rapidly4 ,preparation of ,nitric ,acid4 ,whenever pure nitric acid was required1 it was purified by distilling against a platinum dish and collecting the distillate in a smaller one of the same metal4 ,the nitric acid used was dilute and free from chlorine4 ,purification of ,water4 ,the water used in this work was purified by distilling twice from an alkaline solution of potassium permanganate1 always rejecting the first part of the distillate4 ,whenever water was needed in the preparation of a pure compound e4g4 cadmium oxalate1 oxalic acid1 cadmium nitrate1 etc41 it was subjected to the additional process of being distilled against a large platinum dish which was kept cool by placing ice inside it4 ,purification of ,oxalic ,acid4 ,commercial oxalic acid was heated with a fifteen percent solution of hydrochloric acid until all was dissolved4 ,the solution was then warmed for twenty four hours4 ,on cooling1 crystals of oxalic acid separated out and these were washed with a little cold water to remove the mother liquor4 ,they were then dissolved in hot ninety-five percent alcohol and allowed to crystallize slowly on cooling4 ,the acid was next crystallized from ether in which it is only sparingly soluble4 ,after this it was boiled with water until the odor of ethyl acetate had disappeared4 ,finally it was recrystallized three times from water and dried in the air at ordinary temperatures4 ,preparation of ,cadmium ,oxalate4 ,a weighed piece of cadmium was dissolved in nitric acid and the excess of acid evaporated off4 ,the nitrite was then dissolved in a large quantity of water and an equivalent amount of oxalic acid in solution added4 ,the oxalate separated in a few moments as a crystalline precipitate4 ,it was collected on a porcelain filter and washed thoroughly to remove nitric acid and ammonium nitrate4 ,a considerable amount of ammonium nitrate was formed during the solution of the cadmium in nitric acid4 ,the oxalate was finally dried in an air-bath for fifty hours1 at #aej;,c4 ,procedure ,enough cadmium oxalate for a determination was placed in a weighing tube which had been tared against a similar vessel and dried at #aej;,c4 until the weight remained constant4 ,it was then poured into a weighed porcelain crucible4 ,the tube and its tare were now dried again at the same temperature to constant weight in order to avoid any error resulting from moisture being absorbed by the cadmium oxalate which adhered to the weighing-glass4 ,the crucibles used in these determinations were arranged in the same manner as those employed by ,morse and ,jones in their work on this method4 ,a small porcelain crucible on whose edge were placed three short platinum wires bent in the shape of the letter ,u1 was placed in a larger porcelain crucible4 ,the platinum wires prevented the lid from sticking to the crucible after heating and also allowed the products of decomposition to escape4 ,the glaze was removed from the outside of the larger crucible with hydrofluoric acid to avoid sticking when heated to a high temperature4 ,a second pair of crucibles arranged in the same manner was tared against the first one and in all cases treated like it4 ,after the oxalate had been poured into the weighed crucible1 it was decomposed by placing the crucible with its contents in a cylindrical asbestus covered air-bath1 and slowly raising the temperature until the mass beams uniformly brown in color4 ,in the last five determinations1 the temperature was not allowed to exceed #cjj;,c and after from forty to eighty hours the loss in weight was about ninety percent of the amount calculated for complete decomposition4 ,in the first four the temperature was much higher and the time employed shorter4 ,after the oxalate had been thus treated nitric acid was added and the contents of the crucible dissolved completely4 ,the crucible was then transferred to a bath constructed by placing a larger porcelain crucible in a still larger one of iron and filling the intervening space with sand4 ,it was slowly heated until the nitric acid had all evaporated and the dry nitrate began to give off red fumes4 ,the crucibles were then removed to a similar bath containing iron filings instead of sand4 ,this bath was heated by means of a single burner as long as red fumes were observed1 and then for about five hours with a triple burner4 ,finally1 the crucibles were transferred to a nickel crucible in the bottom of which a plate of unglazed porcelain was placed4 ,the nickel crucible which had previously been set tightly into a hole cut in an asbestos board was then heated over the blast lamp for two hours4 ,after this the porcelain crucible and contents were weighed and then reheated for half hour periods as before until three successive weighings remained constant4 ,this usually required from three to four hours of blasting4 ,in all determinations1 the resulting product was tested for oxides of nitrogen with potassium iodide1 starch and hydrochloric acid1 but none was found4 ,all weighings were reduced to the vacuum standard on the assumption of #h4d for the ,sp4 ,gr4 of brass1 #ba4 for platinum1 #c4ca for the oxalate and #h4ae for cadmium oxide4 ,the results are3 ,cadmium ,oxalate4 ,cadmium ,oxide4 ,at4 ,wt4 ,cd4 ,i #a4igfgd #a4bfdad #aaa4gc ,,ii #a4idiab #a4bdfhb #aaa4hb ,,iii #a4ifghf #a4behhf #aaa4gg ,,iv #a4hgjii #a4aifge #aaa4gg ,v #a4ihida #a4bgbdb #aaa4gi ,,vi #a4cgeej 4#hgiid #aaa4he ,,vii #a4cccac 4#hecjh #aaa4ie ,,viii #a4iddej #a4bddeb #aab4jd ,,ix #b4jahdf #a4bibaj #aab4ji ,a glance at these results shows that there is a variation of 4#cf of a unit and that the atomic weight in general increases with the number of determinations4 ,in the first four determinations1 there may have been loss of cadmium by reduction and subsequent volatilization1 but in the later determinations this is not probable4 ,it is believed that the greater part of the variation was due to imperfect dehydration of the oxalate4 ,this and other sources of error in this method will be referred to later4 ,the nickel crucible used gave a slight sublimate on heating1 even after fifteen hours' blasting4 ,this condensed on the porcelain crucible as a brownish coating but1 as both the crucible and its tare were blasted for the same length of time1 it did not seem to change the difference of their weights4 ,more than a dozen nickel crucibles were tried but none was found not to give a sublimate4 ,the amount was so slight that no attempt was made to determine its nature4 ,the ,sulphide ,method4 ,this method is based on the conversion of cadmium oxalate into cadmium sulphide by heating in a current of hydrogen sulphide4 ,the method has been used by ,partridge4 ,this result was #aaa4fa for the atomic weight of cadmium4 ,preparation of ,hydrogen ,sulphide ,in the present work this gas was always prepared from potassium hydrosulphide which was made from barium sulphide 7commercial74 ,barium sulphide was treated with dilute hydrochloric acid and the resulting hydrogen sulphide washed thoroughly with a solution of potassium hydrosulphide and then with pure water4 ,it was then passed into a strong solution of potassium hydroxide until the later was saturated4 ,when it was required1 it was set free from this solution by adding dilute sulphuric acid and again washing the resulting gas with a strong solution of potassium hydrosulphide4 ,preparation of ,nitrogen4 ,whenever a current of nitrogen was required1 it was prepared by passing air over a layer of hot copper gauze in a combustion tube4 ,a short layer of copper oxide was first introduced1 then the copper gauze and finally another layer of copper oxide4 ,the air was dried with caustic potash before entering the tube and the nitrogen obtained was also passed through a long tube filled with lumps of this substance before being used4 ,mode of ,procedure4 ,a number of weighing tubes #adj millimetres long and #ac millimetres internal diameter were made especially for this work4 ,they were always used in pairs1 one being kept as a counterpoise4 ,a porcelain boat of such dimensions as just to slide into the tube was placed in each one4 ,for a determination1 a tube and its boat were tared with another tube and boat1 glass against glass and porcelain against porcelain until the difference in weight was less than two tenths of a milligramme4 ,both boats were heated in a current of hydrogen sulphide to incipient redness for about one hour4 ,the current of hydrogen sulphide was then replaced by one of nitrogen1 in which the boats were cooled1 but while still warm they were transferred to their weighing tubes and allowed to cool in a dessiccator containing caustic potash and weighed4 ,before weighing1 the stoppers of the weighing tubes were loosened for a moment in order to equalize the internal and external pressure4 ,this treatment was usually repeated two or three times and the difference in weight remained perfectly constant4 ,a portion of cadmium oxalate sufficient for a determination was placed in the weighed boat and dried at #aej;,c4 ,the oxalate had been prepared exactly like that used in the oxalate method which has already been described4 ,the gas pressure in the laboratory varied very much while this method was under investigation and great difficulty was experienced in maintaining a constant temperature although a thermoregulator was used4 ,sometimes a specimen of oxalate which was supposed to be dry would lose several tenths of a milligramme when the thermometer would only have gone up to #afj;,c or #afe;,c for an hour by accident4 ,under these conditions the drying was so uncertain that only four determinations were completed although many were started4 ,the boat containing the oxalate which had been dried and weighed was placed on supports of unglazed porcelain in a combustion tube and a current of dry hydrogen sulphide passed over it4 ,as soon as the air was expelled1 the tube1 which was in a combustion furnace1 was slowly heated until all the oxalate seemed to be decomposed and then raised to dull redness4 ,after this temperature had been maintained for about an hour1 the sulphide was allowed to cool to a temperature of about #bjj;,c4 and the current of hydrogen sulphide replaced by dry nitrogen1 using a three-way stopcock4 ,when nearly cold the boat was slipped into its weighing-tube and weighed1 the same precautions being used as when weighing the empty boat4 ,at this stage the sulphide was always from one to two milligrammes lighter than at the end of the determination4 ,it was reheated for periods of one hour until the weight remained constant4 ,this generally required from three to five hours4 ,all weighings were reduced to the vacuum standard on the basis of #d4e for the ,sp4 ,gr4 of cadmium sulphide1 #c4ca for the ,sp4 ,gr4 of cadmium oxalate1 #h4d for the ,sp4 ,gr4 of brass weights and #ba for the ,sp4 ,gr4 of platinum weights4 ,the results are as follows3 ,cd ,c#b,o#d ,cd,s ,at4 ,wt4 ,cd4 ,i4 #b4efcai #a4hdgaf #aab4be ,,ii4 #b4ahcfd #a4egcda #aab4ag ,,iii4 #b4aafdc #a4ebdfb #aab4je ,,iv4 #c4acaje #b4beehb #aab4ab ,the first three determinations were made exactly as above described1 the heating in hydrogen sulphide being done in a ,bohemian glass combustion tube4 ,the hydrogen sulphide was dried with calcium chloride4 ,the fourth determination was made under somewhat different conditions4 ,the boat containing the weighed oxalate was placed in a combustion tube which passed through an asbestus covered air-bath4 ,the air was displaced by a current of dry hydrogen sulphide and the bath slowly heated4 ,when the temperature had risen to #baj;,c4 it was maintained there for three hours1 and then raised to #bej;,c4 for three hours4 ,the sulphide then weighed #b4bg grammes1 being #ad milligrammes heavier than when the determination was finished4 ,it was replaced in the tube and reheated in a current of hydrogen sulphide at a temperature of #cjj;,c4 for four hours4 ,it was then transferred to a porcelain tube and heated to redness for one hour4 ,it then weighed #b4bedcg grammes1 being #a4de milligrammes lighter than at the end of the determination4 ,the weight did not become constant until it had been heated six hours more to redness in a current of hydrogen sulphide4 ,when this oxalate was slowly heated in ,h#b,s1 a small amount of oxalic acid sublimed to the colder part of the tube1 but1 in the other cases where the heating was more rapid1 only carbon monoxide1 carbon dioxide1 and water were observed4 ,discussion of the ,method4 ,when hydrogen sulphide is passed through a red-hot tube1 sulphur is deposited on the colder parts because at this temperature hydrogen sulphide dissociates and the elements do not recombine on cooling4 ,in this work1 a faint sublimate was noticed before coming to the zone of sulphur deposit4 ,on exposure to air1 it deliquesced in a few minutes forming small yellow drops which had a saline taste1 and gave tests for potassium and sulphur4 ,the sublimate had a yellow color and was evidently formed by the action of sulphur on glass4 ,it seemed to do no harm1 but in the fourth determination an effort was made to avoid it by using a porcelain tube instead of a glass combustion tube for heating to redness in a current of hydrogen sulphide4 ,the fact that sulphide of cadmium was always too light after the first hour's heating in hydrogen sulphide proves that it must have contained some oxide of cadmium even after this heating4 ,oxide of cadmium is readily absorbed by the glaze on porcelain1 and some error must have been introduced in this way because it would not be converted into sulphide after forming a silicate4 ,the effect of this would be to give a low result for the atomic weight of cadmium4 ,to get some idea of the magnitude of this error1 the sulphide was poured out of the boats used in the first and second determinations4 ,they were then warmed with nitric acid for a few moments1 washed in water1 and heated over the blast lamp for a few minutes4 ,the boats used as tares were treated in exactly the same manner4 ,on weighing1 the boats in which the oxalate in determinations ,i and ,,ii had been decomposed1 were found to be #a4ab milligrammes and 4#hb milligrammes heavier respectively than at the beginning of the determinations4 ,this would only introduce an error of 4#jc of a unit in the atomic weight on account of the small difference in weight between these amounts of oxide and equivalent amounts of sulphide4 ,the boats were warmed1 as above mentioned1 with nitric acid to remove any adhering sulphide4 ,this might have decomposed some cadmium silicate at the same time1 and the error due to cadmium oxide thus be found smaller than it really is4 ,the following experiment was made in the hope of avoiding the formation of cadmium silicate4 ,the glaze was removed from the inside of a porcelain boat by hydrofluoric acid followed by a thorough scouring with sand and water4 ,the boat was then heated in the flame of a blast lamp for several minutes1 tared against another boat which was not treated with hydrofluoric acid4 ,both were heated to redness in a current of hydrogen sulphide for an hour1 cooled1 weighed1 and then heated in hydrogen sulphide for another hour1 and weighed again4 ,the boat gained #a4g milligrammes during this second heating1 showing that a boat whose glaze has been removed by hydrofluoric acid could not be used in this method4 ,throughout this work1 great care was taken to exclude the oxygen of the air from the cadmium sulphide1 while hot4 ,the current of hydrogen sulphide in which the cadmium sulphide is heated must not be too slow1 otherwise the sulphur in the dissociated gas will diffuse to the colder parts of the tube and condense1 the residual gas becoming very rich in hydrogen4 ,the hydrogen will then reduce some of the sulphide to metal1 causing loss by volatilization4 ,one determination was lost in this way1 over two milligrammes of the sulphide being sublimed out1 and it could easily be detected on the side of the tube4 ,it is believed that the cause of the variations in the four determinations made by this method1 is due to imperfect dehydration of the oxalate4 ,it did not seem advisable to continue this part of the work any farther2 therefore the chloride method was taken up4 ,the ,chloride ,method4 ,huntington had determined the ratios of ,cd,br#b to ,ag,br and also ,cd,br#b to ,ag very carefully1 obtaining the result #aab4bd for the atomic weight of cadmium4 ,morse and ,jones had obtained #aab4jg for this constant by the oxide method4 ,the object of the work about to be described was to find the cause of this discrepancy if possible4 ,it was thought advisable however to make some determinations of the ratio of ,cd,cl#b to ,ag,cl before beginning the bromide method4 ,dumas1 in #ahei1 used cadmium chloride to determine the atomic weight of the metal4 ,he did not establish its ratio to silver chloride but to silver by titration4 ,he prepared cadmium chloride by dissolving the metal in hydrochloric acid and melting the resulting product in a platinum capsule for five or six hours4 ,he made two series of three determinations4 ,the chloride used in the first series was yellow in places and not completely soluble4 ,the result was #aab4dgf4 ,the second series was made with chloride which was perfectly white and soluble and gave #aab4jjg for the atomic weight of cadmium4 ,it is evidently more reliable than the first series and ,dumas himself concluded that the atomic weight is very near #aab4ja4 ,preparation of ,cadmium ,chloride ,four different specimens of cadmium chloride were used in this work and from these specimens portions were taken for analysis4 ,these portions were treated differently in different analyses1 therefore it will be necessary to give a brief descriptions of them and mention the number of the determinations1 in which each one was used4 ,chloride of cadmium was prepared in the following manner4 ,a solution of pure hydrochloric acid was prepared by passing a current of hydrochloric acid gas into pure water which was contained in a porcelain crucible until no more was absolved4 ,the water used had been purified by distilling against a platinum dish and the hydrochloric acid gas was obtained by heating ordinary concentrated chemically pure hydrochloric acid in a distilling bulb whose neck had been closed by fusion in order to avoid the use of a cork or rubber stopper4 ,hydrochloric acid thus prepared will leave no residue on evaporation when air is excluded 7,stas1 ,aronstein's ,german translation1 p4 #aaa74 ,a piece of platinum foil freed from iron by heating in the vapors of ammonium chloride as recommended by ,stas 7,aronstein's translation1 p4 #aab7 was introduced and a piece of cadmium laid on it4 ,solution begins at once1 the hydrogen being liberated on the platinum foil4 ,during the later part of the process1 heat was applied4 ,after all of the metal had dissolved1 the solution was evaporated1 the platinum foil having previously been removed4 ,the crystals of cadmium chloride which separated were not dried but allowed to remain slightly moist with hydrochloric acid4 ,if no platinum foil is used1 the solution of the pure metal becomes exceedingly difficult1 unless a very large excess of acid is used4 ,no objection can be raised to the use of platinum foil for in making fifty grammes of cadmium chloride it cost less than a tenth of a milligramme and even this could probably have been avoided by using a somewhat larger amount of hydrochloric acid4 ,the foil was always kept submerged in the acid liquid4 ,the moist crystals of cadmium chloride were transferred to a combustion tube passing through an asbestus covered air-bath1 and dried in a current of hydrochloric acid gas for several hours at #cjj;,c4 ,the hydrochloric acid gas had been passed through a long calcium chloride tube to dry it1 although calcium chloride probably does not do this very thoroughly4 ,the hydrochloric acid gas was then replaced by a current of nitrogen prepared as has already been described under the sulphide method4 ,after the current of nitrogen had been passing for about half an hour1 the tube was allowed to cool1 and the chloride transferred to another combustion tube1 one end of which had been sealed in the flame of a blast lamp4 ,the other end was drawn out and attached to a ,sprengel mercury pump4 ,after exhausting1 the chloride was sublimed in the vacuum4 ,this takes place at a moderate temperature and the sublimate has a beautiful crystalline structure and is perfectly white4 ,the crystalline mass exposes so much surface that water is taken up very rapidly when exposed to the air4 ,this action is so rapid that the crystals cannot be transferred to a weighing-glass without introducing an appreciable error4 ,the whole sample was accordingly transferred to a stoppered glass bottle which was kept under a bell jar with sticks of caustic potash4 ,three samples were prepared in this manner1 the first being used in determination one1 the second in determinations two to seven inclusive1 and the third in determinations eight to nineteen inclusive4 ,the samples used in determinations twenty and twenty-one were prepared in the following manner3 ,about three grammes of cadmium were placed in a combustion tube in which three bridges 7as in the distillation of pure cadmium7 had been made4 ,a section may be represented thus ,illustration ,the metal was placed in cavity ,a and a stream of chlorine passed through the tube4 ,the chlorine was prepared from potassium bichromate and hydrochloric acid and dried by passing it through a long tube containing calcium chloride4 ,when the air had been displaced1 the cadmium was heated4 ,it fused and began to burn to the chloride which partly flowed over the bridge into cavity ,b and partly distilled over into this cavity4 ,when the reaction had ended1 the current of chlorine was replaced by one of dry nitrogen1 and the tube was allowed to cool and the chloride taken for analysis ,,xx4 ,the specimen used in analysis twenty-one was prepared in exactly the same way1 only the chlorine used was obtained from manganese dioxide1 sodium chloride and sulphuric acid1 and was dried with phosphorous pentoxide instead of calcium chloride4 ,the special treatment of the portions taken for analysis was as follows3 ,those taken for determinations ,i1 ,,ii and from ,,xi to ,,xix inclusive were placed in a platinum boat and put into combustion tube4 ,a current of hydrochloric acid gas obtained by heating the aqueous acid was passed through the tube4 ,the gas had been dried by calcium chloride4 ,when the air was displaced1 the chloride was heated somewhat higher than its fusing-point i4e4 to incipient redness1 and maintained there for a length of time varying from a few minutes to more than an hour4 ,the hydrochloric acid was then displaced by a current of nitrogen1 and the chloride allowed to cool4 ,the boat with the chloride1 while still slightly warm1 was placed in a weighing-tube1 cooled in a dedicator containing caustic potash and weighed4 ,the chloride thus prepared is transparent and presents only a small surface to the air4 ,it takes water up so slowly that no error is introduced from this source4 ,this was tested in one case by allowing a boat containing some chloride thus prepared to stand in the air for a certain length of time and noting the increase in weight4 ,it was quite slow4 ,in several cases specimens of chloride were tested for hydrochloric acid using tropaeolin as an indicator4 ,it was always found neutral4 ,the portions used for determinations ,,iii and ,,vi to ,x inclusive were prepared in exactly the same manner as the preceding ones except that the hydrochloric acid gas in which they were fused was not dried but used just as it came from the aqueous acid4 ,in some cases the platinum boat in which the chloride was fused was weighed before and after the fusion4 ,the weight remained unchanged4 ,for determinations ,,iv and ,v1 about six grammes of cadmium chloride were placed in a platinum boat1 and more than two-thirds of it distilled out in a current of hydrochloric acid gas which had not been dried4 ,part of the distillate was collected after cooling in nitrogen and used in determination ,,iv while the residue remaining in the boat was used for determination ,v4 ,the method of preparing the chloride used in determinations ,,xx and ,,xxi has already been described4 ,the ,filters4 ,thinking that a ,gooch crucible with a platinum sponge on the bottom in place of asbestus would be desirable for this work one was accordingly made and answered the purpose very satisfactorily4 ,all determinations were made by using such filters4 ,c4 ,e4 ,munroe 7,chem4 ,news1 ,vol #eh1 p4 #aja7 has described the preparation of these filters4 ,a platinum ,gooch crucible was placed on a filter paper and some ammonium platonic chloride which had been thoroughly washed introduced by suspending it in alcohol and then pouring this into it4 ,the precipitate settles to the bottom forming a uniform layer and the alcohol drains1 off through the filter paper4 ,the crucible was then dried slowly in an air-bath4 ,after this it was transferred to a porcelain crucible and slowly heated until decomposition was complete4 ,in this manner a layer of platinum felt is obtained which acts as a very efficient filter4 ,another layer of double chloride was then decomposed as before so that if there were any imperfections in the first layer they would be covered by the second layer4 ,the surface was smoothed down by means of a glass rod4 ,to prepare a good filter the drying and subsequent heating should be very slow4 ,the heating must not be at too high a temperature1 otherwise the felt becomes very compact and is useless for filtering purposes4 ,pressure produces the same effect4 ,the filters were always treated with strong nitric acid1 washed and reheated before being used1 but in no case was chlorine detected in the nitric acid after the washing1 nor any loss in weight of the crucible4 ,an objection to the use of these crucibles for the purpose named was found in the course of this work1 but it will be discussed later4 ,the crucibles were always set in a large weighing-glass1 and another weighing-glass containing an equal amount of platinum foil used as a tare1 in weighing4 ,this precaution was perhaps unnecessary1 but at least it did no harm4 ,analytical ,process4 ,the weighed cadmium chloride was dissolved by placing the boat containing it in an ,erlenmeyer flask containing water4 ,the boat was then washed1 dried and replaced in its weighing-tube4 ,on weighing again1 the loss in weight is equal to the weight of cadmium chloride taken4 ,all samples gave a perfectly clear solution except those used for determinations ,,xx and ,,xxi4 ,a drop of nitric acid 7#a3c7 was added to each solution except in determination ,,xiv where the cubic centimetres were added1 and in ,,xvi where ten cubic centimeters were added4 ,a solution of silver nitrate was then added to precipitate the chlorine4 ,this as well as the subsequent washing was done in a dark-room illuminated by a single gas light whose rays had to pass through a strong solution of neutral potassium chromate4 ,the precipitate was contracted by warming on the water-bath4 ,it was then collected in the prepared ,gooch crucibles and washed4 ,before filtering1 the flask containing the precipitate and mother-liquor was allowed to cool4 ,silver chloride is soluble in water to a considerable extent but is reprecipitated by adding an excess of either silver nitrate or hydrochloric acid4 ,stas 7,ann4 de ,chem4 et ,phys4 #d1 #be1 #bb2 #e1 #c1 #ade2 #e1 #c1 #bhi47 investigated this very thoroughly4 ,cooke also did some work on it and used a dilute solution of silver nitrate to wash the chloride thus preventing solution 7,proc4 ,amer4 ,acad4 #ag1 #g474 ,in the above work1 therefore1 a solution containing #j4aj grammes of silver nitrate per liter was first used1 followed by one only one-tenth as strong1 and finally pure water was used4 ,only two or three washings could be made with water as the chloride went into solution after this owing to the removal of the silver nitrate4 ,the last silver nitrate solution used is so weak that any error introduced by not washing it out completely is insignificant4 ,after washing1 the silver chloride was dried at temperatures varying from #aej;,c4 to #cjj;,c4 to constant weight4 ,a glass air-bath was used in order to prevent products from the burning gas from coming in contact with the chloride4 ,it was then weighed4 ,the quantity of silver nitrate used in the determinations was varied very much4 ,the excess over what was required to precipitate the chloride is given in the table of results in those cases in which it is known4 ,the quantity of water used in each determination is also given where it is known4 ,it is given in the number of cubic centimetres used per gramme of cadmium chloride and does not include wash water4 ,all weighings are reduced to the vacuum standard on the basis that ,sp4 ,grs4 of ,cd,cl#b #c4id and ,ag,cl #e4e4 ,the results are3 ,no4,cd,cl#b ,ag,cl ,h#b,o ,excess ,ag,n,o#c;,at4 ,wt4,melted in per ,grm4 ,i #c4jiahcd4hchef #aab4cci ,dry ,h,cl ,,ii #b4bfajjc4eched #aab4cbi ,,iii #a4cegbib4abdca #aab4cbj,moist ,h,cl ,,iv #b4jeehbc4bagbg #aab4cci ,v #a4higgdb4igjda #aab4cjf ,,vi #c4ejcfge4dhdgc #h4ijaab4bhc ,,vii #b4gjbibd4bcjhg #bjj #a4giaab4cja ,,viii #d4bdbgf #f4fcih #cjj #h4ajaab4chg ,,ix #c4djbjje4cbcad #cjj #ah4ieaab4cfh ,x #d4fjfeig4bjchf #cjj #be4fbaab4dgb ,,xi #b4djhcb #aab4dcd ,dry ,h,cl ,,xii #b4aiaadc4dbgbd #aab4dcc ,,xiii #b4hdfbhd4dedgg #cjjd4de #c;cc4 ,,hno#caab4cai ,,xiv #b4efgdhd4jafea #cjj 4#ajaab4cii ,,xv #b4cajjcc4facgj #cjj4aj #aj;cc4 ,,hno#caab4djf ,,xvi #a4bejjha4iefeb #cjj #d4ffaab4cai ,,xvii #a4ifjaec4jfeda #cjj #c4bbaab4dff ,,xviii #b4bighgc4eicia #cjj #d4bgaab4ddh ,,xix #a4idbbgc4jchaa #cjj #c4faaab4dbc ,dry ,h,cl ,,xx #a4ajigfa4gcedg #aab4dga ,,xxi #a4fcjhjb4eejaf #aab4dgf -------------- ,average#aab4chc ,discussion of the ,results4 ,in the first five determinations1 the analytical operations were conducted as nearly as possible alike1 but the preparation of the portions of cadmium chloride taken for analysis was varied very much as will be seen by referring back to this part of this paper4 ,the results do not vary more than #j4jae from their average4 ,this is very strong evidence of the purity of the chloride used for1 if it contained any impurity1 we should have expected to vary the amount in the different portions4 ,after this1 attention was paid especially to the analytical process1 for it was thought that there probably was some serious error in the method1 the result being higher than any that had previously been obtained1 if we exclude ,dumas' first series which he himself did not accept4 ,the conditions were varied in many ways to see how much the result could be influenced1 but under no conditions were results as low as ,huntington's average 7#aab4bd7 obtained4 ,a number of errors were found in the method during the work1 but they seem to neutralize each other to a great extent4 ,the more important ones will now be given4 ,nearly every filtrate including the corresponding wash water was examined for chlorine after the silver and cadmium had been precipitated by hydrogen sulphide4 ,the excess of hydrogen sulphide was expelled by boiling1 after the addition of some nitric acid4 ,in two cases an inverted condenser was used4 ,on adding silver nitrate a precipitate was always obtained showing the presence of chlorine4 ,care was always taken to filter off sulphur formed by the oxidation of hydrogen sulphide1 before adding the silver nitrate4 ,the precipitate was never very heavy1 and was not estimated quantitatively4 ,it is evident that cadmium nitrate exerts a solvent action on silver chloride4 ,in some cases a very large excess of silver nitrate was added but it did not change the results markedly4 ,silver nitrate itself dissolved silver chloride to some extent4 ,the increase in insolubility1 if any1 on adding an excess of silver nitrate is probably counterbalanced by the increased error due to occlusion of nitrates in the silver chloride4 ,stas 7,aronstein's ,trans4 p4 #aef7 says it is impossible to contract silver chloride or bromide in a solution containing salts without there being occlusion and that the precipitate can only be freed from them by dividing up the contracted mass by shaking with pure water4 ,this was not done here owing to the solubility of silver chloride in pure water1 and the complications introduced in the analytical part4 ,the occlusion of nitrates by the silver chloride would lower the atomic weight found4 ,the silver chloride obtained always darkened on heating and contained cadmium1 as was shown in the following manner3 ,the lump of silver chloride was attached to the negative pole of a cell and electrolyzed in a bath containing dilute sulphuric acid4 ,the resulting metal was then dissolved in nitric acid and the silver precipitated by adding hydrochloric acid4 ,the filtrate was evaporated to expel the nitric acid and the residue taken up with water and tested for cadmium with hydrogen sulphide4 ,an appreciable quantity was always found4 ,this method of examination does not show the occluded silver nitrate4 ,another error which tends to lower the atomic weight found is due to the platinum crucibles used for filtering4 ,if a silver nitrate solution is filtered through such a crucible there will be an increase in weight due to silver being deposited4 ,this takes place in acidified solutions as well as in neutral ones4 ,washing with ammonia does not remove the deposit1 but strong nitric acid does1 the washings giving a test for silver4 ,whether the depositing of silver is due to the action of spongy platinum in contact with the compact metal of the crucible or to some impurity in the platinum sponge was not determined1 but the former seems by far the most probable4 ,the increase in weight during the time required for filtering a determination must have been quite small however4 ,the samples of cadmium chloride employed for determinations ,,xx and ,,xxi were prepared by burning cadmium in a current of chlorine4 ,the glass tube used was attached somewhat and the solution of the chloride was very slightly turbid in each case4 ,the turbidity was so slight however1 that no very serious error could have resulted from it1 particularly as it was probably partly counterbalanced by the formation of some potassium chloride4 ,for more accurate work1 it should have been made and redistilled in a porcelain tube4 ,these two samples were tested for free chlorine with potassium iodide and starch paste1 but none was found4 ,some of the specimens of chloride prepared by fusion in a current of hydrochloric acid were found to be neutral1 using tropaeolin as an indicator4 ,as nearly as can be judged1 the above errors would probably counterbalance each other to a great extent1 and thus give a fairly close approximation to the atomic weight of cadmium when the average of all the determinations is taken4 ,the value #aab4chc thus obtained can only be regarded as tentative4 ,the ,bromide method4 ,huntington 7,proc4 ,amer4 ,acad4 #aa4bh7 working under the direction of ,j4 ,p4 ,cooke1 determined the ratio of cadmium bromide to silver bromide and using the total quantities for the calculation the result for the atomic weight of cadmium is #aab4bci4 ,he also determined the ratio of cadmium bromide to silver1 obtaining #aab4bde for the atomic weight of cadmium4 ,the work which will now be described was carried out very much like the work described under the chloride method4 ,the ratio of cadmium bromide to silver bromide was investigated4 ,preparation of ,cadmium ,bromide and ,hydrobromic ,acid4 ,a large quantity of hydrobromic acid was prepared according to the method described by ,dr4 ,edward ,r4 ,squibb 7,trans4 of ,med4 ,soc4 of the ,state of ,n4 ,y474 ,one part of water was added to seven parts of strong sulphuric acid 7,sp4 ,gr4 #a4hc7 and the mixture cooled4 ,then six parts of potassium bromide were dissolved in six parts of hot water and the diluted sulphuric acid added to this hot solution4 ,it was set aside until cold in order to allow the sulphate of potassium to crystallize out4 ,the crystals were drained on a filter-plate and quickly washed with two parts of water4 ,the mother-liquor and washing were then distilled until no more acid was obtained on further heating4 ,the acid thus obtained was distilled three times from potassium bromide1 twice from cadmium bromide formed by adding a piece of pure cadmium to it1 and twice without the addition of anything4 ,it was tested and found to be free from sulphuric acid4 ,cadmium bromide was prepared from it1 in exactly the same way that the cadmium chloride used in the chloride method was prepared from pure metal and hydrochloric acid4 ,while the crystalline mass of cadmium bromide was still moist1 it was transferred to a combination tube and dried at #cjj;,c for several hours in a current of nitrogen4 ,it was then sublimed in a vacuum as the chloride had been4 ,this specimen served for the first three determinations4 ,about nine grammes of it was placed in a platinum boat in a combustion tube1 and part of it distilled in a current of nitrogen4 ,the distillate1 a portion of which had been tested with tropaeolin and found neutral1 was used for determination ,i4 ,the residue in the boat was used for determination ,,ii4 ,another portion of the main sample was resublimed in a vacuum and used in determination no4 ,,iii4 ,cadmium bromide is not hygroscopic or at least only slightly1 therefore the sublimed cadmium bromide can be transferred to a weighing-glass without taking up water4 ,this cannot be done in the case of the chloride4 ,it is probable that the hydrobromic acid as above prepared was perfectly free from hydrochloric acid4 ,chlorine in cadmium bromide would cause the atomic weight to be found lower than it really is4 ,it was thought desirable1 however1 to prepare an acid which would certainly be free from chlorine4 ,the method described by ,stas 7,aronstein's ,german translation1 p4 #aed47 was employed with the additional precaution that the above purified acid was used to start with and all reagents employed had been especially prepared so as to be free from chlorine4 ,pure silver was prepared according to ,stas' description 7see ,aronstein's translation1 page #cd1 also page #ajd7 by the action of ammonium sulphite on an ammoniacal solution of silver nitrate and copper sulphate4 ,the silver was dissolved in nitric acid free from chlorine1 and then slowly added to a dilute solution of the above-described hydrobromic acid1 and the precipitated silver bromide thoroughly washed4 ,it was then digested for a long while in a strong solution of potassium bromide1 first in the cold1 then by heating4 ,the potassium bromide had been made thus3 ,twice recrystallized potassium hydrogen tartrate was heated in a platinum dish in a muffle furnace until it was converted into carbonate1 and the excess of carbon burned off4 ,it was then dissolved in water1 filtered and neutralized with some of the hydrobromic acid already described4 ,the carbonate had been tested for both sulphuric acid and chlorine with negative results4 ,after the silver bromide had been digested with the potassium bromide1 it was washed very thoroughly1 suspended in water1 and a current of hydrogen sulphide passed into it4 ,this converts it into sulphide hydrobromic acid being liberated4 ,the acid was drained off on a porcelain plate1 and then distilled a number of times4 ,it was finally tested and found to be perfectly free from sulphates and also did not contain free bromine4 ,having started with an acid which was probably pure and subjected it to these operations with reagents free from chlorine1 there can be no doubt as to the purity of the resulting acid4 ,the hydrogen sulphide used was prepared from potassium hydrosulphide as in the sulphide method1 and washed first with a solution of the hydrosulphide1 then very thoroughly with pure water4 ,from the hydrobromic acid obtained1 a specimen of cadmium bromide was prepared as before and sublimed twice in a vacuum4 ,this specimen was used for determinations ,,iv and ,v4 ,method of ,analysis4 ,the first three determinations were made exactly like those in the chloride method4 ,the last two were also made in the same manner1 only the washing of the precipitate was varied4 ,after the silver bromide had been contracted by warming on a water-bath it was washed by decantation and then agitated violently with cold water to remove occluded nitrates1 but it was then so finely divided that it could not be filtered4 ,the artifice used by ,stas to contract it a second time was to pass a current of steam into the milky liquid4 ,this was tried here1 but for some reason or other did not work very well1 and considerable difficulty was had in filtering it4 ,the results of the five determinations are tabulated below4 ,all weighings are reduced to the vacuum standard on the basis of ,sp4 ,gr4 of ,cd,br#b #d4f and ,sp4 ,gr4 ,ag,br #f4fb4 ,no4,cd,br#b ,ag,br ,h#b,o ,ex4 ,ag,n,o#c ,at4 ,wt4,remarks ,i #d4ciida #f4jgbjd #aab4dc;,distillate ,,ii #c4ahjcj #d4chhca #aab4db,residue ,,iii #c4fjccf #d4igaej #aab4de,resublimed4 ,,iv #d4jdbdj #e4ehjfb #aab4bi ,v #c4fjeje #d4igeai #aab4ch ,average #aab4cid ,discussion of the ,results4 ,the first three specimens were prepared under widely different conditions yet the results agree quite closely4 ,the last two were prepared from the repurified hydrobromic acid4 ,if chlorine had been removed during the second purification we should expect a higher result but the results are lower4 ,there seems to be hardly any doubt that this is due to analytical errors rather than a change in the composition of the bromide4 ,whether this be true or not1 the five determinations all fall within the limits obtained by the chloride method and confirms it as fully as can be expected4 ,the errors of the method are the same as those of the bromide method1 only they are probably less in most cases4 ,one filtrate was examined for bromium1 but none was found showing the method to be more perfect in this respect4 ,syntheses of ,cadmium ,sulphate4 ,it was next thought of examining the method based on the conversion of cadmium sulphate into cadmium sulphide1 which has been used by von ,hauer whose result is #aaa4id for the atomic weight of cadmium1 and more recently by ,partridge who obtained a much lower result1 namely #aaa4gc4 ,they dried cadmium sulphate in porcelain boats1 and then reduced it to sulphide by heating in a current of hydrogen sulphide4 ,the reduction begins in the cold and is probably complete or at least nearly complete before the temperature is sufficiently high for cadmium sulphate to decompose into cadmium oxide1 for the sulphate is very stable with respect to heat4 ,this being the case1 probably no error results from the formation of a silicate of cadmium in this method4 ,the main difficulty in this method would be to prove that the cadmium sulphate used is free from water4 ,neither von ,hauer nor ,partridge has done this because drying a substance to a constant weight is not sufficient evidence of its anhydrous character1 especially if the drying is done at a constant temperature4 ,this has been shown very clearly in the case of copper sulphate1 by ,richards 7,proc4 ,amer4 ,acad4 ,sci4 #bf4 #bfc47 ,it was therefore decided to attempt the synthesis of cadmium sulphate1 hoping to be able to fix a minimum value for the atomic weight of cadmium4 ,a piece of hard glass tube was closed at one end by fusion and the other end drawn out into a small tube which was then bent twice at right angles4 ,the large part was cut off near the beginning of the smaller tube1 and the edges rounded by fusion4 ,it was filled with dilute sulfuric acid and heated for some time to remove soluble matter from the glass4 ,after removing this acid1 a weighed piece of cadmium was introduced and an excess of dilute sulphuric acid 7#a3 #c7 added4 ,the tube contained a small piece of platinum to aid the solution of the cadmium4 ,during the process of solution1 the two parts of the glass tube were held together by a rubber band1 and the outlet of the smaller tube dipped under pure water contained in a small tube closed at one end4 ,illustration3 ,fig4 #b4 ,a section of the arrangement is shown in figure #b4 ,solution was aided by the application of heat4 ,these precautions in dissolving the metal were taken to prevent loss by spraying4 ,after the metal had been dissolved1 the solution and the water through which the hydrogen had escaped were transferred to a porcelain crucible4 ,an equal amount of sulphuric acid was then added to the tare and both were heated until fumes of sulphuric acid ceased to come off4 ,the crucible containing the dry sulphate was next placed an a porcelain plate in a nickel crucible set in a hole in an asbestos board4 ,this was placed over the flame of a ,bunsen burner1 so that the bottom of the nickel crucible was barely at a red heat4 ,the temperature on the inside of this bath was considerably lower4 ,after the weight had become nearly constant1 the sulphate was tested for sulphuric acid by means of standard alkali using tropaeolin as an indicator4 ,it was found acid1 but so slightly that no attempt was made to estimate it4 ,result #aab4ce is preliminary4 ,another synthesis was made as follows3 ,a platinum crucible1 lid and perforated cone were place in a large weighing-glass and tared with a similar weighing-glass containing a platinum crucible1 platinum foil being added until the weights were equal4 ,after these had been accurately weighed1 a weighed piece of cadmium was added to the one containing the cone4 ,the cone was inverted over the piece of metal on the bottom of the platinum crucible4 ,a considerable excess of dilute 7#a3 #c7 sulphuric acid was then added1 the lid whose edge was bent down placed on the crucible1 and the weighing-glass stoppered loosely4 ,this was placed in an air-bath1 and gently warmed during the later part of the process of solution4 ,there is no difficulty in getting complete solution if a sufficient excess of acid is used4 ,a vertical section of the crucible and weighing-glass is shown in figure #c4 ,illustration3 #c ,this arrangement avoids loss from spraying1 and the necessity of transferring the solution from a tube to a crucible as in the first experiment4 ,an equal quantity of sulphuric acid was added to the crucible used as a tare and evaporated4 ,after the metal had been dissolved1 the platinum cone was lifted to one side and the excess of acid evaporated off4 ,it was then heated in a glass air-bath for a long time at a temperature which was probably about #djj;,c4 ,after the weight had become constant1 the amount of free sulphuric acid was estimated by titration with a standard alkali using tropaeolin as an indicator4 #a4be milligrammes were found and this weight was subtracted from that found at the balance4 ,weighing were reduced to the vacuum standard1 assuming the ,sp4 ,grs4 of cadmium and anhydrous cadmium sulphate#a to be #h4ed and #c4j respectively4 ,the results were as follows3 ,footnote #a3 ,could not find any record of its ,sp4 ,gr41 #c4j is assumed4 ,cd ,cd,s,o#d ,at4 ,wt4 ,i4 7#aab4ce can only be regarded as a preliminary experiment7 ,,ii4 #a4aegha #b4adggf #aab4ce ,discussion of the ,results4 ,these results agree fairly well with those obtained by the chloride and bromide methods4 ,the second experiment is more trustworthy than the first4 ,in it1 we started with pure metal and the manipulations were so simple that no serious error could have been made in them4 ,hence it will only be necessary to consider the end-product1 i4e41 the cadmium sulphate4 ,the titration showed that the sulphate was not basic owing to loss of sulphur trioxide1 and after deducting the weight of the excess of sulphuric acid we must have left a weight of cadmium sulphate which is equivalent to the metal employed4 ,the question now is1 did it contain anything else and what would be its effect8 ,clearly the effect of water or any other impurity would be to lower the atomic weight found1 hence the atomic weight must be at least as high as the experiment indicates4 ,as the cadmium sulphate is deposited1 at least the later part of it is from a strong sulphuric acid solution1 it probably does not contain any water and in this case would fix a maximum value as well as the minimum value1 and thus determine the atomic weight4 ,it might be objected to the second experiment that the sulphuric acid found may have been present as ,,so#c and not as ,h#b,,so#d as was assumed4 ,this seems highly improbable1 and even if it were so the error introduced would be only about 4#jc of a unit in the atomic weight4 ,as the first determination was found practically neutral1 it does not apply to it at all4 ,the most probable conclusion from these experiments is that the atomic weight of cadmium is about #aab4ce4 ,a more thorough study of this method would have been made if time had permitted it4 ,the ,oxide ,method4 ,as the chloride and bromide methods and the synthesis of cadmium sulphate all lead to approximately the same high result1 it seemed probable that the oxide method which had given a much lower result 7,morse ,jones #aab4jg7 must be affected by some error4 ,accordingly it was examined in the manner about to be described4 ,a set of crucibles was prepared as described by ,morse and ,jones in their work on this method1 and in the present paper under the oxalate method4 ,after they had been heated in a nickel crucible over a blast lamp and weighed1 a weighed piece of cadmium was introduced into the smaller inside crucible1 and dissolved in nitric acid with the aid of heat4 ,an equal quantity of nitric acid was added to the tare4 ,the acid was then evaporated off1 and the resulting nitrate converted into oxide exactly as has already been described under the oxalate4 ,the first experiment was made in this way and the second one exactly like it1 only the porcelain crucible used was the one which had been employed in the first determination4 ,the glaze had been removed by the cadmium oxide of the first determination1 and before using for the second one the crucible was boiled out with nitric acid1 and heated to constant weight over a blast lamp as before4 ,determinations ,,iii1 ,,iv and ,v were made in the same way except that the small inner crucible was platinum instead of porcelain4 ,all weighings were reduced to the vacuum standard on the basis of #h4ed for the ,sp4 ,gr4 of cadmium and #h4ae for the ,sp4 ,gr of cadmium oxide and #h4d for the brass and #ba for the platinum weights4 ,the results are as follows3 ,cd ,cd,o ,at4 ,wt4 ,cd4 ,i4 #a4bfadb #a4ddadd #aab4aa ,,ii4 4#iighe #a4adjce #aab4jd ------------ ,average #aab4jh ,,iii4 #a4aacba #a4bgbdg #aaa4hd ,,iv4 #a4jbdab #a4agjed #aaa4ia ,v4 #b4hjiff #c4baaeb #aaa4hg ------------ ,average #aaa4hg ,the oxides resulting from these determinations were always tested for oxides of nitrogen1 sometimes by using meta phenylene diamine and at other times by sulphanilic acid and naphthylamine sulphate1 but no traces were ever found4 ,the average of the determinations made in porcelain crucibles is #aab4jh4 ,morse and ,jones obtained the same figure or1 if their results are reduced to the vacuum standard1 #aab4jf1 by the same method under the same conditions4 ,the results of the determinations made in platinum crucibles are equally constant1 but their average is #aaa4hh being 4#bj of a unit lower4 ,therefore1 more oxide is obtained when platinum crucibles are used instead of porcelain ones4 ,in two cases the platinum crucibles were weighed at the end of the determinations after the cadmium oxide had been removed4 ,their weight remained unchanged4 ,the most probable explanation of these facts seems to be that something is retained in the oxide in both cases1 but that the amount is greater in the determination made in platinum crucibles than in those in which porcelain ones were employed4 ,we should expect this1 because in porcelain crucibles some of the oxide is absorbed forming a silicate1 and any volatile impurity must be expelled from this part of the oxide4 ,not finding oxides of nitrogen1 it was thought that gases probably nitrogen and oxygen might be occluded although ,richards and ,rogers 7,amer4 ,chem4 ,jour4 #ae1 #efg47 had examined cadmium oxide prepared from the nitrate and found only a trace of gas4 ,accordingly two specimens of cadmium oxide obtained in the above determinations were powdered in an agate mortar and boiled with water for some time in order to remove any adhering air4 ,they were then dissolved in dilute hydrochloric acid from which the air had been removed by boiling4 ,a small amount of gas was found in each case but not nearly enough to account for the difference of 4#ca unit in the atomic weight of cadmium between #aab4ch and the oxide method4 ,in fact not more than about one sixth of the amount required was found4 ,it may be that the powdering of the oxide and then boiling up in water may have been to severe a treatment1 and that the greater part of the occluded gas escaped during these processes4 ,it seems that there is at least some error due to occluded gases in methods involving the decomposition of cadmium nitrate to oxide1 but no satisfactory idea of its magnitude could be obtained from these two experiments as carried out4 ,the following experiments were then made and they seem to give definite evidence not only of the existence of an error but also of its magnitude4 ,carbonate of cadmium was made by dissolving pure cadmium in nitric acid1 adding an excess of ammonia and a small quantity of ammonium carbonate4 ,after standing for some time the cadmium carbonate was filtered off and rejected4 ,the filtrate was treated with an excess of ammonium carbonate and the precipitated cadmium carbonate allowed to digest in it for some time4 ,after washing by decantation several times the carbonate was transferred to a funnel containing a porcelain filter-plate1 covered with a piece of ashless filter paper of slightly larger diameter1 and washed thoroughly4 with water4 ,it was then transferred to a platinum dish1 care being taken to avoid contamination with filter paper and heated gently to convert it into oxide4 ,the resulting oxide was powdered in an agate mortar1 returned to the platinum dish and heated to incipient whiteness for seven hours in a muffle furnace4 ,the temperature must not be too high1 otherwise the oxide will distill readily leaving no residue4 ,the oxide is slightly volatile at good red heat as was observed in trying to make a determinant at this temperature by the oxide method4 ,a weighed portion of the oxide which had been prepared from the carbonate in the manner described was dissolved in a weighed porcelain crucible and the resulting nitrate converted into the oxide again by heat just as in the oxide method4 ,this constitutes experiment ,i4 ,experiments two and three were made in exactly the same way except that a platinum crucible was used instead of a porcelain one4 ,the results are3 ,initial ,wt4 ,final ,wt4 ,gain ,corresponding ,error in ,at4 ,wt4 ,i4 #b4iedfi #b4iefej 4#jjjha 4#bd ,,ii4 #b4fggag #b4fghce 4#jjaag 4#ci ,,iii4 #c4jjbie #c4jjdbb 4#jjabg 4#ch ,as we started with cadmium oxide1 and1 after passing to the nitrate1 converted it back into the oxide1 the weight should remain unchanged if the method is correct4 ,however1 this is not the case1 but a large increase in weight takes place4 ,the increase is larger in a platinum crucible than in a porcelain one1 which accounts for the fact that a lower value for the atomic weight is found by the oxide method when they are used4 ,the use of a porcelain crucible therefore diminishes the error1 but does not eliminate it4 ,the explanation of this has already been given4 ,the oxides obtained in these three experiments were tested for occluded gases in the manner already described1 but only small amounts were found4 ,both of those made in platinum crucibles were tested for nitrate of cadmium with brucine and sulphuric acid with negative results4 ,to show that the impurity was not converted into an ammonium salt when the oxide was dissolved in hydrochloric acid1 a slight excess of caustic potash was added to the solution1 the precipitate allowed to subside and the clean1 supernatant liquid tested for ammonia with ,nessler's reagent4 ,no ammonia was found4 ,in order to make these experiments as severe a test as possible1 a somewhat higher temperature was employed than had in the five experiments described under the oxide method4 ,this was accomplished by boring out the stopcocks of the blast lamp so that a larger supply of gas was furnished4 ,the two oxides in the platinum crucibles seemed to be constant in weight1 but that in the porcelain crucible seemed to lose in weight slowly4 ,the weight given was taken after four hours blasting1 which is longer and at a higher temperature than was used in any of the five determinations made by the oxide method4 ,if the cadmium oxide prepared from the carbonate retained any carbon dioxide1 it would lose weight in being dissolved and reconverted into oxide4 ,the above experiments therefore seem to furnish very strong evidence that there is an error of at least 4#bd unit in the oxide method when porcelain crucibles are used and 4#ci of a unit when platinum ones are employed4 if 4#bd of a unit is added to #aab4jg the result obtained when porcelain crucibles are used we get #aab4ca and adding 4#ci to #aaa4hg gives #aab4bf4 ,considering the small number of experiments made1 the fact that they were made in such a way as to give a low value 7numerically7 for the error rather than a high one1 and also that the error is probably variable to some extent1 especially when porcelain crucibles are used1 the corrected results agree as closely with #aab4ch1 the average of the chloride1 bromide and sulphate 7synthetical7 methods as could be expected4 ,it must also be borne in mind that #aab4ch is only to be regarded as an approximation to the atomic weight of cadmium4 ,the increase in weight observed in converting the nitrate back into oxide might also be explained by assuming that the cadmium oxide used in the beginning of the experiments was richer in metal than the formula ,cd,o indicated and that the increase in weight is due to this excess of metal being changed to oxide4 ,the method of preparation of the oxide from the carbonate and the known properties of cadmium oxide render this view highly improbable1 and the following two observations render it untenable3 #ast4 ,if this were the cause of the increase1 the amount of increase would necessarily be the same in both platinum and porcelain crucibles1 which is not the case4 ,illustration #bnd4 ,three grammes of cadmium oxide made from the carbonate were dissolved in dilute hydrochloric acid from which the air had been expelled by boiling4 ,the oxide1 which is very compact1 was placed in a glass bulb which had been blown at the end of a tube4 ,after displacing the air by filling the entire apparatus with recently boiled water1 the exit of the tube was placed under boiling dilute hydrochloric acid1 and the bulb heated until the water boiled4 ,it was then turned over so that the steam displaced nearly all the water4 ,on removing the flame the dilute hydrochloric acid at once filled the bulb4 ,the exit tube was then quickly placed under a narrow tube filled with mercury and inverted over mercury in a dish4 ,the bulb was then heated until the oxide had dissolved4 ,by this method the gas would be boiled out of the solution and collected in the top of the narrow tube4 ,as only a very small amount of steam and dilute hydrochloric acid go over at the same time1 there is no danger of the gas formed being absorbed to any considerable extent4 ,it is well to put the oxide into the bulb before the tube is bend4 ,if the hydrochloric acid is too strong1 it must be cooled before entering the bulb as otherwise the reaction is too violent1 and the experiment may be lost4 ,this experiment shows that there is no excess of cadmium present in the oxide employed for no gas was found4 ,if three grammes of the oxide contained enough metal to take up 4#jjabf grms4 of oxygen1 4#jjjaf grms of hydrogen should have been set free1 and its volume under ordinary conditions of temperature and pressure would have been about #a4i cubic centimetres4 ,this experiment would also have shown the presence of carbon dioxide if any had been present4 ,discussion of the ,oxalate ,method4 ,after having done the work which has just been described1 we are in a position to turn to the oxalate method1 which is the first method described in this paper4 ,it involves the decomposition of cadmium nitrate1 and is therefore affected by an error from this source1 only it is not as large as in case of the oxide method4 ,if #b4iefej grammes of cadmium oxide prepared in a porcelain crucible contain 4#jjjha grammes of impurity1 an error of 4#bd of a unit would be introduced in the atomic weight as determined by the oxide method or 4#aj in case the oxalate method were employed4 ,that is the oxalate should give about #aab4dh for the atomic weight of cadmium1 but it really gives a very much lower result4 ,morse and ,jones obtained #aab4jd 4#jce by it1 while ,partridge obtained #aaa4ha 4#jce by it4 ,if we take #aab4ch for the atomic weight of cadmium1 there appears to be a second error of 4#dd of a unit in the method as used by ,morse and ,jones1 while ,partridge's result indicates an error of 4#eg of a unit4 ,partridge only moistened the oxide obtained from the oxalate with a few drops of nitric acid before making the final heating1 and it seems probable therefore that he made no appreciable error on account of the final oxide retaining products of decomposition from cadmium nitrate4 ,the most probable cause of this large error seems probably to be incomplete dehydration of the oxalate1 or reduction to metal during the decomposition of the oxalate1 and subsequent volatilization of some of it1 or a combination of both of these4 ,the nine determinations given in the earlier part of this paper of course vary so much that they are of no value whatever in determining the atomic weight4 ,the reason that the first four are low is probably due in part to sublimation of cadmium1 for on dissolving the resulting oxide in nitric acid a considerable quantity of metal was noticed in each case4 ,in the others1 the temperature was kept lower1 and the decomposition took a longer time4 ,no metal was observed on taking up in nitric acid4 ,to be certain of what the cause of error is would require some very carefully conducted experiments1 but as there are a number of much more reliable methods for determining the atomic weight of cadmium1 it does not seem desirable to spend the time required in making them4 ,it should be mentioned that ,lenssen1 in #ahfj1 first employed this method4 ,he made three determinations4 #a4efig grms of cadmium oxalate giving #a4jjdg grammes of oxide1 which gives a value of #aab4jdc for the atomic weight of cadmium 4 ,the difference between the highest and lowest determination was 4#cia of a unit4 ,other ,methods ,a great deal of time was spent in trying to effect a partial synthesis of cadmium bromide in exactly the same manner as had been used in case of cadmium sulphate4 ,no results were obtained because cadmium bromide is slowly volatile at #aej;,c1 the temperature used1 and retained some hydrobromic acid ever after more than #ajj hours of drying4 ,some work was done in trying to establish the ratio between silver and ,cadmium by dropping a weighed piece of cadmium into a solution of silver sulphate1 the reaction being3 ,cd ,ag#b,,so#d ,cd,s,o#d #b;,ag ,silver nitrate cannot be used because it becomes reduced to nitrate even at a temperature of #j;,c41 as was shown by its reducing action on potassium permanganate1 and by the reaction with meta-diamido benzene after the reaction had been completed4 ,the main difficulty with the method is that air must be excluded in order to prevent oxidation and solution of some of the precipitated silver4 ,the silver is perfectly free from cadmium if an excess of silver sulphate is used and the precipitated metal digested with it for some time4 ,since this part of the work was done1 a paper by ,mylius and ,fromm 7,ber4 #ahid1 #fcj7 appeared in which one of the reactions studied was that of cadmium on silver sulphate4 ,they also found the resulting silver free from cadmium4 ,the method seems very promising1 but the work had to be discontinued for lack of time4 ,conclusion4 ,i4 ,the work on the oxalate and sulphide methods described in this paper is of no value for determining the atomic weight of cadmium4 ,it does not even enable us to fix an approximate value4 ,,ii4 ,there are a number of errors in the chloride and bromide methods as they were used in this work1 but they are not very large and partially compensate each other4 ,their results1 #aab4chc and #aab4cif respectively1 may be regarded as approximations to the true value4 ,,iii4 ,the synthesis of cadmium sulphate as carried out is of especial value in fixing a minimum value for the atomic weight of cadmium4 ,the result is #aab4ce1 agreeing closely with that obtained by the bromide and chloride methods4 ,,iv4 ,there is an error in the oxide method due to products of decomposition of the nitrate being retained4 ,direct experiments gave 4#ci of a unit for this when platinum crucibles were used and 4#bd of a unit when porcelain ones were used4 ,the calculated errors for porcelain and platinum crucibles are 4#cj and 4#ea of a unit respectively1 if #aab4ch is assumed as the atomic weight of ,cadmium4 ,v4 ,the average of the chloride1 bromide1 and sulphate methods is #aab4ch4 ,this result is to be regarded as tentative and not as final since the main object of this work has been to find the cause of the discrepancy in some methods employed in determining this constant1 rather than to make an atomic weight determination4 ,biographical ,sketch4 ,john ,emery ,bucher was born near ,hanover1 ,pa41 ,august #ag1 #ahgb4 ,he entered ,lehigh ,university in #ahhh and graduated in #ahia4 ,during the past three years he has been a graduate student in the ,johns ,hopkins ,university4 ,subjects3 ,chemistry1 ,mineralogy and ,mathematics4 ---------------------------------------- -------------------------------- ,,transcriber',s ,,notes #a4 ,silently corrected obvious typographical errors and variations in spelling4 #b4 ,retained archaic1 non-standard1 and uncertain spellings as printed4 #c4 ,enclosed underlined font in underscores4 #d4 ,denoted subscripts by an underscore before a series of subscripted characters enclosed in curly braces1 e4g4 ,h#b,o4