THE ANALYSIS OF CADMIUM CHLORIDE. 7 



methods, have found that silver prepared in the above fashion is at least as 

 pure as any/ Since the buttons of silver obtained from the fusion in hydrogen 

 were of very considerable size, they were cut into fragments of from i to 5 gm. 

 by means of a clean steel chisel and anvil. A sHght surface contamination with 

 iron was removed by etching the fragments several times with dilute nitric 

 acid, until the acid remained free from iron, and drying them at 200°. 



Two different samples, purified in the same way, were employed. One was 

 prepared especially for this investigation and was used in analyses 4, 5, 6, and 

 14. The other was a portion of the material employed in an investigation upon 

 the atomic weight of iodine by one of us " (analyses 7, 8, and 9). Still a third 

 specimen of silver, used in analyses 13 and 15, was twice deposited electrolyt- 

 ically before the final fusion in hydrogen. 



Water was purified by double distillation through tin condensers, first from 

 alkaline permanganate solution, finally with a trace of sulphuric acid. Con- 

 nection between the flasks and the condensers was made by constricting the 

 necks of the flasks to fit the ends of the condenser tubes, avoiding thus the use 

 of rubber and cork.^ 



Nitric acid was twice distilled with a platinum condenser, the first third being 

 rejected in both distillations. The product of the first distillation contained 

 only the merest trace of chlorine. 



PREPARATION OF THE CADMIUM CHLORIDE FOR THE PRELIMINARY 



ANALYSES. 



The method of analysis differed little from that used in the analysis of other 

 halogen salts in atomic weight investigations in this laboratory. The cadmium 

 chloride was freed from ammonium chloride by fusion. Then, after solution in 

 water, the chlorine content was found either gravimetrically as silver chloride 

 or by titration against weighed amounts of silver. 



The apparatus used for the expulsion of the ammonium chloride from the 

 double salt was similar to that employed for a hke purpose by Richards and 

 Parker* in their analysis of magnesium chloride. Since this apparatus was 

 used in two other researches described in this collection, a detailed description 

 is given here. Hydrochloric-acid gas was generated by the action of concen- 

 trated sulphuric acid upon concentrated hydrochloric acid in the flask A (fig. i), 

 and, after bubbling through concentrated hydrochloric-acid solution in the 

 wash bottle B, it was dried by passing through four towers about 30 cm. long 

 and 4 cm. in diameter filled with glass beads saturated with concentrated sul- 

 phuric acid, C, D, E, F. In the first series of experiments the hydrochloric-acid 



* Loc. cit. 



^ Baxter: Proc. Amer. Acad., 40, 419 (1904); Jour. Amer. Chem. Soc, 26, 1577; Zeit. 

 anorg. Chem., 43, 14 (1905). (See page 92.) 



3 Richards: Proc. Amer. Acad., iO,^^o{i2>g^); Zeit. anorg. Chem. ,S, 261 (iSgs). 



* Proc. Amer. Acad., 32, 59 (1896); Zeit. anorg. Chem., 13, 85 (1897). 



