THE SYNTHESIS OF ARGENTIC NITRATE. 



53 



When the nitrate was wholly solid but still hot, the flask with its con- 

 tents was transferred to its support of platinum wire in a large, tight 

 desiccator, which was wrapped in a black cloth and left near the bal- 

 ance over night. Then the weight of the flask was determined as before. 

 Thus in the entire cycle of operations nothing but platinum, clean glass, 

 and pure air touched the outside of the flask. 



It remains to be proved that no silver was carried out by the air cur- 

 rent. This was inferred because no trace of silver was ever found in the 

 U-tube through which all the vapors passed; but more definite evidence 

 was obtained by redissolving two finished determinations, and evaporat- 

 ing them again with the customary precautions. 



The first residue in the case of No. 15 was slightly darkened by pro- 

 longed heating ; still no fixed tendency toward either loss or gain is shown 

 by these figures, and the reliability of the method is demonstrated. 



Two preliminary experiments were not finished, and one was rejected 

 because of known error. Six preliminary determinations carried out in 

 the way just described gave results varying from 157.483 to 157.475 

 parts of nitrate from 100.000 parts of silver, in the mean 157.479. This 

 is very nearly the same as the final series, given later, but because 

 of sundry irregularities these determinations are individually much less 

 trustworthy than the latter. One of the preliminary determinations was 

 made with a piece of silver kindly given us by Professor Baxter for 

 the sake of comparison, and for which we are much indebted. It gave 

 a result perhaps higher than the average, but not by an amount greater 

 than the limit of error of the experimentation at that time. It is greatly 

 to be regretted that this piece was not examined after every detail of the 

 process had been perfected, because the comparison would have been in- 

 teresting, although not at all essential for the completeness of our work. 



When it appeared impossible to improve upon the details of the experi- 

 mentation, a final series of six consecutive determinations was carried 

 out with all possible care. In each case, except Nos. 14 and 15, the argen- 

 tic nitrate was maintained for an hour in a fused condition while dry air 

 swept over it. In No. 14 only one-quarter of an hour was allowed, 

 whereas in No. 15 the fusion was prolonged for three hours. Sample D 



