THE PURITY OF THE FUSED ARGENTIC NITRATE. 61 



Attention was now directed to other foreign substances besides water 

 and air which might be present in the synthetic argentic nitrate. Further 

 careful investigation was needed to show that all the silver was combined 

 as nitrate and that no other impurities were concealed in the salt. The 

 pure pearly whiteness of the cold fused material precluded the possibility 

 of there having been a trace of reduction to metallic silver. The salt was 

 soluble in pure water without residue or turbidity, and maintained its 

 clearness when diluted to half or quarter normal ; hence oxide and halogen 

 salts must have been absent. The only other likely impurity seemed to be 

 ammonium salts, nitrite, and excess of nitric acid. Of these possibilities, 

 Stas thought only of the likelihood of the presence of free acid ; but each 

 was carefully considered in the present work. 



It is known that copper dissolving in nitric acid forms perceptible quan- 

 tities of ammonic nitrate. Apparently, no similar reaction has been noted 

 with silver, and from an electrochemical standpoint it seemed unlikely; 

 moreover, ammonic nitrate if present would probably be for the most part 

 decomposed by the hour's fusion of the silver salt. Nevertheless, thor- 

 oughness demanded evidence on this point. Nessler solution is the most 

 convenient for this test, but silver must first be precipitated from solution 

 in the dark. Light generates chlorine which interferes with the test. 



In order to prepare for this search for ammonia, the synthetic nitrate 

 of silver resulting from several experiments was shaken with a slight ex- 

 cess of standard pure sodic chloride until the supernatant liquid was clear ; 

 the latter was decanted, made up to 50 cc., and placed in a comparison 

 cylinder. The sodic chloride gave no test with Nessler solution. 



The cylinder full of liquid prepared from the argentic nitrate was finally 

 tested by comparison with other cylinders containing known traces of am- 

 monic nitrate mixed with sodic nitrate in concentration equal to that exist- 

 ing in the actual determination. The sodic nitrate had been several times 

 recrystallized with centrifugal draining, and was shown to be free from 

 ammonia. In this way the following results were attained : Synthesis 12 

 was found to contain 0.05 mg. of ammonic nitrate, synthesis 13, 0.06 mg., 

 and synthesis 14, 0.05 mg. ; in all, 36.5 grams of argentic nitrate were 

 proved to contain no more than 0.00016 gram 1 of ammonic nitrate less 

 than one two-thousandth of 1 per cent. The source of this ammonia was 

 not determined ; it might have come from the reduction of nitric acid or 

 from the large volume of air used in evaporating the argentic nitrate. 

 The only possible place where it could have entered with the reagents 

 used in the test was in the sodic chloride solution ; this was indeed tested, 

 with negative results, but Nessler's reagent is not very sensitive in the 

 presence of chloride, and a trace of ammonia might have eluded detection. 

 If the amount found had been larger, more time would have been spent 

 upon the matter, and a sample of the argentic nitrate often recrystallized 



