82 MOLECULAR WEIGHT OF ARGENTIC SULPHATE, ETC. 



surface, at intervals of about 1 minute, by grasping the exit end with 

 platinum forceps. The agitation can be performed without danger of loss, 

 because of the high surface tension of fused argentic chloride. This mate- 

 rial when liquefied does not adhere to quartz, and therefore is not drawn 

 into the end tubes by capillarity. At the expiration of 20 minutes the 

 current of acid gas was stopped by means of the stopcock (K), and a cur- 

 rent of pure dry air was passed through the tube through L, the argentic 

 chloride being still maintained in the liquid state for at least 5 minutes 

 with occasional agitation. The tube was rotated while subsequently cool- 

 ing in a similar manner to that employed with the sulphate. 



The condensed sulphuric acid evolved by the reaction and the condenser 

 tube were tested for silver by means of the nephelometer. 1 The acid was 

 transferred to a small flask and the tube was rinsed with ammonia, which 

 was added to the acid. The excess of ammonia was then neutralized with 

 nitric acid, and hydrochloric acid was added to precipitate any trace of 

 silver present as an opalescent cloud of argentic chloride. This opalescence 

 was compared in the nephelometer with a standard which had been made 

 in a manner very similar to the unknown solution. 2 A measured volume of 

 a standard silver solution was taken ; to it were added approximately the 

 same amounts of sulphuric acid, ammonia, and nitric and hydrochloric 

 acids as were present in the unknown solution ; and it was made up to the 

 same volume (about 30 ml.). 



The greatest amount of argentic chloride thus found in any experiment 

 was 0.00009 gram and the average amount 0.0000-1 gram. The trace 

 found in this way was of course added to the weight of the silver chloride. 

 In three of the experiments (Nos. 4, 5, and 7) this determination was not 

 made, but the average amount is added in these cases. The probable rea- 

 son for the escape of this trace of silver will be discussed later. 



The question as to whether or not this reaction is complete is, of course, 

 of fundamental importance. There are four pieces of evidence bearing 

 on this point. 



In the first place, the argentic chloride was fused for twenty minutes in 

 a current of almost pure hydrochloric acid. Since the temperature was 

 far above the boiling-point of sulphuric acid, this product of the reaction 

 was driven off as fast as formed. Therefore according to the law of 

 concentration-effect it is to be expected that through the agency of the 

 continually renewed hydrochloric acid all the argentic sulphate would be 

 decomposed and all the sulphuric acid would be driven off. This would 

 be hastened by the fact that fresh surfaces were continually exposed 

 through agitation. 



iRichards and Wells, Amer. Chem. Jour., 31, 235 (1904), 

 2 Richards, Amer. Chem. Jour., 35, 510 (1906), 



