84 MOLECULAR WEIGHT OF AfcGENTIC SULPHATE, ETC. 



' 



chloride, the mass being translucent or almost opaque, instead of transpar- 

 ent. It was then fused in a current of hydrochloric acid for twenty minutes 

 after the sulphuric acid could no longer be seen escaping from the tube, as 

 before. On the assumption that the sulphate was converted completely 

 into chloride the loss in weight would have been 0.00039 gram, while the 

 actual loss in weight was 0.00044 gram. The reaction was evidently com- 

 plete, and a fourth argument was added to the other reasons for believ- 

 ing that the process should yield satisfactory results. 



It will be recalled that the narrow end tubes were kept very hot by small 

 stationary burners in order to prevent the condensation of sulphuric acid. 

 At the close of several of the experiments a very slight sublimate was 

 observed on the portion of the narrow tubes which was kept somewhat 

 cooler by the protection of the supporting hooks. This sublimate, although 

 never large in amount, appeared largest in experiments 6 and 10. There 

 was a smaller amount in experiments 7, 11, and 14, but none worthy of 

 consideration in experiments 4, 5, 12, 13, and 15. In experiments 10 and 

 14 a slight amount of the sublimate was visible in the condenser also, near 

 the end of the tube. 



Although the most rational explanation of this trace of sublimate, which 

 was usually too slight to be weighable, was probably to be found in the 

 assumption that it was argentic chloride and therefore entirely without sin- 

 ister meaning except as suggesting the risk of the loss of other traces, 

 the matter was studied further. Careful tests for arsenic 1 and copper were 

 made with negative results, and the hydrochloric acid was demonstrated 

 to contain no trace of anything which could be deposited in a red-hot 

 quartz tube. On the other hand, the sublimate was soluble in ammonia 

 and behaved in every way like argentic chloride, so that its nature was 

 considered as nearly proved as was possible with such a minute amount of 

 material. Having settled the nature of the sublimate, its source and signi- 

 ficance must be traced. Evidently it could not have come from the main 

 body of the silver sulphate, because it appeared at the very beginning of the 

 experiment, as soon as the current of hydrochloric acid was started and 

 the end tubes heated, before the heat was applied to the main body of the 

 argentic sulphate. Moreover, the mass of the argentic chloride was never 

 heated to a temperature high enough to volatilize weighable amounts of 

 this substance, as was shown by the constancy of weight on continued 

 heating in a current of gas. 2 



In view of these considerations, it seemed probable that a few invisible 

 crystals of argentic sulphate had been left in the end tubes by the feather 



1 This test was kindly made by Mr. O. F. Black. 



2 See the preceding description; also Richards and Wells, loc. cit., p. 60; Baxter, 

 Proc. Amer. Acad., 41, 83 (1905). 



