THE CONVERSION OF ARGENTIC SULPHATE INTO CHLORIDE. 85 



used. in cleaning it, or carried into the end tube by the current of sulphur 

 trioxide before fusion. As soon as the hydrochloric acid was admitted and 

 the end tubes heated, these small invisible crystals of silver sulphate must 

 have been at once converted into chloride and sublimed to the cooler por- 

 tion of the tube - - for the end tubes were usually raised to a red heat. This 

 explanation is consistent with the frequent absence of any significant sub- 

 limate, especially in the case of experiment 15. In this experiment the 

 tube had been dusted and treated with particular care, in order to test the 

 point. 



Because the sublimate was weighed in the tube which had previously 

 contained the sulphate, its presence could not affect the accuracy of the 

 results even if it had been weighable. Nevertheless the suggestion that 

 another portion might have been carried out of the tube was worth con- 

 sidering. Doubts on this point were set at rest by the analysis of the con- 

 tents of the condenser tube which received the volatile products of the 

 reaction. The average amount of silver found in this tube was less than 

 0.001 per cent of that taken in each experiment, and the small appropriate 

 correction was easily applied. 



Although it was not probable that argentic chloride which had been 

 fused in air for five minutes still retained any dissolved hydrochloric acid, 

 this point also was tested. In experiment 13, the silver chloride after the 

 first heating in hydrochloric acid and fusion in air for five minutes as 

 usual, weighed 4.74491 grams. After the second fusion in hydrochloric 

 acid, and finally in air, the weight was 4.74489 grams. After another 

 fusion for twenty minutes in a current of pure air, the weight was 4.74493 

 grams. These slight changes in weight can only be ascribed to errors in 

 the weighing ; the outcome shows that the argentic chloride after the usual 

 treatment did not retain any dissolved hydrochloric acid. Richard and 

 Wells have already shown that it does not dissolve weighable amounts 

 of air. 1 



In still another case the outside of the tube was washed with water to 

 make sure that nothing had deposited on it during the long exposure to 

 the flame and acid. The loss in weight was only 0.02 mg., which again is 

 not greater than the possible error in weighing. 



1 Richards and Wells, loc. cit, p. 60. 



