154 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



poise tube, one stop-cock of each tube being open during the weighing. 

 Before being weighed both tubes were wiped with a damp cloth and 

 allowed to stand near the balance for at least thirty minutes. 

 The following table gives the results of these experiments : 



The amount of water evolved is hardly greater than the probable 

 error in weighing the phosphorus pentoxide tubes, and is less than the 

 probable error in determining the amount of silver in the salt. We 

 are therefore justified in concluding that the material which was used 

 for the determinatiQn of silver was essentially free from water and that 

 no correction need be applied to the results for inefficient drying. 



This result also furnishes evidence that the samples are free from 

 acid phosphates, which, owing to conversion into pyro- or metaphos- 

 phate, would evolve water when fused, although it is possible that 

 occluded acid phosphates might have been converted into pyro- or 

 metaphosphates during the drying. Sample O, which was prepared 

 under conditions most favorable for the formation of the acid silver 

 phosphate, does not appear to contain more water than Sample P, 

 which was prepared under conditions which were unfavorable to the 

 formation of acid phosphate. Since these two samples, which differed 

 most widely in their method of preparation, showed no difference in 

 the amount of water retained, it seemed unnecessary to test the other 

 samples also. Unfortunately this method of detecting acid phosphate 

 is not very sensitive, owing to the unfavorable relation of the atomic 

 weights involved, — one molecule of water corresponding to a deficiency 

 of two atoms of silver. 



