Mr Clark on a Nezo Phosphate of Soda. 31 1 



merely because it bears upon the subject of this notice ; for, 

 unfortunately the habit to which I refer is by no means pecu- 

 liar to the eminent Professor. But the reader will probably 

 agree with me in considering his experiment of more value 

 than his inference ; and that the arseniate of soda, contains, 

 like the phosphate, 25 and not 24 proportions of water. 



Dr Thomson has published two examinations of the arse- 

 niate of soda ; one in the fifteenth volume of the Annals of' Phi- 

 losophy^ and another in his First Principles. The water in the 

 one examination differs from the water in the other by not 

 less than 14 parts in the 100 of crystals. The reason is that 

 he used in one case the arseniate with 25 proportions of wa- 

 ter ; and in the other, the arseniate with 15 proportions of 

 water. 



The arseniate which is of the same crystalline form with 

 phosphate of soda, and which contains 25 proportions of wa- 

 ter becomes speedily dim from loss of water, while the other 

 does not. I propose that the one with the 25 proportions of 

 water be called the Efflorescing arseniate of soda, and that the 

 other be called simply the Arseniate of soda. 



The proportions of water in the pyrophosphate, the phos- 

 phate and the arseniates of soda, which we have been considering 

 are 10, 15, 25. It is not imworthy of observation that these 

 proportions contain, twice, thrice, and five times, the oxygen 

 in the acid of the salts. 



August iSth, 1827. 



Art. XIX. — On a New Phosphate of Soda. By Mr Thomas 

 Clark, Lecturer on Chemistry and Mechanics in the Glasgow 

 Mechanics' Institution. Communicated by the Author. 



Professor Mitscherlich having found that the crystalline 

 arseniates and phosphates, when they contained the same water 

 of crystallization, were identical in their forms, I was curious to 

 try whether a phosphate of soda could be produced, corresponds 

 ing, in its form and water of crystallization, with the arseniate of 

 soda, mentioned in the last paper, as containing 15 proportions 

 of water. Aware of the effect of a warm temperature on so- 

 lutions of the sulphate dnd carbonate of soda, in producing 



