+02 Mr. Graham's Reply to Mr. Phillips's 



There is, I suppose, only one phosphoric acid, an integrant 

 particle of which may be represented as consisting of 



One atom of phosphorus 392*3 



Five atoms of oxygen 500 



892-3 



and of which the formula is P. But this acid is capable of 

 combining intimately with water in three different propor- 

 tions, viz. one atom of acid, with one, two and three atoms of 

 water respectively; and each of these hydrates is capable of 

 dissolving in a large quantity of water without change. Now 

 solutions of these hydrates possess respectively the properties 

 of metaphosphoric, pyrophosphoric and common phosphoric 

 acids. Hence, if we retain these names (and any immediate 

 change in the nomenclature of the phosphates, however faulty 

 it may be, is of doubtful propriety,) the acids are composed 

 as follows : 



When these acid hydrates are treated with alkali, the whole 

 combined water does not follow the acid into the salt formed, 

 and cause the differences between metaphosphates, pyrophos- 

 phates and phosphates, as might, perhaps, be expected. The 

 water in these hydrates discharges the function of a base to 

 the acid, and, on the addition of an alkali, is displaced by an 

 equivalent quantity of the stronger base. Thus, when we 



treat a solution of common phosphoric acid (H 3 P ) with 

 caustic soda, the three atoms of water are displaced by three 



atoms of soda, and a salt results, of which the formula is N s P. 



When pyrophosphoric acid (H 3 P ) is treated in the same way, 

 the two atoms of water are replaced by two atoms of soda, and 



no more, and the salt N 3 P results. Sometimes, however, the 

 water in the acid hydrate is only partially displaced, as when 



we treat H'P with carbonate of soda; then only two of the 

 three atoms of water are supplanted by soda, and a salt is 

 formed consisting of two atoms of soda, one water and one 



