SALTS 



} atom phosphoric acid 3-5 

 1 atom soda . 4- 



12 atoms water 13-5 



21-0 



8 * Biphosphate of soda. I formed this salt 

 by mixing together solutions of 210 grains of 

 phosphate of soda and 78 '75 grains of phosphate 

 of ammonia. The solution was evaporated to 

 dryness, and the dry mass exposed to a red heat 

 to drive off the whole of the ammonia. By this 

 process it is obvious, that the salt contained just 

 2 atoms of phosphoric acid united to 1 atom of 

 soda. The salt is very difficult to crystallize ; 

 it usually concretes into a thick mass when eva- 

 porated ; it is only by spontaneous evaporation 

 that crystals can be got, and the quantity must 

 be considerable otherwise no crystals can be pro- 

 cured. I did not succeed in procuring crystals 

 in the vacuum of the air pump. 



This salt has an acid and saline taste, reddens 

 vegetable blues, and is usually crystallized in 

 four-sided prisms terminated by four-sided pyra- 

 mids. The inclinations of the faces of the prisms 

 are to each other, according to Mitcherlich's 

 measurement, 78 30' and 101 30'. He considers 

 the primary form to be a rectangular octahe- 

 dron. 



From the method of forming this salt, it is ob- 

 vious that its constituents are 2 atoms of acid 



