of Phosphoric. Acid, 327 



obtained in a crystalline state. According to Fleitmann, the 

 solution of the soda salt produces no precipitates with solu- 

 tions of nitrate of silver, nitrate of lead, chloride of barium, 

 chloride of calcium, chloride of strontium, sulphate of mag- 

 nesia, protosulphate of manganese, protosulphate of iron, the 

 sulphates of zinc, cobalt or nickel. In the solutions of the 

 proto- and pernitrates of mercury, the solution of the soda 

 salt at first produces no turbidity, but after a considerable 

 time a precipitate is formed. It also produces a precipitate 

 in a solution of acetate of lead. 



The solution of the soda salt, as also that of Graham's salt, 

 produces no precipitate with albumen i but this is the case 

 when acetic acid is added. According to Fleitmann, the acid 

 may be readily isolated from the solution of the crystallized 

 silver salt by a current of sulphuretted hydrogen. The solu- 

 tion of the free acid immediately produces a copious precipi- 

 tate with albumen. When saturated with carbonate of soda, 

 the original soda salt is again obtained ; and if its solution, 

 after neutralization with ammonia, is treated with nitrate of 

 silver, the crystallized silver salt can be procured from the 

 solution. 



3. The acid contained in those salts which were formerly 

 called acid phosphates and have long been known, may be 

 regarded as forming the third modification of metaphosphoric 

 acid. These salts have recently been examined by Maddreli*. 

 In obtaining them, Maddreli made use of salts of the most 

 different kinds — metallic chlorides, sulphates, nitrates, car- 

 bonates and chlorates, which were heated to + 600° F. 

 with free phosphoric acid. I shall presently show, that an 

 insoluble pyrophosphate, possessing similar properties to those 

 presented by Maddrell's metaphosphates, may be simulta- 

 neously formed. The heating with free phosphoric acid must 

 therefore be continued until a portion of the heated mass, 

 when removed, is found to precipitate a solution of albumen. 



The insoluble metaphosphates dissolve when heated with 

 concentrated sulphuric acid. According to Fleitmann, the 

 acid cannot be isolated, or at least only very imperfectly, by 

 transmitting a current of sulphuretted hydrogen through the 

 copper salt suspended in water. The decomposition of it is 

 best effected by treating the above salt with sulphuret of 

 sodium. A soluble soda salt is then obtained, which some- 

 what resembles Fleitmann 's metaphosphate of soda, but differs 

 from it in many respects, and can only be procured with half 

 its water of crystallization. 



* Phil. Mag., S. 3, vol. xxx. p. 322. 



