332 Prof. H. Rose on the Isomeric Modifications 



tion*. Even the silver salt contains some, although a small 

 quantity of soda. Persoz and Fleitmann have also procured 

 and examined insoluble double salts of the pyrophosphate of 

 soda with the pyrophosphate of copper. 



The following are the special reactions of a solution of 

 pyrophosphate of soda with salts of the metallic oxides : — 



Solution o^ chloride of barium produces a precipitate, which 

 is insoluble in excess of the soda salt; at least the filtered 

 liquid either yields no precipitate, or at most a very slight 

 troubling with dilute sulphuric acid. 



Solution o^ chloride of calcium produces a precipitate, which 

 is soluble in a very large quantity of the pyrophosphate of soda. 

 The clear liquid however becomes spontaneously turbid when 

 set aside, and in 24 hours a very slight precipitate only of 

 oxalate of lime is caused by a solution of oxalate of potash. 



Solution of sulphate of magnesia produces a precipitate, 

 which is soluble in excess of the pyrophosphate of soda ; but 

 on ebullition a copious precipitate is produced in this solution, 

 which does not disappear as the liquid cools. Ammonia 

 does not cause a precipitate in a solution of the pyrophosphate 

 of magnesia in pyrophosphate of soda, even when set aside for 

 a long time. The precipitate of the pyrophosphate of mag- 

 nesia is also readily soluble in excess of sulphate of magnesia. 

 Ebullition causes a precipitate in this solution, which does not 

 disappear on cooling. 



Solution o^ nitrate of silver produces the well-known white 

 precipitate. It is not wholly insoluble in a very large excess of 

 the pyrophosphate of soda. The supernatant liquid does not 

 affect litmus paper, and only renders it blue when excess of 

 the soda salt has been added. 



Sol ution of pernitrate of mercury , although it necessarily 

 contains free nitric acid, produces a copious white precipitate, 

 which becomes basic and of a reddish-yellow colour on the 

 addition of excess of the pyrophosphate of soda. 



Solution of the protonitrate of mercury produces a white 

 precipitate, which is soluble in excess of the pyrophosphate of 

 soda. In this solution, ammonia causes a blackish gray, sul- 

 phuret of ammonium a black, and hydrochloric acid a white 

 precipitate ; the latter consists of chloride of mercury. 



Solution oi bichloride of mercury does not immediately pro- 

 duce any precipitate. After a considerable time, a dense red 

 precipitate is formed, which is still more rapidly thrown down 

 when heat is applied. 



Solution oi sulphate of copper produces a bluish-white pre- 

 cipitate, which is readily soluble in excess of the pyro- 

 * PoggendoriTs Anncden, vol. Ixxv. p. 152. 



