of Phosphoric Acid. 335 



undecomposed portion of the lime-salt does not therefore be- 

 come converted into the c-phosphoric acid. With the appli- 

 cation of a high temperature, the conversion can be better 

 effected in this manner in the case of the pyrophosphate of 

 strontia, and still better of the pyrophosphate of baryta; 

 pyrophosphate of magnesia may be completely decomposed, 

 and the pyrophosphoric acid contained in it completely con- 

 verted into c-phosphoric acid, even by fusion over a spirit- 

 lamp with a mixture of carbonate of potash and carbonate of 

 soda in atomic proportions. 



It is well known that the conversion of pyrophosphoric acid 

 is perfectly effected by acids, especially when it is heated with 

 them. The stronger the acid, the more completely the con- 

 version is effected ; it succeeds best when concentrated sul- 

 phuric acid is used. 



An aqueous solution of pyrophosphoric acid, immediately 

 after its preparation, exhibits the following reactions : — 



Solution oi chloride of barium produces no precipitate; after 

 a long time a very inconsiderable troubling occurs. A pre- 

 cipitate is produced in the liquid by ammonia. 



Solution of chloride of calcium produces no precipitate, even 

 after long repose. Ammonia causes a precipitate, although it 

 is not very copious. Lime-water immediately causes a pre- 

 cipitate, even when the solution is slightly acid ; if however 

 excess of pyrophosphoric acid is added, the precipitate is re- 

 dissolved ; ammonia does not then cause a precipitate in this 

 solution. 



If chloride of ammonium be added to pyrophosphoric acid, 

 and it then be supersaturated with ammonia, solution of sul- 

 phate of magnesia produces a precipitate, which is however 

 soluble in a very large quantity of water. If a solution of 

 c-phosphate of soda be added to this liquid, a precipitate is im- 

 mediately thrown down. 



Solution of nitrate of silver usually causes no precipitate. 

 On saturation with ammonia, a white precipitate is produced, 

 which, if the solution of pyrophosphoric acid has stood for 

 some time, is of a yellowish tint. Solution of acetate of silver 

 produces a white precipitate, which is soluble in a large quan- 

 tity of pyrophosphoric acid. 



A dilute filtered solution of albumen causes no precipitate. 

 It is a remarkable fact, that even in the last edition of 

 'Qev'/.eXms^sLehrbiichy he ascribes to pyrophosphoric acid the 

 property of precipitating albumen, and thus distinguishes 

 it from the c-phosphoric acid. Also, according to his state- 

 ment, solutions of the pyrophosphates after the addition of 

 acetic acid precipitate albumen. It is however a very cha- 



