328 Prof. H. Rose on the Isomeric Modifications 



The various sub-modifications of metaphosphoric acid all 

 agree in having the same capacity of saturation ; one atom of 

 acid saturates one atom of a powerful base. Graham supposes 

 that the different capacity of saturation of the various modifi- 

 cations of phosphoric acid is the cause of their different reac- 

 tions. This difference in the capacity of saturation of the 

 various phosphoric acids, however, is indisputably a result of 

 their isomeric state, and, as I have remarked on a former 

 occasion, cannot be the cause of them*. 



A second general property of all the varieties of metaphos- 

 phoric acid is, that their aqueous solutions precipitate a solu- 

 tion of albumen. This is almost the only property by which 

 the various kinds of metaphosphoric acid can be recognised in 

 qualitative examinations, and unequivocally distinguished from 

 the other modifications of phosphoric acid ; for neither pyro- 

 phosphoric acid nor the ordinary c-acid precipitates albumen. 

 The soluble salts of metaphosphoric acid do not precipitate 

 albumen until acetic acid has been added to their solutions. 



The property of metaphosphoric acid to produce a copious 

 precipitate in the solution of chloride of barium is especially 

 peculiar to the acid produced by the combustion of phosphorus 

 only. 



When a concentrated solution of c-phosphoric acid is heated 

 very gently for several hours, so that none of it volatilizes, an 

 acid is obtained, the aqueous solution of which does not pro- 

 duce any precipitate with albumen; nor does it produce a 

 precipitate with chloride of barium, or merely an inconsider- 

 able troubling after a long time. Nitrate of silver however 

 produces a white precipitate. These are the properties of 

 pyrophosphoric acid. When the same acid is heated in a 

 platinum crucible longer and more strongly, so that it com- 

 mences to be copiously volatilized, its aqueous solution then 

 immediately produces a copious precipitate with albumen and 

 chloride of barium, and a white precipitate with nitrate of 

 silver, which when shaken becomes resinous. Thus by strongly 

 heating it, metaphosphoric acid is formed, and apparently the 

 same modification as that obtained by the combustion of phos- 

 phorus. 



. By the rapid application of a certain degree of heat, how- 

 ever, an acid can be obtained, the aqueous solution of which 

 affords with albumen a copious piecipitate, but none with chlo- 

 ride of barium, andwhich, after saturation with ammonia, yields 

 a white precipitate with nitrate of silver, in which, after some 

 time, an admixture of yellow can be distinctly perceived. In 

 this case, the same acid as that which 1 separated from the 

 * Chem. Gaz. vol. vi. p. 383. 



