330 Prof. H. Rose on the Isomeric Modifications 



acid, giving rise to the numerous modifications of metaphos- 

 phoric acid. This conjunct per se probably alone possesses 

 the property of precipitating albumen, and thus this property 

 is communicated to all the varieties of metaphosphoric acid. 



b-Phosphoric Acid {Pp-ophosphoric Acid). 



At least two submodifications of this modification of phos- 

 phoric acid must also be admitted ; for there are two different 

 kinds of pyrophosphates. One of these consists of the well- 

 known pyrophosphate of soda, which is obtained by heating 

 the c-phosphate of soda, 2NaO, P^O^ HO, to redness, and 

 the salts which are formed from this soda salt by decomposi- 

 tion. The second variety is produced in the same manner as 

 Maddrell's insoluble metaphosphates, that is, by heating the 

 salts with excess of phosphoric acid, the heat not being so 

 great as to cause the production of metaphosphates. Thus 

 by treating nitrate of copper with phosphoric acid, a salt of 

 copper is formed which resembles the insoluble metaphospliate 

 of copper, especially as regards insolubility. But the acid 

 existing in it may be readily isolated by a current of sulphu- 

 retted hydrogen, and its aqueous solution possesses the same 

 properties as the solution of ordinary pyrophosphoric acid. 

 As this modification of the pyrophosphates has not been suffi- 

 ciently examined, a more detailed notice of it cannot now be 

 given. 



As is well known, the pyrophosphates are formed when the 

 c-phosphates, which contain two atoms of a fixed and one atom 

 of a volatile base (oxide of ammonium or water), are heated 

 to redness. The usual process is the conversion of the ordi- 

 nary phosphate of soda (2NaO, P^O^HO) into pyrophosphate 

 of soda {2NaO, P^O^). 



Graham ascribes the difference in the properties of the py- 

 rophosphates from the phosphates, to the difference in the 

 capacity of saturation of the two acids contained in the two 

 kinds of salts. It cannot be denied that pyrophosphoric 

 acid especially saturates two atoms of a base, and thus differs 

 characteristically from the c-phosphoric acid, which requires 

 three for its saturation. But I have remarked above that 

 this is a consequence of the isomerism of the two acids; hence 

 it must appear as not improbable, that an atom of water may 

 be expelled from the ordinary phosphate of soda without con- 

 verting it into a pyrophosphate. 



Some experiments which were made with this point in 

 view, have not however yielded a favourable result. The ordi- 

 nary phosphate of soda was exposed to a very gentle heat, so 

 that it still contained more than one atom of water ; 3*0635 



