322 Prof, H. Rose on the Isomeric Modifications 



phoric, pyrophosphoric, and ordinary phosphoric acid, which 

 withBerzelius we may denominate a-,6-, and c-phosphoric acid, 

 it is the metaphosphoric acid which especially exhibits the 

 greatest anomalies. The pyrophosphoric acid also presents 

 some ; and the ordinary phosphoric acid, the c-phosphoric 

 acid, is that which has most analogy with other oxy-acids in 

 its behaviour towards reagents. This is the one which can be 

 best separated and determined quantitatively. Fortunately 

 the other modifications can be more or less easily converted 

 into the c-phosphoric acid ; hence in their quantitative deter- 

 mination this conversion must in most cases be previously 

 effected. 



I shall now make some remarks upon each of these three 

 modifications of phosphoric acid. 



a-Phosphoric Acid {Metaphosphoric Acid). 



For the purpose of elucidating to a certain extent, if only 

 for the present, the chaos of anomalous phaenomena which 

 this acid exhibits, we are compelled to admit the existence of 

 several submodifications of it : at least three of these are 

 now distinguishable. 



1. One of these submodifications consists of the acid exist- 

 ing in Graham's metaphosphate of soda, which is obtained by 

 fusing the acid phosphate of soda with the phosphate of soda 

 and ammonia (microcosmic salt). After fusion, the mass 

 must be cooled rapidly, and not slowly. The solution of this 

 salt, as is well known, possesses a neutral or very slightly acid 

 reaction, and is especially characterized by giving precipitates 

 with neutral solutions of several salts of the earths and me- 

 tallic oxides, which are generally soluble in an excess of the 

 salt of soda, and possess the remarkable property of forming 

 a heavy, thick, oleaginous mass when shaken. The solution 

 of the salt alone does not yield any precipitate with a dilute 

 filtered solution of albumen, but a copious dense precipitate 

 immediately appears on the addition of acetic acid. 



The following are the special reactions of a solution of the 

 metaphosphate of soda : — 



Chloride of barium produces a voluminous precipitate, the 

 supernatant liquid reddening litmus-paper; it is entirely so- 

 luble in excess of the salt of soda; ammonia does not produce 

 a precipitate in this solution. The precipitate is not oleagi- 

 nous, nor does it become so, either when set aside for some 

 time, or on ebullition. 



Chloride of calcium produces a voluminous precipitate, which 

 on agitation, even in the cold, collects at the bottom of the 

 vessel in the form of a thick, oily or turpentine-like mass. 



