116 On the Polymerization of the Metallic Oxides. 



Phosphoric acid, on the contrary, is equivalent to three 

 different acids, the heats of neutralization of the three basicities 

 of the acid by the same metal being unequal. 



H 3 P0 4 + NaHO = 14-68 cals. 

 + 2NaHO = 26-33 „ 

 + 3NaHO = 33-59 „ 



The substitution of hydrogen by sodium thus causes suc- 

 cessively the evolution of 14*68, 11*65, and 7*26 cals. As 

 regards two of its hydroxyls, orthophosphoric acid is strongly 

 acid, though unequally, the one having an acidity similar to 

 that of hydrochloric or nitric acid, and the other to carbonic 

 acid ; whilst the third hydroxyl is more like that of an alcohol 

 or phenol. 



The action of heat on phosphoric acid is really the action of 

 heat on an acid-alcohol, and ought therefore to exhibit phe- 

 nomena similar to those observed in the case of lactic acid. 

 These phenomena ought even to be more complicated, because 

 for one molecule of PO(OH) 3 acting as an alcohol there is 

 another molecule acting as an acid, and can function by one 

 or other of its hydroxyls, which are not only acid, but un- 

 equally acid. 



The formation of pyrophosphoric acid seems to be perfectly 

 analogous to that of phosphogly eerie acid, thus : — 



(HO) 2 PO . . PO(OH) 2 (H0) 2 . C 3 H 5 . . PO(OH) 2 . 



Two isomers, however, appear possible. Besides the three 

 hydroxyls of phosphoric acid having a different chemical 

 value, it follows that the products of the phosphoric etherifi- 

 cation, from the partial dehydration of H 3 P0 4 , ought to be 

 very numerous and complicated. Our present knowledge of 

 the action of heat on this acid is therefore very superficial. 



Can we refer the condensation of the metallic poly hydroxyls 

 under the action of heat to the same cause — i. e. to a difference 

 in the nature and value of the several hydroxyls ? It seems 

 natural and logical to do so, but it is difficult to find sufficient 

 authority. 



Phosphoryl being a multiple radical, formed of hetero- 

 geneous atoms, one can rigorously account for the fact that 

 the three hydroxyls, which arQ grouped around it, are un- 

 equally placed as regards these elements, and can therefore 

 have different values. But to conclude that the different 

 hydroxyls attached to the same polyvalent atom, such as Si, 

 Sn, &c, have not the same value, it would be necessary to 

 assume that the polyvalent atoms are not identical at all 



