Existence of Compound Radicals in Amphide Salts. 61 



Old theory. New theory. 



Monobasic acid, PO s +HO P0 6 +H 



Bibasicacid, PCM+2HO P0 7 +H 2 



Tribasic acid, PO+3HO P0 8 +H 3 



u Now it appears very useless, where the older view accounts so 

 simply for the properties and constitutions of these salts, to adopt 

 so violent an idea, as that there are three distinct compounds of 

 phosphorus and oxygen which no chemist has ever been able to 

 detect. But here again other circumstances must be studied; 

 first, the difference of properties of phosphoric acid, in its three 

 states, is totally inexplicable, on the idea of their being merely 

 three degrees of hydration. Nitric acid forms three hydrates, 

 but when neutralized by potash, it always gives the same salt- 

 petre ; sulphuric acid forms two perfectly definite hydrates, but 

 with soda forms always the same glauber's salt ; whilst phos- 

 phoric acid, when neutralized by soda, gives a different kind of 

 salt according to the state it may be in. Also, the permanence 

 of these conditions of phosphoric acid is a powerful proof that 

 they do not consist in the adhesion of mere water. The idea 

 that the phosphoric acid is a different hydracid in each of its 

 three conditions, on the other hand, not merely explains the fact 

 of these differences of properties, but it renders the formation of 

 bibasic and tribasic salts, which is such an anomaly on the old 

 theory, a necessary consequence of the new, for the phosphoric 

 salt radicals, PO 6 , PO 7 , and PO 8 , differ not merely in the quan- 

 tity of oxygen they contain, but are combined with different 

 quantities of hydrogen, and hence in acting on metallic oxides 

 (bases), there is a different number of atoms required for each to 

 replace the hydrogen and form water. Thus — 

 PO.H and NaO give HO and PO".Na. monobasic phos. of soda, 

 P0 7 .H 2 and 2NaO give 2HO and P0 7 .Na 2 . bibasic phosphate, 

 P0 8 .H 3 and 3NaO give 3HO and P0 8 .Na 3 . tribasic phosphate. 

 A circumstance which gives additional reason to infer that the 

 water is not merely as base in the phosphoric acid, is the follow- 

 ing : if it were so, then it should be most completely expelled 

 by the strongest bases, and the bibasic and tribasic phosphates of 

 the alkalies should be those least likely to retain any portion of 

 the basic water; but the reverse is the fact; whilst oxide of 

 silver, a very weak base, is that which most easily and totally 

 replaces the water. On the idea, however, of hydracids, this is 



