Remarks on the Theory of Compound Salt Radicals. 55 



pable of combining in more than one proportion ? Why have we 

 not such compounds as M+2P0 6 , M + 3P0 6 , M-{-5P0 6 , 2M-f- 

 7P0 6 , 2M + 5P0 7 , 2M + 7P0 7) 3M+3P0 3 , 3M-f 5P0 3 , corres- 

 ponding to M+2CI, M+3C1, M + 5C1, M 3 +7C1, M 2 +7F? The 

 instances of such agreement brought forward by Graham in re- 

 gard to the oxysulphion S0 4 , and cited in the last paragraph, go 

 but a very little way toward establishing the complete parallelism 

 asserted to exist between the two classes of compounds. No at- 

 tempt is made by either Graham or Kane to carry out this as- 

 sumption in the case of the bibasic and tribasic salt-radicals. 



9. No simple substance whatever, whether amphigen or halo- 

 gen, can be said to be either monobasic, bibasic, or tribasic. An 

 amphigen or halogen body combines with but one or at most 

 two equivalents of an electro-positive radical or basyle, and there 

 is no such thing as assigning a fixed number of electro-positive 

 atoms to any of the simple electro-negative ions. 



10. It seems to have escaped notice that the phosphorous acid 

 is tribasic as well as the phosphoric. This being the case, the 

 formula of a phosphite P0 3 +3MO becomes on the new view 

 P0 6 + 3M. But that of a monobasic phosphate is also, on the 

 same view, P0 6 +M. Consequently the oxyphosphion P0 6 is 

 both monobasic and tribasic ; is not this at least as incomprehen- 

 sible as that phosphoric acid should by some change in its mole- 

 cular structure, perhaps by the doubling or trebling of its atomic 

 weight, become capable of combining with one, two, or three 

 atoms of base? Recourse must either be had to the doctrine of 

 isomerism, and it must be considered that there are two oxyphos- 

 phions each of which has the formula P0 6 but of which one is 

 monobasic and the other tribasic, or else the very same difficulty 

 presents itself upon the new view which was formerly urged 

 against the old. But it should be remembered that if such an 

 explanation be admitted in the case of the salt-radical P0 6 , it 

 must, be equally good in the case of the acid P0 5 , and we may 

 assume that there are three isomeric phosphoric acids respectively 

 capable of combining with one, two, or three atoms of base. 



12. The admirable researches of Graham on the constitution 

 of salts, have demonstrated that one oxysalt enters into com- 

 bination with another only by a replacement of its constitu- 

 tional water. Thus the double sulphate of zinc and potassa 

 (ZuO,S0 3 4-KO,SO. ( )-f-6Aq is formed from common sulphate of 

 zinc, (ZnO.S0 3 -f-HO)-f6Aq by the substitution of an atom of 



