154 HISTORY OF CHEMISTRY. [LECTOR?: IX. 



(as base), both water atoms are driven off, and a hitherto 

 unknown salt, sodium metaphosphate, is produced. The acid 

 contained in this salt is characterised by being saturated by 

 one atom of base, whilst, in the free state, it contains one atom 

 of water. The silver compound was again different from either 

 of the others. In this case the ratio of the quantities of oxygen 

 in base and acid was as i to 5. 



Finally, it was shown in the investigation, that meta- and 

 pyrophosphoric acids, as well as the majority of their salts, 

 pass into ordinary phosphoric acid or a salt derived from it, 

 when boiled with water, or still better, when fused with sodium 

 carbonate. 



Two important theoretical conclusions can be directly de- 

 duced from Graham's investigation. 



(i.) In acids there is a certain number of atoms of water, 

 and salts are formed by the replacement of these. 



(2.) The atoms of the acids are not always equal in number 

 to the atoms of the bases, and in some, the ratio is even 

 variable. Thus Graham showed how, from the same phos- 

 phoric anhydride, to prepare three hydrates which were able to 

 take up quite different quantities of base. 



Liebig, in 1838, stated these conclusions with great clear- 

 ness and precision. 8 A man of his genius could not, however, 

 rest satisfied with publishing thoughts that were merely conclu- 

 sions drawn from the experiments of others. We are indebted 

 to Liebig for an excellent investigation of a series of organic 

 acids, from which it appeared that phosphoric acid does not 

 stand alone with respect to its behaviour towards bases, but 

 that in the cases of certain other acids, one atom likewise pos- 

 sesses the property of saturating several atoms of base. Found- 

 ing, as he did, upon a broader basis, he was then able to 

 introduce the idea of the polybasic acids. 



Liebig's experimental investigation embraces fulminic, 

 cyanic, meconic, comenic, tartaric, malic citric, and other acids. 

 He finds relations amongst the salts of each of these acids, 



8 Annalen. 26, 113 ; compare Comptes Rendus. 5, 863. 



