LECTURE IX.] HISTORY OF CHEMISTRY. 155 



which are similar to those in the case of phosphoric acid. But 

 he endeavours, especially, to range the three cyanogen acids, 

 i.e. cyanic, fulminic, 9 and cyanuric, side by side with the three 

 phosphoric acids. In the former, as well as in the latter, there 

 is present, according to him, a group of atoms which has the 

 power of saturating sometimes one, sometimes two, sometimes 

 three atoms of base. But whilst the atomic weight is not 

 altered in the case of the phosphoric acids, it increases in that 

 of the cyanogen acids in the same ratio as the saturating 

 capacity, so that the resulting salts are polymeric with one 

 another. In the latter case, the quotient obtained by dividing 

 the quantity of oxygen in the acid by that in the base, remains 

 unchanged, whereas this, according to Graham, is not the case 

 with the varieties of phosphoric acid. 

 Liebig writes : 



3MO.P 2 O 5 Phosphate. 3MO Cy 6 O 3 Cyanurate. 



2MO.P 2 O 5 Pyrophosphate. 2 MO Cy 4 O 2 Fulminate. 



MO.P 2 O 5 Metaphosphate. MO Cy 2 O Cyanate. 



Of distinctly greater importance are the considerations 

 which lead Liebig to propose a separation from the other 

 acids, of those which behave in a way analogous to phosphoric 

 acid. The course of his argument in this matter is approxi- 

 mately as follows : The relations are not so complicated in 

 the cases of all the acids which share with phosphoric acid the 

 characteristic property of neutralising several atoms of base by 

 One atom of acid, as they are in the case of phosphoric acid 

 itself; and hence it is not so easy to establish in all cases that 

 they belong to this category. In the case of phosphoric acid, 

 no matter what number may be chosen as its atomic weight, it 

 can never be shown that one atom of acid saturates one atom 

 of base in all three modifications. 10 What, now, are the 

 characteristics that enable us to recognise that we have to do 

 with a substance belonging to this group ? 



9 Liebig assigns to fulminic acid the formula 2rLO.Cy 4 O 2 [H = i, 

 C=I2, 0=16]. 10 Here, as in the foregoing, the word acid is to be 

 understood as referring to the anhydride. 



