142 CHEMICAL PROPERTIES AND COMPOSITION 



formation of negative ions due to substitution of chlorine, 

 that is, with the increase in dissociation constant of the 

 substituted acetic acids. But it is plain that other factors, 

 hitherto quite unknown, have to be considered, for the 

 introduction of oxygen, which exerts a negative influence 

 fairly generally, i. e. causes or increases acidity, converts, 

 on the contrary, formic acid into the weaker carbonic acid. 

 This residue of facts that cannot be brought under the two 

 main headings is most evident in the cases where a par- 

 ticular atomic group causes chemical properties that cannot 

 even distantly be expected from the atoms themselves and 

 their mutual influence. 



First, in this connexion, come the cases in which an 

 element brings new valencies into play. The best known 

 instance is that of the ammonium bases, which are com- 

 parable with potash, such as tetramethyl ammonium 

 hydroxide, (CH 3 ) 4 NOH, in which nitrogen appears with 

 a fourth and fifth valency. The similarity to potash, due 

 to the strongly positive character of the radicle, (CH 3 ) 4 N, 

 may be attributed to the positive influence of the methyl 

 groups, rich in hydrogen : the same may be said to explain 

 the similar behaviour of the phosphorus and arsenic deri- 

 vatives, and even the sulphonium bases such as trimethyl 

 sulphonium hydroxide, (CH 3 ) 3 SOH, are to be regarded from 

 the same point of view. 



This attempt at explanation fails, however, for diphenyl 

 iodonium hydroxide, (C 6 H 5 ) 2 IOH, also a strong base in 

 which also new valencies of iodine play a part : but they 

 are here exerted on phenyl, which otherwise always exerts 

 a negative influence, so that, in the words of the discoverer, 

 Victor Meyer *, it is astonishing that : 



1. Iodine should act as a base-forming element ; 



2. A compound which, beside hydroxyl, only contains the 

 otherwise negative radicles iodine and phenyl, should have 

 the properties of an alkaline base ; 



3. Phenyl, which does not form with nitrogen and 



1 Bert. Ber. 25. 506. 



