﻿Dynamical Ideas in Chemistry. 465 



In the year 1809 Avogadro published a most remarkable me- 

 moir, entitled " Idees sur l'Acidite et l'Alkalinite"*, which ap- 

 pears to have hitherto almost escaped the attention of chemists ; 

 yet it embraces, with marvellous skill and simplicity, the whole 

 of this interesting question. After pointing out the well-known 

 difficulties which stood in the way of the oxygen theory of acids, 

 he shows that the idea of acidity involves two factors — namely, an 

 antagonist force (reciprocated by alkalies), and a great tendency 

 to unite with bodies in general. The latter seems to depend 

 chiefly on a certain state of aggregation, which may either allow 

 full play to the former or almost entirely prevent its action ; 

 hence this state of aggregation is not a cause, but the condition 

 of acidity. " Such being the case, all the phenomena are easily 

 explained if we consider acid and alkaline antagonism as purely 

 relative properties, only becoming somewhat absolute when re- 

 ferred to a middle term fixed arbitrarily in the scale of acidity 

 and alkalinity ; so that the same substance A which, with refer- 

 ence to B, has the acid antagonism, may possess the alkaline 

 antagonism with reference to a third substance, C ; whence what 

 we term absolutely acids and alkalies are merely bodies which 

 have the acid or alkaline antagonism in respect of certain others 

 whose position in the scale is approximately indicated by certain 

 properties, such as inability to affect vegetable blues, though 

 their state of aggregation be suitable for the purpose/' The 

 degree of acidity or alkalinity of a compound depends on the 

 degree of those properties in its constituents. Thus considered, 

 " of two substances in the act of combination, one always plays the 

 part of acid and the other of alkali; and it is this antagonism 

 which constitutes tendency to combination, or affinity properly 

 so called." 



Bodies might thus be arranged in a series, the position of each 

 marking its true affinity to any successor. Oxygen and sulphur 

 would probably come first, and the neutral salts in the middle ; 

 while hydrogen, carbon, and the like would occupy the other 

 extremity. The measure of chemical antagonism is electric he- 

 terogeneousness ; its appropriate name is oxygenicity\. Oxygen 

 is the most oxygenic of bodies ; and a substance is evidently 

 more oxygenic the less it is oxidizable. Avogadro concludes by 

 recommending (as Professor Foster did subsequently) the disuse 

 of the word acid, on account of its representing, as commonly 

 received, a merely accidental property. It will suffice, he 

 thinks, to employ the nomenclature of oxides (e. g. higher or 



* Joam. de Pliys. p. 142 et seq. 



f Electricity and electric are obviousfy the pattern words for oxygenicity 

 and oxygenic. Avogadro seems to have proposed the latter on account of 

 their reference to chemistry. 



