﻿Dynamical Ideas in Chemistry. 467 



different ; and Laurent, Graham, and Brodie have successively- 

 contributed (each from his own point of view) to the furtherance 

 of the idea of polarity. 



One result of these dynamical doctrines has been, that we have 

 now current among us a tolerably pure idea of a salt — as a sub- 

 stance prone to double decomposition. The term base (now 

 including the ancient alkali) is admitted on all sides to in- 

 volve an idea complementary to that of acid. This last word is 

 still under discussion. According to the prevailing definition, 

 an acid is a salt of hydrogen ; according to "Professor Williamson 

 it is what was called by Gerhardt an anhydride. Neither of 

 these is in accordance with the criterion ; for they both agree in 

 calling acid something particular. Now if we really mean to 

 assign to acids properties which are opposite to those of bases, it 

 follows that hydric sulphate and hydric acetate are, with sul- 

 phuric teroxide and diacetylic oxide, equally acids. Thus, in 

 the equations 



KHO + H 2 SO 4 = KH SO 4 + H 2 0, 



KHO + SO 3 = KHS0 4 , 



KHO + C 2 H 4 O 2 = KC 2 H 3 O 2 + H 2 0, 



KHO + (C 2 H 3 0) 2 = KC 2 H 3 O 2 + HC 2 H 3 2 , 



the four bodies indicated are alike antagonistic to hydropotassic 

 oxide. Again, the reactions 



As 2 3 + 6HCl=3H 2 + 2AsCl 3 

 and 



As 2 O 3 + 2KH0 = H 2 + K 2 As O 4 



prove either (1) that arsenious oxide is both a base and an acid, 

 or (2) that hydric chloride and hydropotassic oxide are both acids 

 or both bases. Such are the contradictions which must neces- 

 sarily ensue as long as we attempt to carry out in practice a sta- 

 tical definition on a dynamical understanding. 



The value of the idea of motion as a criterion in chemical 

 theory has, I trust, been indicated in the preceding paper. As 

 a criterion, however, it really has a far wider usefulness than I 

 have here assigned it ; for it throws light into every branch of 

 knowledge. Several advanced problems (more especially in 

 ethics) yield remarkable results on its application, and I intend 

 to take an early opportunity of again referring to its efficacy. 



