Dr. E. J. Mills on Chemical Substance and Chemical Functions, 259 



why the mean temperature of the southern hemisphere is so 

 much lower than that of the northern . 



We shall now proceed to consider the objections which have 

 been urged against the theory that ocean-currents are due to the 

 impulse of the trade-winds. 



[To be continued.] 



Erratum. 



In Part I. of this paper, vol. xxxix. p. 89, 8th line from bottom, 

 for 9-83 read 9-08. 



XXX. On Statical and Dynamical Ideas in Chemistry. — Part II. 

 Chemical Substance and Chemical Functions, By Edmund J. 

 Mills, D.Sc* 



IN the preceding Part the history of the ideas connected with 

 acid, alkali (base), and salt was concisely stated, and it was 

 shown that while, on the one hand, those ideas are erroneous and 

 self-contradictory when they designate something particular, so, 

 on the other hand, the most consistent and general theory that 

 has been stated with respect to them is that of Avogadro, who is 

 their modern expounder in the sense of chemical polarity. These 

 results were in harmony with the idea of motion, the criterion 

 adopted in these papers. The practical result is that there is no 

 such thing as an acid, base, or salt, though the use of the adjec- 

 tives and qualitative nouns derived from these terms might pro- 

 bably be successfully defended. If any one deny this conclusion 

 he is bound to give a satisfactory definition of an acid, for ex- 

 ample — a task in which, as history clearly shows, success is un- 

 likely to accrue. 



Having thus pointed out the value of the idea of motion in 

 the concrete sphere of external chemistry, I may now penetrate, 

 or perhaps ascend, to the remoter regions of Chemical Substance 

 and Chemical Functions, where the service of the same idea will 

 prove available. 



1 . Chemical Substance. 



We are accustomed, in the language of everyday chemistry, to 

 say that such and such bodies or substances undergo certain 

 operations; sulphur, hydric nitrate, aniline, &c. are spoken of as 

 bodies or substances indifferently. In recording the facts of an 

 analysis (even of a mechanical mixture), it is customary to say 

 that so much substance contained or furnished so much of a pro- 

 duct ; and this product may be volatile matter or organic matter, 

 which, in its turn, may become substance for analysis. A che- 



* Communicated by the Author. For Part I. see Phil. Mag. 1869, 

 vol. xxxvii. p. 461. 



