260 Dr. E. J. Mills on Chemical Substance 



mical substance, however, is always understood to mean an object 

 that is chemically homogeneous in its own class. But the name 

 is refused to a mechanical mixture ; and I have often heard it 

 stated, in that sense, "this is not a chemical substance/' or, 

 more curtly, "this is not a substance." Chemical body and 

 chemical matter are phrases that seldom occur, even in a parti- 

 cular signification. On the whole it appears that " substance," 

 considered as a chemical term, 'is used in two ways : — (1) as a 

 loose expression*, synonymous with " body " or " matter," them- 

 selves being then loose expressions ; but more especially (2) as 

 indicating a specific scientific distinction. This latter employ- 

 ment is worthy of attentive examination. 



The elder chemistry, possessing few known objects for expe- 

 riment, had regarded more their fundamental unity than their* 

 individual diverseness. Then, as at the present day, but few 

 chemists were cultivators of philosophy, so that the general pre- 

 valence of that philosophical regard was rather an accident than 

 a merit. Indeed it can often be traced, almost with certainty, to 

 a belief in the primitive unity of human races, and the tree of life 

 in the midst of the garden, doctrines whose origin is known not 

 to have been philosophical. In modern times more definiteness 

 has permeated the idea of substance. Qualitative analytical me- 

 thods, gradually increasing in precaution and refinement, were 

 able to demonstrate when a substance was pure; quantitative 

 processes followed with tardy corroboration. From the latter 

 sprang the law of definite proportions discovered by Higgins 

 and Dalton, with its immediate consequence — the theory of che- 

 mical composition. In this manner an a priori control was ac- 

 quired over quantitative analysis f. Constancy in composition 

 was regarded as a proof of purity, and purity was inevitably 

 attended with constancy in composition. Such was the first 

 precise notion of a chemical substance. "Peculiar earths" 

 might be discovered, and "peculiar elements" afterwards pre- 

 pared from them ; and so long as the latter were accounted as 

 being merely means to an end (composition, namely), the no- 

 tion of constancy could be universally maintained. 



But what of the means themselves? Were the elements com- 

 pound or absolutely simple ? The prevalent tendency has been 

 to affirm the latter alternative. Mercuric sulphide, for example, 

 can be made by the direct addition of mercury to sulphur; but 

 it did not appear that any two substances, on being placed in 

 contact, produce sulphur. The polar theory, it is true, has re- 

 presented sulphur and other elements as intrinsically dual, like 



* Thus Naquet, Principes de Chimie, first edition, p. 1, says, "Ce qui 

 constitue les corps s'appelle matiere ou substance." 

 t Compare Dalton, ' New System/ p. 213. 



