and Chemical Functions, 261 



mercuric sulphide; but inasmuch as it has excluded, by its own 

 fundamental condition, the existence in the free state of what (in 

 sulphur) would correspond to the mercury and sulphur of the 

 experiment, no chemist, probably, has ever considered the ele- 

 ments compound in the same sense as he has entertained that 

 consideration in respect of other bodies. Hence it is that con- 

 stancy of composition has been insensibly supplemented, perhaps 

 supplanted, by another idea of universal applicability, namely 

 that of homogeneousness. 



The definition that a chemical substance is that which is che- 

 mically homogeneous in its own class may become more intelli- 

 gible on illustration. Each element is, as has been stated, 

 esteemed homogeneous ; that is, the whole list of elementic dis- 

 criminants fails to show that it consists of more than one thing, 

 or that it can be made by putting two or more things together. 

 Each amine is homogeneous ; because the varied application of 

 aminic discriminants, such as potassic hydrate, hydric chloride, 

 platinic chloride, reveals one thing only. [An elementic discri- 

 minant such as an extremely high temperature, would of course 

 remove any amine from its own class.] The definition is evi- 

 dently in the main analytical. It moreover proves to be not 

 unjust when tested by the idea of motion. Eor in the idea of 

 homogeneousness there is no limit reserved ; while the process 

 and result of classification, depending partly on experiment, 

 partly on convenience, are confessedly destitute of finality and 

 absoluteness — indeed of any statical property. 



Whatever theory may have been proposed as to the nature of 

 substance in general, there does not appear to be any real ob- 

 stacle in adding thereto the idea of homogeneousness. Spinosa, 

 who defined substance as " that whose conception needs not the 

 conception of another thing as necessary to its formation," 

 Hobbes and Berkeley, whose subjective doctrine is well known, 

 and Leibnitz, who stated substance to be " a being capable of 

 action," have more in common than at first appears. I cannot find 

 on examination any thing in their views or tendency excluding 

 homogeneousness or even inconsistent with it. On the other 

 hand, the idea of homogeneousness is preeminently chemical, no 

 other science offering it so frequently, and none on so especially 

 inductive a basis. When, therefore, to our idea of substance in 

 general we add that of homogeneousness, we know what is che- 

 mical substance ; and no further supplement is necessary. 



The substantial in chemistry is, consequently, wholly unre- 

 lated to indivisibles ; and it cannot be known or determined by 

 theories of constitution or the canons of formulae. For many 

 years past chemists have been in the habit of using methods of 

 symbolic representation which, while they undoubtedly express 



