CLAIMS Ot LAVOISIER. 257 



be done, we must, I fear, look in vain for any thing like a 

 complete theory of combustion. 



But whilst some substances, as sulphurated hydrogen, are The theoiy ef 

 found to possess acid properties, though they contain no oxigen ; ^^u ^^ ^f ' 

 and many inflammable and metallic bodies unite with oxigen acidification, 

 during combustion, and yet have nothing of the character of ^^ '"^^ 

 an acid ; we must either deny that oxigen is universally tl^e 

 acidifying principle, or that the ordhiary characters by Avhich 

 acids are distinguished are arbitrary and false. " If we lay it 

 *' down as an axiom that oxigen is the acidifying principle, Ave 

 *^ must either include among acids a great number of bodies 

 *' which have not the smallest resemblance to those substances 

 " which are at present reckoned acids, or exclude from thj5 

 ^' class several bodies, which have the properties of acids in 

 *' perfection. The class of acids being perfectly arbitriary, 

 *' there cannot be such a thing as an acidifying principle in the 

 " most extensive sense of the word."* But ifthe acidifying prin- 

 ciple be unknown, it must be held premature in M. Lavoisier 

 to claim the discovery of the theory of acidification ; and his 

 merits, therefore, in this case will consist not in forming a just 

 and general theory, but in improving and extending our know- 

 ledge of the facts from which, perhaps, a true theory may 

 hisreafter be deduced, 



I have sometimes thought, that it might be well to indulge The new no- 

 M. Lavoisier and his associates in their present unqualified ^^JJ^I^*"''®^^^^ 

 claims to the theories of modern chemistry, and of physiology caused various 

 founded on chemical principles, from a conviction that the rjes^to^be^ad^' • 

 duration of these theories Will be temporary only, and that mitted with- 

 many parts of them ere long will undergo a complete revolu- gxaiBination 

 tion ; and that, therefore, with the fall of the theories, the 

 claim.s would necessarily cease. It is the introduction of the 

 new nomenclature that has chiefly supported these claims; 

 and their authors seem to have imagined that by giving a 7iew 

 name they established a right to the thing which it was meant 

 to designate. But as if to expose and punish their injustice and 

 presumption, later discoveries are daily proving their theories 

 are false and insufficient, and reducing their new names to mere 

 arbitraiy terms, lititle better, in some respects, than those which 

 they supplanted. Oxigen is not proved to be the acidifying 



* Thon^on, ii. 5, edit. 1» 



prin= 



