t66 On the identity of Silex and Oxygen, 



elementary bodies is, I presume, too diffuse, in respect 

 to the number of subdivisions ; and many of the titles 

 employed might, with propriety, be expunged. But, 

 though there are many other imperfections in chemical 

 arrangement that require reform, T mean on this occasion 

 to confine the following observations to one article only 5 

 and shall endeavour to prove that, in this instance at least, 

 we should revise the list of simple substances, aS far as re^ 

 gards silex; which is still continued, I think, with great 

 impropriety, to rank as a species of earth. 



To include in any one genus both silex and the other 

 earths, as they are now called, seems extremely improper 

 and palpnbly erroneous; nor can this classification be sup- 

 ported by any reasonable argument whatever. The defini- 

 tions given frpm time to time, to distinguish an earth .from 

 any other elementary body, have never been sufficiently ex- 

 plicit, for they do not precisely exclude the alkalis : they 

 make a useless division under the name of alkaline earths; 

 and, as salifiable bases, an earth, a metal, an alkali, and 

 silex, may be said to range as fotir distinct species of the same 

 genus. -. t 



All earths are declared to be salifiable bases, snd this I 

 take to be the most essential clause in every definition; for, 

 generally speaking, the earths have a ready affinity for every 

 acid, even from the weakest, particularly the carbonic acid, 

 to the most powerful that exists. Indeed, as far as concerns 

 the combination with carbonic acid, with which the earths 

 form nearly insoluble compounds, this peculiar property 

 alone might have served to distinguish an earth from an al- 

 kali. Here, however, the principal force of the definition 

 fails, the exception to silex is decisive; there is nocarbonate 

 of silex; no nitrate, no sulphate, nor, in short, any other 

 salt, in which the acid is saturated by this simple element : 

 neither art nor nature ever produced a perfect neutro-saline 

 compound, in which silex could fairly be considered as a 

 real and independent base. 



To constitute a true salt, we know, there must not he less 

 than one acid and one base, reciprocally saturating each 

 other; and when the nmnber of either exceeds, and the 



salt 



