Modifying the force of Chemical Attraction. 241 



no influence in any case. The probability is, that hke the 

 attraction which it is supposed to modify, (and which, pow- 

 erful as it is well known to be between oxygen and the bases 

 of the alkalies, becomes evanescent in the case of carbon 

 and the metals,) its influence varies through the whole range 

 of chemical agents, and that it sometimes produces no effect 

 whatever. But unless we will abandon the fundamental 

 maxim of the Baconian philosophy — that our opinions are 

 to follow in the track of observation and experiment, it ap- 

 pears to me that we must admit it to be a law of extensive 

 application, that the quantity of matter modifies the force of 

 chemical attraction^ so as often to compensate for a weak af- 

 finity : and having admitted it, apply it in the explanation 

 of the fact, that in the manufacture of nitric acid, it is of 

 advantage to employ more sulphuric acid than is barely suf- 

 ficient to neutralize the potash of the nitre ; and other cor- 

 responding cases, without resorting to the intricate and 

 roundabout hypothesis of Bergman. 



The principal obstacle to the general reception of these 

 views, seems to have been found in their supposed inconsist- 

 ency with the truth of the doctrine of definite proportions 

 and the atomic theory, though it would be difficult to show 

 that they are absolutely incompatible. Thus with regard to 

 Berthollet's first experiment with potassa and sulphate of 

 baryta, instead of supposing with him, that the sulphuric 

 acid detached from the baryta, combines in the first instance 

 with all the potassa, and that the existence of the sulphate, 

 with definite proportions, is determined by the force of cohe- 

 sion, we may hold, (if it be safe to hold any opinion about 

 the mode of existence of the chemical elements in a solu- 

 tion,) that there are in the boiling liquid, four different sub- 

 stances, sulphate of baryta, sulphate of potassa, baryta and 

 potassa ; the influence of the uncombined baryta, being ex- 

 erted to prevent the decomposition of the sulphate of baryta 

 from proceding any farther, and that of the uncombined po- 

 tassa to maintain in existence the sulphate of potassa that 

 has been already formed. 



I will, in closing, only call the attention of any reader of 

 the Journal, who may have had the patience to accompanv 

 me thus far, to the following extract from the preface to 

 Thomson's First Principles of Chemistry. 



" But it is much more difficuh to obtain substances in a 

 state of complete purity, than chemists in general are aware : 

 Vol. XVI.— No. 2. 4 



