dSil Royal Institution, 



the result was attained is even more important than the result itself, 

 and has led to our drawing from that result a conclusion different 

 from that which was generally expected. Chemistry aims at dis- 

 covering the nature of that action by which substances of opposite 

 properties undergo those remarkable changes which we call che- 

 mical combination ; and it naturally follows from this view of its 

 objects, that chemical science is more advanced by the discovery of 

 a new process than by the discovery of a new substance ; and its 

 theories are more immediately affected by the nature of a process 

 of change than by any physical fact, such as the existence of a pe- 

 culiar body or class of bodies. Thus it is that the method of iso- 

 lating the anhydrous organic acids has afforded evidence of a new 

 view of the constitution of acids and salts. 



A few words may serve to give an idea of the previous state of 

 the question. 



Compounds of oxygen acids were supposed to consist of the an- 

 hydrous acid united with an oxide. Thus hydrated sulphuric acid 

 was represented as containing the anhydrous group SO^ plus an 

 atom of water, H* O ; and in the saturation of this hydrated acid by 

 a base such as potash, it was conceived that this oxide replaced the 

 water. The existence of anhydrous sulphuric acid in an isolated 

 state, and the fact that it so readily combines with water, was urged 

 as an argument in favour of this theory ; and the same holds good 

 with phosphoric, carbonic, sulphurous, lactic, nitrous, and even 

 (according to the recent discovery of Dessaignes) nitric acid. 



However simple this view might appear, and however satisfactory 

 it might be in explaining those cases of combination for which it 

 was specially intended, chemists soon became acquainted with bodies 

 perfectly analogous in their general properties to the oxygen acids, 

 and producing by their action upon bases similar effects, but which, 

 from the fact of their containing no oxygen, could not possibly be 

 conceived as made up of water and an anhydrous acid. For instance, 

 hydrochloric acid was proved, both analytically and synthetically, 

 to be composed of nothing but chlorine and hydrogen ; and when 

 it combines with potash, the hydrogen is found to leave the chlo- 

 rine, whilst potassium takes its place. 



Being desirous of simplifying as far as possible their views of these 

 phaenomena, and of extending the same explanation to all like cases, 

 certain chemists were led to imagine a new mode of representing 

 the constitution and reactions of oxygen acids, which had the ad- 

 vantage of connecting the two classes of analogous reactions by the 

 same theory. This consisted in conceiving, that in the formation 

 of a hydrated acid, a compound radical is produced in combination 

 with hydrogen; so that hydrated sulphuric acid is the hydrogen 

 compound of SO*, in the same way as hydrochloric acid is the hy- 

 drogen compound of chlorine. There were many arguments in 

 favour of this view, amongst which the most prominent was derived 

 from the fact, that when a salt of the one class, as chloride of potas- 

 sium, decomposes a salt of the other, as sulphate of silver, the result 

 is exactly in conformity with what must occur on the supposition of 



