366 QUARTERLY JOURNAL. 



the name of Liebig is, moreover, associated Avith several of 

 most important theoretical speculations, among which may 

 mentioned the now prevalent views, originally started by the 

 gacious genius of Humphrey Davy, of the true nature of at 

 and of salts ; accortling to which, acids, instead of being, as j 

 voisier supposed, invariably compounds of oxygen, are rat 

 compounds of hydrogen, the latter element being the true acidi 

 ing principle ; while salts are compounds in which the hydro{ 

 of the acids has been replaced by metals. The doctrine of pc 

 basic acids, that is, of acids requiring more than one equivalenl 

 alkali to neutralize them, and the neutralizing power of which 

 measured by the proportion of replaceable hydrogen they conts 

 owes its development entirely to Liebig j and the same may' 

 said of his profound and beautiful views on the process of : 

 mentation, putrefaction, and decay. Were I asked to point 

 a good example of Liebig's researches, without particular re} 

 ence to agriculture, I would select; out of many equally valual 

 his researches on aldehyde and on the origin of acetic acid, 

 all know that no fermented alcoholic liquor can be produced 

 cept from the vinous fermentation of sugar ; and also that all : 

 mented liquors, under certain circumstances, are changed i 

 vinegar, or, in common language, undergo the acetous fermei 

 tion ; in more exact terms, the alcohol they contain is convei 

 into acetic acid. Now, if we compare the composition of ao 

 acid with that of alcohol, we find that the former contains less ': 

 drogen and more oxygen than the latter. It was therefore nei 

 sary to study the action of oxygen on alcohol ; and Liebig, pui 

 ing some observations of Doebereiner, soon found that this act 

 constituted two stages. In the first, oxygen removes part of 

 hydrogen of the alcohol, forming with it water, and leaving al 

 hyde, a pungent volatile neutral liquid ; and in the second, an 

 ditional quantity of oxygen combines with the aldehyde, convert 

 it into acetic acid. This discovery at once cleared up the wl 

 theory of the formation of vinegar from alcohol, put an enc 

 the fancy of acetous fermentation, the process being one sim 

 of oxidation ; and, by detecting the source of loss in the pro( 

 followed abroad for obtaining vinegar from brandy, (which i 

 shown to be the escape of aldehyde unoxidised from a defici 

 supply of oxygen,) enabled the manufacturer to improve { 

 economise his process. (Loud cheers ) ]3ut if I were cal 

 upon to selct, out of the ideas suggested by Liebig in agric 

 tural chemistry, those which do him the greatest honor, < 

 which have added^ and will add, most to our knowledge, I kn 

 not that I could do better than refer to his doctrine of 

 uses of the phosphates and of the alkalies in plants and animi 

 (Cheers. What is the use of the phosphates ? of those s 

 stances which are never absent in a fertile soil : and which, ac 



