188 M. Chevreul on Fatly Bodies, and [Sept. 



margarine be presented to a heated solution of potash, contain- 

 ing a considerably larger proportion of alkali than was necessary 

 to convert it into the pearly matter, a more alkaline compound 

 would be formed. Upon making the trial, this was found to be 

 the case; by digesting in water a quantity of potash and marga- 

 rine, a white matter was formed, which was soluble in heated 

 alcohol, and was deposited from it as it cooled in the form of 

 small needles, which, when treated with muriatic acid, were 

 found to be composed of 100 parts of margarine, and 17*77 parts 

 of potash, or almost exactly double the proportion of potash in 

 the pearly matter described above. This compound of margarine 

 and potash is white, not so soft as the pearly matter, and 

 slightly alkaline to the taste ; it is decomposed by water, the 

 pearly matter being reproduced and the additional quantity of 

 potash separated. This decomposition, however, only takes 

 place when the quantity of water employed is large ; for if it be 

 used in small quantity, the decomposition is only partial, and a 

 thick transparent mucilage is formed. M. Chevreul regards this 

 as a saturated compound of the two substances. Margarine 

 decomposes the subcarbonate of potash, carbonic acid is disen- 

 gaged, and tiie pearly matter is formed. 



As it appears that margarine possesses some of the leading- 

 properties of acids, it becomes a question for consideration, how 

 far it is entitled to the denomination of an acid. It is necessary, 

 therefore, to determine what are the characters of acids ; and 

 M. Chevreul states the following as those which have been 

 generally considered to be essential ; the sour taste, their attrac- 

 tion to the positive galvanic pole, their neutralizing salifiable 

 bases, and their effect upon vegetable colours. The value of 

 these several characters, as indicative of acidity, is then dis- 

 cussed ; it is stated that the sour taste is not found in all acids, 

 that the attraction for the positive pole is not confined to acids, 

 and that the same is the case with the neutralization of alkalies ; 

 with respect to the effect of acids upon vegetable colours, that, 

 the reddening of litmus has been generally regarded as the most 

 characteristic property, and that no body which is considered as 

 an acid is destitute of it. Upon the whole, the properties of 

 margarine are such as have generally been supposed to entitle 

 a body to the denomination of an acid ; for it not only reddens 

 litmus, but it separates potash from carbonic acid, and forms 

 combinations that are, in all respects, analogous to neutral salts, 

 its composition may, perhaps, appear an objection to this deci- 

 sion ; but it is now generally admitted by the modern chemists, 

 that, in the classification of bodies, analogy of properties is to 

 be considered more than composition. 



M. Chevreul's Second Memoir .* 

 In the former paper, the- author had examined the nature of 



* Abstracted from Ann. de Cliiui. xciv. 80. 



