On Soaps considered with regard to Smell. 1 1 1 



liiilable fats and oils, a proportion which may be inferred from their 

 degree of fusibility, we may predict the degree of hardness or 

 softness of the soaps produced ; 2, that it is possible to imitate 

 any given soap, by taking stearine and oleine in such proportions 

 that the stearic, margaric, and oleic acids, which they are suscep- 

 tible of furnishing by the action of alkalis, may be, in the same ratio, 

 as in the fat of the soap proposed for imitation. Thus, by adding, 

 to oils which would afford only soft soaps with soda, bodies 

 abounding in stearine, such as the wax of the mijrica gale, a sub- 

 stance produced in large quantity by a tree in Africa, and which 

 was handed to M. Chevreul by an enlightened English traveller, 

 we may imitate the soap of olive oil, which differs from the soap of 

 rape-seed oil, only in containing less oleic acid. 



These notions are obviously the fundamental base of the art of 

 the soap manufacturer, and they may give him a degree of preci- 

 sion which he could not have had, while ignorant of the analysis of 

 the fat part of soap into three acids, and of the reason why saponi- 

 fiable fat bodies produce hard or soft soaps. 



2d. Section. Of Soaps considered with regard to Smell. 



Soaps are either inodorous, as those of human fat, and hog's 

 lard, or odorous, as those of butter, oil of the dolphin, and suet. 

 The odours of soaps are owing to principles absolutely distinct 

 from the stearic, margaric, -and oleic acids ; for, on decomposing 

 these soaps dissolved in water, by tartaric acid, and submitting 

 the filtered aqueous liquids to distillation, we obtain products which 

 have exactly the same smell as the soaps from which they are 

 taken ; and, in the second place, by washing sufficiently, the stea- 

 ric, margaric, and oleic acids, we succeed in bringing these acids 

 to such a state of purity, that when they are combined with pot- 

 ash and soda, they form absolutely scentless soaps. 



The odorous principles of soaps have properties important 

 enough to require being investigated. It is a remarkable fact, that 

 they all possess a very strong acidity ; to this property they join 

 that of the volatile oils. Hence it may be asserted, that these acids 

 form a new class of bodies, which are to the volatile oils, what the 

 stearic, margaric, and oleic acids are to the fixed oils. Mr. Chev- 

 reul calls phocenic acid, the odorous principle of the soap of the 

 dolphin oils ; hircic acid, the odorous principle of the soap of 

 mutton suet ; butiric acid, the odorous principle to which the soap 

 of butter of the cow, and even the butter itself, owe particularly 

 their characteristic smell; he says, particularly, because these 

 bodies contain besides, two other acids which he styles capric and 

 caproic acids. He does not describe the processes by means of 

 which he has obtained the three acids of butter in a state of pu- 

 rity ; he remarks, however, that the method which he adopted, by 

 giving more precision to the use of solvents in analysis in general, 



