1818.] their Combinations with Alkalies. 259 



In the fourth memoir, saponification was examined under two 

 relations ; 1. Under that of the bases which form it; 2. Under 

 that of the quantity of alkali necessary to saponify a certain 

 quantity of fat. The first inquiry, by showing that barytes, 

 strontian, lime, oxide of zinc, and protoxide of lead, cause fat to 

 undergo the same change that it does with potash and soda, has 

 enabled us to generalize saponification, by proving that this oper- 

 ation depends upon an alkaline force which overcomes the obstacle 

 which the cohesion of some bases and the insolubility of others 

 seem to oppose to the change of fat into the sweet principle and 

 the oily acids. The second inquiry, by showing that we can 

 effect the saponification of a given weight of fat, merely by 

 employing the quantity of alkali which is exactly necessary to 

 neutralize the margarine and the fluid fat, into which tins weight 

 of fat can be converted, has formed a determinate basis for the 

 art of the soap-maker. In this memoir, likewise, the capacity 

 of the saturation of margarine has been exactly determined, and 

 all the analyses of the soaps of this substance have shown that 

 100 parts of it saturate a quantity of base containing three parts 

 of oxygen. There appears then to be a perfect analogy between 

 margarine and the acids, so as to confirm the opinion of its 

 nature which had been advanced in the preceding memoirs. 



The crystallized matter of the human biliary calculus, sperma- 

 ceti, and the adipocire of carcasses, had been confounded 

 together under the same species of fatty matter ; and the object 

 of the fifth memoir was to show that this opinion is erroneous. 

 The biliary calculus and spermaceti possess the characters of 

 pure proximate principles, whilst adipocire, which is formed of 

 margarine, of fluid fat, and of an orange coloured principle, 

 possesses all the properties of a saponified fat. On the other 

 hand, biliary calculus differs essentially from spermaceti, as the 

 latter is perfectly saponified under circumstances in which the first 

 absolutely resists the action of alkalies. The soap of spermaceti 

 contains two oily acids, one of which only has been examined ; 

 it is in its general characters analogous to margarine and the 

 fluid fat, but is distinguished from them by possessing only 

 about half as much capacity for saturation. 



The knowledge of the immediate principles- which compose 

 the different kinds of fats and oils accounts for the different 

 degrees of fluidity of their compounds, but it does not explain 

 the differences in colour and odour which many of them present. 

 The discovery of the cause of these differences gives rise to a 

 new order of facts, which will form the subjects of the succeeding 

 up -moire. In the present memoir, the sixth, M. Chevreul pro- 

 poses to examine the fat of man, of the sheep, the jaguar, and 

 the goose ; and to determine how far the proximate principles of 

 these fats, and the oily acids which they are capable of produc- 

 ing, resemble those of hog's-lard. 



The author remarks that he has hitherto made use of peri- 



k 2 



