1818.] their Combinations with Alkalies. 189 



one of the compounds resulting from the union of hog's-lard 

 and potash, which he found to consist of the alkali and marga- 

 rine. He now proposes to examine the other compound, which 

 differs from the former in the obvious and essential circumstance 

 of being soluble in cold water. 



M. Chevreul began by carefully purifying the fat, and after- 

 wards digested 250 parts of it with 150 of potash for two days, 

 at a temperature of about 175°, by which the fat was completely 

 dissolved ; the compound became opaque, and a yellowish fluid 

 spontaneously separated from it, the nature of which was exa- 

 mined. It was found to consist of the carbonate of potash, with 

 a great excess of base, arising from too large a proportion of 

 potash having been added to the fat, a little acetic acid, an 

 aromatic principle, and the sweet principle of oils. The soap 

 itself was next examined : it was completely dissolved by boiling 

 water ; but as the fluid cooled, a large quantity of the pearly 

 matter separated, and it required 10 successive operations, per- 

 formed at an interval of several days, to remove all this matter 

 from it. The solution of the pure soap was decomposed while 

 hot by pure tartaric acid ; the fat appeared in the form of white 

 masses, which melted into a yellowish oil. The fluid which 

 contained the acidulous tartarate of potash was poured off and 

 distilled, and a quantity of acetic acid, of the aromatic principle, 

 and a little of the sweet principle, were procured. The fat, 

 which had been separated from the potash by the tartaric acid, 

 was of a yellow colour, melted at about 60° ; its weight compared 

 to that of the fat originally employed was as 120 to 250. These 

 120 parts were melted, and added to 72 parts of potash, dissolved 

 in 480 parts of water, at the temperature of 86°. When the 

 soap thus formed was added to cold water, a very small quantity 

 only of the pearly matter was precipitated ; but this was found, by 

 repeating the experiment with a smaller quantity of potash, to 

 depend upon an excess of alkali preventing the separation of 

 the pearly matter ; for under these circumstances, a portion of 

 it was still deposited. When by this means the pearly matter 

 was completely separated, the fat was obtained nearly in a fluid 

 state, and was then found to possess the following properties. 

 It had a rancid odour and taste ; at the temperature of 66° its 

 specific gravity is '898 ; at about 43° it concretes into white 

 needles ; while it remains fluid it possesses a light yellow colour, 

 similar to that of olive oil. Suspecting that this yellow colour, 

 as well as that of other oils and resins, depended upon a matter 

 extraneous to it, M. Chevreul endeavoured to separate it bj 

 boiling the fluid fat with carbonate of barytes, in the proportion 

 of two parts of the latter to one of the former, mixed with a 

 quantity of water. The result of this operation is the disengage- 

 ment '-I' carbonic acid, and the combination of the fluid fat with 

 the barytes, so as to form a yellow, viscid, saponaceous mass. 



