1818.] their Combinations with Alkalies. 273 



which, when concentrated to half its volume, was covered with 

 little drops, of a yellow oily appearance ; these by cooling became 

 solid, absorbed water, and formed a thick, white, mucilaginous 

 fluid. This was diluted with a large quantity of water, and had 

 all the soluble part' of it removed by repeated ablutions. The 

 insoluble matter resembled a gelatinous hydrate of alumine ; 

 when heated gently in a small capsule of platinum, it was con- 

 verted into a milky fluid, which was quickly covered with yellow 

 oily drops ; as the matter cooled, it resumed the form of an 

 opaque mucilage ; and by dissipating all the water, a substance 

 was obtained, which, when melted, resembled a yellow oil. This 

 was found to consist of a fatty matter, which, by the test of litmus, 

 appeared to be very slightly acid, and a minute quantity of potash, 

 in the proportion of 100 to 0-63. From this result, M. Chevreul 

 concludes, that the water had removed from the flexible sapona- 

 ceous matter a great part of its alkali, and an atom of saponified 

 fat ; and that the substance left after the washing, although it 

 contained very little potash, was capable of forming a mucilage 

 with water. 



We now proceed to a more particular examination of the fatty 

 substance of the flexible saponaceous matter. This substance, 

 after remaining for some days in contact with water, did not 

 become mucilaginous ; it only absorbed a little of the water, and 

 became white. After adding some drops of potash, and expos- 

 ing it to a gentle heat, a mucilage was immediately formed which 

 was clotted, and not homogeneous, like that described above. 

 This want of homogeneity depended upon an excess of potash, 

 which, not having formed a union with the fatty matter, had 

 exercised such an affinity that it could no longer form a mucilage. 

 This is similar to the action of an alkaline water, which has not 

 the power of dissolving soap. What proves this to be the correct 

 method of viewing the subject is, that if the clotted mucilage 

 be thrown upon a filter and sufficiently lixiviated, a residuum is 

 procured, which, when diluted with water, forms a homogeneous 

 mucilage ; the water which passed through the filter held a little 

 soap in solution. This experiment decidedly proves that potash 

 is the cause of the mucilage which the fatty substance forms; but 

 it still remains to be determined whether tins substance is united 

 to the alkalies by means of an acid fat, or of the oleic or mar- 

 garic acid united to a fat which is not acid, or if it possesses this 

 property without any addition. 



In order to resolve this question, a portion of the fatty sub- 

 stance was boiled for the space of an hour with hydrate of 

 barytes ; the solid matter that was formed was dried, and added 

 to 15 times its weight of alcohol of the specific gravity of -791, 

 at the temperature of 53*5°; the fluid was filtered, and there 

 remained upon the paper some white flakes, which, after having 

 been treated with muriatic acid and washed with warm alcohol, 

 yielded barytes and an acid fat, fusible at about 68°, which. 

 Vol. XII. N° IV. !> 



