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■with water to wafh out the adhering fait, andthen framed in the ufual manner. After twomonths it weighed only 5 lbs. and was hard,white, and of an agreeable fmell. The fameexperiment was repeated with fimilar refults,employing the fulphat of foda inftead of themuriat.

It is rather lingular however that this accu-rate chemift did not (as appears) examine thefpent ley to difcover in it the potalb, which hefuppofes to be difplaced from the firft foap,but the experiment may eafily be made. Afimilar trial was alfo made with 3 lbs. of fuetand potalh, which after the addition of com-mon fait, gave a hard foap, weighing, in twomonths time, about 6 lbs.

The common yellow foaps are made in thiscountry with tallow and barilla, to which, afterfaponification, is added a quantity of rofin, andfometirnes a very little palm-oil.

The tallow is firft compleatly faturated withthe iey till the clear liquor, which is drawn offafter due boiling, is nearly as alkaline as whenadded, after which the rofin is melted in, andthoroughly incorporated.

The following gives a good yellow foap,viz. 25 cwt. of tallow, 4-I cwt. of oil, 7 cwt.of rofin, 18 cwt. of barilla; and 10 cwt. ofblack afhes (or wafte ley evaporated and cal-cined) and -j cwt. of palm oil. The produceis about 64 cwt. of yellow foap.

In the preparation of all the hard foaps, afeparation of the foap from the watery falinefolution always takes place towards the end ofthe procefs, and it is this feparation whichenables the artift to collect and dry the foap.But the queftion occurs, how this feparationtakes place; for the liquor from which itfeparates is ftill alkaline, often very ftrongly fo,and if the fame foap, after it is fully preparedand dry, is rediffolved in an alkaline liquor, itwill mix with it uniformly into a white fapona-ceous flu'd.

Pelletier 8 has endeavoured to fhew by fomeingenious reafoning, and by experiment, thatcarbonic acid is an effential ingredient in the■hard foaps, and from the fact that cauitic alkaliwill decompofe alcohol, and become more orIefs carbonated by the carbonic acid, which isthereby generated, (for which fee the articlePotafj) he infers that during foap-boiling, thepure alkali and oil firft unite into a faponace-ous mafs, during which he fuppofes that part.of the oil is decompofed, and furnifhes car-bonic acid, which then unites with the fapona-

® Memoirs de

ceous fluid, and forms with it a triple com-pound of oil, alkali, and carbonic acid, whichconftitutes hard foap. In the preparation offoap without heat he further fuppofes tlratf part,if not all, of the carbonic acid may be furnilhedby the atmofphere, which will account for thelength of time required before the foap madein this way will harden and feparate from theley.

He alfo gives the following experiments:Four ounces of cauftic foda ley were mixed,without heat, with eight ounces of oil of al-monds, and with frequent ftirring, but it wasnot till after many days, that the foap began toharden. On the other hand 4 oz. of the fameley, 8 oz. of oil, and 4 oz. of water flightlycarbonated, were mixed together ; the com-pound foon began to ftiffen, in a quarter of anhour it had acquired the confidence of an oint-ment, and in 12 hours it was hard enough forufe. Alfo 4 oz. of the ley were mixed with8 oz. of the oil previoufly aerated with carbonicacid, and here too the foap became folid muchfooner than in the firft inftance, though laterthan in the fecond experiment. If it be ob-jedted to this opinion of the necefiity of car-bonic acid to hard foap, that a carbonated al-kali will not make foap, the author brings theanalogy of calcareous cements or mortar; forfand and carbonat of lime will not cohere intoa mortar, hut when the combination betweenfand and quicklime is once made, the indura-tion is much haftened by adding carbonatedwater.

To this ingenious hypothefis however wemay objedl that there is no proof brought thatfoap actually contains carbonic acid, and thecontrary may be inferred from its not efter-vefcing with a ftronger acid, fo that the analogywith calcareous mortar is defective in the molteffential point. To afcertain the precife adlionof the alkali on oils, it will alfo be neceffary toexamine the fpent ley, which appears to containwhat alkali remains in it, in a much morecarbonated ftate than the frelli ley; Jo thatinftead of fuppofmg that the foap containscarbonic acid, we might with as much proba-bility conjecture that in the procefs a part ofthe alkali becomes to a certain degree car-bonated at the expence of the other, and that itis the latter portion, or the pure alkali, whichunites with the oil into foap, whilft the formerfeparates from it through the affiftance of itscarbonic acid. This would perhaps explainequally well the adlion of carbonated water in

Pelletier, tom. I.

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