Dr. Playfair’s Lecture on the Great Exhibition of 1851. 31 
Soap.—Soap is probably not older than the Christian era, for 
the soap of the Old Testament seems to have been merely alkali. 
Profane history, previous to Christ, does not allude to soap, and, 
in all the detailed descriptions of the bath and of washing, it is 
never mentioned. Pliny describes its manufacture, but ascribes 
to it as singular a use as that given to the potato by Gerarde, 
who, in his “‘ Herbal,” assures us that it “is a plant from Amer- 
ica, which is an excellent thing for making sweet sauces, and 
also to be eaten with sops and wines; so Pliny, in regard to 
soap states, that its main purpose was to dye the hair yellow, 
and that men used it for this purpose much more than women. 
Gradually its use became more extensive, and its manufacture 
considerable. Soap generally consists of a fatty acid, combined 
with the alkali of soda. This soda was imported from Spain 
under the name of barilla, itself the ashes of plants grown near 
the sea, As these plants derived their soda from the sea, near 
which they flourished, chemistry, though singularly enough 
in the person of N 
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oil; that of butter in palm-oil; and horse fat and train-oil are in 
many oily seeds, Was it, then, necessary to submit to the high 
prices of Russian tallow? Now, palm and cocoa-nut oil largely 
replace the fat of the Russian oxen and sheep, although the 
cheap importation of similar fats from Australia and South Amer- 
ica has rendered the substitution less necessary. 
Perfumery.—Much aid has been given by chemistry to the 
art of perfumery. It is true that soap and perfumery are rather 
