PROCESS II.
To extract the Fat Oils of Plants by Decoction in boiling Water. Cacao Butter.
Pound or bruise in a marble mortar your vegetable substances, abounding with the Fat Oil which you intend to extract by decoction: tie them up in a linen cloth; put this packet into a pan, with seven or eight times as much water, and make the water boil. The Oil will be separated by the ebullition, and float on the surface of the water. Skim it off carefully with a ladle, and continue boiling till no more Oil appear.
OBSERVATIONS.
The heat of boiling water is capable of separating the Fat Oils from vegetable matters that contain any: but this is to be effected by actual decoction only, and not by distillation; because these Oils will not rise in an alembic with the heat of boiling water. We are therefore necessitated to collect them from the surface of the water, as above directed. By this means a much greater quantity of Fat Oil may be obtained than by expression alone; because the degree of heat applied greatly facilitates the separation of the Oil. For a convincing proof of this truth, take the remains of any vegetable matters, from which the Oil hath been so thoroughly expressed that they would yield no more; boil them in this manner, and you will obtain a great deal more Oil.
The water used in this coction generally becomes milky, like an emulsion; because it contains many oily particles, that are dispersed in it just as in an emulsion. Nevertheless, this way of obtaining the Fat Oils is not generally practised; because the heat, to which they are exposed in the operation, occasions their being less mild than they naturally are: but it is an excellent method, and indeed the only one that can be employed, for extracting from particular vegetables certain concrete oily matters, in the form of Butter or Wax; which matters are no other than Fat Oils in a fixed state. The Cacao yields, by this means, a very mild butter; and in the same manner is a Wax obtained from a certain shrub in America.
The heat of boiling water melts these oily matters, which then ascend to the surface of the liquor, and float on it like other Oils. They afterwards fix as they cool, and resume their natural consistence. We shall see in the sequel, that they cannot be extracted in a concrete form by distillation, which requires a greater degree of heat than that of boiling water; because distillation changes their nature, partly decomposes them, and prevents their returning to their proper consistence as they cool.
PROCESS III.
To extract Essential Oils of Plants by Distillation with the Heat of boiling Water. Distilled Waters.