Volume 1

The chemical works of Caspar Neumann ... / abridged and methodized. With large additions, containing the later discoveries and improvements made in chemistry and the arts depending thereon by William Lewis.

  • Caspar Neumann
Date:
1773
Catalogue details

Licence: Public Domain Mark

Credit: The chemical works of Caspar Neumann ... / abridged and methodized. With large additions, containing the later discoveries and improvements made in chemistry and the arts depending thereon by William Lewis. Source: Wellcome Collection.

    447/464 page 427
    Though all eflential Oils diftil freely along with Essen- boiling water, there are many which cannot be ele- tial vated by the heat that boiling water communicates Oils. through the Tides of another veflel. If O^Js already feparated from the fubied: be committed to difbilla- bitude to X /*» » 1 • /» tion by themfelves, there are few that will begin to j?ree*” arife, till the heat has become ftrong enough to alter cumftances or deftroy their peculiar flavour, and give them a burnt fmell and tafte. It is obfervable, that the moft fubtile and volatile eflential Oils require a confider- ably ftronger heat to make them boil than water does (0). Water they may be varioufly mixed with one another, or the dearer fophifti- .cated with the cheaper, without any pofiibility of difcovering the abufe by any trials of this kind. And indeed, it would be of little advantage to the purchafer, if he had infallible criteria of the genuinenefs of every individual Oil. It is of as much importance that they be good as that they be genuine 5 for 1 have often feen genuine Oils, from incurious diftillation, and long and carelefs keeping, weaker both in fmell and tafte than the common fo- phifticated ones. The fmell and tafte feem to be the only certain tefts that the nature of the thing will admit of. If a bark has, in every refpeft, the appear¬ ance of good Cinnamon, and is proved indifputably to be the genume bark of the Cinnamon-tree, yet if it wants the Cinnamon flavour, or has it but in a low degree, we reject it ; and the cafe is the fame with the Oil. It is only from ufe and habit, or comparifon with fpecimens of known quality, that we can judge of the goodnefs either ohthe Drugs themfelves or their Oils. Moft of the eflfential Oils, indeed, are too hot and pungent to be tafted with fafety, and the fmell of the fubjeft fo much concentrated m them, that a fmall variation in this refjpeft is not eafily diftinguifhed j but we can readily dilute them to any affignable degree. drop of the Oil may be diflolved in Spirit of Wine, or received on a bit of Su¬ gar and diflolved by that intermedium in water: the quantity of liquor which it thus impregnates with its flavour, or the degree of flavour which it communicates to a certain determinate quantity, will be the meafure of the degree of goodnefs of the Oil. (q) Habitude of Oils to fire.] Many Oils, in their firft diftillation from the fubjeft, carry up with them a portion of grofs reftnous mat¬ ter ; which, if too ftrong a heat has been ufed in the operation, proves fometimes very confiderable. On more carefully diftiiling them with water a fecond time, the Refin remains behind, and is generally found to be infipid and inodorous : the Oil by this means becomes more limpid and pure, and at the fame Time is in good meafure freed from any ungrateful empyreumatic taint which it might before have received from the fire. In this rectification of Oils, whether debafed in the dif¬ tillation itfelf, or by age, fome have employed common Salt, Sal mi- rabile, and other additions, which do not appear upon experiment to pc of any advantage, -' ' ^ JEflcntial
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