The new dispensatory: containing, I. The elements of pharmacy. II. The materia medica ... III. The preparations and compositions of the new London and Edinburgh pharmacopoeias / [William Lewis].

  • Lewis, William, 1708-1781
Date:
1785
Catalogue details

Licence: Public Domain Mark

Credit: The new dispensatory: containing, I. The elements of pharmacy. II. The materia medica ... III. The preparations and compositions of the new London and Edinburgh pharmacopoeias / [William Lewis]. Source: Wellcome Collection.

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    It muff be obferved, however, that to change blue flowers to a green, is not univerfally a mark of alkalies, for fome folutions of earthy bodies in acids have the fame effeft: thefe laft may be di- ftinguifhed from alkalies, by adding to them a known alkali, which will immediately precipitate the earth, and form a neutral com- pound with the acid. Fixt alkaline falts, perfectly purified, appear to be one and the fame, from whatever kind of vegetable they were produced ; thofe of fome marine plants excepted, of which hereafter. In volatile alkalies, and in the pure earthy part of the afhes, there appears to be, refpedfively, the like identity. Empyreumatic oils differ fomewhat in the degree of acrimony and fetidnefs, and the acid fpirits differ in degree of ftrength, or in the quantity of water with which they are diluted ; how far they may differ in any other refpecfts, is little known, thefe preparations hav- ing been rarely ufed or examined. It may be obferved, that the alkaline falts, both of the fixt and of the volatile kind, are entirely creatures of the fire, being never found to exift naturally in any vegetable: the oil, doubtlefs, pne- exifted in the fubjed, but owes its acrimony and fetidnefs to the fire; for the mod mild and infipid oils receive the fame qualities on being urged with the fame degree of heat : the acid, which is likewife naturally contained in vegetable fubjeds, proves always tainted, in the prefent procefs, with the ill fmell and tafte of the oil that accompanies it; but whether the acid itfelf fuffers any change in its nature, is unknown. When chemiftry began fir fir to be formed into a rational fcience, and to examine the component parts and internal conftitution of bodies, it was imagined, that this refolution of vegetables by fire, difcovering to us all their active principles, unclogged and unmixed with one another, would afford the fureft means of judging of their medicinal powers. But, on profecuting thefe experiments, it was foon found that they were infufficient for that end : that the ana- lyfes of poifonous dnd eicuient plants agreed often as nearly with one another as the analyfes of one plant: that by the action of a burning heat, two principles of vegetables are not barely feparated, but altered, tranfpoled, and combined into new forms ; infomuch that it was impofiible to know in what form they exifted, and with what qualities they were endowed, before thefe changes and tranf- pofitions happened. If, for example, thirty-two ounces of a cer- tain vegetable lubftance be found to yield ten ounces and a half of acid liquor, above one ounce and five drams of oil, and three drams and a half of fixt alkaline fait; what idea can this awalyfis give of the medicinal qualities of gum Arabic? q- Sub-