PART III.

Extracts.

6i:

in a water-bath; but the alcohol need not be allowed to eva-porate in the air, as by employing a distilling apparatus, thegreater part of it may be again obtained either altogether freefrom any vegetable principle, or containing a small portiononly of the more volatile; which renders it fitter for being againemployed for the preparation of the same kind of extract.

Whether water, proof spirit, or pure alcohol be employed,the medicinal properties of the extract are always in some de-gree injured, the volatile parts are dissipated, and some of thefixed decomposed by the degree of heat required for the eva-poration, particularly if water be the menstruum; or the pro-per extractive is oxidized, and consequently rendered inert.These are strong objections to this form of preparation; and,as Dr. Murray has properly observed, " with the exception ofsome of the pure bitters, as gentian; or some of the saccharinevegetables, as liquorice; there is no medicine perhaps but whatmay be given with more advantage under some other form." 1Extracts require to be kept in a hard and a soft state. Ahard extract should be in such a state as to admit of its beingeasily pulverized, and the soft extract should be such as to retainthe round form of a pill, without the addition of any powder.Both kinds should be preserved in a dry place; and the softshould be wrapped in oiled bladder, and kept in covered pots.The London College does not arrange the extracts under thetitles Watery and Spirituous, which is the arrangement of theEdinburgh College, or Simple and Besinous, which is that ofthe .Dublin: and the London Pharmacopoeia being our textbook, we have followed its arrangement. The following ge-neral directions are given by the London College for thepreparation of extracts.

" In preparing all kinds of extracts, evaporate the fluid asquickly as possible in a broad shallow dish placed in a water-bath, until the extract acquires a consistence proper for form-ing pills, and towards the end of the operation stir assiduouslywith a spatula.

" Sprinkle a small quantity of rectified spirit upon all thesofter extracts."

The Edinburgh College gives its general directions forthe preparation of the Extracts by Water, under the Extract ofGentian; and for the Extracts by Water and Alcohol, underthe Extract of Bark. 2

' System of Materia Medica, S(c. ii. 119.

1 The following method of preparing narcotic extracts, invented by Mr. Battley,Chemist, Fore-Street, London, had been found to answer every purpose in preservingthe green colour and the medicinal properties of the plants.

" Plants which from circumstances cannot be operated upon immediately after