4>7S Preparations and Compositions. . Part III.

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filtration, heat, and clarification. Rest may be employed withjuices, which are very fluid, do not contain volatile matter,and are not susceptible of alteration, and with subacid juices,as ihat of lemon. By rest these undergo a kind of slight fer-mentation, and all their mucilaginous, and other viscid parts,separate. Filtration is perhaps the most perfect means of de-fecation, but it is tedious, and applicable only to very fluidjuices. In many instances it may be facilitated by the addi-tion of water. The action of heat is more expeditious, andis employed for juices which are very alterable, or which con-tain volatile matter. It is performed by introducing thejuice into a matrass, and immersing it in boiling water forsome minutes. The fecula are coagulated, and easily sepa-rated by filtration. Clarification by white of egg can only beused for very viscid mucilaginous juices, which contain no-thing volatile. The white of two eggs may be allowed toeach pint of juice. They are beat to a fine froth, the juicegradually mixed with them, and the whole brought to ebulli-tion. The albumen coagulating envelopes all the parenchy-matous and feculent matters, and the juice now passes thefilter readily. By this process, juices are rendered sufficient-ly fine ; but the heat employed deepens their colour, and ma-nifestly alters them, so that it is not merely a defecating buta decomposing process. When depurated, juices are yellowor red, but never green.

The fluids thus extracted from succulent fruits, whetheracid or sweet, from most of the acrid herbs, as scurvy-grassand water cresses, from the acid herbs, as sorrel and wood-sorrel, from the aperient lactescent plants, as dandelionand hawkweed, and from various other vegetables, containgreat part of the peculiar taste and virtues of the respectivesubjects. The juices, on the other hand, extracted frommost of the aromatic herbs, have scarcely any thing of the fla-vour of the plants, and seem to differ little from decoctions ofthem made in water boiled till the volatile odorous parts havebeen dissipated. Many of the odoriferous flowers, as thelily, violet, and hyacinth, not only impart nothing of theirfragtance to their juice, but have it totally destroyed by theprevious bruising. From want of sufficient attention to theseparticulars, practitioners have been frequently deceived inthe effects of preparations of this class : juice of mint hasbeen often prescribed as a stomachic, though it wants thosequalities by which mint itself and its other preparations ope-rate.

There are differences as great in regard to their preserving