604 Preparations and Compositions. Part III.

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The real advantage of so expensive an agent as alcohol, inpreparing any of these extracts, has not been demonstrated ;and, if I be not misinformed, it is seidom employed by theapothecaries in preparing even what are called the ResinousExtracts.

Resina flava. Dub.Yellow Resin.This remains in the retort after the distillation of oil of tur-pentine.

Turpentines are combinations of volatile oil and resins,which are easily separated by distillation. The process, how-ever, cannot be curried so far as to separate the whole of theoil, without charring and burning part of the resin. In thisstate it has a brown colour, and a certain degree of transpa-rency, and is well known under the name of Fiddlers Rosin.But if water be added to the residuum of the distillation, andbe thoroughly mixed with it by agitation, it becomes opaque,and is called Yellow Rosin.

Yellow rosin is a useful ingredient in the composition ofplasters and hard ointments.

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Gummi kesin;e. Land.• Gum Resins.

Those gum-resins are to be reckoned the best which are se-lected so pure, that they do not stand in need of purifica-tion. But if they seem impure, boil them in water untilthey grow soft; then squeeze them through a canvas bag,by means of a press. Let them remain at rest till the resi-nous part subside ; then evaporate, in a water-bath, thepart of the water decanted off; and towards the end of theevaporation, mix the resinous part with the gummy into ahomogeneous mass.

Gum-resins which melt easily may be purified by putting theminto an ox bladder, and holding it in boiling water till theybecome so soft, that they can be separated from impuritiesby pressing them through a hempen cloth.

As one, and perhaps the most active, constituent of gummyresins, as they are called, is of a volatile nature, it is evidentthat it must be, in a great measure, dissipated in the processjust described, and that we cannot expect the same virtues inthese substances after they are purified, which they possess intheir crude state. This process is, therefore, contrary to theprinciples of good pharmacy; and such specimens of these