duce an inflammable vapour-force, by which engines, pumps, and machinery, may be set in motion. His method consists in placing an iron cylinder with a counter-sunk touch-hole in the lower surface, over a stove. When the bottom is sufficiently heated, a little spirit of turpentine, or of tar (in the proportion of 10 drops to a cubic foot), is poured into a funnel; which falls on the hot part of the cylinder, and produces an inflammable vapour. The external, condensed air, is then admitted to the touch-hole, where such fumes become ignited; and, by their concentrated force, a piston is raised, that communicates with, and works the pump or machinery, at the opposite end.—A farther account of Mr. Street's contrivance, is also given in the volume above quoted, where it is illustrated by an engraving.—For an ingenious and economical method of heating rooms by the evaporation of water in the form of steam, we refer the reader to the article Warmth.
Vapour-baths. See vol. i. pp. 192-93.
VARNISH, a clear liquid composition, which by age, and exposure to the air, becomes hard, without losing its transparency: it is employed by painters, carvers, gilders, and other artisans, for imparting lustre to their works, while it defends or preserves them from the effects of dust, moisture, and air.
Varnishes are of various colours, derived from the ingredients of which they consist: their bases are resins, dissolved in fixed oil, in volatile oil, or in alkohol; and, accordingly as either of these fluids are used, the varnishes are distinguislied by the names of fat or oily, essential, and spirit-varnish.
Amber-varnish. See vol. i. p. 274.
The fine black varnish, obtained from China and Japan, is a resinous juice exuding from a tree called tsi-chu, and which is conjectured to be the Cashew-nut tree, or Anacardium occidentale; but, being frequently adulterated, it may easily be imitated, by dissolving 4 oz. of gum-lac, a small piece of camphor, and a sufficient quantity of lamp or ivory-black, in 24 oz. of spirit of wine, over a gentle heat, for 24 hours; the vessel being occasionally shaken. The whole must then be strained, the pure liquid poured into a bottle, and suffered to stand for one or two days, till a clear fluid appear on the surface, which is then fit for use.
Copal varnish, of a superior quality, may be procured in the following manner: Take a certain portion of finely-pulverized copal; let it be thoroughly washed in soft or rain-water, then perfectly dried, and put in a glazed earthen vessel well covered, over a moderate coal-fire. After all the gum has been slowly melted, the vessel is to be removed from the fire, and half the quantity of prepared linseed-oil must be added, by gradually dropping it into the former; both being in a state nearly boiling. In order to prepare the latter, take one pound of pure linseed-oil, and an equal quantity of filtrated water; pour them together into a new earthen or tinned vessel; place this mixture over a fire, and suspend the following five ingredients in a coarse linen bag, which, however, must not touch the bottom; namely: amber, green and white vitriol, litharge of gold, and red-lead; of each half an ounce. When the oil begins to foam, all
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