Distillation is a more useful process, or, at any rate, one more frequently employed, and is used to separate a volatile body from substances not volatile. A distilling apparatus (_distillo_, to drop) converts a liquid to vapour by means of heat, and then condenses it by cold in a separate vessel. The distilling apparatus consists of three parts,—the vessel in which the liquid is heated (the still, or retort), the condenser, and the receiver. The simple retort and receiver are shown in fig. 81. But when very volatile vapours are dealt with, the arrangement shown on next page is used (fig. 82). Then the vapour passes into the tube encased in a larger one, the intervening space being filled with cold water from the tap above (_c_), the warm water dropping from _g_. The vapours are thus condensed, and drop into the bottle (or receiver) B. [Illustration: Fig. 82.—Distilling apparatus.] The apparatus for distilling spirits is shown below. The “still” A is fitted into a furnace, and communicates with a worm O in a metal cylinder filled with water, kept constantly renewed through the tube TT′. This spirit passes through the spiral, and being condensed, goes out into the receiver C. [Illustration: Fig. 83.—Spirit still.] There are even more simple apparatus for spirit distilling, but the diagram above will show the principle of all “stills.” In former days, in Ireland, whiskey was generally procured illegally by these means. CHAPTER VIII. SPECIFIC HEAT—FUSION—LATENT HEAT—CONDUCTION AND CONVECTION OF HEAT—CALORESCENCE. We have considered the effects of heat upon water, and touched upon one or two kindred experiments. But we have some other subjects to discuss, two in particular; viz., _Specific Heat_, and _Latent Heat_.