The operation of distilling is often carried on in the apparatus represented in Fig. 22. It is termed the Patent Simplified Distilling Apparatus; it was originally invented by Corty, but it has since undergone much improvement. _A_ is the body of the still, into which the wash is put; _B_ the head of the still; _c c c_ three copper plates fitted in the upper part of the three boxes; these are kept cool by a supply of water from the pipe _E_, which is distributed on the top of the boxes by means of the pipes _G G G_. The least pure portion of the ascending vapors is condensed as it reaches the lowest plate, and falls back, and the next portion as it reaches the second plate, while the purest and lightest vapors pass over the goose-neck, and are condensed in the worm. The temperature of the plates is regulated by altering the flow of water by means of the cock _F_. For the purpose of cleaning the apparatus, a jet of steam or water may be introduced at _a_. A regulator is affixed at the screw-joint _H_, at the lower end of the worm, which addition is considered an important part of the improvement. The part of the apparatus marked _I_ becomes filled soon after the operation has commenced; the end of the other pipe _K_ is immersed in water in the vessel _L_. The advantage claimed for this apparatus is that the condensation proceeds in a partial vacuum, and that there is therefore a great saving in fuel. One of these stills, having a capacity of 400 gallons, is said to work off four or five charges during a day of 12 hours, furnishing a spirit 35 per cent. over-proof. [Illustration: FIG. 10.--Corty's Simplified Distilling Apparatus.] Fig. 11 represents a double still which was at one time largely employed in the colonies. It is simply an addition of the common still _A_ to the patent still _B_. From time to time the contents of _B_ are run off into _A_, those of _A_ being drawn off as dunder, the spirit from _A_ passing over into _B_. Both stills are heated by the same fire; and it is said that much fine spirit can be obtained by their use at the expense of a very inconsiderable amount of fuel. [Illustration: FIG. 11.--Double Still.] =Compound Distillation.= Where stills of the form shown in Figs. 6 and 8 are used the alcohol obtained is weak. Hence it is necessary that the distillate be again itself distilled, the operation being repeated a number of times. In the better class of still, however, compound distillation is performed the mash is heated by the hot vapors rising from the still and the vapors are condensed and run back into the still greatly enriched. [Illustration: FIG. 12.--Dorn's Compound Still.]