At the smaller distilleries where malt whiskies are produced, and where it is the object of the distiller to retain in the product some of the esters, higher alcohols, and other bodies which give the spirit its characteristic flavour, the apparatus employed is the relatively simple "pot" still. This may consist merely of a boiling vessel, with a retort head and a worm condenser. Or the head may be attached to one or more fractionating vessels similar to Woulfe's bottles, through which the alcoholic vapours pass before reaching the condenser. Or, again, the simple retort head may be replaced by a rectifying still-head, consisting of a series of water-jacketed vessels arranged one above the other, the vapour rising through each of these successively.

Fig. 22. - simple pot-still, fire-heated, with condenser. (1) Boiling vessel; (2) still-head; (3) condenser worm (Haslam Foundry Co., Ltd., Derby).

Usually the pot still is heated by the direct flame of a furnace, though steam is now frequently used as the heating agent. The steam is applied either as a "jacket" outside the still, or by means of coils inside the vessel. When a furnace is employed, a stirring apparatus is often fitted into the still to remove the sediment of vegetable matter which is prone to settle on the bottom, and which, if not displaced, is decomposed by the heat and communicates an empyreumatic flavour to the spirit.

With a pot still, the spirit produced by the first distillation is always very impure, and has a disagreeable odour and taste. It is called "low wines." On redistillation of the low wines, the first portion of the distillate ("foreshots") is contaminated with oily matters, including apparently esters of fatty acids deposited in the condenser towards the end of the previous distillation and now re-dissolved by the strong spirit. As the distillation proceeds the proportion of oily matters diminishes until the distillate no longer becomes turbid on dilution with water, when the spirit is considered sufficiently pure to be collected as potable alcohol. Towards the close of the process the spirit again becomes oily ("tailings"). The impure portions of the distillate obtained in this second distillation are termed "feints"; they are redistilled with the succeeding "low wines" to recover the alcohol from them. It is usual to have separate stills for the two distillations, one for the " wash ' only ("wash still") and a smaller one for the low wines ("low wines still "); though occasionally one still serves for both operations The low wines still is generally of about one-half the capacity of the wash still; the latter is of any size up to 10,000 gallons, or even more, occasionally 20,000. Not infrequently, a second low wines still ("spirit still") is used to obtain the final product from the low wines, or for the re-distillation of the strong feints.

Fig. 23. - steam-heated pot-still, with rectifying head (Corty's). (2) Rectifying-baths (Haslam Foundry Co., Ltd., Derby).

The residue from the distillation of the wash is termed "pot ale "; that from the low wines is called "spent lees." Both are run to waste, as a rule, though the pot ale is sometimes evaporated and the product used as a fertiliser.

In the following table1 are shown the approximate boiling points of wash or feints containing various proportions of alcohol, and also the percentage of alcohol in the distillate, as obtained from a simple still:

As an example of the effect of successive distillations in a simple still upon the proportion of alcohol in the distillate, the following series of experiments may be quoted.2

A fermented wash containing, by weight, 11.3 per cent, of alcohol, was distilled until practically free from spirit. The distillate was then treated in the same way, the operation being repeated five times: -

Simple pot stills are also used to some considerable extent for the distillation of wine in the making of brandy. Often, however, a rectifying still of more effective type is employed, which at the same time is not effective enough to give a "neutral" spirit by removing all the characteristic esters, higher alcohols, and aldehydes. The use of a high still-head, or the insertion of a perforated

1 Groning (adapted from). Maercker.Delbruck, "Handbuch der Spiritus fabrikation," 1908, p. 771.

2 Maercker.Delbruck, loc. cit.

plate in the upper part of the still, tends to increase the rectifying effect and to give a purer distillate. With the simpler forms of still, two distillations are necessary, as described above for ordinary alcohol, but "continuous" stills are also in use, giving potable spirit from wine by a single distillation.

Fig. 24. - coffey's patent continuous-working steam-still (Blair, Campbell, and McLean, Ltd., Glasgow). Exterior.