2. Simple stills, with closed washwarmers, in which the mash is previously heated by the latent heat of vaporization.
3. Double pot-stills, generally consisting of two superimposed stills. While the mash in the lower still is being deprived of its alcohol, the mash in the upper still is enriched with alcohol and heated by the vapors of the lower mash, until the latter after sufficient concentration is heated to the boiling point. From this time on alcoholic vapors develop in the upper pot which are cooled in a dephleginator and absorb still more alcohol. The concentrated vapors pass over into the condenser, while the condensed liquid flows back into the upper still. Such apparatus is either heated by direct firing be low the lower sill, or by means of steam, which is introduced into the lower still.
4. Two, three or more chamber charge-stills, with or without charging chamber in one ap paratus, in which the single compartments are placed one over the other, and the heat from the lower serves to enrich the one above. Steam is used for heating.
All these apparatus, when heated by direct firing, are made either of copper or iron; when heated with steam are made generally of cop per, but oftimes of wood, such as heavy cypress or white oak. These are more suitable for intermittent working, and are used mostly in distilleries which distil rye whisky, etc.
5. Continuous pure still apparatus (on ac count of their form called column apparatus), which are used mainly in large distilleries, can be regarded as a combination of a large num ber of small stills, in which the mash, contin uously flowing from the upper compartments to the lower, constantly comes in contact with steam flowing in the opposite direction. Through this countercurrent, the rising vapors become more rich in alcohol, through the dephlegma tion and rectification taking place in each of the compartments, while the mash flowing down ward is constantly deprived of its alcohol until it flows from the lowest chamber as slop, free from alcohol. The concentrated alcoholic va pors, escaping from the uppermost chamber of the column, are then liquefied in a condenser when alcohols of only moderate strength (125 to 150 proof) are to be produced; but, if very pure highly concentrated alcohols are to be man ufactured, these vapors pass over into a simi larly constructed rectification column, where they meet with the liquids (luster or phlegrna), returning from the dephlegmator or condenser.
The vapors take up alcohol from the liquids and into from the upper chamber of the recti fier into the dephlegmator, in which a continual countercurrent between the condensed liquids constantly takes place.
The advantages of the continual column appa ratus in comparison with the simple pot-stills, are, that the mash is more quickly vaporized, that the expense for fuel is diminished and that, as a rule, a more highly concentrated product is obtained. But, on the other hand, they also require more care and attention and skilled Besides, there is a possibility that might sometimes pass off with the slop. In the simple stills this possibility is consider ably reduced, so that it is still advisable for small distilleries to erect good pot-stills, because they manufacture mostly alcoholic liquors with about 50 per cent alcohol by vol ume (100 proof ).
The alcoholic liquid obtained in the distillery with the best modern apparatus contains, besides the highly concentrated alcohol (96 per cent by volume, 192 proof), more or less fusel oil, a mixture of amyl, propyl and isobutyl alcohols. Up to the present time, the following impurities contained in 50 to 95 per cent alcohol have been determined: acetic aldehyde, propylic alcohol, isopropylic alcohol, butylic alcohol, acetic ether, butylic ether, acetal, secondary amylic alcohol, isoamylic alcohol, isobutylic alcohol, furfurol and various amines. In the corn and potato spirits amylic alcohol is in predominance, and therefore it is briefly called fusel oil. Techni cally, fusel oil is not a uniform substance, but the higher boiling part of the impurities accom panying the alcohol distillation.