ALCOHOL IN INDUSTRY.
This may be described as a process by which, on the application of heat, one substance can be volatilized from another and recovered by subsequent condensation. Thus, a sol vent, such as water, can be separated from solid matter which it holds in solution, or two liquids, boiling at different temperatures, can be freed one from the other. In the case of spirituous liquors the primary object of distillation is the separation, as far as possi ble, of the alcohol from the non-volatile constituents of the wash. Incidentally other volatile substances, such as water and products of fermentation other than ethyl alcohol are distilled off, but the proportion of these is reduced by further distillation and by vari ous elaborations of the apparatus in which the process takes place. The modifications thus introduced vary according to the materials used and the type of spirit it is desired to produce. The essential parts of a still are the vessel in which the mixture can be heated, a tube or still head to carry off the vapour, a condenser for cooling and thus reducing the vapour once more to the liquid state, and a vessel for receiving the liquid.
This apparatus embodies these features with the minimum of elaboration. Experience has shown that, for wines producing the finest brandies, the most simple form of still is the best. For the distillation of wines which do not produce brandy of the best quality more complicated apparatus is used in order to facilitate higher rectification. In Scotland the pot stills are larger and are adapted more particularly to the requirements of the whisky industry. They vary in size from about 3,00o to 8,000 gal., the usual capacity being 5,000 to 6,000 gallons.
The pot stills used in Ireland differ materially from the Scotch stills. They are very large, ranging up to 20,000 gallons. A char acteristic feature is the great length and height of the "lyne arm," i.e., the pipe connecting the still with the condensing coil. This lyne arm generally runs up vertically from the still for a dis tance of Io to 20 ft., then horizontally for another 3o to 4o ft.,
again vertically for I o to 20 ft., and is then connected to the con denser. The horizontal portion of the lyne arm lies in a shallow trough fitted with a water supply, and the temperature of the spirit vapours prior to their passing to the condenser may thus be regulated at will. According to the length and height of the lyne arm and the temperature of the water jacket, more or less of the vapours condense and are carried back to the still by means of a pipe. This return pipe is fitted with a cock which enables the distiller to regulate the flow. Occasionally there is a further return pipe for the condensing coil, but this is not usual. The advantage of this form of plant is that it is possible to work up far greater quantities of wash and to obtain a much higher rectification in a single operation than is possible in the case of the Scotch pot still. It will be noticed that in the type of Irish pot still shown in fig. 3 there is no return pipe from the lyne arm.
This was designed by Aeneas Coffey in the early part of the 19th century with a view to accomplishing in one process that which necessitates several operations in the pot still, of economizing time, fuel and material, and also of obtaining at will a spirit of higher purity than that which can be produced by the older and more simple form of apparatus. It is the still usually employed for the production of Scotch and Irish grain whiskies. It can, however, be adapted for the distillation of a spirit intended for methylation, or for the pro duction of spirit having a high degree of strength and purity. In the preparation of spirit approximating closely to absolute alcohol, however, the product of the patent still must undergo further treatment and rectification. In certain details the Coffey still since first devised has undergone certain modifications, but in general principle it remains unchanged.