1868 The complete Practical Distiller

45

CONTINUOUS DISTILLATION.

large size, and used for distilling simple fluids, is called a Those for experiments in a small way, and also for distilling acids, ammonia, ether, &c., are called retorts; the vessel that receives the distilled matter being called a receiver. When the worm-tub is employed, the still requires such a shape that the greatest possible surface may be exposed to the fire. Its shape is then that of a frustum of a cone. The neck should be of such width as to con- vey the vapour away as fast as formed. The height of the neck is regulated by the nature of the substance operated upon : if it is mucilaginous, the neck should be longer, to prevent its boiling over ; and the exterior of the lower part should be polished to prevent the escape of heat ; the descending part painted black, and its end inserted into the end of the worm. The worm-tub is a wooden vessel, about six or eight times the capacity of the still ; the length to the diameter should be about ten to seven. The worm consists of a spiral tube, which enters on one side of the tub at the top ; it then passes spirally, in six or eight convolutions, to the bottom, where it comes out of the side in order to discharge the liquid arising from the vapour condensed within it by the agency of the cold water with which the tub is filled. The water is constantly changing, by the warm water running away from the top, while a supply of fresh water comes in at the bottom. The section of the tube being a circle, its capacity should not be less than one-fifth of that of the still ; the diameter of the ends of the tube being about three to one. The object is not merely to effect a condensation, but to cool the liquid : the means still.