They are usually filtered, on the small scale, through bibulous or unsized paper placed on a funnel; and on the large scale, through thin and fine cotton bags. In general, however, they clarify themselves by the subsidence of the suspended matter, when allowed to repose for a few days. Hence it is the bottoms alone that require filtering; the supernatant clear portion need only be run through a small hair sieve, a piece of tow or cotton placed in the throat of a funnel, or some other coarse medium, to remove any floating substances, as pieces of straw, etc. Absorbent cotton not only strains, but, by fairly tight packing, filters brightly. Spirits which are largely loaded with essential oil, as those of aniseed, etc., run rapidly through paper or calico, but usually require the addition of some chalk or magnesia before they will flow quite clear. When possible, tinctures, spirits, and all similar volatile fluids, are better and more economically cleared by subsidence or clarification than by filtration, as, in the latter way, a portion is lost by evaporation, and the strength of the liquid is thereby altered Clarification and Filtration of Vegetable Juices. - Vegetable juices should be allowed to deposit their feculous portion before filtration. The supernatant liquid will then be often found quite clear. It is only when this is not the case that filtration should be had recourse to. A small quantity may be filtered through coarse or woolen filtering paper, supported on a piece of coarse calico placed on a funnel; when the quantity is large, one of the conical bags before described should be employed. The bottoms from which the clear portion has been decanted should be placed on a separate filter, or else not added until the whole of the other portion has drained through. Vegetable juices are often rendered clear by simply heating them to about 180° or 200° Fahr., by which their albumen is coagulated; they are also frequently clarified by the addition of a little white of egg or commercial albumen and heat, in the same way as syrups, Many of them are greatly injured by heat, and must consequently be filtered, or only simply decanted after repose. In all cases they should be exposed to the air as little as possible, as they rapidly suffer decomposition.

Fig. 376.   Frame Strainer

Fig. 376. - Frame Strainer.

Fig. 377.   Globe Filter

Fig. 377. - Globe Filter.