=222. Scheibler’s Extraction Tube.=—In order to secure a speedy extraction of large quantities of pulp, Scheibler recommends the use of the extraction tube shown in Fig. 70.[184] The apparatus is composed of three concentric glass cylinders. The outer and middle cylinders are sealed together at the top, and the inner one is movable and carries a perforated diaphragm below, for filtering purposes. Near the top it is provided with small circular openings, whereby the alcoholic vapors may gain access to the condenser (not shown). The middle cylinder is provided with two series of apertures, through the higher of which the vapor of alcohol passes to the condenser, while the alcohol which has passed through the pulp and collected between the inner and middle cylinders, flows back through the lower into the flask (not shown) containing the boiling alcohol. The middle cylinder is provided with a curved bottom to prevent the filtering end of the inner tube from resting too tightly against it. The tube containing the pulp is thus protected from the direct heat of the alcoholic vapors during the progress of extraction by a thin cushion of liquid alcohol. =223. Alcoholic Digestion.=—The fourth method of determining sugar in beet pulp, is by means of digestion with hot alcohol. The principle of this method is precisely the same as that which is involved in aqueous diffusion in the cold. The diffusion, however, in the case of the alcohol, is not instantaneous, but is secured by maintaining the mixture of the pulp and alcohol for some time at or near the boiling point. The methods of preparing the pulp, weighing it and introducing it into the digestion flask are precisely those used for aqueous digestion, but in the present case a somewhat coarser pulp may be employed. The method is commonly known as the rapp-degener process.[185] Any convenient method of heating the alcohol may be used. In this laboratory the flasks are held on a false bottom in a bath composed of two parts of glycerol and one of water. One side of the bath holder is made of glass, as shown in Fig. 71, in order to keep the flasks in view. In order to avoid the loss of alcohol, the digestion flask should be provided with a reflux condenser, or be attached to an ordinary condenser, which will reduce the vapors of alcohol again to a liquid. Unless the weather be very warm, the reflux condenser may consist of a glass tube of rather wide bore and at least one meter in length, as shown in Fig. 71. A slight loss of alcohol during the digestion is of little consequence. A convenient method of procedure is the following.