. Practical methods of organic chemistry . denser for a short time. Thesubstance is melted by the hot steam and flows into the after this operation the water is to be turned into the condenseragain, it must be done slowly at first, otherwise the cold watercoming in contact with the hot condenser may easily crack the melting-point of the substance is above ioo°, in orderto keep the condenser free from crystals, the distillation is inter-rupted for a short time, and the crystals are pushed out of thetube by a long glass rod. The end of the operation is indicated, if the subst
. Practical methods of organic chemistry . denser for a short time. Thesubstance is melted by the hot steam and flows into the after this operation the water is to be turned into the condenseragain, it must be done slowly at first, otherwise the cold watercoming in contact with the hot condenser may easily crack the melting-point of the substance is above ioo°, in orderto keep the condenser free from crystals, the distillation is inter-rupted for a short time, and the crystals are pushed out of thetube by a long glass rod. The end of the operation is indicated, if the substance is diffi-cultly soluble in water, by the fact that the water passing overcarries no drops of oil or crystals with it. But when the substanceis soluble, even though the condensed water is apparently pure, itmay still contain considerable quantities of the dissolved this case, to determine when the end of the operation has beenreached, a small quantity, about 10 , is collected in a test-tube, DISTILLATION WITH STEAM 39. 40 GENERAL PART shaken up with ether, the ether decanted and evaporated. If noresidue remains, the distillation is finished. When a substanceshows a colour reaction, aniline with bleaching powder,advantage is taken of this to decide the question. After thedistillation is ended the rubber tubing is first removed from thedistilling flask, and then, after this has been done, the flame underthe generator is extinguished. This point is also carefully ob-served when the distillation is interrupted; otherwise it mayhappen that the contents of the flask will be drawn back intothe generator. Superheated Steam. — In dealing with very difficultly volatilecompounds, it is frequently necessary to conduct the distillationwith the aid of superheated steam. A conically wound coppertube is interposed between the steam generator and the distilling
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