Identifier: practicalmethods00gatt Title: Practical methods of organic chemistry Year: 1901 (1900s) Authors: Gattemann, Ludwig. [from old catalog] Subjects: Publisher: [n.p.] Contributing Library: The Library of Congress Digitizing Sponsor: The Library of Congress

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Text Appearing Before Image: a-— Fig. 19. In place of the flask b, a suction-flask such as finds applicationin filtering under pressure, may be used (Fig. 20). But this kindof flask is used only in case low boiling substances are to bedistilled, since the contact of too hot liquids with the thick wallscauses them to crack easily : this is likely to prove very destructivein vacuum distillation. With low boiling substances, in order toget complete condensation of the vapours, the jacket of a Liebigcondenser through which water is allowed to flow is fitted overthe outlet tube of the fractionating flask. These simple formsof apparatus are used only when it is desired to collect a fewfractions, since it is troublesome to be obliged to change thereceiver, and thus destroy the vacuum, for each new fraction.If it is desired to collect a larger number of fractions, an DISTILLATION 27 apparatus is employed by means of which the receiver can bechanged without destroying the vacuum.

Text Appearing After Image: Fig. 20. Briihls apparatus is very well adapted to this purpose (Figs. 21and 22). By turning the axis b, so arranged that it supports thereceivers firmly, each receiver may in turn be brought under theend of the condenser tube c. The receiver shown in Fig. 23 is also very convenient for frac-tional distillation in a vacuum. By grasping the cork a and thetube c firmly with the fingers and turning, the different portionsof the receiver may be brought under the condensing tube. Construction of a Vacuum Apparatus. — In vacuum distillationsthe evolution of bubbles of vapour occurs to a much greaterextent than under ordinary conditions. In order to prevent theliquid from foaming up and passing over, a flask of such a size isselected, that when it contains the liquid it must in no case bemore than half full; it is better to have it but one-third full. Theindividual parts of the apparatus are connected by rubber stoppers.Ordinary corks may also be used with almost equally good results,but o

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