File:Image from page 45 of "Practical methods of organic chemistry" (1901) (14769262194).jpg

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: cemore distilled separately, and the portion passing over a few de-grees above and below the true boiling-point, for phosphorus oxy-chloride about io5°-ii5°, for benzoyl chloride, i90°-205° arecollected. Vacuum Distillation. — Many compounds, not volatile at theatmospheric pressure without decomposition, may be distilledundecomposed in a partial vacuum. The vacuum distillation isused advantageously for the fractionation of small quantities of asubstance, since the separation of the individual constituents canbe effected more rapidly and more completely than at the atmospheric pressure. Vacuum Apparatus. — The simplest form of a vacuum apparatus 26 GENERAL PART is represented in Fig. 19. Two fractionating flasks a and b areconnected by a cork. The neck of a is closed by a tightly fittingcork bearing the glass tube d, reaching to the bottom of the flask,its lower end being drawn out to a fine point, the object of whichwill be explained below. A thermometer is placed in the tube.

Text Appearing After 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.

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