File:Image from page 32 of "Practical methods of organic chemistry" (1901) (14748611476).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: e solution siphons off and flows back into the flask a.This operation may be continued as long as necessary. Theamount of solvent used should be one and a half or two timesthe volume of the inner tube up to the highest point of the siphon.The construction of a ball condenser isrepresented in Fig. 8. In order to dis-tinguish the tube by which the water en-ters from the outlet-tube, the former ismarked with an arrow. Comparativelyeasy also is the separation of two sub-stances about equally soluble, if the oneis present in larger quantity than the other.If a mixture of this kind is dissolved, then,on cooling, the substance which was pres-ent in larger quantity generally crystal-lises out. Occasionally, after standingsome time, crystals of the second sub-stance will appear; under these conditions the crystallisationmust be carefully watched, and as soon as crystals differingfrom those first appearing are observed, the solution is filteredwith suction at once, even though it is still warm.

Text Appearing After Image: Fig. 8. 14 GENERAL PART If two compounds crystallise simultaneously at the outset, as isthe case when they possess approximately the same solubility andare present in almost equal quantities, they can be separated me-chanically. If, e.g., one of the compounds crystallises in coarsecrystals, and the other in small ones, they may be separated bysifting through a suitable sieve or wire gauze. A compound crys-tallising in leaflets can frequently be separated from one crystal-lising in needles by a sieve. If these methods fail, the separationmay be effected by picking out the crystals with small pincers or aquill. In all these mechanical operations, the crystals must be asdry as possible. In many cases, when one of the compounds is heavier than theother, it is possible to separate them by causing the lighter crystalsto rise to the top of the liquid, by imparting to it a rotatory motionby rapid stirring with a glass rod. The heavier compound collectsat the bottom of the vessel, and the liqu

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