Theoretical organic chemistry / by Julius B. Cohen.

  • Cohen, Julius B. (Julius Berend), 1859-1935.
Date:
1902
Catalogue details

Licence: Public Domain Mark

Credit: Theoretical organic chemistry / by Julius B. Cohen. Source: Wellcome Collection.

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    tube containing concentrated sulphuric acid or castor-oil. A second hole in the cork admits a stirrer, which is kept in position by a short glass tube in which it slides. The test- tube is clamped on a ring of wire-gauze, and is heated very gradually by a small flame. When a certain temperature is reached, the substance, if pure, melts suddenly within a range of i or 2 . degrees. When approaching the melting-point, it is desirable to remove the flame, or turn it very low, so that the rise of temperature is very gradual. If the liquefaction is protracted it is an indication that the substance is not pure. Some substances do not melt, but, on reaching a certain temperature, decompose. The purity of such substances can only be approximately gauged by repeated crystallisation and careful microscopic examination. It is difficult to establish with certainty that substances like resins, dextrins, and albumins, which do not crystallise, are single individuals or not, and purification is rendered very troublesome. Boiling-Point Determination.—Pure volatile liquids have a constant and definite boiling-point. This is ascertained by distilling the liquid in the apparatus shown in Fig. 2. It consists of a flask with a side-tube (distilling-flask), which is attached to a condenser. A second flask (receiver) is placed below the end