Theoretical organic chemistry / by Julius B. Cohen.

  • Julius B. Cohen
Date:
1912
Catalogue details

Licence: Public Domain Mark

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

    29/628 page 9
    PURIFICATION OF SOLIDS AND LIQUIDS 9 tube. When pressed against the thermometer stem the capillary tube adheres. The thermometer passes through a cork inserted into a pear-shaped vessel with a long neck containing concentrated sulphuric acid or castor-oil. The vessel fits into a metal stand which can be placed upon a tripod, 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. As stated above, 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 whether substances like resins, dextrins, and proteins, 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 Fig. 3.—Apparatus for determining the boiling point. distilling the liquid in the apparatus shown in Fig. & It consists of a flask with a side-tube (distilling-flask), which is attached to
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