Practical organic and bio-chemistry / by R.H.A. Plimmer.

  • Robert Plimmer
Date:
1915
Catalogue details

Licence: Public Domain Mark

Credit: Practical organic and bio-chemistry / by R.H.A. Plimmer. Source: Wellcome Collection.

    24/660 (page 4)
    I. PURIFICATION OF A LIQUID BY DISTILLATION— DETERMINATION OF THE BOILING-POINT. A liquid is purified by distillation. The criterion of the purity of a liquid is its boiling-point. A pure liquid has a constant boiling-. point. A. Drying and Cleaning of Apparatus. — Since organic liquids are very frequently not miscible with water all the apparatus which is used with them must be dry. The apparatus may be dried in an oven for some time, but on removal to prevent deposition of aqueous vapour a current of air is blown through them whilst they are hot and during cooling. The current of air is most conveniently got from bellows, or by suction with a pump. The tubing, or if the glass vessel be narrow, a glass tube inserted in the tubing, is placed inside the vessel so that the farthest extremity is dried and cooled first. More usually since the vessels are wet with water, they are rinsed with alcohol after draining as much water away as possible, then with ether after again draining. A current of air from the bellows or water- pump is drawn through to evaporate the ether. The vessel may be warmed in a luminous flame, when no more ether is present and the vessel is not quite dry, and air driven through as above. It is im- portant that all the ether be evaporated, since it may become ignited or form an explosive mixture inside the vessel. Apparatus which contains charred matter may be cleaned by oxidising it away with potassium bichromate and sulphuric acid, or by heating in it a mixture of concentrated sulphuric and nitric acids, washing with water and proceeding as above to dry it. B. Distillation of a Liquid and Determination of its Boiling- point. . The liquid is placed in a clean, dry fractionating or distilling flask —a round-bottom flask with a side tube in its neck! —of suitable size so that only about half or at most two-thirds of the space is filled. Some small pieces of unglazed porcelain, or porous earthenware, or pieces of platinum, are added to ensure steady boiling without bump- ing. The neck of the flask is closed with a well-fitting cork ? which 1 With liquids of high boiling-point the flask should have the side tube low down so as to prevent decomposition by the high temperature. 2 Rubber corks are dissolved by many organic liquids and consequently are not used, except in special cases.