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.

    33/660 (page 13)
    EVAPORATION OF LIQUIDS. Only aqueous solutions can be evaporated over a flame, and the evaporation should be completed over a water-bath to prevent charring the substance as it becomes concentrated. Evaporation over a flame must be carefully watched to prevent charring and also to avoid spurting when the solution begins to concentrate. Most organic liquids which are used as solvents are readily inflam- mable, and must not be brought near a flame. When a considerable amount of solvent is present it is removed by distillation and in cases where the solvent (ether, acetone, ligroin, etc.) is very readily inflammable the distillation must be carried out on a water-bath, heated by a flame specially protected by a gauze, or by steam, or electrically. If the bath be heated by a burner the end of the condenser should be placed as far away as possible and a sheet of cardboard or asbestos interposed between the burner and receiver. Not only is evaporation by distillation absolutely necessary with inflammable liquids, but also it is economical. The solvent is recovered and after purification can be used again. When only small quantities of liquids up to 25 c.c. require evapora- tion they are set aside, away from flames, and allowed to evaporate spontaneously, or they may be put upon a warm water-bath, with the flame extinguished. 3 Another common procedure is to evaporate Small quantities by placing them in a vacuum desiccator and exhausting. The evaporation is greatly accelerated if the liquid is previously warmed on a water-bath - and whilst warm put into the desiccator. Evaporation /n Vacuo. Evaporation 2% vacuo is the most rapid method of concentrating solutions, especially if the temperature can be kept at an elevated point. Very frequently evaporation of solutions must be carried out at a low tem- perature (35-45) to prevent decomposition. This is carried out in the same way as distillation zz vacuo, the distilling flask being kept in water at 35-45°. With large flasks of 2-3 litres capacity and a good vacuum of about 15 mm., a litre of water can be distilled off in 2-24 hours at 35-45°. Instead of a distil- _ ling flask an ordinary flask fitted with capillary and bent tube may be used and. a similar one as receiver.