Volume 2

Chemical technology and analysis of oils, fats and waxes / by J. Lewkowitsch.

  • Lewkowitsch, J. (Julius), 1857-1913.
Date:
1909
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Chemical technology and analysis of oils, fats and waxes / by J. Lewkowitsch. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    the free fatty acids, as also the improvement of the colour, if need be, by filtering over char or fuller’s earth, is carried out in a similar manner with oils and fats intended to serve as burning oils, paint oils, lubricating oils, etc. (see Yol. III. Chap. XV.). Since the taste is not of paramount importance in judging the quality of commercial oils and fats, bleaching by exposure to the air and sunlight can be resorted to. Methods of this kind are applied to linseed oil for artists’ purposes, as also to the bleaching of beeswax (see Chap. XIY. “ Beeswax ”). Crude oils and fats, as also those beeswaxes which are more or less deeply coloured, require more elaborate processes of refining, and in most cases a treatment with chemicals is resorted to in the first instance. The greatest possible stress must be laid on the fact that there is no universal method of refining which is applicable to every and any oil, fat, or wax. In many cases purification by means of sulphuric acid, invented and patented by Charles Gower in 1792 (and frequently ascribed to TMnard), is still usefully employed, -as in the refining of linseed and rape oils. The method consists in treating the oil or fat with a small percentage of more or less concentrated sulphuric acid— according to the nature of the oil or fat. The acid not only takes up water, but acts on the suspended impurities, carbonising them to some extent, thus causing them to coagulate and separate out in the form of a flocculent mass, which falls down and carries with it mechanically other impurities which have not been acted upon. As another general method the purification by means of strong caustic soda has been recommended by Louis C. Arthur Barreswil, his suggestion being to heat the oil or fat and add 2-3 per cent of a concentrated caustic soda solution. In most cases the purification consisted merely in the removal of the free fatty acids present, the caustic soda forming with the free fatty acids a soap which would either rise as a scum and lift up with it impurities, or fall down to the bottom and carry down the impurities. As a rule, however, this method is a very precarious one, as emulsions are formed which in many cases altogether prevent the separation of the oil (see Yol. III. Chap. XV.). After the treatment with acid or alkali the oils or fats are washed with water to remove the last traces of chemicals, and are then further treated by the physical methods described above. The number of chemical processes which have been proposed from time to time for the last 120 years, and which are still being copied and perpetuated from old text-books, is almost legion. So long as the chemical nature of oils and fats was little understood, a secret trade in oil-purifying chemicals flourished. But our present knowledge enables us to remove most of these chemicals into the limbo of useless things. Too much stress cannot be laid on the necessity of regarding the bleaching of each individual oil or fat as a problem sui generis, and of recognising that the processes adopted