Thomson's conspectus : adapted to the British pharmacopoeia / edited by Edmund Lloyd Birkett.

  • Thomson, Anthony Todd, 1778-1849.
Date:
1875
Catalogue details

Licence: Public Domain Mark

Credit: Thomson's conspectus : adapted to the British pharmacopoeia / edited by Edmund Lloyd Birkett. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    EXPRESSED OILS. These oils are compounds of oxygen, hydrogen, and carbon. They are prepared by nature in the seeds and fruits of some vegetables, from which they are expressed, and hence their ap- pellation : but the title fixed oils is preferable, as it implies their character, and as some of the volatile oils also are obtained by expression. Those which are expressed without heat are to be preferred, as by heat they are apt to acquire acrimony and an empyreumatic odour. The greater number of them, when pure, are liquid in a moderate temperature, unctuous, perfectly trans- parent, colourless, or having a pale yellow or greenish tinge; inodorous; lighter than water, and not miscible with it: they unite with alkalies and form soap ; and with oxide of lead and form plasters. Almond and olive oil should be insipid; linseed and castor oils have some taste, but they should not feel hot nor acrid in the throat. Palm oil is a soft solid, or butter. The rancidity of oils probably depends on the absorption of oxygen, on which account they should be kept in bulk as much as possible, and in narrow-necked bottles; so that a very small surface only will be exposed to the air. DISTILLED OILS. For similar reasons to those stated above, regarding expressed oils, we prefer the title of volatile oils for these preparations. They are mostly compounds of oxygen, hydrogen, and carbon, and in some instances also of nitrogen; and are produced by nature in various parts of the vegetable system; either in the flowers, the fruit, the leaves, the bark, the wood, and sometimes in all of these parts. The majority of them are obtained by distillation, but some of them by expression. They possess the unetuosity, inflammability, and viscidity of the fixed oils; but they are in general coloured, odoriferous, pungent, and acrid. The majority are lighter than water, but some of them are heavier, and some congeal at a moderate temperature. They are dissolved in small quantity, in distilled water, by simple agitation. Almost all of them are soluble in alcohol, and miscible with fixed oils, and with each other; hence they are often adulterated with alcohol, or with oil of olives or of almonds, or with oil of turpentine, which is the cheapest of the volatile oils. The first is discovered by an increase of temperature and a milky appearance, when the oil is mixed with water; the second, by a greasy stain being left on paper on which the oil is dropped and exposed to a considerable heat, and by not being soluble in alcohol; and the third by its odour, when the suspected oil is dropped on paper and heated, or sometimes even when rubbed between the lingers.