Oils and fats must, therefore, not be looked upon as definite chemical individuals, but as representatives of natural species which vary, although within certain narrow limits, according to the climate and soil in which the plants which produce them are grown, or, in the case of animal fats, according to the climate, the race, the age of the animal, and especially the food, and also the idiosyncrasy of the individual animal.
It aids the absorption of fats and may be used with cod liver oil when the latter is administered by the skin.
They are mainly carbohydrates such as starch and sugar, proteids in the form of globulins or albumoses, and in many cases fats and oils, while certain other bodies of similar nutritive value are less widely distributed.
Of the natural fats or glycerides contained in oils the most important in addition to palmitin are stearin and olein, and these it may be sufficient to regard as the principal fatty bodies concerned in soapmaking.
It is obtainable from most natural fatty bodies by the action of alkalis and similar reagents, whereby the fats are decomposed, water being taken up, and glycerin being formed together with the alkaline salt of some particular acid (varying with the nature of the fat).