solid olein obtained
TALLOW is the solid oil or fat of ruminant animals, but commercially it is almost exclusively obtained from oxen and sheep. The fat is distributed throughout the entire animal structure; but it accumulates in large quantities as "suet " in the body cavity, and it is from such suet that tallow is principally melted or rendered. The various methods by which tallow and other animal fats are separated and purified have been dealt with under Oils (see vol. xvii. p. 743). In commerce ox tallow and sheep tallow are generally distinguished from each other, although much nondescript animal fat is also found in the market. Ox tallow occurs at ordinary temperatures as a solid hard fat having a yellowish white colour ; when fresh and new it has scarcely any taste or smell; but it soon acquires a distinct odour and readily becomes rancid. The fat is insoluble in cold alcohol, but it dissolves in boiling spirit of 0'822 sp. gr. in chloroform, ether, and the essential oils. The hardness of tallow and its melting-point are to some extent affected by the food, age, state of health, &c., of the animal yielding it, the firmest ox tallow being obtained in certain provinces of Russia, where for a great part of the year the oxen are fed on hay. New tallow melts at from 42°•5 to 43° C., old tallow at 43°•5, and the melted fat remains liquid till its temperature falls to 33° or 34° C. Tallow consists of a mixture of two-thirds of the solid fats palmitin and stearin, with one-third of the liquid fat olein. A fluid oil known as tallow oil is obtained from solid tallow by the separation by pressure of the greater part of .the olein. To facilitate the separation of the olein, tallow is first melted and just before resolidifying it is mixed with about 10 per cent. of benzene or petroleum spirit. The mixture is then allowed to solidify in flat cakes or slabs, which are placed in press bags and piled between iron plates in a hydraulic press. On the application of pressure the olein mixed with the solvent hydrocarbon flows freely out, leaving a hard dense cake of stearin and palmitin in the bags. The volatile solvents are subsequently driven off by blowing steam through the oil, which remains a turbid fatty fluid from the proportion of solid fats it carries over with it from the hydraulic press. Tallow oil is a useful lubricant and a valuable material for fine soap making, but it is not now abundantly prepared. Mutton tallow differs in several respects from that obtained from oxen. It is whiter in colour and harder, and contains only about 30 per cent, of olein. Newly rendered it has little taste or smell, but on exposure it quickly acquires characteristic qualities and becomes rancid. Sweet mutton tallow melts at 46° and solidifies at 36° C.; when old it does not melt under 49°, and becomes solid on reaching 44° or 45° C. It is sparingly soluble in cold ether and in boiling spirit of 0.822 sp. gr.
In early times tallow was a most important candle-making substance, and candles made from this material are still consumed in no inconsiderable quantity, but the greater proportion of the supply is now absorbed by the soap trade ; the artificial butter trade which has sprung up since 1872 also takes up large quantities of sweet tallow. Tallow is further used extensively as a lubricant and in leather dressing, 8:c. It is of course a product of all cattle and sheep-rearing countries, and it forms an important article of export from the United States, the Argentine Republic, and the Australian colonies. Till within the last quarter of a century Russia supplied nearly all the tallow imported into the United Kingdom ; but now the imports from that source are on the most meagre scale, although Russian P. Y. C. (pale yellow candle) continues to represent the finest commercial brand.