FATS occur in a great number of the animal tissues,being abundant under the skin in what is called the celhilar mem brane, round the kidneys, in the folds of the omentum, at the base of the heart, in the mediastinum, the mesenteric web, as well as upon the surface of the intest ines, and among many of the muscles. They vary in consistence, color, and smell, according to the animals from which they are obtained ; thus, they are generally fluid in the cetaceous tribes, soft and rank-flavored in the carnivorous, solid and nearly scentless in the rumi nants, usually white and copious in well fed young animals ; yellowish and more scanty in the old. Their consistence va ries also adcording to the organ of their production ; being firmer under the skin, and in the neighborhood of the kidneys, than among the moveable viscera. Fat forms about one twentieth of the weight of a healthy animal. But as taken out by the butcher it is not pure, for being of a vesicular structure, it is always enclosed in membranes, mixed with brood, blood vessels, lymphatics, &c. These foreign matters must first be separated in some measure mechanically, after the fat is minced small, and then more completely by melting it along with hot water, pass ing it through a sieve, and letting the whole cool very slowly. By this means a cake of cleansed fat will be obtained. Many plans of purifying fats have been proposed ; one of the best is to mix two per cent of strong sulphuric acid with a quantity of water, in which the tallow is heated for some time with much stirring ; to allow the materials to cool, to take off the supernatant fat, and re-melt it with abundance of hot water. More tallow will thus be obtained, and that consider ably whiter and harder than is usually procured by the melters.
Fat is deposited in cells in the cellular tissues of the animal ; when viewed un der the microscope they are partly poly gonal, partly reniform particles, which are connected together by very thin mem branes. These may be ruptured by me chanical means, then separated by tritu rating the fresh fats with cold water, and passing the unctuous matter through a sieve. The particles float in the water, hut eventually collect in a white granular crystalline appearance, like starch. Each of them consists of a vesicular integu ment, of the nature of stearine, and an interior fluid like elaine, which afterwards exudes. The granules float in the water, but subside in spirits of wine. When digested in strong alcohol, the liquid part dissolves, but the solid remains. These particles differ in shape and size, as obtained from different animals ; those of the calf, ox, sheep, are polygonal, from A to of an inch in diameter ; those of the sow are kidney-shaped, and from A to those of a man are polygon al, and from A to ; those of in sects are spherical, and at most .4. of an inch.
Fats all melt at a temperature much under 212° F. When strongly heated with contact of air, they diffuse white pungent fumes, then blacken, and take fire. When subjected to distillation,
they afford a changed fluid oil, earbureted hydrogen, and the other products of oily bodies. Exposed for a certain time to the atmosphere, they become rancid, and generate the same fat acids as they do by saponification. In their fresh state they are all composed principally of stearine, margarine, and oleine, with a little color ing and odorous matter.
Fats are true chemical salts, being com posed of a fatty acid united to a base. This base is generally glycerine. The acids are either stearw acid, which is found abundantly in the hard fats, as suet and tallow, Margaric acid, also a solid, found in the crystalline portion which cold throws out of olive oil ; it is also found in ani mal fats and oleic acid, which is found abundantly in olive oil, and all liquid fhts and oils.
The properties of stearine and elaine, or of stearic and oleic acids vary at dif ferent seasons and under various circum stances ' • thus, butter, in summer, con sists of 60 of oleine and 40 of stearine ; in winter, of 37 of oleine, and 63 of stear me ; the former substance being yellow, and the latter white. It differs, however, as produced from the milk of different cows, and also according to their pas ture.
Animals oils and fats differ only in fluidity, and may be treated of together. Of animal oils, whale oils, and sperm oils are the most generally known in this coun try: the fats are spermaceti, butter, tallow, lard, and suet. Whale or train oil is ex tracted from the blubber of the whale, principally the balena mysticetes ; origi nally at is a firm solid fat. To obtain the oil, the blubber is me ed in large copper vessels, a large quantity of water sepa rates, and on the surface there floats a solid matter calledfenh, which is proba bly coagulated albumen ; the more mode rate the heat, and the shorter its dura tion, the paler and better the oil. The deep color is owing to too much boiling, and perhaps to blood and impurities mix ed with it. The Greenland oil is pale and free from smell, and burns with a pure and bright flame. By adding cold drawn oil it is made more fluid and com bustible. Chloride of lime deprives it of its offensive odor. It boils at 600°, and may be distilled, but it then is an altered oil. Sperm oil forms part of the oily sub stance in the cranium of the spermaceti whale (physeter macrocephalus). The oil is separated by putting the mass in a woollen bag and pressing it, when the oil runs out. This kind of oil is purer than train, and burns away without leaving charcoal on the wicks. The manner of obtaining the solid fats has been given ; when soft it is called lard, when hard tallow. It is insoluble in water and alcohol, melts at 90° or 100° by raising the heat it becomes acrid, and gives off a pungent vapor. In close ves sels it is decomposed, and among other substances yields a large quantity of ole fiant gas. It is inflammable, and affords by combustion water and carbonic acid.