When waxes are decomposed by alkalies, fatty acids and alcohols of the ethane series are produced.
The natural glycerids formed from glycerol, which is a trihydric (triatomic) alcohol, are found in the neutral state composed of three molecules of the acid, united with one of the base. If R represent the radicle of the fat acid the general formula for the chemical process by which the salt is produced is:
| Glycerol. | Acid. | Salt. | Water. | ||
| O.H | O.R | ||||
| C₃H₅ | O.H | + 3R.OH = | C₃H₅ | O.R | + 3H₂O. |
| O.H | O.R | ||||
The resulting salts are called triglycerids or neutral glycyl ethers.[230] In natural animal and vegetable products, only the neutral salts are found, the mono- and diglycerids resulting from artificial synthesis. For this reason the prefix tri is not necessarily used in designating the natural glycerids, stearin, for instance, meaning the same as tristearin.
279. Principal Glycerids.—The most important glycerids which the analyst will find are the following:
| Olein, | C₃H₅O(O.C₁₈H₃₃O)₃. |
| Stearin, | C₃H₅O(O.C₁₈H₃₅)₃. |
| Palmitin, | C₃H₅O(O.C₁₆H₃₁O)₃. |
| Linolein, | C₃H₅O(O.C₁₈H₃₁O)₃. |
| Butyrin, | C₃H₅O(O.C₄H₇O)₃. |
Olein is the chief constituent of most oils; palmitin is found in palm oil and many other natural glycerids; stearin is a leading constituent of the fats of beeves and sheep, and butyrin is a characteristic constituent of butter, which owes its flavor largely to this glycerid and its nearly related concomitants.
280. Extraction of Oils and Fats.—Preparatory to a physical and chemical study of the fats and oils is their separation from the other organic matters with which they may be associated. In the case of animal tissues this is usually accomplished by the application of heat. The operation known as rendering may be conducted in many different ways. For laboratory purposes, the animal tissues holding the fat are placed in a convenient dish and a degree of heat applied which will liquify all the fat particles and free them from their investing membranes. The temperature employed should be as low as possible to secure the desired effect, but fats can be subjected for some time to a heat of a little more than 100°, without danger of decomposition. The direct heat of a lamp, however, should not be applied, since it is difficult to avoid too high a temperature at the point of contact of the flame and dish. The dry heat of an air-bath or rendering in an autoclave or by steam is preferable. The residual animal matter is subjected to pressure and the combined liquid fat freed from foreign matters by filtering through a jacket filter, which is kept at a temperature above the solidifying point of the contents.
On a large scale, as in rendering lard, the fat is separated by steam in closed vats which are strong enough to withstand the steam pressure employed. For analytical purposes it is best to extract the fat from animal tissues in the manner described, since the action of solvents is slow on fat particles enveloped in their containing membranes, and the fats, when extracted, are liable to be contaminated with extraneous matters. In dried and ground flesh meal, however, the fat may be extracted with the usual solvents. For the quantitive determination of fat in bones or flesh, the sample, as finely divided as possible, is thoroughly dried, and the fat separated from an aliquot finely powdered portion by extraction with chloroform, ether, or petroleum. The action of anhydrous ether on dried and powdered animal matters is apparently a continuous one. Dormeyer has shown that even after an extraction of several months additional matter goes into solution.[231] The fat in such cases can be determined by saponification with alcoholic potash and the estimation of the free fatty acids produced.
From vegetable substances, such as seeds, the fat is extracted either by pressure or by the use of solvents. For quantitive purposes, only solvents are employed. The dry, finely ground material is exhausted with anhydrous ether or petroleum spirit, in one of the convenient forms of apparatus already described ([33->43]). In very oily seeds great difficulty is experienced in securing a fine state of subdivision suited to complete extraction. In such cases it is advisable to conduct the process in two stages. In the first stage the material, in coarse powder, is exhausted as far as possible and the percentage of oil determined. The residue is then easily reduced to a fine powder, in an aliquot part of which the remaining oil is determined in the usual way.