The observed thermal degree of the oil and acid divided by that of the water and acid is termed the specific temperature reaction. For convenience in writing, this quotient is multiplied by 100. The respective quantities of acid and water are ten and fifty cubic centimeters. This method of calculation has the advantage of eliminating to a certain degree the variations which arise in the use of sulfuric acid of differing specific gravities. In the following table are given the comparative data obtained for some common oils.[286]
| Acid of 95.4 per cent. | Acid of 96.8 per cent. | Acid of 99 per cent. | ||||
|---|---|---|---|---|---|---|
| Kind of oil. | Rise of temp. with the oil. | Specific temp. reaction. | Rise of temp. with the oil. | Specific temp. reaction. | Rise of temp. with the oil. | Specific temp. reaction. |
| 0° | 0° | 0° | 0° | 0° | 0° | |
| Olive oil | 36.5 | 95 | 39.4 | 85 | 44.8 | 96 |
| Rapeseed oil | 49.0 | 127 | 37.0 | 89 | 58.0 | 124 |
| Castor oil | 34.0 | 88 | ||||
| Linseed oil | 104.5 | 270 | 125.2 | 269 | ||
325. Method of Richmond.—The rise of temperature produced by mixing an oil and sulfuric acid is determined by Richmond in a simple calorimeter, which is constructed by fitting a small deep beaker inside a larger one with a packing of cotton. The heat capacity of the system is determined by adding to ten grams of water, in the inner beaker, at room temperature, twenty-five grams of water of a noted higher temperature and observing the temperature of the mixture. The cooling of the system, during the time required for one determination of heat of sulfuric saponification, does not exceed one per cent of the whole number of calories produced.[287] Between the limits of ninety-two per cent and one hundred per cent the rise of temperature observed is directly proportional to the strength of the acid.
Relative Maumené Figure.—The total heat evolved per mean molecule is called by Richmond the relative maumené figure. It is calculated as follows:
- Let x = percentage of sulfuric acid in the acid employed;
- h = heat capacity of calorimeter in grams of water;
- R = observed rise of temperature (twenty-five grams of
- oil, five cubic centimeters sulfuric acid);
- K = potash absorbed for saponification (19.5 per cent of
- potassium hydroxid, standard of comparison);
- M = relative maumené figure:
| ThenM = R × | 21.5 | × | 20 + h | × | 19.5 |
| x - 78.5 | 20 | K |
326. Heat of Bromination.—The rise of temperature caused by mixing fats with sulfuric acid has long been used to discriminate between different fats and oils. Hehner and Mitchell propose a similar reaction based upon the rise of temperature produced by mixing bromin with the sample.[288] The action of bromin on unsaturated fatty bodies is instantaneous and is attended with a considerable evolution of heat. Since the action of bromin on many of the oils is very violent it is necessary to dilute the reagent with chloroform or glacial acetic acid. Owing to its high boiling point the acetic acid has some advantage over chloroform for this purpose. The tests are conveniently made in a vacuum-jacket tube. In such a tube there is no loss of heat by radiation. The bromin is measured in a pipette having at its upper end a tube filled with caustic lime held between plugs of asbestos. The bromin sample to be tested and the diluent employed are kept at the same temperature before beginning the trial. They are quickly mixed and the rise of temperature noted. The oil is first dissolved in the chloroform and the bromin then added.
A somewhat constant relation is noticed between the rise of temperature and the iodin number when one gram of oil, ten cubic centimeters of chloroform and one cubic centimeter of bromin are used.
If the rise in temperature in degrees be multiplied by 5.5 the product is approximately the iodin number of the sample. Thus a sample of lard gave a rise in temperature of 10°.6 and an iodin number of 57.15. The number obtained by multiplying 10.6 by 5.5 is 58.3.
In like manner the numbers obtained for some common oils are as follows: