As the amount of fat obtained from 5 grammes of a cacao preparation does not suffice for tests of purity, a larger quantity must be extracted in order to carry out the following investigations. This has reference to
- 1. The determination of the melting point;
- 2. The determination of the iodine value (Welman)[173];
- 3. The determination of the saponification value;
- 4. The determination of the acid value;
- 5. The determination of the Reichert-Meissl value;
- 6. Polen’s value[174];
- 7. Cohn’s investigation[175];
- 8. Melting point of the fatty acids;
- 9. Refraction of the fatty acids;
- 10. Iodine value of the fatty acids;
- 11. Determination of the refractive index at 40° C. in Zeiss’ butter refractometer.
The following process is usually adopted in the determination of the melting point of cacao fat:
The melted fat is sucked up a glass capillary tube, the internal diameter of which does not exceed 2 mm (fluctuating between 1·8 mm and that measurement) to somewhat above the part of the tube which is graduated into tenths, and then so much of the capillary tube cut off as suffices to make the fat column there half the height of the bulb of the mercury thermometer used in the experiment.
As fresh molten fat has a very variable melting point, it is absolutely essential that the fat in this experiment be allowed to cool about a week in some dark chamber, and, because only after the expiration of this period can the melting point be designated as a constant, not to proceed with the further determination until this necessary stage has been reached.
To carry out this determination the capillary tube is attached to the bulb of the mercury thermometer by means of a rubber ring in such a manner that the column of fat occurs directly in the middle.
The whole apparatus is now hung in a test tube of 2½ cm internal diameter, which is just so far filled with water that this can only penetrate to the fat in the capillary tube which is open at both ends from the under side. To regulate the flow of heat, this test tube is further introduced into a beaker also filled with water, which is heated first. As soon as the fat is melted, the water penetrates to the capillary tube and pushes along the fat column.
The reading is now taken at once the degree registered, the thermometer showing the melting point of the fat.
We need not here launch on an exact description of the above mentioned determination, but will only stay to point out the oft-mentioned book of R. Benedikt’s, entitled “Analyses of Kinds of Fat and Wax”, as enlarged and issued by F. Ulzer after the death of the author (Berlin edition, J. Springer).
Should a doubt arise in comparing the results given by these six tests, which may happen with some kinds of ordinary cacao butter, the employment of Björklund’s empirical ether test[176] or Filsinger’s alcohol-ether test is to be recommended, which latter is carried out as follows.[177]