Art. LI.—Note on the Determination of Milk-fat.
[Read before the Philosophical Institute of Canterbury, 2nd December, 1914.]
According to Thorpe,† the official Adams process for determining the fat-content of milk has largely been superseded by the method of Gottlieb. The same writer states that Gottlieb's method is perhaps the easiest and best of all methods of fat-estimation.
Olsen‡ states that it is conceded that higher percentages of fat are generally obtained by the Gottlieb than by the present ether-extraction method.
While a considerable amount of data have been published showing the comparative results obtained by the use of Gottlieb's method in determining the fat-content of various dairy-products, including milk, the author has been unable to find a record of any results comparing the Adams process with Gottlieb's in the estimation of the fat-content of fresh milk.
The author recently had occasion to compare these processes in connection with the examination of a number of milk-samples, and the following results are now put on record.
|Sample No.||Adams's Process. Fat per Cent.||Gottlieb's Method. Fat per Cent.|
[Footnote] † Dict. Applied Chem., rev. ed., vol. 3, pp. 531, 532.
[Footnote] ‡ Bulletin No. 105, U.S. Dept. Agric., p. 109.
The method of Gottlieb as described by Thorpe* was used in the above determinations, and is as follows: 10 c.c. of milk are measured into a tall, narrow cylinder, graduated in 0.5 c.c., and holding 100 c.c.; 1 c.c. of ammonia (sp. gr. 0.96) is added, and then 10 c.c. of alcohol. The mixture is well shaken; 25 c.c. of ether, which need not be dry, are added; and the contents of the tube well mixed. Finally, 25 c.c. of light petroleum are added, and the mixture again well shaken. It is essential that the contents of the tube be mixed after the addition of each reagent, or the results may be very low. The cylinder is then left for six hours, the volume of the ethereal solution measured, and 50 c.c. removed, evaporated, and the fat dried and weighed.
The question naturally arises as to whether or not the increased result is due to some substances other than fat, introduced by the reagents used in the Gottlieb method, or through their action. A blank test of the chemicals used was made and the small amount of residue obtained on evaporation deducted from the results.
Olsen† has shown that the results obtained by the Gottlieb method are the true fat-content of dairy-produce, and this is of special importance in the case of milk or other dairy-products containing only small amounts of fat.
[Footnote] * Dict. Applied Chem., rev. ed., vol. 3, pp. 531, 532.
[Footnote] † Bulletin No. 105, U.S. Dept. Agric., p. 109.