342 



PHYSIOLOGICAL CHEMISTRY 



>C.C;: 



3. Fat. (a) Babcock's Centrifugal Method. 1 Principle. The 

 principle of this method is the destruction of organic matter other 

 than fat by sulphuric acid and the centrifugation of the acid solution 

 in the special tube shown in Fig. 1 1 1 and the subsequent reading of 

 the percentage of fat by means of the tube's graduated neck. The 

 method is one of the most satisfactory in common use 

 and is accurate to within 0.5 per cent. 



Procedure. By means of a special narrow pipette intro- 

 duce milk into the tube up to the 5 c.c. mark. Now add 

 sufficient sulphuric acid (sp. gr. 1.83-1.834) to fill the body 

 of the tube and rotate the tube to secure a homogeneous 

 acid-milk solution. Fill the neck of the tube with an acid- 

 alcohol mixture. 2 Centrifuge the tube and contents for one 

 to two minutes and read off the percentage of fat by means 

 of the graduated neck of the tube. If the top of the fat column 

 is not at zero it may be brought there by the addition of 

 water and a moment's recentrifugation. 



In case very rich milk (over 5 per cent fat) is under ex- 

 animation, it may be diluted with an equal volume of water 

 before examination and the fat percentage multiplied by 2. In 

 the examination of cream it is customary to dilute the sample 

 with four volumes of water and multiply the resultant fat 

 value by 5. 



(b) Quantitative Determination of Fat in Milk by the 

 Meigs 3 Method with Modification and Improved Apparatus 

 by Croll. 4 The method as stated by Dr. Meigs is: Approxi- 

 mately 10 c.c. of milk is carefully weighed and transferred to 

 an ordinary 100 c.c. glass-stoppered graduated cylinder. 

 Twenty c.c. each of distilled water and ether (0.720) are 

 added, the ground-glass stopper tightly inserted in the bottle, 

 and the whole shaken vigorously for five minutes. Then the 

 bottle is carefully unstoppered, 20 c.c. 95 per cent alcohol 

 added, the stopper reinserted and again shaken for five 

 minutes. The bottle is now placed on a table and the con- 

 tents will separate into two distinct strata, the upper of which contains prac- 

 tically all the fat. This stratum is carefully removed by a small pipette and 

 transferred to a carefully weighed glass evaporating dish. The thin ether 

 layer remaining is washed by the addition of 5 c.c. of ether. This is removed 

 by pipetting off. This washing is repeated four times. On each addition the 



1 A modification of this method for use with sweetened dairy products, e.g., ice cream, 

 and entailing the use of a different type of centrifuge tube has been proposed by Halverson 

 (Jour. Ind. and Eng. Chem., 5, 403, 1913;. A more recent modification involving the 

 use of mixtures of glacial acetic, sulphuric and nitric acids instead of sulphuric acid alone 

 has been proposed by Francis and Morgan (Jour. Ind. and Eng. Chem., 9, 861, 1917). 

 These authors use the regulation Babcock tube, and the method is applicable to the analysis 

 of ice cream, and evaporated, malted and dried milk. 



2 This mixture consists of equal volumes of amyl alcohol and concentrated hydrochloric 

 acid. 



3 Original paper by Dr. Arthur V. Meigs in Philadelphia Medical Times, July i, 1882. 



4 Croll: Biochem. Bull., 2, 509, 1913. 



FIG. in. BAB- 

 COCK TUBE. 





