MILK 



325 



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 examination, 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 1 Method with 

 Modification and Improved Apparatus by Croll. 2 The method as stated by Dr. 

 Meigs is: Approximately 10 c.c. of milk is care- 

 fully 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 contents will 

 separate into two distinct strata, the upper of 

 which contains practically 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 remain- 

 ing is washed by the addition of 5 c.c. of ether. 

 This is removed by pipetting off. This wash- 

 ing is repeated four times. On each addition 

 the sides of the bottle should carefully be 

 washed down by the fresh ether. Finally, the 

 pipette is rinsed with a little ether. The 

 evaporating dish with contents is now placed 

 on a safety water-bath and the ether evapo- 

 rated. The drying is continued in a hot-air 

 oven at a temperature below iooC. and finally 

 completed in a desiccator to constant weight. 



Croll's modification consists of subsequent 

 repeated extraction of the end-product of 

 evaporation with absolute ether. The com- 

 bined extracts are filtered and the small filter 



paper is washed repeatedly with absolute ether. The combined extracts and 

 washings are evaporated and dried as before and then weighed. 



The piece of apparatus shown in Fig. 107, above was also devised by Croll 

 to do away with the use of the pipette. 3 On closing the top with a finger and 

 blowing into the mouthpiece, the upper stratum is forced out into the dish. The 

 bottle is washed by simply pouring the ether into the tube. This lessens the 

 possibility of accidental loss. 



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



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



3 If desired a cork with two tubes may be substituted for this somewhat complicated 

 apparatus. 



FIG. 107. CROLL'S FAT 

 APPARATUS. 



