136 



VOLUMETRIC AND INDIRECT ESTIMATION OF FAT. 



the difference between the two will give the percentage of fat ; 

 repeat this once or twice ; the results should be identical (Fig. 16). 

 Each small division is ^ per cent, fat ; if, then, the fatty 

 layer occupies thirty-six of these, the percentage is 3-6. With 

 practice half or a quarter of a division may be read easily. 



Should the fatty layer have sunk below the lowest graduation, 

 a little more diluted acid may be added, and the bottle whirled 

 for a few seconds. 



In very cold weather the fat may solidify in the neck ; in 

 such case it should be warmed slightly before 

 reading ; it is not otherwise necessary to warm 

 the bottles before reading. 



Skim milk and buttermilk should be whirled as 

 soon as possible after mixing ; in very hot weather, 

 or if the bottles stand very long after the acid has 

 been added, the fat may be of a dark colour. 



It is advisable to compare the results given by 

 this method with those given by the Gottlieb or 

 other good gravimetric process whenever a new 

 stock of sulphuric acid or amyl alcohol is used, 

 and, if necessary, to work out a definite correction 

 to be added to or subtracted from the results. With 

 acid and alcohol corresponding to the specification 

 above, no correction should be necessary. 



The difference between the results by the 

 Leffmann-Beam method and those by gravimetric 

 analysis very rarely exceed 0-1 per cent, of fat. 



Testing of Cream, If the cream contains less 

 than 32 per cent, of fat it can be measured direct 

 by the 4-5 c.c. pipette ; if it is thicker than this, 

 it must be diluted with separated milk. Two 

 beakers or tin pots are counterbalanced on a 

 rough balance turning to 0-01 gramme ; in one of 

 them, about 25 grammes of cream are placed, and 

 water is run into the other till the weights are 

 equal. The cream and water are mixed together, 

 and the mixture can be measured. If the cream 

 is sour a few drops of ammonia should be placed in the pot 

 before the weights of water and cream are adjusted. 



The measurement is performed as follows : Fill the pipette 

 with cream by sucking at the top, and close it with the finger ; 

 hold the pipette vertically, and allow the cream to run down 

 till the upper surface is on a level with the mark ; turn the 

 pipette to a horizontal position and wipe the stem ; then return 

 it to the vertical and, holding the point over the neck of a test 

 bottle, allow the cream to run out freely ; after the quick succes- 



Fig. 16. 

 Neck of Bottle. 



