226 



THE CHEMICAL CONTROL OF THE DAIRY. 



sulphuric acid with, water, but when the way is once learned 

 there is no difficulty in doing this. Fill up the bottles to the 

 zero mark with a mixture of one part of sulphuric acid to two 

 volumes of water, and place the bottles in the machine ; rotate 

 by turning the handle at 100 revolutions per minute for about 

 one minute, when the fat will separate in a clear layer. 



Read the fatty layer as follows ; — Note the position of the 

 lower surface of the fat (it is convenient to wait till it has fallen 

 to one of the main graduation lines), then immediately note 

 the position of the lowest point of the curve on the upper surface ; 

 the difEerence between the two will give the per- 

 centage of fat ; repeat this once or twice ; the 

 results should be identical (Fig. 24). 



Each small division is ^^ per cent, fat ; if, 

 then, the fatty layer occupies thirty-six of these, 

 the percentage is 3 "6. Half or a quarter of a 

 division may easily be read with practice. 



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 G-ottlieb 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 specifi- 

 cation above, no correction should be necessary. 



The difEerence between the results by the 

 Lefimann-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 arc counterbalanced on a rough balance 

 turning to O-Ql 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 



Fig. 24. 

 Neck of bottle. 



