68 DAIRY ANALYSIS 



temperature, a property which depends on the 

 fact that mixing margarine with butter often 

 causes overworking, which gives rise to turbidity. 



Owing to the natural variations of the composition 

 of butter fat, and to a less degree of the composition of 

 adulterants, the detection of small quantities of mar- 

 garine is difficult, and unless sesame oil can be found, 

 impossible in minimal amounts ; as only three principles 

 underlie all the methods, one of which has little value, 

 a multiplication of tests does not greatly assist. 



Preparation of the Fat for Analysis. Place 20 

 to 50 grammes of butter in a small beaker, and put 

 this in the water oven till melted ; observe the fatty 

 layer, whether clear or turbid ; pour as much as possible 

 of the fat into a dry filter, taking care that none of the 

 aqueous portion accompanies it, and filter in the water 

 oven, collecting the clear fat in a small beaker. 



Estimation of the Volatile Fatty Acids. Reichert- 

 Wollny Process, Polenske's Modification. Place a flask 

 of 300 c.c. capacity on one pan of a balance and tare 

 it ; add 4.5 grammes to the weights, and run in the 

 melted fat till the flask is weighed down, and place 

 a further 0.5 gramme weight on the other pan ; con- 

 tinue the addition of the fat cautiously, till the weight 

 is exact, if necessary removing a surplus with a small 

 pipette. It is not necessary to wait for the fat in the 

 flask to cool before making the final adjustment, as 

 the error involved in weighing warm fat is within the 

 limits of error of the final titration, nor is it necessary 

 to weigh more accurately than to 0.005 gramme. 

 Weigh in 20 grammes of glycerine. 



Add 2 c.c. of a 50 per cent, solution of caustic soda 

 (see Appendix), preferably from a special measuring 

 apparatus (Fig. 34) ; heat the mixture over a naked 

 flame till the turbid liquid suddenly becomes clear ; 

 allow it to cool a little and add 100 c.c. of hot water 

 which has been previously boiled for at least fifteen 

 minutes, and when all the resulting soap is dissolved 

 0.1 gramme of powdered pumice which has been sifted 



