1 42 MILK AND DAIRY PRODUCTS PART 



reaction (p. 98) can be used with advantage and in the 

 following manner. 



About 25 g. of butter are placed in a suitable beaker and there 

 melted by putting the beaker into warm water of a tempera- 

 ture not higher than 60 C. The clear butter fat is then drawn off 

 and the white sediment mixed with an equal quantity of water. 

 The resulting liquid is then placed in a test-tube and one drop 

 of hydrogen peroxide and two drops of paraphenylenediamine 

 solution added. If a blue coloration is given, then the cream 

 from which the butter was made had not been heated to 80 C. ; 

 if, on the contrary, there is no coloration, then the heating must 

 have exceeded this temperature. This method usually fails if 

 the butter is more than fourteen days old. 



EXAMINATION OF THE BUTTER FAT. 



A. Physical Tests. 



I. DETERMINATION OF THE SPECIFIC GRAVITY OF BUTTER 



FAT (AT 100 C.). 



The sample of butter is melted at about 60 C. and the clear 

 fat poured off from the sediment through a dry filter, care being 

 taken that none of the milky sediment enters. This clear 

 filtered fat is pure butter fat. 



E. Konig recommends that a thin-walled test-tube should 

 be filled with the fat and suspended almost up to the top in a 

 water-bath containing boiling water. By means of a specially 

 constructed hydrometer, 1 having a scale of 0'845-0'870, the 

 specific gravity is then determined. In general this lies 

 between 0'865 and 0'868 at 100 C. if the fat is pure. 



II. DETERMINATION OF THE MELTING POINT AND THE 



POINT OF SOLIDIFICATION. 



(a) The Melting Point. 2 



A piece of glass tubing with an internal diameter of about 

 3 mm. is drawn out in such a way that the change from the 

 wide tube to the capillary is quite sharp. The drawn-out 



1 To be obtained from C. Gerhardt, Bonn. 



2 Bensemann, Rep. der anal. Chem., Vol. IV, p. 165, and Vol. VI, p. 202. 



