272 THE PHYSICAL EXAMINATION OF BUTTER FAT. 



Mercier digests 1 c.c. of melted fat with 30 c.c. of 90 per cent, 

 alcohol for five minutes at 50 to 55 C., the fat and alcohol 

 being mixed well ; and after fifteen to twenty minutes' standing 

 20 c.c. of the alcoholic solution are withdrawn, cooled to 30 

 to 40 C., and filtered ; the fat is then allowed to crystallise 

 slowly, and the crystals filtered out and examined by the micro- 

 scope. If coconut oil is present, little round bunches of crystals 

 consisting of long needles are observed. 



Hinks has devised a process, which also depends on the 

 crystallisation of coconut oil from alcohol ; 5 c.c. of butter fat 

 are dissolved in 10 c.c. of ether in a test-tube, which is then 

 placed in ice. After half an hour, the clear ethereal solution 

 is filtered through a pleated filter, the filtrate evaporated, and 

 the residual fat boiled with three or four times its volume of 

 alcohol (96 to 97 per cent, by volume the strength is important). 

 Complete solution takes place at the boiling point, and the liquid 

 is allowed to cool to room temperature, and then placed in water 

 at 5 C. for fifteen minutes. The alcoholic solution is filtered 

 rapidly into a tube, which is kept at C. for two or three hours. 

 The flocculent deposit is examined by the microscope, using a 

 magnification of 250 to 300 diameters, preferably on a cooled 

 stage ; butter deposits glycerides in round granular masses, but 

 coconut oil yields fine needle-shaped crystals ; a mixture shows 

 the granular butter spores, with numerous fine, almost feathery, 

 crystals generally attached to the butter granules. 



Five per cent, of coconut oil can be detected by this test. 



The Density of Butter Pat. 



Butter fat, on account of the presence of glycerides of low 

 molecular weight, has a greater density than the fats used for 

 its adulteration. As it is more convenient and exact to take 

 the density of a liquid than of a solid, the fat is almost invari- 

 ably melted and the density determined at a temperature above 

 its melting point. 



The methods of estimating the density have already been 

 discussed under the " specific gravity of milk " (p. 68), and 

 (except that for butter a temperature considerably higher than 

 that at which the density of milk is taken is employed) the 

 same methods are employed. 



Expansion. Two questions arise : At what temperature 

 shall the density of butter be taken ? How shall the results be 

 expressed ? The experiments of Skalweit have indicated the 

 most favourable temperature. He took the densities of butter 

 and margarine at various temperatures from 35 C. to 100 C., 

 using Koch's incubator to keep a constant temperature. 



