DENSITY. 345 



density is above 0'865 ; and if it sinks, it is below. This has 

 proved a fairly good rough test. 



The limits observed for pure butter are : — 



Maxinium. Minimum. Mean. 



37*8° 

 Atg^ 0-9140 0-9094 0-9118 



100° 

 At -p—i (in glass) 0-8685 0-86.50 0-8067 



The fats usually employed as adulterants have a density at 

 ^=--5 of 0-901 to 0-905, mean 0-903 ; and at j^ (in glass) of 



0-860 to 0-863, mean 0-861. 



100^ 

 Certain oils have, however, a higher density ; thus, at ^ 



(in glass)— ^^'^ 



Palm-nut oil has a density of 0-87.3 



Coco-nut oil, . . 0-874 



Cotton-seed oil, 0-8725 



Araohis oil, . 0-803 



Sesam"^ oil, . . 0-8675 



Of these oils, palm-nut and coco-nut oils can be readily 

 detected (see Fat), while the other oils cannot be used alone, 

 but must be mixed with fats of less densit}' to obtain the neces- 

 sary consistency. With the reservation that the oils mentioned 

 above would cause somewhat abnormal results, the determination 

 of the density of butter is a very useful test, and, though not 

 reliable as a single test, is of great use for corroborative purposes. 



Molecular Specific Volumes. — A method of calculating 

 which will sometimes be of use is to deduce the specific volume 

 by dividing the density into 1, and to multiply the figure thus 

 obtained by the potash absorption and to divide the result bv 

 19 -.J. 



The mean figure thus obtained for butter is 1-2766, and for 

 margarine 1-1641 at 37-8° C. If the butter is adulterated with 

 beef or other animal fat, the percentage of adulteration calcu- 

 lated with this figure will agree fairly well with that calculated 

 from other determinations. If vegetable oils have been used, 

 the percentage deduced thus is considerably more. 



Refractive Index. 



The Oleo - refractometer. — \\'hen light passes from one 

 medium to another it only passes in a straight line when it falls 

 perpendicular to the surface separating the two media. If it 

 passes through at an angle to the surface, it is bent or refracted. 



