74 DAIRY ANALYSIS 



2 or 3 grammes of kieselguhr are added, and the mass 

 evaporated to dryness, placed in an extraction thimble, 

 and extracted with petroleum ether in a Soxhlet. 



Evaporate the solution, add 5 c.c. of alcoholic soda 



solution, and evaporate to dryness, adding a little 

 sodium bicarbonate before the solvent has completely 

 evaporated. Extract with petroleum ether, and evapo- 

 rate this, and take up with alcohol ; if the solution 

 is dark add a little animal charcoal and filter. Allow 

 the cholesterol or phytosterol to crystallise, and to 

 the crystals add 2 or 3 c.c. of acetic anhydride, and 

 evaporate on the water-bath. Crystallise the acetates 

 several times from alcohol and take the melting-point. 

 Cholesteryl acetate melts at Ii3.2-ii4.6 (corr.) and 

 a higher melting-point shows presence of phytosteryl 

 acetate. 



Estimation of Density. Follow the directions on 

 p. 10, with the following modifications : weigh the 

 tube full of water at 37.8 C. (100 F.) instead of at 

 I 5-5 C. ; dry the tube before filling it with the fat, 

 and take the density at 37.8 C. instead of at 15.5 C. 



Examination under Polarised Light. Place a 

 small portion of the butter (not butter fat) on a micro- 

 scope slide, and press down a cover-glass thereon ; 

 examine with a microscope furnished with a polari- 

 scope, using a i in. or \ in. power, focus with the Nicols 

 parallel, and then cross them, shielding the slide from 

 light except that which has passed through the 

 polariser. Genuine butter appears nearly uniformly 

 dark, while crystalline fats show a more or less well- 

 marked lighting in portions of the field. 



Old butters, especially those which have been 

 submitted to vibrations, and butters prepared by 

 processes in which the cream is churned soon after 

 heating and cooling may show (Fig. 36) a somewhat 

 crystalline appearance, but generally this is due to 

 margarine (Fig. 37) ; this test though very rapid may 

 not be reliable. 



