282 THE PHYSICAL EXAMINATION OF BUTTER FAT. 



should be brought to this point by means of a key just above the 

 prisms. 



Viscosity. Killing suggested the viscosity of butter fat as 

 a test by running it out of a pipette, marked above and below 

 the bulb, recording the time taken for the melted fat to flow 

 from one mark to another. The instrument must be graduated 

 with butters and other fats of known purity. 



He gives the following average times of flow : 



Butter, 3 minutes 43 i seconds. 



Margarine, . . . 4 19 



Lard, 4 28 



Beef fat, 4 33 



Wender uses an apparatus called a fluidimeter. This consists 

 of a U-shaped capillary tube having at one end an enlargement 

 holding 10 c.c., and at the other an enlargement holding 2 c.c. ; 

 the larger bulb is placed higher than the smaller ; liquid, there- 

 fore, flows from it. A solution of the fat in chloroform is used ; 

 the upper bulb is filled with this, the solution allowed to flow 

 into the lower bulb, and the time noted which it takes to pass 

 from the lower mark to the upper one on the smaller bulb. The 

 time taken for chloroform to flow is also noted, and this is taken 

 as 100. 



The viscosity of the fat is calculated by the following 

 formula : 



Let V = viscosity of the fat, 



x percentage of fat in chloroform solution by volume, 

 and T = the time taken divided by the time taken by chloroform 



then y = 100 T- 100 (100-*) ' 



X 



The average time for chloroform to fill the lower bulb was 

 20-04: seconds. 



Wender gives the following values as the mean figures at 

 20 C. (chloroform = 100) : 



Viscosity of pure butter, 344-3 



* margarine, 373-2 



It does not appear that this test has any greater value than 

 other physical determinations. 



Behaviour of Butter on Melting. When butter is melted 

 at a temperature of about 60 C., the fat which flows from the 

 aqueous portion is generally clear and transparent ; when mar- 

 garine is melted, the fat is almost always cloudy. 



This has been used as a test for the purity of butter. It does 

 not appear to depend on any property of the fat, but on the 



