352 



BUTTEE. 



The viscosity of the fat is calculated by the following 

 iormula : — 



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, 

 ^^^^ ^,^ 100T-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 

 ■state in which the fat existed in milk, and the method of pre- 

 paring the butter. Butters which have been overworked invari- 

 ably melt in a cloudy manner. 



Druot has devised an apparatus for observing the behaviour 

 •on melting. It consists of a number of cups stamped in tin 

 plate, in which pieces of the samples to be tested, about \\ 

 ■grammes in weight, are placed. A piece of iron heated to about 

 60°, and of sufiicient thickness to retain enough heat to melt the 

 -samples, is placed over the top, and left till the butters are 

 melted. The appearance of the fat is observed, the polished 

 ■surface of the tin plate materially aiding the observation. 



This method can only be classed as a rough means of deter- 

 mining the purity of butter. 



Melting Point of the Fat. — Formerly some importance was 

 attached to the melting point of the fat ; this, however, depends 

 to some extent on the method employed in determining it. 

 Butter melts at about 33° C. ; and artificial butters are made up 

 to melt at the same temperature. 



Among other physical properties which have been proposed 

 :are the determination of the heat of combustion, which differs 

 materially in butter and other fats, and the relative transparency 

 to the X rays. These methods are not, however, practical 

 .analytical methods. 



