MELTING POINT. 283 



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

 paring the butter. Butters which have been overworked in- 

 variably 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 1J 

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

 60, and of sufficient 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. 



