278 MANUAL OF MILK PRODUCTS 



jar containing the sample should be kept covered to prevent 

 the evaporation of moisture. 

 Operation of the test. 



A sample of butter is taken and prepared as previously de- 

 scribed (see p. 276). After the cup is thoroughly cleaned 

 and dried, it is placed on the scales and balanced by means of 

 the tare weight on the round bar attached to the beam of the 

 scales. The large weight should rest on the zero mark (of the 

 gram scale) and the small weight on 1 while the cup is being 

 balanced. The cup should not be balanced until it is about the 

 same temperature as that of the room. After the cup is bal- 

 anced, the larger weight is moved to the 20 mark (of the gram 

 scale) and the small weight to the zero mark. Butter from the 

 prepared sample is then added to the cup until the scales are 

 accurately balanced. The alcohol lamp is then placed under 

 the iron stand and the asbestos sheet placed on the stand. The 

 lamp is lighted and the cup placed on the asbestos sheet. It 

 is well to light the lamp at least two or three minutes before 

 placing the cup on the asbestos, in order to heat the asbestos 

 and save time. The heat of the flame may be increased or 

 diminished by raising or lowering the wick. The cup should 

 always be handled with the hot pan lifter, as by so doing it will 

 be kept clean and errors in weight due to dirt on the cup will 

 be avoided. 



While the sample is heating it should be shaken from time 

 to time, as this breaks up the blanket of casein on the surface 

 and hastens the escape of moisture. As soon as the casein has 

 lost its snow-white color, the cup should be removed from the 

 flame. When the moisture has all been driven from the sample, 

 a slightly pungent odor may be noticed. This may also be 

 used as a guide to tell when the sample has been heated enough. 

 The foam begins to subside at this point. Often one or two 

 small pieces of casein are slow to give up their moisture. This 

 is indicated by the snow-white color of the pieces. Evaporation 



