452 MILK AND MILK PRODUCTS; DAIRY FARMS 



Operation of the test. 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 balanced, 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 in- 

 creased 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 can be 

 hastened by shaking the sample with a rotary motion and thoroughly 

 mixing these pieces with the hot liquid. If this is not done, one might 

 have to heat the sample so long that some of the fat which had already 

 given up its moisture would volatilize. 



After all the moisture is driven off, the sample is allowed to cool to 

 room temperature. While cooling, the cup should be covered with 

 something (a sheet of paper will do) to prevent the sample taking up 

 moisture from the atmosphere. After cooling, the cup is placed on 

 the scales. The sample is lighter than before heating, because it has 

 lost its moisture. The bar of the scales will therefore remain down. 

 The weights are then reversed until the scales just balance. 



