Useful Rules and Tests 361 



tains no lumps and the entire mass is about the consistency of thick 

 cream. The container is then transferred to cold water and the sample 

 thoroughly mixed as the butter cools. There is a tendency for the fat 

 around the outside of the container to harden rapidly and force the 

 water toward the center of the jar. For this reason special care must 

 be taken to keep the butter scraped off the sides of the container and 

 thoroughly mixed with the softer butter in the center of the jar. When 

 the sample is all of about the texture of ordinary butter the mixing 

 may be stopped. If the process has been properly done, the water will 

 be evenly distributed throughout the sample and any desired amount 

 of the latter may be removed for testing. 



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. T-.e 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 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. 



