140 MILK 



When milk is coagulated the fat is not changed chemically, but 

 it is unevenly distributed. The casein should then be dissolved 

 by adding to the milk one-tenth to one-twentieth its volume of 

 sodium or potassium hydrate solution or strong ammonia. Due 

 allowance must be made for the increased volume caused by such 

 addition when the results are calculated. 



Frozen milk must be thawed completely and the mixed milk 

 sampled. When either through freezing or chm-ning the fat 

 assumes a condition which renders it difficult to distribute, 5 per 

 cent, ether may be added. This dissolves the fat and it can then 

 be thoroughly mixed by a rotary motion. 



Samples should be examined as early as possible after taking, 

 since profound changes in physical condition, chemical composi- 

 tion, and bacterial content take place within a short time. If 

 the milk cannot be examined promptly, it should be packed in 

 ice. Even at this low temperature changes occur which influence 

 the result, and consequently shipping samples for considerable 

 distances renders analyses more or less unsatisfactory. Samples 

 may be preserved by addition of 0.02 per cent, formalin or 0.1 per 

 cent, potassium bichromate. Any such addition should always 

 be clearly stated on a tag attached and, of course, for bacterio- 

 logic examination, addition of preservatives is not admissible. 



Composite Samples. — The introduction of the Babcock method 

 for fat determination has enabled creameries and milk dealers to 

 rapidly test milk for fat content. Since fat is not readily decom- 

 posed it is not necessary to test the contents of each can upon 

 delivery, but aliquot portions may be taken each day and kept 

 for one or two weeks before the test is made. Such samples are 

 known as "composite samples." A measured amount is taken 

 from each can of the producer every time milk is delivered, and 

 these samples placed in suitable vessels. A Mason jar, a glass- 

 stoppered wide-mouthed bottle, or any other style of bottle may 

 be used, as long as air can be excluded to prevent evaporation. 

 The amount of milk delivered is recorded and the average fat 

 content determined by periodic examination. The producer is 

 then paid according to the amount of butter-fat delivered and not 

 according to the quantity of milk. The justice of this method is 

 obvious, since watering milk brings no additional profit when the 

 butter-fat made is the basis of payment. Furthermore, rich 

 milk automatically brings better compensation than does poor 

 milk. 



Composite samples of milk must be properly cared for in order 

 to yield rehable results. As has been mentioned before, the con- 

 tainer must be closed air-tight to prevent evaporation and the 

 contents guarded against decomposition. This is accomplished 



