128 SAMPLING MILK AND CREAM 



thick and tough layer of cream on the surface of the milk. This 

 cream mixes with difficulty back into the remainder of the sample 

 so that the portion transferred to the bottle is often not rep- 

 resentative of the true richness of the milk. This defect is 

 especially pronounced when the samples are not protected 

 against high temperature (summer heat). 



Composite samples, if they must be taken, should be kept 

 not over one week and tested at the end of this period. They 

 should be kept in tightly sealed jars and in the cold. 



In order to prevent composite samples from souring, 

 fermenting and curdling before they are tested, it is necessary 

 to add a small amount of preservative to the sample jar with 

 the first portion of milk. This is most conveniently done in the 

 form of tablets of corrosive sublimate or bichromate of potassium. 

 One tablet during the winter months will preserve a pint sample 

 for at least two weeks. During the hot weather it is advisable 

 to add two tablets. Liquid preservatives, such as formaldehyde, 

 may also be used in the place of the tablets, but they cause slight 

 dilution of the sample and are not considered quite as con- 

 venient as the tablets. After each daily addition of milk to the 

 composite sample jar, its contents should be gently agitated by 

 giving the jar a rotary motion in order to insure a complete 

 mixture of the preservative with the entire contents of the jar. 

 When agitating, care should be taken that the milk does not 

 unnecessarily slobber up along the side of the jar, so as to prevent 

 the coating of the side with cream which subsequently dries and 

 is difficult to mix back into the remainder of the sample at the 

 time of testing. Composite samples should be tightly sealed 

 and should not be held longer than one week. In old composite 

 samples the cream is prone to be so completely separated from 

 the skim milk that it refuses to mix back readily and to form 

 a homogeneous emulsion preparatory to testing. 



Individual Samples of Part of the Deliveries only. In this 

 method, each patron's milk is not sampled daily but only every 

 third, fourth or fifth day. The patrons are divided into groups. 

 Group one is sampled the first day, group two the second day, 

 etc., so that each patron's milk may be sampled say eight to 

 ten times per month. The tests of these samples are averaged 



