Composite Samples of MUk. 167 



need of using any preservatives for milk in this case. Fig. 55 

 shows a convenient rack for holding the test bottles used in com- 

 posite sampling with a "one-third sample pipette." 



Accurate results can be obtained by this method of sampling, 

 if care is taken in measuring out the milk, and if it is not frozen 

 or contains lumps of cream. It is doubtful if the method has any 

 advantage over the usual method of composite sampling. If milk 

 is delivered daily and each lot is sampled with the one-third 

 pipette, twice or three times the number of tests are required as 

 when composite samples are taken in jars and tested once every 

 week or ten days. This method furthermore takes a little more 

 time in the daily sampling than the other, as the quantity of milk 

 must be measured out accurately each time. If a test bottle is 

 accidently broken or some milk spilled, the opportunity of ascer- 

 taining the fat content of the milk delivered during the three 

 days is lost; if a similar accident should occur in testing com- 

 posite samples collected in jars, another test can readily be made. 



PRESERVATIVES FOR COMPOSITE SAMPLES. 



189. When milk is kept for any length of time under 

 ordinary conditions, it will soon turn sour and become 

 loppered, and further decomposition shortly sets in, 

 which renders the sampling of the milk both difficult 

 and unsatisfactory (19). The period during which milk 

 will remain in an apparently sweet or fresh condition 

 varies with the temperature at which it is kept, and 

 with the cleanliness of the milk. It will not generally 

 remain sweet longer than two days at the outside, at 

 ordinary summer or room temperature. 



In order to preserve composite samples of milk in a 

 proper condition for testing, some chemical which will 

 check or prevent the fermentation of the milk must be 

 added to it. A number of substances have been pro- 

 posed for this purpose. 



