CARE OF COMPOSITE MILK SAMPLES 



183 



pose, because of its metal parts and the more or less loosely- 

 fitting cover. Fig. 5 is an all glass jar, consisting of only 

 two parts and is practically air tight, and is an ideal jar in 

 which to preserve composite samples of milk. 



It is necessary that the milk be kept in its natural liquid 

 condition until the composite sample is complete and ready 



for testing. Changes in milk are due to the 

 presence and development of bacteria. To 

 prevent these changes all, or nearly all, bac- 



/^^ — _ xy teria in the milk samples must be killed. For 

 ^■^^^^ \ the purpose of destroying bacteria various 

 inexpensive chemicals or preservatives may 

 be employed. Among the liquid preserva- 

 tives that may be used for this purpose, a 

 40% solution of formalin may be recom- 

 mended. The same amount of formalin 

 placed in ditferent jars of milk taken from 

 the same supply, and the milk kept under 

 the same conditions of temperature will not 

 always produce exactly like results in a given time. In- 

 formation obtained in preserving several hundred compos- 

 ite samples of milk warrants the following statements : 



"^^'IS 6 0TTL.E- 

 ^^0 Rltu'^^" 



Fig. 4. 



^ 



FORMALIN. 



Under ordinary conditions of temperature, 

 varying from 50 to 80 degrees F., four or five 

 drops of formalin will keep a pint of ordi- 

 nary milk or cream in a good liquid condi- 

 tion for from nine to eleven davs. Six or 

 seven drops will preserve a pint of milk for 

 from ten to fourteen days. Eight to ten 

 drops wall preserve the same amount of milk 

 for a period of from fourteen to twenty 

 days. A larger amount of formalin may be 

 successfully used for preserving milk or 

 cream for a longer period. 



Fig. 5. 



C I 



POTASSIUM BICHROMATE, OR BICHROMATE OF POTASH 



J > 



Among the dry or powdered preservatives to be recom- 

 mended for preserving milk and cream samples. Potas- 

 sium Bichromate has proved to be very satisfactory in every 

 instance. This chemical possesses great power as a de- 

 stroyer of germ life and only very small quantities need be 



