IS 



12. Burnt or cloudy readings may be caused by : 



(1) The use of too much or too strong- acid. 



(2) Allowing the acid to fall directly on the milk. 



(3) Having the milk or acid at too high a temperature — the 



higher the temperature the less acid is required. 



(4) Allowing a sample to stand too long after adding the acid, 



before mixing the milk and acid. 



13. Light colored readings and floating particles of curd are usual- 

 ly due to : 



(1) The use of too little or too weak ,acid. 



(2) Having the milk or acid at too low a temperature — the 



lower the temperature of either, the more acid is required. 



(3) Insufficient shaking of the bottles to unite the milk and 



acid thoroughly. 



(4) Lack of required speed or time in whirling, 



14. A convenient method of testing the accuracy of the graduation 

 is to test the same milk in the different test bottles and compare the 

 readings. A bottle that differs by more than .2 (2-lOj in its reading 

 from the rest should be discarded. As the capacity of that part of the 

 neck over which the scale extends should be 2 c.c. , the accuracy of the 

 scale may be tested by filling the bottle to the bottom of 

 the scale with water at the temperature of the room, and then adding 

 2 c.c. of water at the same temperature by means of a 2 c.c. pipette 

 or a finely graduated burette. 



15. Care and exactness in every detail are absolutely essential re- 

 quisites for reliable results in milk testing. There is more to learn in 

 care than in principle. Carelessness on the part of the operator has 

 frequently thrown suspicion on the Babcock test. 



Composite Samples. 



Whole milk creameries, and in many of the advanced cheese fac- 

 tories, the patron receives payment, not in proportion to the amount of 

 milk, but in proportion to the butter or cheese value of the milk sup- 

 plied by him. Such a system, of course, necessitates the use of the 

 Babcock test. A test of the milk cannot be made daily ; and to over- 

 come this difficulty a small sample of the milk supplied by each patron 

 is taken at each time of delivery and put into a bottle, called a composite 

 sample bottle, which contains a small amount of some kind of preser- 

 vative, such as bichromate of potash or corrosive sublimate. It is not 

 advisable to use the latter alone, as it is quite poisonous, and imparts 

 no color to the sample to indicate its presence. An excellent preser- 

 vative is a mixture composed of about seven parts bichromate of potash 

 to one part corrosive sublimate. 



From what can be taken on a five cent piece to what can be taken 

 on a ten cent piece will usually be found sufficient to preserve a sample 

 for two weeks in summer and a month in fall and winter, when an 

 ounce of milk is taken daily. The amount of preservatives requind 



