158 



MILK 



A meniscus forms at both ends of the fat column. The read- 

 ing should extend from the bottom of the lower meniscus to the 

 top of the upper one. By doing this loss of fat in the bottle is 

 compensated for. 



After the test is finished the bottles should be cleaned im- 

 mediately with hot water to prevent the fat from solidifying. 



Otherwise thorough cleaning is rendered 



difficult. 



Of course a representative sample is 

 absolutely necessary. Methods of obtain- 

 ing fair samples have been previously dis- 

 cussed. The pipets are calibrated to hold 

 17.6 c.c. of water (Fig. 45). As milk is a 

 viscous fluid a small amount adheres to the 

 inside of the pipet. Experience has shown 

 that this loss amounts to 0.1 c.c., so that 

 a 17.6-c.c. pipet discharges 17.5 c.c. of 

 milk. If 17.5 is multiplied by 1.03, the 

 average specific gravity of milk, the actual 

 weight is obtained, namely, 18.025 grams. 

 Therefore, this is the basis for calculation. 



The neck of one form of test bottle is 

 graduated from to 10 per cent. (Fig. 46). 

 Each per cent, is again subdivided into 5 

 parts, each of the subdivisions representing 

 0.2 per cent. The volume between and 

 10 is exactly 2 c.c. Therefore, if the grad- 

 uated part of the neck is filled with fat, there 

 are 2 c.c. of fat, or 1.8 grams, since the 

 specific gravity of butter-fat is 0.9. Since 

 the amount of milk used was 18 grams, the 

 milk would contain 10 per cent, of fat if the 

 column between and 10 were filled with 

 fat. This is the basis for graduation of the 

 neck of the test bottles. 



There are different styles of test bottles 

 in use, but the 10 per cent, bottle has been 

 more used than any other. Recently an 8 

 per cent, bottle has been gaining favor, 

 because the graduation between figures has 

 increased from 5 to 10, thus facilitating accurate reading of 0.1 

 per cent. 



After the pipet has been filled with milk it is discharged into 

 a test bottle. The aperture of the pipet should touch the glass 

 inside the neck so that the milk runs down smoothly. This will 



Fig. 45. A pipet 

 holding 17.6 c.c. of 

 milk used in the Bab- 

 cock test. (Circular of 

 Information No. 27, 

 July, 1911, Univ. of 

 Wis. Agr. Exp. Sta.) 



