The Babcock Test. 53 



Mercury forms the most satisfactory and accurate material 

 for calibration of test bottles, on account of its heavy weight 

 and the ease with which it may be manipulated. Equally correct 

 results may, however, with proper care be obtained by using 

 water for the calibration. 



60. Intermediate divisions. The space between 

 and 10 on the scale of the Babcock test bottle is divided 

 into 50 divisions, each five of which, as previously 

 shown, represent 1 per cent. (44). Since these in- 

 termediate divisions are generally made with a dividing 

 machine, they are as a rule correct, but it may happen 

 that they have been inaccurately placed, although the 

 space between and 10 is correct. The accuracy of the 

 intermediate divisions can be ascertained by sliding 

 along the scale a strip of paper upon which has been 

 marked the space occupied by one per cent, and com- 

 paring this space with those of each per cent, on the 

 scale. 



61. Calibration of skim milk test bottles. The 

 value of each division on the common double-necked 

 skim milk bottles (99) is one-twentieth, or .05 of one 

 per cent. ; there are ten of these divisions in the whole 

 scale which, therefore, measures .5 per cent, of fat. It 

 requires very careful work to calibrate this scale and it 

 is best done by weighing the amount of mercury which 

 will just fill the space of 1 cc. between the first and the 

 last divisions (53) ; the correct weight of this mercury 

 is 1.359 grams. 



62. Calibrating cream test bottles. The cream bot- 

 tles may be calibrated by any of the methods given for 

 milk bottles. The neck of a cream test bottle that meas- 

 ures thirty per cent, fat will hold 6 cc., and 6 grams of 

 water or 81.54 grams of mercury. 



