The Babcock Test. 45 



The black stains that sometimes stick to the inside of 

 test bottles after prolonged use, can be removed with a 

 little muriatic acid, or by means of a small stiff brush. 

 48. Pipette. The difference in the weights of various 

 samples of normal milk generally falls within compara- 

 tively narrow limits ; if a given volume of water weighs 

 one pound, the same volume of the usual grades of nor- 

 mal milk will weigh frcm 1.029 to 1.033 pounds, or on 

 the average, 1.03 Ibs. 18 grams of water measures 18 

 cc. 1 ; 18 grams of milk will therefore take up a smaller 

 volume than 18 cc., viz., 18 divided by 1.03, which is 

 \vry nearly 17.5. This is the quantity of milk taken 

 in the Babcock test. A certain amount of 

 milk will adhere to the walls of the pi- 

 pette when it is emptied, and this thin film 

 has been found to weigh about one-tenth' 

 of a gram; consequently 17.6 cc. has been 

 adopted as the capacity of the pipette used 

 for delivering 18 grams of milk. 



r\ LJ 



For convenience in measuring the milk, 



FIG. 17. Pipette 



points the shape of the pipette is of importance. 



A, proper con- 



, Pi The mark on the stem should be two inches 



construction. Qr more from the upper end of the pip _ 



ette. The lower part should be small enough to fit 

 loosely into the neck of the test bottle, and not con- 

 tracted to a fine hole at the point ; the point should be 



- 1 Cubic centimeters (abbreviated: cc.) are the standard used for 

 measuring volume in the metric system, similar to the quart or pint 

 measure iii our ordinary system of measures. One quart is equal to a 

 little less than 1,000 cubic centimeters (1 liter). In the same way, grams 

 represent weight, like pounds and ounces. One cc. of water at ^Centi- 

 grade weighs 1 gram; 1,000 grams < = 1 kilogram) are equal to 2.2 Ibs." 

 Avoirdup. (See Appendix for Comparisons of metric and customary 

 weights and measures.) 



