100 Milk and Its Products 
any variation in the size of the spaces such bottles 
should be discarded. Bottles inaccurate in this 
respect are seldom met with now. When the test 
was first introduced they were of frequent occur- 
rence. Bottles may be readily tested with a pipette 
of 2 c. ¢.* capacity. Fill the bottle carefully with 
water to the 0 point, wipe out the neck carefully, 
and drop in exactly 2 c.c. of water. It should 
just fill the neck to the top of the graduation. 
If delicate balances are at hand, the bottle may be 
weighed full of distilled or clean rain water to the 
0 point, and then again filled to ‘the 10 point. 
The difference in weight should be exactly 2 grams. 
The calibration will be still more accurate if mer- 
cury instead of water is used; 2 c.c. of mercury 
may be measured out, or, what is still better, 
weighed. The specific gravity of mercury is 13.59; 
two e.c. will, therefore, weigh 27.18 grams. This 
weighed or measured quantity of mercury is intro- 
duced into a dry bottle, a close-fitting plug is then 
inserted into the neck of the bottle exactly to the 
top of the graduation, the bottle is then inverted ; 
the mercury should exactly fill the graduated space. 
The same portion of mercury can then be used to 
test another bottle, and with care to have the 
bottles dry, and to see that all of the metcury is 
transferred each time, a large number of bottles can 
be easily and quickly calibrated. 
The pipettes are best tested by weighing a 
pipette full of either water or mercury; the former 
* Cubic centimeter. See metric system, in Appendix. 
