THE BABCOCK TEST 47 



the tester shows the 5 and 10 per cent, marks to be 

 correct. 



In explanation of the use of this form of bottle-tes- 

 ter, it is to be remembered that the neck of the milk- 

 bottle is so graduated as to hold 2 cc. between the o 

 and 10 marks; hence, the volume between the o and 

 5 marks should be i cc., and that between the 5 and 

 10 marks should be also I cc. The brass plunger is 

 so made that each section displaces, or forces up into 

 the neck, i cc. of liquid, the whole instrument displac- 

 ing 2 cc. This tester therefore gives two tests of the 

 scale, one at the 5 per cent, mark and the other at 

 the 10 mark. 



Some of these instruments are made to test the 4 

 and 8 per cent, points, so that with two testers, one 

 can, if desired, test the accuracy of the scale at the 

 4, 5, 8 and 10 points. There are also testers of the 

 same form made for cream-bottles. 



In using this bottle-tester, the following precautions 

 are to be observed : 



(1) Have the upper surface of the liquid exactly 

 on a level with the zero mark in the neck of the test- 

 bottle before putting the tester in. 



(2) Clean the inside walls of the neck of the bot- 

 tle from adhering liquid before testing. 



(3) No air-bubbles should be allowed to adhere to 

 the tester when it is below the liquid. 



(4) The tester should be dry each time before using. 

 (2) Testing with mercury. From an accurately 



graduated burette (Fig. 21), measure 2 cc. of clean 

 mercury into the bottle to be tested. Then push down 

 into the neck of the bottle as far as the top line of 



