5O MODERN METHODS OF TESTING MILK 



is correct to this point. If the surface of the liquid is 

 above or below the 5 per cent, mark, then that portion 

 of the scale is incorrect to extent shown. After the ac- 

 curacy of the 5 per cent, mark is tested, the instru- 

 ment is then lowered into the bottle until the liquid 

 rises about one-eighth of an inch above the top of 

 the upper section of the tester. If the upper surface 

 of the liquid is level with the 10 per cent, mark, the 

 graduation is correct at that point. The graduation 

 of the scale is supposed to be correct, if 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, but does not show the accuracy for .any 

 other point. 



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. 



In using this bottle-tester the following precautions 

 are to be observed: 



(i) 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. 



