THE BABCOCK TEST 45 



ing caused by acid may be remedied by treatment with 

 ammonia, if not too long delayed. Acid on tables, 

 floors, etc., may be neutralized by treatment with 

 washing soda or other alkali. 



METHODS OF TESTING ACCURACY OF 

 APPARATUS 



The correctness of the graduation of the glassware 

 used in the Babcock test is a fundamental condition of 

 accuracy in the results obtained. In some states all 

 graduated glassware used in the Babcock test must 

 be tested by the state and found correct before its use 

 is permitted in commercial operations. Reliable deal- 

 ers guarantee the accuracy of their glassware, and it 

 is found to be much more reliable than formerly. How- 

 ever, it is a safe precaution always to test new appa- 

 ratus before using it. Testing graduated glassware 

 is known technically as calibration. 



Testing or calibrating milk-bottles. Test-bottles 

 which show a variation, above or below, of more than 

 one division, or .2 per cent., in the 10 per cent, scale, 

 should not be used. The different methods of test- 

 ing will now be considered. 



(i) Testing zvith special bottle-tester. The quick- 

 est method of testing the accuracy of the scale of a 

 test-bottle is to use a special device, which is essentially 

 a simple brass plunger (Fig. 19). This instrument is 

 divided into two equal portions, each part being made 

 of such a size as to displace exactly one cubic centi- 

 meter of liquid. This bottle-tester is used as follows : 

 The test-bottle is filled to the zero mark with milk, or 

 one may use water or, better, wood alcohol, imparting 



