48 Testing Milk and Its Products. 



acid passes has a diameter of at least one-eighth of an 

 inch, as is generally the case. We have used or in- 

 spected some half a dozen other devices, which have 

 been placed on the market by various dealers for de- 

 livering the acid, but cannot recommend them for use 

 in factories or outside of chemical laboratories. 



52. Instead of measuring out the acid, Bartlett 1 has suggested 

 adding 20 cc. directly to the milk in the test bottles, till the mix- 

 ture rises to a mark on the body of the bottle at the point 

 where this will hold 37.5 cc., i. e., the total volume of milk and 

 acid (83). This method of adding the acid is in the line of sim- 

 plicity, but has not become generally adopted. If the method is 

 used, the marks should be put on by the manufacturers, as the 

 operator in attempting to do so will be apt to weaken or break 

 the bottles. 



CALIBRATION OF GLASSWARE. 



53. Test bottles. The Babcock milk test bottles are 

 so constructed that the scale of graduation on the neck 

 measures a volume of 2 cubic centimeters, between the 

 zero and the 10 per cent, marks (44). The standards 

 adopted by Eastern experiment stations for test bottles 

 and other Babcock glassware are given at the close of 

 this book (306). It will be seen that the limit of error 

 for test bottles is one of the smallest graduations on the 

 scale, or .2 per cent. The correctness of the gradua- 

 tions may be easily ascertained by one of the following 

 methods : 



54. (A.) Calibration with water. This may be done 

 by means of a delicate pipette or burette, or by weigh- 

 ing the water that the graduated portion of the neck 

 will hold. 



1 Maine '\p<>rim<'nt station, bull. 31. 



