The Babcock Test. 49 



a, Measuring the water. Fill the test bottle with 

 water to the zero mark on the scale; remove any sur- 

 plus water and dry the inside of the neck with a piece 

 of filter paper or clean blotting paper; then measure 

 into the bottle 2 cc. of water from an accurate pipette 

 or burette, divided to -I of a cubic centimeter. If the 

 graduation is correct, 2 cc. will fill the neck exactly to 

 the 10 per cent, mark of the scale. 



b, Weighing the water. Fill the bottle with water 

 to the zero mark of the scale and remove any surplus 

 water in the neck, as before. Weigh the bottle with the 

 water contained therein. Now fill the neck with water 

 to the 10 per cent, mark, and weigh again. The differ- 

 ence between these weights should be 2 grams. 



In all cases where calibrations are to be made, the 

 test bottles, or other glassware to be calibrated, must be 

 thoroughly cleaned beforehand with strong sulfuric 

 acid or soda lye, and washed repeatedly with pure 

 water, and dried. Glassware is not clean unless water 

 will run freely over its surface, without leaving any 

 adhering drops. 



55- (B). The Trowbridge method of calibration. 1 

 An extremly simple and accurate method of calibrating 

 test bottles has been proposed by Mr. 0. A. Trowbridge 

 of Columbus, Wis. He conceived the idea of measur- 

 ing the capacity of the graduated portion of the neck 

 of a milk test bottle with a piece of metal which is care- 

 fully filed to such a size that it will displace exactly 

 two cubic centimeters of water. He used a thirty-penny 

 wire nail, cutting off the head of the nail and attaching 



1 Hoard's Dairyman, Mar. 8, 1901, by DeWltt Goodrich. 



4 



