50 Testing Milk and Its Products. 



55. a, Measuring the water. Fill the test bottle with 

 water to the zero mark of the scale; remove any surplus 

 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 ^ 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. 



56. 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 when calibrations are to be made, the test 

 bottles, or other glassware to be calibrated, must be thor- 

 oughly cleaned with strong sulfuric acid, or soda lye, and 

 washed repeatedly with pure water, and dried. Glass- 

 ware is not clean unless water will run freely over its 

 surface, without leaving any adhering drops. 



57. (C.) The Trowbridge method of calibration. 1 An 

 extremely simple and accurate method of calibrating test 

 bottles has been proposed by Mr. O. A. Trowbridge of 

 Columbus, Wis. He conceived the idea of measuring 

 the capacity of the graduated portion of the neck of a 

 milk test bottle with a piece of metal which is carefully 

 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 to it a short 

 piece of fine wire, either looped at one end, as shown in 



i Hoard's Dairyman, Mar. 8, 1901, by De Witt Goodrich. 



