METHODS OF TESTING MILK FOR SALT 1 29 



SHAW TEST FOR SALT IN BUTTER 



This test is carried out in connection with Shaw's 

 method for determining fat in butter (p. 103). 



The solutions are a silver nitrate solution containing 

 14.525 grams of pure silver nitrate per liter (just one- 

 half the strength used in the Perkins test) and a 10 per 

 cent, solution of potassium cjiromate. Besides the 

 50 cc. burette and a beaker or white cup, as in the Per- 

 kins test, there are required a volumetric flash with a 

 250 cc. mark and a 25 cc. pipette. 



To determine the percentage of salt in butter in con- 

 nection with that of fat, a solution of the salt con- 

 tained in the butter is obtained in the manner described 

 in paragraph 4 (p. 106), the wash-water being al- 

 lowed to run into the 250 cc. flask and the operations 

 in paragraph 4 are performed three times instead of 

 once, the wash-water each time being run into the 

 flask. 



When the washings have become cool, the flask is 

 filled to the mark with cold water and shaken until the 

 contents are well mixed. Then measure with the pi- 

 pette 25 cc. of the wash-water (representing 2 grams 

 of the original sample or one-tenth of 20 grams) into 

 the cup or beaker, add 2 or 3 drops of chromate solu- 

 tion and then run into the mixture from the burette ' 

 the silver nitrate solution, stirring constantly, until the 

 permanent reddish tinge .appears. 



The silver nitrate is of such strength that I cc. re- 

 presents 0.005 grams (or 0.5 per cent.) of salt in but- 

 ter when a i-gram portion is used, 0.25 per cent, where 

 a 2-gram portion is taken, etc. In the foregoing des- 

 cription, 2 grams are represented and we, therefore, 



