644 TESTING BUTTER 



Determination of Salt in Butter 



Principle of Salt Tests. All salt tests are based on the same 

 principle. In their operation two chemicals are used, namely silver 

 nitrate (Ag NO 3 ) and potassium chromate (K 2 Cr O 4 ). The silver 

 nitrate has the power of chemically acting on both, the salt or sodium 

 chloride (NaCl) and the potassium chromate. With sodium chloride 

 the silver nitrate forms silver chloride which is a white precipitate. 

 With the potassium chromate the silver nitrate forms silver chro- 

 mate which is a brick-red precipitate. The silver nitrate acts first 

 on the sodium chloride. Hence, when silver nitrate is added to a 

 solution of sodium chloride (salt) which contains some potassium 

 chromate, the silver nitrate first combines with the sodium chloride 

 until all the chloride is used up and has been converted into silver 

 chloride. This precipitate is white. Now, if more silver nitrate is 

 added, the silver combines with the chromate, changing the color of 

 .the precipitate to a brick-red. The moment the brick-red color be- 

 comes permanent, therefore, all the salt has been neutralized, and 

 the amount of silver nitrate required to produce this brick-red color 

 furnishes the basis for the calculation of the per cent of salt in 

 butter. 



Calculation of Per Cent Salt in Butter. The calculation of 

 the per cent salt in butter rests on a similar principle as the calcula- 

 tion of the per cent acid in cream. A normal solution of silver 

 nitrate neutralizes an equal amount of a normal solution of sodium 

 chloride. A normal solution of silver nitrate contains, in 1,000 cc. 

 of water, 170 grams of silver nitrate. A normal solution of sodium 

 chloride contains, in 1,000 cc. of water, 58.5 grams of sodium chlor- 

 ide. Hence, 1 gram of sodium chloride is neutralized by ^Q-F or 

 2.906 grams of silver nitrate. 



If, therefore, a silver nitrate solution is used which contains, in 

 1,000 cc. of water, 29.06 grams of silver nitrate, then each cc. of this 



solution will contain 1f ' m or .02906 grams of silver nitrate, and 



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.02906 grams of silver nitrate will neutralize 2.906 : 1 = .02906 : X, 

 or .01 gram of sodium chloride. If a 10 gram sample of butter is 

 used and all of this sample is tested, each cc. of silver nitrate solution 



required represents ' r or .1 per cent salt. 



