CHAPTER IX 



Methods of Testing Butter for Salt 



All methods for the determination of salt are based 

 upon one principle. When a solution of silver nitrate 

 and a solution of common salt (sodium chloride) are 

 brought together, a chemical reaction takes place, by 

 which the silver combines with the chlorine, forming 

 silver chloride, which is a white precipitate or solid 

 substance, t Moreover, a given amount of silver always 

 combines with a definite amount of chlorine. If, there- 

 fore, to a solution containing salt, we add a silver ni- 

 trate solution of known strength until the chlorine of 

 the salt is all changed intcfcthe solid, white silver chlo- 

 ride, we can tell just how much salt is in the tested 

 solution by keeping a record of the amount of silver 

 nitrate solution used. One part by weight of salt re- 

 quires for complete precipitation about 2.9 parts by 

 weight of silver nitrate. The only point of difficulty 

 is to know just when the chloride is all precipitated, 

 but we have a simple, accurate way of telling precisely 

 when this point is reached. A solution of potassium 

 chromate also forms a precipitate when treated with 

 silver nitrate but in this case the solid substance (silver 

 chromate) is deep-red or brick-red in color. Further- 

 more, if we add silver nitrate solution to a solution 

 containing both chloride and chromate, stirring or 

 shaking vigorously during the addition, the chloride 



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