TESTING 259 



to distribute the salt throughout the solution. The 

 agitation should continue about one minute. 



7. Allow the sample to stand until the fat rises to the 

 surface. This may require two to five minutes. 



8. With a 17.6 c.c. Babcock pipette, draw a pipetteful 

 of the clear liquid and put it in a titration container which 

 may preferably be a white cup or an Erlenmeyer flask. . 



9. Add three or four drops of the potassium chromate 

 (K2Cr04) which acts as an indicator. 



10. Titrate this solution with tenth-normal silver 

 nitrate (AgNOa) until a very light brown color appears. 

 It should be remembered that the solution must be 

 agitated constantly during titration. It must also be 

 kept in mind that the first permg,nent brownish color is 

 the end point. i 



11. In obtaining the final reading, it must be borne in 

 mind that each cubic centimeter of tenth-normal silver 

 nitrate that is titrated into the salt solution is equal to 



1 per cent salt. 



12. Record the results. 



233. Notes on the chemistry of the salt test. — The 

 first reaction in this test is as follows : AgNOs (silver 

 nitrate) -|- NaCl (sodium chloride, salt) = AgCl (silver 

 chloride) -f- NaNOa (sodium nitrate). When all the chlo- 

 rine from the salt in the butter solution has been satisfied 

 and an excess of silver nitrate is added, another chemical 

 reaction occurs between the silver nitrate and the potas- 

 sium chromate, which is used as an indicator. This 

 reaction is as follows : 2 AgNOs (silver nitrate) -j- K2Cr04 

 (potassium chromate) = Ag2Cr04 (silver chromate) -|- 



2 KNO3 (potassium nitrate). The silver chromate is the 

 substance that gives the reddish brown color indicating 

 that all the salt is neutralized. 



