DETERMINATION OF CASEIN 59 



the fat globules pass. Repeat extraction from ten 

 to fifteen times, using from 10 to 20 c.c. of hot water 

 each time. The resulting washings contain all but 

 a mere trace of the sodium chloric! originally present 

 in the butter. The sodium chlorid is determined in 

 the separated fluid by a standard solution of silver 

 nitrate, AgN0 3 using a few drops of solution of po- 

 tassium chromate as an indicator. 



NaCl + AgN0 3 = AgCl + NaN0 3 . 



23.0 At. wt. of Na 



35.5 At. wt. of Cl. 



58.5 Molecular wt. of NaCl. 

 For every 35.5 Cl there are 58.5 NaCl. 



When a permanent reddish brown color is obtained, 

 note the number of c.c.'s used. Each c.c. of stand- 

 ard solution AgN0 3 used indicates the presence of 

 .0585 grams of salt. 



Example : 10 grams butter in sample, and solution 

 required 4 c.c. AgN0 3 . 4 X. 0585 = .234 grams. 10 X 

 .234-2.3 per cent salt, or .234 -=-10X100 = 2.3 per 

 cent. 



METHOD FOR THE QUANTITATIVE DETERMINATION OF 

 PROTEIDS OF MILK 



Bogg's Method 



Phosphtungstic acid in hydrochloric acid solution 

 precipitates instantly all the proteids in a finely di- 

 vided condition. The precipitate contracts evenly in 

 a vertical direction and reaches a constant minimum 



