78 CHEMICAL EXAMINATION 



of barium chloride has been added, a little phosphoric acid, or 

 ammonium phosphate, may now be added to the filtrate, 

 although it is not necessary if the quantity of barium chloride 

 given above has been employed. A quantity of ferric chloride 

 solution, sufficient to colour the solution brown, is added and 

 the filtrate made alkaline with ammonia. After boiling, the 

 precipitate is filtered off and well washed: the filtrate is evap- 

 orated and cautiously ignited: this weight represents the alka- 

 line chlorides. When the residue is dissolved in hot water, the 

 solution should be perfectly clear; if this be not so, a little 

 ammonium carbonate solution is added, the liquid evaporated 

 to dryness and the residue cautiously ignited; the residue is 

 again taken up with water, the solution filtered and evaporated, 

 and the residue cautiously ignited and weighed. This puri- 

 fication of the mixed alkaline chlorides is often found necessary 

 and it is essential, in order that accurate results may be obtained, 

 that the process should be carried out with great care, always 

 bearing in mind that alkaline chlorides are volatilised at com- 

 paratively low temperatures. 



The chlorine in the mixed chlorides may be estimated by 



N 

 titration with - silver nitrate, using potassium chromate as 



N 

 indicator. Each cubic centimeter of AgNOs is equivalent 



to 0.00355 grm. chlorine. The potassium and sodium are cal- 

 culated from the formulae. 



The weight of sodium = 2.997C - 1.4254W, 

 The weight of potassium = 2.4254W-3.987C. 



in which W = the weight of the mixed alkaline chlorides, 



and C=the weight of chlorine therein. 



Examination of Milk Serum. As the fat and proteids are 

 the most variable constituents of milk, an examination of the 

 milk serum often affords valuable assistance in determining 



