MILK AND MILK PRODUCTS 43 



originally in the sample, the residue from the petroleum spirit 

 and ether solution is dissolved in 50 c.c. of dilute hydrochloric 

 acid, bromin water added in excess, the liquid shaken well, 

 and filtered. Salicylic acid is completely removed as a bromi- 

 nated derivative. The filtrate is made strongly alkaline with 

 sodium hydroxid, evaporated, and fused as described above. 



Sodium Carbonate. — The following test is due to Schmidt. 



10 c.c. of the milk are mixed with an equal volume of alcohol, 

 and a few drops of a i per cent, solution of rosolic acid added. 

 Pure milk shows merely a brownish-yellow color, but in the 

 presence of sodium carbonate a more or less marked rose-red 

 appears. The delicacy of the test is enhanced by making a 

 comparison cylinder with the same amount of milk known to 

 be pure. If the salt is present in considerable amount, it may 

 be detected by the increase in the ash, its marked alkalinity and 

 effervescence with acid. 



Ahrastol. — i c.c. of acid mercuric nitrate solution (page 30) 

 is added to 20 c.c. of milk. A yellow tint indicates abrastol. 

 The delicacy of the test may be increased by comparison with 

 an untreated portion of the sample. The absence of other 

 preservatives should be assured. 



Fluorids. — 50 grams of the sample are made slightly alka- 

 line with ammonium carbonate, heated to boiling, a few centi- 

 meters of calcium chlorid solution added, and heating con- 

 tinued for 5 minutes. The precipitate is collected, washed, 

 dried, transferred to a platinum crucible, and ignited. When 

 the mass is cold, a few drops of strong sulfuric acid are added, 

 and the crucible covered with a piece of glass partly protected 

 on the lower side by paraffin. The bottom of the crucible is 

 then heated for an hour at a temperature between 75" and 80°. 

 The glass is etched if fluorids are present. 



Preservation of Milk-samples. — Formaldehyde is now gen- 

 erally used; 0.05 per cent, will keep milk for a month and 

 larger proportions for an indefinite period. 



