QUESTIONS AND ANSWERS 357 



How is milk tested for the presence of (a) boric acid, (b) salicylic 

 acid, and (c) sodium bicarbonate? 



(a) Add to a few drops of milk, contained in a white dish, a drop 

 or two of hydrochloric acid, and then several drops of a saturated 

 alcoholic solution of turmeric. Heat the dish gently for a few 

 minutes, and if boric acid or borax is present, a pink or dark-red 

 color will appear. Cool, and add a drop of ammonia, when a dark- 

 blue or green color should be seen. 



(b) Add two or three drops of sulphuric acid to 20 e.c. of milk 

 and then shake gently with 20 c.e. of a mixture of equal parts of 

 ether and petrolic ether. Then, after standing for several hours, 

 the upper ethereal solution is poured off and the remaining liquid 

 is evaporated in a porcelain evaporating dish. Add to the residue 

 a few drops of water, and if salicylic acid is present a violet or 

 purple color will be produced on adding a drop of a ferric chloride 

 solution. 



(c) Add to the suspected milk an equal volume of alcohol and 

 two drops of a 1 per cent, solution of rosalic acid. If sodium bicar- 

 bonate is present, a red-rose color will appear. 



Classify milk from the stand-point of its number of harmless bacteria. 

 Class 1. Certified milk : not over 10,000 bacteria per cubic centi- 

 metre. 



Class 2. Inspected milk: not over 100,000 bacteria per cubic 



centimetre. 



Class 3. Pasteurized milk: none, or a variable low number of 

 bacteria. 



What is pasteurized milk? 



Milk which has been heated to a temperature below the boiling- 

 point but sufficiently high to destroy all pathogenic microorganisms 

 (140° F., or 46° C. for 30 minutes ; 150° F., or 65° C. for 20 minutes ; 

 160° F. or 70° 0. for 10 minutes). This should be done as soon as 

 practicable after milking in inclosed vessels, preferably the final 

 containers, and after such heating immediately cooled to a tempera- 

 ture not exceeding 50° F., or 10° C. 



Give a test to prove that milk has been pasteurized. 



Pasteurization cannot be proven unless the milk has been heated 

 to 170° F., or over, because this temperature is necessary to destroy 

 the ferments upon which the test depends. 



Storch's test: Add to 5 c.c. of milk two drops of a freshly- 

 prepared 2 per cent, solution of paraphenylenediamine hydrochlor- 



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