CERTIFIED MILK 507 



filtered. A strip of turmeric paper moistened with the filtrate will be col- 

 ored reddish brown when dried at 100 C. on a watch-glass, if boric acid is 

 present. 



If a little alcohol is poured over the. ash to which concentrated sulphuric 

 acid has been added, and fire is set to the alcohol, after a little while this will 

 burn with a yellowish-green tint, especially noticeable if the ash is stirred 

 with a glass rod and when the flame is about to go out. (Testing Milk and 

 Its Products, Farrington and Woll, p.' 247.) 



Test for Salicylic Acid (Salicylates, etc.). Twenty cubic centimeters of 

 milk are acidulated with sulphuric acid and shaken with ether; the ether 

 solution is evaporated, and the residue treated with alcohol and a little iron- 

 chlorid solution; a deep violet color will be obtained in the presence of salicylic 

 acid. (Testing Milk and Its Products, Farrington and Woll, p. 248.) 



Test for Benzoic Acid. Two hundred and fifty to five hundred cubic 

 centimeters of milk are made alkaline with a few drops of lime or baryta 

 water, and then evaporated to about a quarter of the bulk. Powdered 

 gypsum is stirred into the remaining liquid until a paste is formed, which is 

 then dried on the water-bath. The gypsum only serves to hasten the drying, 

 and powdered pumice stone or sand can be used equally well. When the 

 mass is dry, it is finely powdered and moistened with dilute sulphuric acid 

 and shaken out three or four times with about twice the volume of 50 per 

 cent, alcohol, in which benzoic acid is easily soluble in the cold, the fat only 

 being dissolved to a very slight extent or not at all. The acid alcoholic liquid 

 from the various extractions, which contains milk-sugar and inorganic salts 

 in addition to the benzoic acid, is neutralized with baryta water and evapor- 

 ated to a small bulk. Dilute sulphuric acid is again added, and the liquid 

 shaken out with small quantities of ether. On evaporation of the ether, the 

 benzoic acid is left behind in almost pure state, the only impurities being 

 small quantities of fat or ash. 



The benzoic acid which is obtained is dissolved in a small quantity of 

 warm water, a drop of sodium acetate and neutral ferric chlorid added, and 

 the red precipitate of benzoate of iron indicates the presence of the acid. 

 (Milk and Dairy Products, Barthel; translated by Goodwin, p. 121). 



85. Detection of Heated Milk. Certified milk or cream shall not be sub- 

 jected to heat unless specially directed by the commission to meet emergencies. 



86. Tests to determine whether such milks and creams have been. sub- 

 jected to heat shall be applied at least once each month. 



Detection of Heated Milk Storch's Method. Five cubic centimeters of 

 milk are poured into a test-tube; a drop of weak solution of hydrogen dioxid 

 (about 0.2 per cent.) which contains about 0.1 per cent, sulphuric acid, is added, 

 and 2 drops of a 2 per cent, solution of paraphenylendiamin (solution should 

 be renewed quite often), then the fluid is shaken. If the milk or the cream 

 becomes at once indigo blue, or the whey violet or reddish brown, then this 

 has not been heated or, at all events, it has not been heated higher than 

 78 C. (172.5 F.); if the milk becomes a light bluish gray immediately or 

 in the course of half a minute, then it has been heated to 79 to 80 C. (174.2 

 to 176 F.).' If the color remains white, the milk has been heated at least to 

 80 C. (176 F.). In the examination of sour milk or sour buttermilk, lime- 

 water must be added, as the color reaction is not shown in acid solution. . 



Arnold's Guaiac Method. A little milk is poured into a test-tube and a 

 little tincture of guaiac is added, drop by drop. If the milk has not been 

 heated to 80 C. (176 F.) a blue zone is formed between the two fluids; heated 

 milk gives no reaction, but remains white. The guaiac tincture should not 

 be used perfectly fresh, but should have stood a few days and its potency 

 have been determined. Thereafter it can be used indefinitely. These tests 

 for heated milk are only active in the case of milks which have been heated 

 to 176 F. or 80 C. (Jensen's Milk Hygiene, Pearson's translation, p. 192.) 



Microscopic Test for Heated (Pasteurized) Milk Frost and Ravenel. 

 About 15 c.c. of milk are centrifuged for five minutes, or long enough to throw 

 down the leukocytes. The cream layer is then completely removed with 



