﻿34 BULLETIN 1, TJ. S. DEPARTMENT OF AGEICULTURE. 



to settle) ; the contents of the Jena flask are now heated to boiling, and the dis- 

 tillation is continued for 40 minutes to an hour, until all ammonia has been dis- 

 tilled over. 



The excess of acid in the Erlenmeyer receiving flask is then accurately 

 titrated back by means of a tenth-normal standard ammonia solution, using a 

 cochineal solution as an indicator. From the amount of acid used the per cent 

 of nitrogen is obtained; and from it the per cent of casein and albumen in 

 the milk by multiplying by 6.25. The amount of nitrogen contained in the 

 chemicals used is determined by blank experiments and deducted from the nitro- 

 gen obtained as described. (Farrington and Woll, Testing Milk and Its 

 Products, p. 221.) 



82. Coloring matter and preservatives. — All certified milks and creams shall 

 be free from adulteration, and coloring matter and preservatives shall not be 

 added thereto. 



S3. Tests for the detection of added coloring matter shall be applied whenever 

 the color of the milk or cream is such as to arouse suspicion. 



Test for coloring matter. — The presence of foreign coloring matter in milk is 

 easily shown by shaking 10 c. c. of the milk with an equal quantity of ether ; 

 on standing, a clear ether solution will rise to the surface; if artificial coloring 

 matter has been added to the milk, the solution will be yellow colored, the 

 intensity of the color indicating the quantity added ; natural fresh milk will 

 give a colorless ether solution. (Testing Milk and Its Products, Farrington and 

 Woll, p. 244.) 



84. Tests for the detection of formaldehyde, borax, and boracic acid shall 

 be applied at least once each month. Occasionally application of tests for the 

 detection of salicylic acid, benzoic acid, and the benzoates is also recommended. 



Test for the detection of formaldehyde. — Five cubic centimeters of milk is 

 measured into a white porcelain dish, and a similar quantity of water added; 

 10 c. c. of HC1. containing a trace of Fe- Clo, is added, and the mixture is heated 

 very slowly. If formaldehyde is present, a violet color will be formed. (Test- 

 ing Milk and Its Products, Farrington and Woll, p. 249.) 



Test for boracic acid {borax, borates, preservaline, etc.). — One hundred cubic 

 centimeters of milk are made alkaline with a soda or potash solution, and then 

 evaporated to dryness and incinerated. The ash is dissolved in water, to which 

 a little hydrochloric acid has been added, and the solution filtered. A strip of 

 turmeric paper moistened with the filtrate will be colored reddish brown when 

 dried at 100° C. on a watch glass, if boracic 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 alcohpl, 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 Prod- 

 ucts, 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 solu- 

 tion ; 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 centi- 

 meters 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 pow- 

 dered pumice stone or sand can be used equally well. When the mass is dry, 

 it is finely powdered and mois'ened 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 evaporated to a small bulk. 

 Dilute sulphuric acid is again added, and the liquid shaken out with small quan- 

 tities 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. 



