34 BULLETIN 1. U. S. DEPARTMENT OF AGRICULTURE. 
- 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 Erlermieyer receiving flask is then accurately 
titrated back by means of a tenth-normal standard ammonia solution, using a 
tinea] solution as an indicator. From the amount of acid used the per cent 
. oiti gen 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. I Farrington and Woll. Tesring Milk and Its 
Lucts, ; 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 their 
83. Tests for the detect* n of added coloring matter shall be applied whenever 
the color of the milk or cream is such as to arouse suspicion. 
Test fo% 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 dear 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.) 
54. 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 o. c. of HC1. containing a trace of Fe^ Ch. 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 I -ax, 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 a: 1*X' : C. on a watch glass, if boracic add 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. I Testing Milk and Its Prod- 
ucts, Farrington and Won, p. 247.) 
Test for ■ 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-ehlorid solu- 
tion : a deep violet color will be obtained in the presence of salicylic acid. 
I Te-ting Milk and Its Products. Farrington and Woll p. 24S.) 
Test for ':■ nzoic 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. 
:hen 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 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 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. 
