METHODS OF EXAMINING MILK 301 



below normal the color remains yellow or orange. When 

 the color becomes yellowish-brown the condition of the 

 milk must be regarded as doubtful. The presence of a 

 large amount of fat is likely to interfere with the reaction 

 and it is therefore best to remove the fat from the milk 

 before applying the test. Milk sugar is decreased in 

 quantity and is sometimes entirely absent in inflamma- 

 tion of the udder. It is also reduced in quantity during 

 the colostral period and toward the end of lactation; 

 exercise sometimes decreases it. It is present in greatest 

 amount in the middle of a milking and lowest at the 

 beginning and end. Fresh market milk will always give 

 a normal reaction to this test. 



EXAMINATION FOR COLORING MATTERS 



When the yellow color of milk is natural it is largely 

 confined to the cream, and if opportunity is given for 

 the cream to rise the milk beneath it has a bluish tinge. 

 But when the yellow color is artificial not only the cream 

 but the milk beneath it is of the same color. Artificial 

 coloring matters are sometimes added to milk to give it 

 a rich color when it has been adulterated with water. 

 Annatto, also called arnatto and annotto; analin orange, 

 an azo-dye, and caramel are the substances most fre- 

 quently used. Leach recommends the following pro- 

 cedure for the detection of artificial coloring: 



Place 150 c.c. of milk in a casserole, add a little acetic 

 acid and heat until curdling occurs. Gather the curd 

 together with a glass rod and pour off the whey, or sepa- 

 rate by filtration. Macerate the curd with ether in a 

 stoppered bottle for several hours. Evaporate the ether 

 extract on a water bath, add sufficient sodium hydroxide 

 to the residue to make it alkaline and pour the mixture 



