1240 



flocculent precipitate is formed ; if the acid used contains 

 nitrates a green precipitate is formed." 



Skimmed or watered milk, or skimmed and watered milk, 

 may iaave sufficient cheese or butter color added to give it a 

 rich yellow appearance, which readily deceives the average 

 purchaser. 



"The presence of foreign coloring matter in milk is easily 

 shown by shaking lOc.c. of milk with an equal quantity of 

 ether; on standing, a clear ether solution will rise to the sur- 

 face; the solution will be yellow colored if artificial coloring 

 matter has been added to the milk, the intensity of the color 

 indicating the quantity added ; natural, fresh milk will give 

 a colorless ether solution."* 



"Annatoor Butter Color: lOOc.c. of milk, made strongly 

 alkaline with sodium carbonate, are placed in a small cylin- 

 der; a strip of filter-paper, about ^ inch wide and five inches 

 long, is introduced, and the whole allowed to stand in the 

 dark for twelve hours. If annato is present, the strip of 

 paper, after washing, will he a pale salmon color, which is 

 changed to a decided pink by moistening with a solution of 

 stannous chloride, and after drying at the temperature of 

 the room to a bluish color, on treatment with strong sulphuric 

 acid."t 



Acidity of Milli. — Freshly drawn milk exhibits an ampho- 

 teric reaction to litmus ; it colors red litmus blue, and blue 

 litmus red ; but in a short time after the milk is drawn, it 

 shows an acid reaction to the phenolphtalein test. This acidity 

 is probably due to acid phosphates, to carbonic acid gas and 

 to the acid reaction of the casein. This milk will not taste 

 sour and is considered sweet. The acid or sour tasting milk 

 IS due to lactic acid, which is a product of the action of bac- 

 teria on lactose or milk sugar. If Lhere is .3 to .35 per cent, 

 of lactic acid in milk it will taste sour. The acid-forming 

 bacteria get into the milk at the time of milking, through 

 uncleanliness ; and after milking, through careless handling 

 (keeping it in a warm room, unclean bottles or cans, adding 



*Farrington and Woll's Testiug Milk, p. 92. 



t N. Y. City Board of Health Report, J896, p. 169. 



