2 BULLETIN IIU, U, S. DEPAETMEXT OF AGRICULTURE. 



with the protein, giving- rise to a yellow-colored compound, the 

 shade of the color depending on the amount of iodin liberated. If, 

 however, only small amounts of iodin were liberated, then the colored 

 protein compound would be masked by the large excess of unaltered 

 protein. The small amount of colored protein could then be made 

 to react with starch, producing a blue color which could be more 

 readily discerned, thus making the test more delicate. 



In order to determine in what dilution the hypochlorites and 

 chloramins can be detected in milk and cream a series of solutions, 

 each containing 100 cubic centimeters of milk or cream plus definite 

 amounts of hypochlorite or chloramin solution, were prepared, so 

 that the final results were solutions containing chlorin from 1 : 1,000 

 to 1 : 100,000 parts of milk or cream. The flasks containing these 

 solutions were placed in the ice box for 24 hours and then examined 

 for chlorin. After standing at room temperature for several hours, 

 the flasks were returned to the ice box, and again examined after 

 48 hours. A flask of plain milk was added as a control. 



PREPARATION OF REAGENTS. 



(a) Potassium iodid solution. — Dissolve 7 grams of potassium 

 iodid in 100 cubic centimeters of distilled water. Prepare fresh. 



{h) Ilydrochlonc acid. — To 100 cubic centimeters of concentrated 

 hydrochloric acid add 200 cubic centimeters of distilled water. 



{c) Starch solution'. — Boil 1 gram of starch in 100 cubic centi- 

 meters of distilled water. Cool before using. 



THE TEST. 



(1) To 5 cubic centimeters of milk or cream in a medium-sized 

 test tube add 1.5 cubic centimeters of the iodid solution, mix thor- 

 oughly by shaking, and observe the color of the milk. 



(2) If unaltered, add 4 cubic centimeters of hydrochloric acid, 

 mix thoroughly by means of a glass rod flattened at one end, and 

 note the color of the curd. 



(3) Next place the tubes in a large water bath, previously heated 

 to 85° C, and allow to remain for 10 minutes. During this in- 

 terval the curd will have risen to the surface. 



(4) The tubes are then cooled rapidly by placing in cold water, 

 and when cold are examined for any color change that may have 

 taken place, either in the curd or in the liquid below. 



(5) Finally, add 0.5 to 1 cubic centimeter of starch solution to 

 the liquid below the curd and note the result. 



REACTION IN MILK. 



Milk containing 1 part of chlorin in 1,000 parts of milk acquires 

 a distinct reddish color, while at 1 : 2.500 dilution it is still slightlv 



