Useful Rules and Tests. 265 



rennet, stir quickly, and place in such a position that the milk may- 

 flow freely from the orifice. When the milk ceases to flow, note the 

 number of graduations exposed. The riper the milk the less the 

 number of exposed graduations. 



Hot Iron Test. 



A test used to indicate the maturity of curd in cheese making. 

 The maturity is usually coincident with the amount of lactic acid 

 present, so that the test is commonly called the hot iron test for 

 acid. 



The test is made by heating a bar of iron just short of redness, 

 or so that it will hiss readily. A mass of curd is squeezed in the 

 hand till all the whey possible is pressed out. The curd is then 

 applied to the iron ; the surface of the curd, melted by the heat, 

 sticks to the iron, and the remainder is carefully and gently pulled 

 away. If the cui-d is very immature, the melted part readily sep- 

 arates from that not affected by the heat, but when more mature, 

 numerous fine threads of casein are drawn out when the two parts 

 are separated, the length of these threads depending upon the ma- 

 turity of the curd, and commonly measured in terms of acid, thus, 

 34-inch acid, 2-inch acid, etc. 



To Calibrate or Test the Accuracy of Graduation of 

 Glassware Used in the Babcock Test. 



Observe that the graduations are at equal distances apart. Fill 

 the bottle carefully to the o point with clean rain water, wipe out 

 the neck carefully, and add from a pipette or burette 2 c. c. water. 

 It should fill the bottle exactly to the 10 point. Or, weigh the 

 bottle filled with clean rain water to the o point with delicate bal- 

 ances, fill to the 10 point and weigh again. The difference in weight 

 should be 2 grams. Or, into a dry, empty bottle put 2 c. c. or 

 27.18 grams mercury, insert a tight-fitting plug carefully to the 10 

 point, and invert the bottle ; the mercury should just reach to the 

 o point. The pipette should hold 17.6 grams of water, or 239 

 grams of mercury. Any piece showing a discrepancy of 2 per cent 

 should be discarded. 



To Test Butter or Cheese With the Babcock Test. 



Weigh out on a balance sensitive to .1 gram, from 4 to 8 grams 

 of the substance to be tested. Divide into small pieces and put 

 into an ordinary test bottle, or bottle with detachable neck, with 



