30 



solid tablets. .One tablet is dissolved so as to make 100 cubic centi- 

 meters of solution, which is added in small amounts to 17.6 cubic cen- 

 timeters of milk or whey until the pink color remains. Each cubic 

 centimeter of solution used stands for 0.01 per cent of lactic acid. 

 Thus a milk using; 15 cubic centimeters of alkali solution contains 0.15 

 per cent of acid (reference No. 3, p. 112, or No. 12, p. 99). Some 

 precautions must be used about keeping tablets dry until used, and 

 solutions a day old shoidd not be used. 



[Suggestions to lecturer: Make sure that the relation of acids and 

 alkalis and the use of indicators are understood by the student. Per- 

 form the test (one or both), explaining each step, using milk from 

 fresh to sour and also whey from fresh to a day old. Also have each 

 student make several tests, so as to become familiar and accurate in 

 the manipulation. Impress the necessity of using exact quantities.] 



3. Methods of testing rennet extracts. — The rennet test is a method 

 for ascertaining in what time a definite amount of rennet extract will 

 coagulate a certain amount of milk at a given temperature. It is of 

 value for learning the strength of rennet extract and the ripeness of 

 milk. Two forms are in common use — (1) the Monrad test, and (2) 

 the Marschall test. 



(a) The Monrad rennet test (reference No. 3, p. 67, or No. 8, p. 38). 

 The conditions used in this test are as follows: Amount of milk used, 

 160 cubic centimeters; temperature of milk, 82° to 86° F.; amount of 

 rennet, one-half of 1 cubic centimeter diluted with 5 cubic centimeters 

 of water. The diluted rennet is added to the milk at the fixed tem- 

 perature, stirred in, and the time noted by the second hand of a 

 watch. The time is again noted when the milk has coagulated. 

 The more quickly the coagulation takes place the stronger the rennet. 

 Precautions to be used in comparing rennet extracts: (1) Use the same 

 milk if possible, (2) and the same degree of temperature. Special 

 apparatus for this can be purchased. 



(6) The Marschall test (reference No. 3, p. 68, or No. 8, p. 39). 

 In this test the same general rules of procedure apply, but the 

 coagulation takes place in a cup having on its sides graduated lines 

 and in the bottom a glass tube with a very small bore. After the 

 rennet is added the glass tube is opened and the milk allowed to 

 trickle out until it coagulates and ceases to nui. The marks made 

 inside the cup show how much milk has run out. The stronge.' the 

 action of the rennet the more quickl}' the milk coagulates, the less runs 

 out, and the fewer spaces are uncovered. One disadvantage of the test 

 is that the bore of the glass tube differs in different cups, which makes 

 difference in results. In trying different cups for comparison, always 

 use the same sample of milk. The Marschall test is convenient for 

 ordinary factory work, but it is not capable of so great delicacy as the 

 Monrad test. 



