+83. Marschall rennet test.+--To make a Marschall rennet test, 1 c.c. of rennet extract is measured, with the 1 c.c. pipette, and placed in the bottle. Care should be exercised to rinse out the pipette. The bottle is then filled to the mark with cold water. After the milk has been heated to the setting temperature, 84°-86° F., the cup is filled with milk and set on the edge of the vat so that the milk running out through the hole in the bottom of the cup will flow into the vat. Just as the surface of the milk reaches the 0 mark on the cup, the diluted rennet extract is added and thoroughly mixed with the milk, using the small spatula to stir it. The rennet and milk should be mixed until it has run down at least one-half space on the scale in the cup. As the rennet begins to coagulate the milk, it runs slower from the hole in the bottom of the cup, until it finally stops. When it stops, the point on the scale indicated by the surface of the coagulated milk is noted. The test is recorded by the number of spaces the surface of the milk lowers from the time the rennet is added until it is coagulated. This test depends on three factors: the strength of the rennet extract, the temperature of the milk, the acidity of the milk. The more acid, the quicker the milk will coagulate. To measure any one of these factors, the other two must be constant. The variable factor is the acidity of the milk. This test will not indicate the percentage of acid in the milk, but is simply a comparative test to be used from day to day; for example, if the rennet test to-day shows three spaces, and the operator makes that milk into cheese and the process seems to be normal, it shows that for good results in this factory, milk should be ripened to show three spaces every day. If the next day the milk showed four spaces, it should be allowed to ripen more until it shows three spaces. If it shows only two spaces, this indicates that the milk has too much acid development or is over-ripe. A cheese-maker will have to determine at what point to set his milk, because the test will vary from one factory to another. +84. Comparison of acid and rennet test.+--Each of these tests has its advantages and disadvantages. The advantage of the acid test is that it can be made as well of warm as cold milk. This is of great importance in determining whether the milk delivered by any patron is too ripe to be received. The acidity of other materials, such as whey and starter, can be determined as well as that of milk. The disadvantages are that it is difficult to get the alkali solution of the proper strength and the solution is liable to deteriorate on standing. It requires a careful exact operator to make the test.