ILLINOIS DAIRYMEN'S ASSOCIATION. 173 



buttermakers who use the alkali test is that they can get a 

 greater uniformitty by its use than when they are simply 

 depending on their noses and tastes. 



There are two tests on the market, the Mann's test (so- 

 called) and the Farrington test. What I propose to give you this 

 afternoon is a slight modification of these which we have found 

 very much more convenient in our laboratory at Purdue Uni- 

 versity. 



These tests, as you know, are based on the principle that a 

 given quantity of a standard alkali neutralizes a definite quantity 

 of acid. When cream ripens, as the buttermaker calls it, the 

 milk sugar in the cream is changed to acid. By measuring the 

 amount of acid developed he has a fair index of the ripeness of 

 his cream. It is perfectly possible to have the desired degree 

 of acidity and yet have a very undesirable quality, to have a 

 desirable flavor and yet not have sufficient acidity, so that the 

 acidity alone is not an absolute measure of the butter. 



The handiest method of referring to acidity, or rather of 

 expressing the acidity, is in percentage. Farrington's test is 

 based on the use of an alkaline solution of such strength that 

 when you use 17.6 cubic centimeters of cream, which is the 

 amount held by the ordinary Babcock teste pipette, and neutralize 

 that with the solution of alkali, which in terms of the chemist 

 is fiftieth normal, then' each cubic centimeter of that alakli neu- 

 tralizes .01 of 1 per cent of acid. With the Farrington test, in 

 order to get a solution of that strength, tablets are prepared of 

 such strength that when five of them are dissolved in 97 cubic 

 centimeters of pure water (that is water condensed from steam, 

 or rain water) the resulting alkali will have the desired strength. 

 The modification which I give you is the way we have used it 

 for nearly two years in our dairy school, and is as follows. 



During the ripening of cream the milk sugar in it is con- 

 verted into lactic acid by bacteria. The measurement of the 

 amount of acid developed during the ripening is the nearest 

 rpproach we have to a measure of the ripeness of the cream. 

 For this purpose Mann's acid test and Farrington's alkali test. 



