2 BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 



tate when mixed with equal volumes of 75 per cent alcohol is rejected 

 by this company. We are not aware that any practical use of the test 

 is made by any one else in America. In Europe the alcohol test is 

 more generally used, but we are unable to state to what extent the 

 test is employed at present, although Farrington and Woll (9) say 

 that in European creameries and city milk depots the alcohol test is 

 often applied to every can of milk received; milk that is sufficiently 

 sour to be noticed by the taste will coagulate when mixed with an 

 equal volume of 70 per cent alcohol. 



The Berlin police regulation of 1902 (32) regarding the sale of milk 

 and cream required that cow's milk coming from a distance must, 

 at the time of delivery to the consumer, stand without coagulation 

 the cooking or alcohol test (mixture of 70 per cent alcohol by volume 

 with equal parts of milk). According to Devarda and Weich (6), 

 only fresh milk, which shows no precipitate or only a very fine coagu- 

 lation with the alcohol test, is accepted in the Vienna market. 



OBJECT OF THIS Wt>EK. 



The principal object of this work was to determine the practical 



value of the alcohol test as a test for the quality of market milk. As 



incidental to our primary object, it was our purpose to determine 



some of the causes for the precipitation or coagulation of milk by 



alcohol. 



METHOD OF MAKING THE ALCOHOL TEST. 



In our work we have used the single alcohol test; that is to say, a 

 mixture of equal volumes of alcohol and milk. A few investigators 

 have used the double alcohol test, in which two parts by volume of 

 alcohol are mixed with one part of milk. In general equal volumes 

 of 68 per cent alcohol and milk are mixed for the test, but in our 

 work 75 per cent, 68 per cent, and 44 per cent alcohol were used. 

 Three tests were made on each sample of milk, 2 c. c. of alcohol 

 being mixed with 2 c. c. of milk in a test tube. The milk was always 

 at a temperature of from 15° to 20° C. After adding the milk to the 

 alcohol the tube was shaken and examined for the appearance of a 

 precipitate. The precipitate appears as flakes the size of which were 

 recorded as follows: VS for very small, S for small, M for medium- 

 sized, and L for large. 



The different percentages of alcohol were obtained by diluting a 

 high grade of absolute alcohol with distilled water. Reiss (27) has 

 shown that alcohol should always be tested for acid before using in 

 the alcohol test, as acetic acid sometimes found in the alcohol may 

 make the milk sufficiently acid to cause a coagulation with alcohol. 

 The acidity was determined by titrating 10 c. c. of milk with N/10 

 NaOH, and is expressed throughout this paper as per cent of normal acid. 



Any special methods employed in this work will be discussed when 

 .mentioned in the text. 



