2 BULLETIN 944, IT. S. DEPARTMENT OF AGRICULTURE. 



to withstand a temperature sufficiently high to insure the subsequent 

 sterilization without causing an objectionable curd. While it is as- 

 sumed, and no doubt correctly, that acidity is an important factor 

 in determining the coagulating point of concentrated milk, it is by 

 no means certain that other factors may not be of equal or even 

 greater importance. Sommer and Hart (2) have shown that there 

 is no consistent relation between the titratable acidity and the heat 

 coagulating point of milk. This they found also to be true of the 

 ' hydrogen-ion concentration or true acidity of the fresh milk, but 

 they express the opinion that it may become a factor under com- 

 mercial conditions. They found, on the other hand, that the varia- 

 tions which occur normally in certain of the ash constituents have 

 an important part in determining the temperature at which it 

 coagulates. 



The titration of milk in the usual way will give no indication of 

 the condition of the ash and may be very misleading as to the hydro- 

 gen-ion concentration. 



The alcohol test has been used to a limited extent for determining 

 the quality of milk with special reference to its sanitary condition. 



This test is usually made by mixing equal volumes of milk with 68 

 to 75 per cent alcohol and observing whether a coagulation results. 

 It is generally considered that a coagulation indicates bacterial 

 change in the milk, but Auzinger (3) shows that fresh milk not in- 

 frequently coagulates under these conditions and offers some evi- 

 dence to show that it is due to changes in the milk salts, particularly 

 in the calcium. Ayers and Johnson (4) show that while the alcohol 

 test becomes positive when an appreciable amount of acid or rennet 

 is produced in the milk there is no consistent relation between the 

 alcohol test and the total number of bacteria present. 



They found that while the addition of acid phosphates to milk in- 

 creased the tendency to coagulate with alcohol, the neutral or dibasic 

 phosphate had the opposite effect. When dibasic phosphate is added 

 to milk considerably more acid is required to produce a positive 

 alcohol test than with the normal milk. 



While the work of Ayers and Johnson shows that the alcohol test 

 is not a reliable index of the sanitary quality of the milk, there is a 

 possibility that its action on milk may be correlated with the heat 

 coagulation point of the evaporated milk in such a way as to render 

 it of some value in grading milk in condenseries. 



TEST METHODS USED. 



The alcohol test as used in this investigation was made by mixing 

 equal parts of 75 per cent alcohol and milk and observing whether 

 coagulation takes place. In case the milk shows a visible coagulation 



