EXPERIMENT STATION BULLETINS. 2/0 



The averages of these are 



in unexposed milk 16.535 per cent. 



in milk directly after milking 27.17 



in milk after aeration 



over glass 38.842 " " 



over tin 44.618 " " 



over copper 40.416 



through glass wool and copper sieves 50.8775 " " 



The relation of oxygen to residual gas is best shown by the determination of per- 

 centages of oxygen to the residual gas plus oxygen. This is done to bring out any 

 atmospheric relationship. 



Percentages in case of 

 unexposed milk, 



10.29, 14.09, 14.70, 11.80, 8.06 and 15.26; 



milk after milking, 



33.83, 28.19, 33.S8, 35.16 and 31.96; 



milk after aeration 

 over glass, 



37.01, 35.44, 34.00, 33.89, 35.45, 31.86; 



over tin, 



32.14, 31.70, 33.61, 31.30, 28.05; 



over copper, 



46.16, 30.15, 30.21, 22.83, 19.44; 

 through glass wool and copper sieves, 



30.75, 38.60, 29.32, 25.65. 



The average percentages are 



in unexposed milk 12.376 



in milk directly after milking 32.53 



in milk after aeration 



over glass 33.94 



over tin 31.16 



over copper 29.76 



through glass wool and copper sieves 31.13 



We gather from these studies that after the milk leaves the udder of the row tliere 

 is a diminution in the amount of carbon dioxide and an increase in oxygen to a certain 

 low percentage which is dependent upon the thoroughness with which the milk is 

 brought in contact with the air. From the extreme results it is evident there has 

 been a falling off in carbon dioxide of 73.86 per cent and an increase of 35.06 per cent 

 of oxygen, thus indicating that there is no equi-volumetric interchange. Even the 

 average results show no intimate relationship between the oxygen and carbon dioxide. 

 This may, however, be due to the difference in the solubilities of the gases, carbon 

 dioxide being dissolved volume for volume, while oxygen enters only comparatively 

 meagerly into solution, about four per cent by volume. It would be possible by the 

 direct determination of carbon dioxide in milk before the beginning of fermentation 

 to say to what extent the milk has been aerated. 



Further studies of the gases of milk and their interchange will reveal other aspects 

 of the subject. 



Mil. NO APPRECIABLE INTERCHANGE OF GASES BETWEEN STERILIZKD MILK 



AND THE AIR CONFINED OVER IT. 



In six experiments an attempt was made to ascertain whether or not there was a 

 decrease in the amount of oxygen in the air confined over sterilized milk and a develop- 

 ment of carbon dioxide. Liter (lasks were taken and 500 c. cm. of fresh milk was 

 added and sterilized on three consecutive days for one hour each day. They were then 

 sealed with sterilized rubber stoppers through the single perforations of which passed 

 two way stop-cock tubes by means of which the air content could be drawn at will. 

 Besides the rubber stopper seal, a mercury seal was made about the rubber stopper by 



