EXPERIMENT STATION BULLETINS. 267 



Considering the extremes of the six analyses there exists a difference of 7.84 per cent. 

 In Pfliiger's the difference is 3.28 per cent. Between the two sets of averages, Pfliiger's 

 and ours, there is 7.30 per cent difference. Thus the possible variation in six analyses 

 i- greater than the difference between the averages of the two sets of analyses. The 

 uniformity obtained in the six analyses also indicates that there can be no serious 

 discrepancies in 'the analytical work, and it is difficult to say how much variation 

 Pfliiger might have had, had he made six analyses instead of two; furthermore, there 

 i- probably as much variation in the gas content of milk as there is in other constituents. 

 This fact was brought out plainly in some of the preliminary tests which are not cited 

 here because those tests served only to pave the way for these six analyses and to 

 develop those points necessary for recording the systematic work. Pfliiger further does 

 not state the temperature at which .the gas was pumped from the milk nor does he enter 

 specifically into a discussion of the influences which might alter further the gas-content 

 of milk. 



He obtained a larger amount of gas from milk than we obtained. This alone may 

 answer why more carbon dioxide was secured by him. In two of our preliminary 

 tests we first pumped off the gas, which came with ease, collected it in a burette, and 

 then began pumping again, when we obtained a larger percentage of carbon dioxide 

 than we did in the first pumping; however, we did not carry out this work repeatedly, 

 therefore cannot state with any degree of assurance that this will always follow. It was 

 not our purpose to ascertain the amount of gas that may be obtained from milk, but 

 rather to secure a qualitative estimation of any changes that may occur in milk under 

 aeration. 



To do this it became necessary to hold to the same time and temperature and pressure, 

 as far as possible, while pumping the gas from the milk. After trying the temperature of 

 the room in several tests, about 22° centigrade, the conclusion was reached that the 

 yield in amount of gas in milk was reduced. This amount was greater than we could 

 account for by the contraction of the gas due to a change in temperature : neither did 

 we desire to heat the milk lest some change might occur. That heat increases the gas 

 liberated from a definite amount of milk is proved by ThSrner'a (13) work where 

 large amounts of gas were obtained from comparatively small amounts of milk. Taking 

 milk at 37i/o C. or thereabouts it is believed that the milk does not undergo any change 

 and that the greatest amount of gas could be obtained without altering the milk. 



Furthermore it was also found necessary, after the preliminary tests, to limit the 

 time of pumping because at no time was the milk totally exhausted, although most of the 

 gas pissed off within fifteen minutes after pumping began. The time limitation was 

 fixed arbitrarily at one hour, believing that this limitation practically precluded the 

 possibility of fermentation. 



A pressure of 756 mm. to 759 mm. was recorded upon the manometer of the Geissler 

 pump and from these have been deducted the errors in measurement resulting from 

 \j]>or tension, yielding the results recorded. With three constants, which intluence the 

 amount of gas under our control, we were able to obtain fairly uniform results. There 

 was, however, an error creeping in occasionally due to the presence of obstructions in 

 the upright capillary tube connecting with the container. In this respect the apparatus 

 designed is not as perfect as it should be, for mercury would sometimes fail to be 

 drawn over from the capillary tube extending from the container to the horizontal 

 portion of the arm. and thus interfere with the suction power of the pump upon the 

 milk. T have given in two or three instances the analyses of very small amounts of 

 gas; the explanation for these small amounts will be found in such obstructions. 

 \\ henever they occurred they could easily be detected while pumping. 



Pfliiger in his studies has made reference to the possible atmospheric source of some 

 oxygen and nitrogen as found in milk and places himself againsl such a view. Both 

 in his work ami in our analyses this relationship is not established, therefore his views 

 are upheld. The percentage of oxygen falls far below that of the air ami even below 

 the solubility of oxygen in water. The percentages of oxygen obtained from unexposed 

 milk ate 



2.88, 3.09, 2.69, 2.14. l.(i. 2.12. 



These figures represenl men' traces "t oxygen when viewed in the light of percentage 



of gas volume obtained instead of milk volume, which has nol been employed in the 



estimation of any of our percentages. The following arc the percentages of oxygen in 



it- relation u> total gas less carbon dioxide: however woe these figures the ><duhilities 



(13.) Chemlker Zeltung, L894, Bd. XVIII. 



