3204. —- H. W. Turpin 
Before seeding, some preliminary studies were made in order to ascertain 
the best method of obtaining the sample of soil air for analysis. It seemed 
impracticable to use any method other than one that could be carried 
out rapidly, since it was planned to run the test for two seasons and to 
take the samples twice each week thruout the year. As a result of the 
preliminary studies, it was found that by aspirating four liters of air thru 
the soil cans in five minutes, and passing the air thru two graduated 
500-cubic-centimeter Erlenmeyer flasks, samples could be obtained in the 
two flasks which checked with each other, indicating that the air originally 
present in the flasks had been replaced by a representative sample of the 
air in the soil. If more or less than four liters was aspirated thru the 
soil, the amounts of carbon dioxide in the two flasks did not check, indi- 
cating, in the first case, that the original air in the soil had been replaced 
by air from the atmosphere and that some of the latter was passing into 
the flasks, and in the second case that the original air in the flasks had 
not been completely replaced in the flask nearer the aspirator. The 
method of sampling is shown in figure 45. After the aspiration was 
completed, the cocks on the flasks were closed and the flasks were removed 
to the headhouse, where they were allowed to reach room temperature. 
The excess pressure in the flasks was relieved by opening one of the cocks 
foramoment. The temperature was noted at this point, as all calculations 
were reduced to per cent by volume of carbon dioxide at standard 
atmospheric conditions, that is, 760 millimeters pressure and 0° C. 
Excess of standard barium hydroxide was next run into the flasks. 
The volume of the barium hydroxide added was noted, and was sub- 
tracted from the total volume of the flask. The cocks were then closed, 
and the flasks were allowed to stand, with occasional vigorous shaking, 
for about thirty minutes, after which the excess barium hydroxide was 
determined by titrating with standard oxalic acid whose equivalent in 
terms of carbon dioxide had been previously determined by titrating 
with standard potassium permanganate solution. 
The method of aspirating air thru the soil has been criticized by Pot- 
ter and Snyder (1916) in a paper describing experiments in which 
they determined the carbon dioxide evolved by drawing a current of air 
continuously over the soil surface. They maintain that the occasional 
drawing of air thru the soil will result in a temporary decrease in the 
content of carbon dioxide, which, however, will soon be restored by the 
