648 



STATE BOARD OF AGRICULTURE. 



FIG. 15. 



A— Peat . 



B — Clyde Sill Loam. 



C— Clay. 



D— Quartz. 



E— Sandy Loam. 



F — Silt Loam. 



G— Empty Tube. 



CURVE SHOWING THE PRESSURE EXERTED BY AIR IN ONE HALF CUBIC 

 FOOT OF MOIST SOIL AT DIFFERENT TEMPERATURES. 



Before entering into the discussion of the data presented in the pre- 

 ceding tables and charts, an explanation of their form of presentation 

 is necessary. The first eleven columns of tables 9 and 10 show the 

 weight of the soils contained in the tube, the percentage of pore space, etc., 

 and the actual number of cubic centimeters of air obtained at the various 

 temperatures. The last seven columns to the right show the same ex- 

 perimental results reduced to the volume of air that one-half cubic foot 

 of soil would give, provided it had the same percentage of pore space as 

 the soil in the tube. This basis makes the figure more practicable and 

 more comprehensible. As ^^il! be seen, the volumes are not reduced to 

 the standard condition of temperature and ])ressure. which can be done 



P 



bj the use of the formula of Vq = V — or Vq = 



700 (1 + O.OOSOTt) 



where A^n is the volume under standard condi- 



r — M 



\T 



760 (1 4- 0.00367t) 

 tions, V the observed volume, P the pressure expressed in millimeters of 

 mercury, t the observed temperature, and M the vapor pressure of the 

 liquid, because the data as given above represent more closely the true 

 state of affairs. As will be shown later, the amount of gas expelled or 

 pressure produced, are very greatly influenced by the aqueous vapor 

 present, and if the results were reduced to the standard conditions, this 

 factor would have to be eliminated. The principal object of the re- 

 search is to ascertain to what extent temperature affects the ventilation 

 of soils in toio, and not necessarily the increase of volume of the pure 

 gases in the soil. Nor are the data reduced to any common pressure. 

 The atmospheric pressure varied about .20 inches on the barometer for 

 different experiments. Repeated tests showed, however, that the error 

 resulting from the difficulty of expelling all the gas from the soils, ex- 

 ceeds that due to the small variations in the atmospheric pressure. 

 Hence, the changes in atmospheric pressure have been disregarded in 



