546 



STATE BOARD OF AGRICULTURE. 



which coutained a bent glass tube to be connected to the gas burette. 

 The soil column in the tube occupied a space of 152 cubic centimeters, 

 and was about <).5 indies in length. The length was calculated to rei)re- 

 sent the deptli tliat the up]ier surface of soil is tilled, and in which the 

 amplitude of temperature is most marked. There were six ditfereut 

 classes of soil used, namely : (pmrtz sand, and sandy loam, silt loam, and 

 clay of the ^liami scries, and (Myde silt loam and i)cat. All these soils, 

 both in the dry and moist condition, were passed through a sieve, mixed 

 well, and compacted in the tube as uniformly as possible. The packing 

 was done by allowing the tube to fall in a vertical position a certain 

 number of times from a definite height. Tlie soil was lieated to any de- 

 sired temperature by varying the temjterature of the water contained in 

 the vessel in which the soil tube was plac^ed. There were six dilTerent 

 temperatures employed, 0°, 10°, 20°, 30°, 40^ and 50" C. These tempera- 

 tures are within the limits of the temperature; changes that occur in the 

 bare soil between winter and sunnner, and between day and night in suc- 

 cession, or at intervals of a few days. The soil was kept at the same tem- 

 perature until no more gas was expelled or pressure exerted. In the 

 ca,se of the moist soil the equilibrium was attained in about 30 minutes, 

 but in the case of the dry soils, a somewhat longer time was required. 

 It is doubtful, however, whether all the air was expelled, even when 

 equilibrium was established, because there are films or small bubbles of 

 air which adhere with great tenacity to particles, and especially to those 

 coated with oily substances. Moreover, some air is imprisoned and can- 

 not escape. Some very slight irregularities which will be noticed in some 

 of the results, may be attributed to these factors. But the error resulting 

 from the ditficulty of expelling all the gas must relatively be very small 

 on account of the large volumes of gas expelled. The following tables 

 and diagrams represent the results obtained. Table 9 contains the ob- 



FIG. 13. CURVE SHOWING THE EXPULSION^OF AIRIFROM ONE HALF CUBIC FOOT 

 OF AIR DRY SOIL AT DIFFERENT TEMPERATURES. 



