550 STATE BOARD OF AGRICULTURE. 



CaCLj or HoSO^ before it entered the tube. This procedure had an ob- 

 ject in view which will be revealed subsequently. Since the tube was 

 empty its "porosity" was 100 per cent. Reducing, for sake of compari- 

 son, its volume to that of an empty half-cubic foot, the increase in vol- 

 ume of the air by increments of 10° C. will be found at the bottom of the 

 right hand half of the table. An examination of these results show that 

 they follow the law of Charles in that the increase in volume is the 

 same for equal raise in temperature. The total increase in volume from 0° 

 to 50° C. is greater than that of quartz sand, sandy loam, silt loam, Clyde 

 silt loam, and clay but is 261.4 cc. less than that of peat. TJiis is indeed 

 very interesting, the half cuhic foot tube filled ivith moist peat and hav- 

 ing a pore space of S'l^O cc. should give a greater increase in volume of 

 air from a temperature rise of from 0° to 50° G. than- the same half 

 ciihic foot ttihe containing nothing hut dry air, and having a pore space 

 of lJf,160 cc. On the other hand, when the air of this empty tube is not 

 X)reviously dried, the increase in volume for every 10° C. raise of tem- 

 perature ascends exactly as that of the moist soils, and that the total 

 volume increase is far greater than that of all the soils, including peat. 

 This difference in the results between the dry and moist air in the tube 

 suggested the explanation as to the cause of the difference between the 

 actual and calculated results already considered. 



Taking up now table 10 with the air dry soils, it will be seen that the 

 results follow in order those of the moist soils. The only difference is 

 that in the former the actual increase in volume with the various incre- 

 ments of temperature is not so marked and so regular, and that the total 

 volume increase is not so great, as in the latter. An explanation for 

 these apparent variations will be offered subsequently. 



Table 11 and the accompanying figure 14 show, as already stated, the 

 pressure exerted in atmospheres of mercury by the moist soils contained 

 in the tube of 152 cc. capacity, or in half cubic foot (14,160 cc.) tube. 

 An examination of these data will at once reveal the fact that the pres- 

 sure produced by the ino'ease in volume loith rise in temperature is 

 tremendous. The amount of pressure that would actually be produced 

 by raising the temperature of the upper half cubic foot of soil from O'^ 

 to 10° C. amounts 3.187 atmospheres in quartz sand, 3.187 in sandy loam, 

 3.187 in silt loam, 3.379 in Clyde silt loam, 3.308 in clay, and 4.291 in 

 peat. This pressure increases in all the soils regularly and rapidly with 

 a rise in temperature so that the temperature elevation of from 40° to 

 50° C. the pressure exerted by the quartz sand is 6. 436 atmospheres, by 

 the sandy loam 6.498, by the silt loam 6.498, by the Clyde silt loam 

 6.734, by the clay 6.616 and by the peat 8.337. Evidently the pressure in- 

 creases as abnormally as the volume, and consequently both must possess 

 a common cause. Theoretically, the amount of pressure produced by the 

 various 10° C. increments must be the same as the results of the empty 

 tube show, which were obtained from dried air. 



The foregoing abnormalities, both in the volume and pressure increase 

 with a continued rise in temperature, and the great deviation from the 

 theoretical volumes as calculated from the porosity of the soil, are due 



(1) to the pressure or expansion of the water vai)or, and (2) to the 

 gases absorbed by the soils and given off at the various temperatures. 



As already mentioned, water is transformed into vapor by the ap- 

 plication of heat and the quantity vaporized increases with rise of 

 temperature, and is usually deduced from the pressure exerted. The 



