EXPERIMENT STATION BULLETINS. 



505 



about one hour later by the cultivated, and by about one and one-half 

 hours later by the sod land. Evidently the uncultivated ground is the 

 best conductor of heat, the sod the poorest, while the cultivated lies 

 intermediate. The greater moisture content in the cultivated and the 

 vegetation on the sod plots undoubtedly affected the rate of heat trans- 

 mission. 



HEAT CONDUCTIVITY OP SOILS IN THE DRY STATE. 



Mention has been made that the heat conductivity of the foregoing 

 types of soil was also studied in the air dry condition. The object of 

 this investigation was two-fold: First, it was desired to ascertain the 

 relative heat transmission of these soils in their water free state as 

 compared with the transmission in their moist or wet state; and second, 

 to see what relationship heat conductivity has to heat radiation of soils 

 in the air dry condition. 



This study was conducted in the same manner as the foregoing with 

 the exception that the vessel used to hold the material was a wooden 

 cylinder constructed for the purpose, instead of a box as in the former 

 experiments. This cylinder consisted of white pine and was 8 inches 

 long, 4 inches in diameter and with walls 1 inch thick. On one end 

 was a wooden cover 1 inch thick which could be screwed on, and on 

 the other was a very smooth copper plate tightly fastened on. The 

 soil was poured in always from the side with the wooden cover and 

 then compacted. The compacting was done by Bowman's compacting 

 machine with few modifications. This whole apparatus is shown in 

 Fig. 2. A is an arrangement especially made for the cylinder to rest 

 on the copper cover and placed downward. The soil was poured in 

 the top of the cylinder until the latter was full and then the crank 

 was turned 20 times. The cylinder was filled more and the crank was 

 turned again five times. The cylinder was then taken off the pack- 

 ing machine and all the edges were paraffined to make it air tight, and 

 seven thermometers were placed along its axis at a distance of one inch 

 apart and two inches deep. The cylinder was then placed on a stand 

 as in the preceding experiment, and allowed to remain in the room 

 several hours in order that the soil might acquire the room tempera- 

 ture, the latter remaining quite constant from day to day. The copper 

 end of the cylinder was then brought in contact with the copper side 

 of the source of heat. The temperature of the water in the bath was 

 kept at about 33.5° C. as in the foregoing experiment, and the time 

 required for the mercury column of the different thermometers to show 

 a rise was noted. For simplicity as before, only the data for the 

 thermometer 7 inches from the source of heat are represented below. 



TABLE 9.— HEAT CONDUCTIVITY OF SOILS IN DRY STATE. 



