EXPERIMENT STATION BULLETINS. 



529 



water of the same temperature to percolate. The soil column was con- 

 tained in a brass tube 14 inches long, and 3 inches in diameter. The soil 

 was placed in the tubes in air dry condition, compacted lightly, and then 

 water allowed to flow through it for three or four days in order to give 

 it a more uniform structure before it was used for experimental purposes. 

 About 2 inches of space was left at the top for a constant head of w^ater 

 pressure. Surrounding the soil tube was a cylindrical compartment 14 

 inches long, and 10 inches in diameter, and soldered to the soil tube at 

 the bottom as shown in figure 7. In this outer compartment was con- 

 tained the water at the desired temperature. A channel at the upper part 

 of the soil tube connected the head of water pressure with the level of 

 the outside mass of water. As the percolation in all the soils, except in 

 the sand, is slow, the constancy of the head of water pressure was 

 maintained with no difficulty. The temperature of the water in the outer 

 compartment, and consequently that which flowed through the soil, was 

 changed and maintained to any desired degree, by the addition of either 

 hot water or ice. There are electrical devices which could have been 

 used for this purpose, but it was not considered expedient and necessary, 

 as the above method answered the purpose almost equally well. The soil 

 was allowed to remain and water to percolate through it at any particu- 

 lar temperature for two hours before readings were taken of the velocity 

 of percolation. Inasmuch as the volume of the water in the outer com- 

 partment was large and the vessel well insulated on the outside, the 

 temperature remained fairly constant for long periods of time. The 

 temperatures employed were 0°, 10°, 20°, 30° 40°, and 50° C. The classes 

 of soils employed were sand, sandy loam, silt loam, clay loam, 

 clay, and muck. The results obtained are detailed in table 5. They give 

 grams of water percolated during a period of 30 minutes. Figure 8 

 represents these data in a graphical form. 



TABLE 5.— EFFECT OF TEMPERATURE ON THE PERCOLATION OF WATER IN SOILS. 



An examination of these data at once reveals the fact that the rate of 

 percolation of water does not increase in all cases Avith rise in tempera- 

 ture. On the contrary, with exception of sand, in all the other soils the 

 velocity of flow increases up to a certain temperature and then diminishes 

 again with continued ascent of temperature. The temperature at which 

 the maximum rate of percolation occurs and then commences to descend, 

 is about 30° C. In the case of sand, however, the velocity of flow in- 

 creases regularly and rapidly with rise in temperature. 



Obviously then, the prevalent a priori reasoning that the rate of perco- 

 lation of water in soils increases with increase of temperature is neither 

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