Evaporation.
The retentive property of a soil for water tends to retard evaporation. The following table by Schübler shows the rate at which evaporation proceeds in different soils. The experiment was conducted in the following way. The soil experimented upon was saturated with water and spread over a disc, and allowed to evaporate for four hours, when it was weighed. The amount of time required for the evaporation of 90 per cent of the water was also estimated. Of 100 parts of water in the wet soil there evaporated, at 60° Fahr.—
| In four hours— | Time required to evaporate 90 per cent. | ||
| From— | per cent. | Hours. | Minutes |
| Quartz | 88 | 4 | 4 |
| Limestone | 76 | 4 | 44 |
| Sandy clay | 52 | 5 | 1 |
| Stiffish clay | 46 | 6 | 55 |
| Loamy clay | 46 | 7 | 52 |
| Pure grey clay | 32 | 11 | 17 |
| Loam | 32 | 11 | 15 |
| Fine calcium carbonate | 28 | 12 | 51 |
| Humus | 21 | 17 | 33 |
| Magnesium carbonate | 11 | 33 | 20 |
NOTE III. (p. 76).
Hygroscopic Power of Soils.
Davy found the hygroscopic power of soils to be as follows. He found that 100 parts by weight of three samples of different sands absorbed 3, 8, and 11 parts of water, respectively, in one hour; while three loams absorbed similarly 1.3, 1.6, and 1.8 parts.
The following samples of soil were dried at 212° Fahr., and exposed to an atmosphere saturated with water and a temperature of 62° Fahr., when it was found they absorbed the following amounts in twelve hours' time:—
| Quartz sand | 0.0 |
| Limestone sand | 0.3 |
| Lean clay | 2.1 |
| Fat clay | 2.5 |
| Clay soil | 3.0 |
| Pure clay | 3.7 |
| Garden-loam | 3.5 |
| Humus | 8.0 |
Gases present in Soils.