76 UErAKTMEISTAL KErORTS. 



PHYSICAL INVESTIGATIONS. 



The work in the physical laboratory has been largely in coopera- 

 tion '>vitli the soil-survey work in explaining j^roblems which are con- 

 stantly observed by tlie field parties. 



An extended series of experiments were carried on to determine to 

 what extent the soluble mineral salts, commonly found in alkali soils, 

 influence the height to which water will be raised in dry soils and the 

 rate of evaporation from moist soils. It was found tliat for concen- 

 trations approximating those found in alkali soils the salts liad no 

 influence on the lieight of capiUary rise, with tiie exception of sodium 

 carbonate, which increased the capillary rise about 8 per cent. For 

 concentrations approaching saturation the capillary action was con- 

 siderably decreased on account of the increased viscosity of the solu- 

 tion. In moist soils the salts decreased the rate of evaporation from 

 the surface, owing to the formation of a crust. If the surface of the 

 soil be kept constantly stirred, so that no salt crust can form, the salts 

 have no appreciable effect on the evaporation. Under field conditions 

 the soil is always more or less moist; so investigations have been car- 

 ried on to determine the height through which capillary action may 

 take place in moist soils. These data are obtained by measuring the 

 amount of evaporation from the to}) of columns of soil connected with 

 water reservoirs below. In some soils from James Island, S. C, in 

 which water rises only 14 inches when the soil is dry, there is marked 

 capillary action when the Avater table is 3 feet below the surface, 

 but none when the water table is G feet below. These are matters 

 of very great importance in connection with some of the Western 

 soils, on account of the very remarkable properties exhibited by some 

 of these soils in subirrigation and in the rise of alkali. 



Experiments have also been made upon the absorption of salts or the 

 withdrawal of dissolved salts from solution by soil grains. One gram of 

 a fine quartz sand removes one-tenth of a milligram of sodium carbonate 



when the soil is saturated with a -— - solution of that salt. In this con- 

 nection, it has been shown that soil grains, or other finely divided 

 materials, have the property of condensing on their surfaces relatively 

 largo amounts of carbon dioxid, considering the small partial pressure 

 of this substance in the air above the soil. It has been found that 

 when sodium carbonate is added to a soil more or less of the normal 

 carbonate is always converted to the form of bicarbonate, due to the 

 reaction with the carbonic acid condensed on the soil grains. Very 

 large quantities of sodium bicarbonate have been found in the alkali 

 lands of Utah and California by our survey parties, although the 

 presence of this salt was never suspected. The influence of tempera- 

 ture, concentration, and carbon dioxid on the equilibrium between 

 sodium carbonate and bicarbonate has been. studied conjointly with 

 the chemist of the Division. It is believed that this is an important 

 problem for the black alkali lands. 



The time and labor involved in making mechanical analyses of soils 

 have been materially reduced by the use of a centrifuge for separa- 

 ting the finer grades of soil particles. This apparatus, besides requir- 

 ing less time, can be used with a much smaller quantity of water and 

 is particularly valuable in the analj'sis of the soluble gypsum soils 

 found in many places in the "W^est. During the j^ear 260 mechanical 

 analyses have been made in the laboratory in connection with the soil 

 survey. 



