526 STATE BOARD OP AGRICULTURE. 



explain correctl}^ In the opinion of the writer the above results offer an 

 excellent proof that temperature aids and hastens the formation of a 

 mulch, and tends to conserve the soil moisture in the manner previously 

 set forth. 



This is a remarkable paradox indeed, that temperature which causes 

 the loss of water should also cause its conservation. 



^ THERMO-OSMOSE IN SOILS. 



In the course of the foregoing studies on thermal movement of mois- 

 ture in soils, the question arose : What would happen if on two sides of 

 a soil membrane is placed water of an unequal temperature? Would 

 there be a diffusion of water? And if so would the hot water diffuse to- 

 wards the cold, or vice versa? The difference in temperature between the 

 two faces of the membrane is analogous to the difference in concentration 

 of solution. If any movement of water occurred in either direction it 

 might be classed under the category of thermo-osmotic phenomena, prob- 

 ably similar to those observed by Lippmann^*' in the case of the gelatine, 

 and golden beaters skin where cold water moved towards the hot. In 

 such an event the soil would act as a semi-permeable membrane in the 

 same manner as in solutions of different concentrations as shown by 

 Lynde" and Robinson.^^ It was at first thought that certain of the fore- 

 going data on thermal translocation of water might be attributed to 

 thermo-osmotic phenomena. 



Considerable time was expended in endeavoring to devise a method to 

 attack the problem. After several trials the apparatus shown in figure 

 6 was devised and finally adopted. It consists of a brass tube 11 inches 

 long and 1^/2 inches in diameter having 4 one-half inch holes, two cap 

 nuts C, and two compressing plungers P. The holes were 1 inch apart at 

 the two ends of the tube, and Si/o inches at the center. The soil whose 

 thermo-osmose or thermo diffusion was to be investigated was placed in 

 the middle of the tube and pressed together by the two compressing 

 plungers. The outer ends of the plungers were loosely connected to the 

 cap nuts and by screwing the latter to the tube the soil in the middle 

 could be pressed to any desired degree. The heads of the plungers were 

 fitted to the tubes tightly and were perforated so as to allow free com- 

 munication between the soil and water. To prevent the soil from being 

 forced out through these perforations a very fine gauze was inserted on 

 the inner side of each plunger which came in contact with the soil. For 

 maintaining a difference in temperature at the opposite compartments 

 of the soil membrane a wooden box with a partition in the center was 

 employed. The tube was inserted through a hole in the partition and the 

 soil membrane came under this hole and extended equally in both direc- 

 tions. After the two compartments of the wooden box were made water 

 tight either by paraffin or by a compound called "chlorine putty," the tAvo 

 enclosures of the soil membrane were filled with water, and in the inner 

 two holes of the tube were placed two straight glass tubes, and in the 



"Comptes rendus 1907, p. 104. 



"Journal of American Society of Agronomy, Vol. 4, p. 108 (1912). 



"Results obtained at the Michigan Experiment Station but not as yet published. 



