SOIL MOISTURE AND TO EVAPORATION. 21 



of closing care was taken to include no air and in pressing the stopper 

 into place the column of solution was forced up into the tube to a 

 height of several centimeters. After the cylinders were filled and 

 stoppered they were placed in water for several hours and only those 

 which failed to leak sugar were used in the experiments. 



After testing with water the osmometers were placed in soils from 

 the vicinity of the Desert Laboratory, containing various amounts of 

 water, and observations upon the height of the column of solution were 

 made at intervals for a period of from 10 to 24 hours to determine 

 whether water movement took place from the cell into the soil or in the 

 opposite direction. Of course the osmometers act like water ther- 

 mometers and slight changes in the height of the columns will accom- 

 pany variations in temperature. A thermometer was placed in the soil 

 and in the critical cases care was taken to have the soil temperature at 

 the time of observation approximately the same as at the start. In 

 these experiments the soil was placed in tin cylinders of the form used 

 in determining its power to hold water, but without perforations in the 

 bottom. The soil was worked up with the required amount of water 

 and was tamped firmly into the cylinder around the osmometer, the 

 upper suf ace of the soil being on the same level as the top of the rubber 

 stopper. 



Five different osmometers, each used several times, gave the fol- 

 lowing result: In soils containing 5, 10, and 15 per cent of water by 

 volume the column of sugar solution gradually sank, showing that water 

 was being extracted from the cell. In the 20 per cent soil a very slight 

 rise was noted in some tests and an equally slight fall in others; this 

 soil seems to have approximately the same attraction for water as has 

 a 1.5-molecular cane-sugar solution. In the 25 per cent soil the column 

 of sugar solution rose, showing that the cell was absorbing water from 

 the soil. 



We may conclude, then, that the force with which the 20 per cent 

 soil resists absorption of water by one of these osmotic cells is about 

 equal to the osmotic pressure of a 1.5-molecular cane-sugar solution, 

 or, according to Morse and Frazer (1902), about 54 atmospheres. This 

 pressure is surprisingly high, much higher than the osmotic pressure 

 of most plant cells, and suggests that either the osmometers here used 

 do not form as good contact with the soil grains as do the root hairs, 

 or else that osmotic pressure does not indeed play the important part in 

 water absorption which has hitherto been assigned to it. 



At the University of Chicago, during January and February, 1905, 

 a number of experiments similar to the above were performed upon a 

 very finely divided quartz sand. The sand used .was the finest one of 



