[LYNDE-DUPREj 



ON OSMOSIS IN SOILS 



109 



the "clay" and decided to make a separate experiment with it. This 

 "fine clay" gave us remarkable osmotic pressures and led us to make 

 experiments with still finer clay which in turn gave us much more 

 remarkable osmotic pressures (see below). 



The grains of soil in the "clay" were chiefly between «005 and 

 •001 m.m. diameter. The grains of soil in the "fine clay" were for 

 the most part less than «001 m.m. diameter. 



Apparatus. The apparatus used with the sands, silt, and clay was 

 similar to that shown in Fig. 3. The apparatus used with the fine 

 clay was the same also in the beginning, but the osmotic pressure 

 was greater than we had anticipated and the solution ran out at the 



MANOMETER- 



MERCURY— 



THERMOMETER 



:[; a|:z^^^|^ SOIL SOLUTION 



50IL 



COTTON CLOTH 



M}Mf^>}>wj^^}^^^^^?v^y>>'. 



Figure 4. Apparatus used with the "fine clay." 



top of the tubes. ^We then used the apparatus shown in Fig. 4. This 

 is the same as the apparatus shown in Fig. 3 except that an open arm 

 mercury manometer is used in place of the vertical glass tubes. 



The tubes A (Fig. 3) are of glass approximately 1 cm. inside di- 

 ameter, and 15 cm. long. The lower end of each is covered with one 

 thickness of cotton cloth. The tubes B are between 1 and 2 m.m. 

 inside diameter and 15 cms. long. 



How the apparatus was set up. — Duplicate 6 gram samples of the 

 air dry soil constituents were weighed out. Each sample was placed 

 in a test tube with about 25 c.c. of distilled water, shaken up and 

 allowed to stand over night. The test tubes with their contents were 

 then placed in a larger vessel of water and the water was boiled for three 

 hours. This helped to disintegrate the soil, sterilize it and free it from air. 



