SOILS — FEETILIZEKS. 217 



Measurements were made of the vapor pressure of two soils, a clay loam aud 

 a sand, treated with potassium carbonate and monocalcium phosphate. Por- 

 tions of the soil with and without addition of the soluble salts were placed in 

 weighing bottles and enough water added to bring the soil almost to saturation. 

 " These bottles after weighing were left open and placed in ordinary glass fruit 

 jars and the top screwed down tightly. Weighings were made again after two 

 or three weeks. In almost every case tried it was found that the soil con- 

 taining the salt had lost more weight than the soil without salt." 



Observations were made with, a microscope and lantern to obtain visual evi- 

 dence of the difference in soil structure produced by the addition of soluble 

 salts. The microscopic examinations were unsatisfactory and were abandoned. 

 In using the lantern " the soil, placed in an ordinary Petrie dish, was moistened 

 with water and then placed in a horizontal position on the condenser of the 

 lantern. The lantern is so made that vessels containing specimens to be exam- 

 ined can be placed either in a vertical or horizontal position. The image of the 

 soil particles was then thrown upon a screen or upon a photographic plate in a 

 camera, if it was desired to preserve them. The water was then allowed to 

 evaporate from the soil and the movement of the soil particles was noticed as 

 the moisture content of the soil was reduced. ... As the soil dried out, the 

 particles could be seen to arrange themselves into groups, and the soil became 

 much more open in structure. The same phenomenon was observed when 

 salts were added, but in addition a difference is noted in the aggregation of 

 the smallest particles present. When a clay or clay loam was used and the 

 projection largely magnified, the small particles could be seen to be in almost 

 continuous motion. ... In the case of the calcium phosphate the small particles 

 seem to collect in aggregates and these aggregates act as larger particles ; with 

 the potassium carbonate the small particles do not form aggregates by them- 

 selves, but appear to collect about the larger particles and to form aggregates 

 with sand grains as centers." 



The results as a whole, therefore, furnish evidence " that the addition of 

 small amounts of soluble salts affect the physical properties, and therefore the 

 structure of the soil. . . . The effect of salts is more pronounced in a soil con- 

 taining a large percentage of fine soil particles, and this leads to the conclusion 

 that colloidlike clay particles are affected most by soluble salts, and in turn 

 affect most the structure of the soil." 



The osmotic pressure of soils, J. Konig (Jahresher. Ver. Angew. Bot., 8 

 (1910), pp. XXIII-XXVI, fig. i).— The osmotic pressure of 6 different kinds 

 of soil, fertilized and unfertilized, was determined by means of a special 

 method and form of apparatus, using cylinders of the Pasteur-Chamberland 

 filter prepared with a semipermeable coating as described in previous articles 

 (E. S. R., 20, p. 713; 24, p. 521). 



In the method adopted 15 gm. of soil was mixed with asbestos moistened with 

 water and placed in the porcelain cylinder of the filter. The cylinder was then 

 closed with a rubber stopper carrying a capillary tube filled with machine oil 

 • of specific gravity 0.9091. The whole apparatus was then placed in a large 

 vessel of distilled water kept at constant temperature. After a short time the 

 water passing through the semipermeable membrane increased the volume of 

 the soil solution, forcing an equal volume of oil out of the capillary tube. This 

 was collected in a graduated cylinder and weighed daily at the same hour. 

 The quantity of oil displaced reduced to its water equivalent and calculated for 

 100 gm. of soil and unit of time (one day) was taken as a measure of the 

 osmotic pressure of the soil. 



In tests of unfertilized soils and soils fertilized with small amounts of potas- 

 sium sulphate, superphosphate, and sodium nitrate it was found that osmose 



