SOILS FERTILIZERS. 219 



methods are more or less defective. The author recommends the use of hydro- 

 chloric acid instead of nitric acid to break up soil aggregates and sodium 

 hydroxid instead of ammonia for extraction of humus. It is pointed out that 

 the root hairs of leguminous plants are too large to penetrate a soil consisting 

 of particles finer than 0.03 mm., which is the dividing line between fine sand 

 and silt. The root hairs of grasses can not penetrate a soil composed of par- 

 ticles finer than 0.002 mm. Most bacteria are not active in soils composed of 

 particles under 0.003 mm. in size. 



Meohanical soil analysis, P. Vinassa de Regny (Resume [1], pp. 11, 12). — In 

 this abstract is described a modified Appiani sedimentation cylinder which is 

 provided with a movable siphon permitting control of the depth of water used 

 in the sedimentation. The advantage claimed for this apparatus is that it 

 saves time, requires a smaller quantity of water, and secures greater uniformity 

 in size of soil particles. 



The importance of colloids in soils, B. Ramann (Resume [1], pp. 13-rl6). — In 

 this abstract it is stated that colloids may consist of crystalloids as well as 

 of amorphous bodies. The amorphous bodies, however, were moi*e easily 

 changed into the colloidal state. Very finely powdered crystals went into sus- 

 pension with all the characteristic properties of colloids. Reduction of sur- 

 face, as by drying, freezing, etc., greatly decreased absoi'ption. Fixed com- 

 pounds of a soil rich in colloids went into solution when the soil was dried. 

 Air-dry soils allowed from two to three times as large a quantity of salts to go 

 into solution with water as moist soils. 



Protective colloids, or bodies with colloidal properties, enable many sub- 

 stances to go into the colloidal state. Certain humus substances act as pro- 

 tective colloids, iron and aluminum hydroxids and silicates becoming active 

 under their influence in the presence of water. Under certain soil conditions 

 and the influence of certain salts the protective colloids lose their characteristic 

 properties and approach the crystalloids in character. Such retarding bodies 

 are called protective crystalloids. The strongest of these are the metallic salts, 

 especially the calcium compounds, the latter being the typical protective crystal- 

 loids of the soil. 



Absorptive unsaturated bodies lilce clay and humus are very plastic, more or 

 less slimy, swell with water, and form impervious soils. Absorptive saturated 

 soils are porous, and do not swell with water. Absorptive saturated soils were 

 easily made unsaturated and changed into the colloidal state by causing the 

 absorbed bases to go into solution by treatment with acid. The action of the 

 colloids was stronger with soils poorer in soluble salts. 



The surface soil, unlike the subsoil, is exposed to many factors which were 

 found to reduce the colloidal properties of the soil substances. Periodical drying 

 and freezing showed a tendency to change the " sols " into " gels." Cultivation 

 and fertilizers affected the colloids of the surface soil much less favorably than 

 those of the subsoil. The constituents of the surface soil were more easily 

 saturated and changed into the " gel " condition than those of the subsoil. 



The action of the colloids is apparently important in the nutrition of plants. 

 The author is of the opinion that the colloids of the roots establish an equilibrium 

 with those of the soil, and thus enable the nutrients of the surface soil to be 

 taken up more readily than those of the deeper layers. 



The colloid substances in soils and their determination, D. J. Hissink 

 (Resume [1], pp. 17-20). — This article discusses the Van Bemmelen acid 

 method of determining colloids (E. S. R., 16, p. 957) and compares results by 

 this method with those obtained with the Atterberg, the sedimentation, and 

 the color methods (E. S. R., 22, p. 610). 



