772 EXPERIMENT STATION RECORD. 



With regard to the influence of water, experiments have shown that 

 the vohiine weight of soils increases with the water content, and the 

 increase is proportional to the water capacity of the soil. The difi'er- 

 ences in volume weight correspond, in general, when soils are approxi- 

 mately equally saturated, to those in air-dry soils, though the values 

 are more concordant in moist soils. 



The expressions "heavy" and "light" soils, used in practice, have 

 no reference to the weight of the mass, but to the resistance which the 

 soil opposes to cultivation. 



It is sometimes advisable to examine the soil in its natural state on 

 account of the not inconsiderable variations in the volume weight. This 

 is most conveniently done by lifting out a column of the soil by means 

 of a sampling tube which is driven to a definite depth in the earth and 

 drying and weighing the sample.^ 



THE COI.OU Ol'' THE SOIL. 



This is due to the presence of certain constituents. The principal 

 mineral ingredients of the soil (clay, lime, and quartz) are white 

 when pure. When the soil is of some other color it is caused by the 

 presence of humus matter or iron compounds. The humus substances 

 produce a gray, brown, or black color, according to the quantity j^res- 

 ent, while iron, as ferric oxid or hydrate, causes a yellow, brownish, or 

 red color. The coloring power of these constituents depends on the 

 constitution of the soil. In sands 0.2 to 0.3 per cent of humus mate- 

 rials or 1 per cent of ferric oxid or hydrate suffice to cause either a gray 

 or a red or brown coloration in the dry state, but in clays more (2 to 5 

 per cent humus, 5 to 10 jjer cent ferric oxid or hydrate) is required to 

 produce the same eflect. This is due, as a rule, to more intimate mix- 

 ture of the clayey soils with the coloring matters. A green coloration is 

 almost without exception caused by ferrous compounds, and is seldom 

 noticed in well aerated soils. 



A change in color in a soil is caused on the one hand by a change in 

 humidity, on the other by a change in the iron compounds. In general, 

 soils are darker colored when they contain more water, and vice versa. 

 This is especially true of soils containing much humus, wbich are dark 

 brown or black when wet, become lighter as the moisture decreases, 

 and when dry show a gray or whitish-gray color. Soils colored red or 

 brown by ferric oxid or hydrate assume a lighter color and under cer- 

 tain circumstances (deficiency of air) a greenish color when these com- 

 pounds are converted into ferrous compounds. The reverse process, 

 i. e., the oxidation of ferrous salts, is shown by an immediate change 

 in the color of the mass to yellow, red, or brown."^ 



'G. Schiibler, 1. c, p. 61. Meister Programm des Jahresberichtes, 1857-'58 dcr k. 

 laudw. Centralschule zu Weihenstephau, 1. A. von Liebenberg, 1. c, p. 6. E. Wullny, 

 Forsch. Geb. agr. Phys., 8, p. 349. E. Ramann, 1. c, p. 62. 



"W. Schnmacher, Die Physik des Bodeus, 1864, p. 139. E; Ramann, Forstliche 

 Bodeukuude, 1893, p. 36. E. Wolluy, Forscb. Geb. agr. Pbys., 4, p. 354. 



