SOILS FERTILIZERS. 119 



Experiments were coudiicted to determiue the siieed of the exchanjre reaction 

 between the calcium (CaO) of chernozem soil and normal solutions of sodium 

 chlorid and ammonium chlorid, and parallel thereto the speed of the exchange 

 reaction between acid sodium phosphate and calcium carbonate. It was found 

 that the reaction between soil calcium and sodium chlorid was instantaneous, 

 and that that between soil calcium and ammonium chlorid, while not instan- 

 taneous, was extraordinarily quiclc. The speed of reaction between sodium 

 phosphate raid calcium carbonate was much slower, and it is considered evident, 

 therefore, that the soil calcium is not chemically combined. 



To determine the colloidal nature of soils saturated with different bases, 200 

 gm. portions of a loamy chernozem soil containing 1.395 per cent of calcium 

 oxid were treated 20 successive times with 1 liter of solutions of variable con- 

 centration of sodium, potassium, and ammonium chlorids. It was found that 

 such treatment with normal and four times normal salt solutions almost en- 

 tirely displaced the calcium oxid content soluble in 10 per cent hydrochloric 

 acid. 



In a study of the so-called zeolitic compounds in soils samples of chernozem 

 soils were washed repeatedly with water saturated with carbon dioxid until 

 no acid was freed on contact with neutral solutions of sodium chlorid and the 

 water extract was neutral. A comparison of soil so treated with the same soil 

 repeatedly washed with water showed the former to have a much smaller base 

 content but a correspondingly larger colloidality and saturation capacity. It is 

 concluded, therefore, that the zeolitic and humus substances of the soil repre- 

 sent gels of hydrophilous colloids. 



Treatment of the chernozem soil with tbe alkalis sodium, potassium, and 

 ammonium caused the displacement not only of calcium but of iron, magnesia, 

 and potassium, and the soils became saturated, not always exclusively but 

 usually prevailing, with an alkali metal. The colloidality of the soil increased 

 as the saturation with alkali metals increased. This was especially marked 

 when the soil was saturated with sodium. The colloidality was increased 

 less by saturation with ammonia and less still with potassium. It is concluded 

 that when the zeolitic and humus substances are saturated with any of the 

 three alkalis they assume the character of gels of hydrophilous colloids. 



Treatment of the original chernozem soil with solutions of iron and aluminum 

 salts caused the displacement of bases, reduced the colloidality, and caused 

 the zeolitic and humus sub.stances to assume the amorphous character of gels of 

 colloids which do not readily take up water. 



With reference to the colorimetric method of determining the quantity of 

 colloids in soil, studies were made of the absorption of methyl and crystal 

 A'iolet by eight samples of chernozem soil consisting of the original soil, sam- 

 ples repeatedly treated witb 0.2 normal solutions of the chlorids of sodium, 

 potassium, ammonium, calcium, aluminum, and iron, and a sample repeatedly 

 washed out with water saturated with carbon dioxid. A complete adsorption 

 of the coloring matter v/as observed only by the soil saturated with iron. The 

 adsoi-ption was weak by the soils saturated with aluminum and calcium and 

 the soil washed out with carbon dioxid water. The coloring of the surface film 

 of the samples saturated witb potassium, ammonium, and sodium was rather 

 marked, and increased in the order named. 



A comparison of the quantities of color adsorbed by the eight soil samples 

 witb their so-called colloidalities, that is, the amounts of swelling after satura- 

 tion with water, showed the color adsorption to proceed not only not parallel 

 with the colloidality but in an opposite direction. It is therefore concluded 



