84 THE ROYAL SOCIETY OF CANADA 



The Formation of Alkali. 



In humid districts, i.e., those enjoying a more or less generous 

 rainfall, the mineral salts formed by these processes, known popularly 

 as "weathering," are practically disposed of as produced. In part 

 they are utilized by vegetation, and any remaining injurious salts 

 leach downwards and drain away; the conditions are such that 

 there can be no accumulation of them in the surface soil. 



But such is not always or necessarily the case in arid or semi-arid 

 districts. Here we find the scanty rainfall, while sufficient to promote 

 the formation of these soluble mineral salts, quite inadequate to their 

 removal by drainage. If they descend a few inches, or even a few 

 feet, there is not enough flow of water through the soil to carry them 

 right away and subsequent evaporation of the water that holds them 

 in solution and the action of capillarity brings them to the surface, 

 where they accumulate, forming the so-called alkali, and rendering 

 the soil more or less unsuitable for agricultural purposes. The 

 alkali may impregnate the sub-soil, the surface soil, or if evaporation 

 greatly exceeds the rainfall, it may appear as an incrustation or 

 efflorescence. 



Alkali soils, therefore, are characteristic of arid or semi-arid 

 districts only and these in Canada may be said to be restricted chiefly 

 to certain areas in British Columbia, Southern Alberta and South- 

 western Saskatchewan. 



Nature of "Alkali." 

 The compounds known collectively as alkali comprise chiefly 

 sodium sulphate, sodium carbonate, sodium chloride, magnesium 

 sulphate, calcium sulphate (gypsum) when present in large quantities, 

 and occasionally chlorides of calcium and magnesium. Sulphate 

 and chloride of sodium and sulphate of magnesium and of calcium, 

 when crystallized in the surface of the soil, appear as white substances 

 and constitute what is known as "white alkali." "Black alkali" is 

 characterized by the presence of sodium carbonate, though this com- 

 pound is almost always associated with one or more of the sulphates 

 mentioned above. Sodium carbonate is, as is well known, white, but 

 from the fact that it acts upon and dissolves the decayed vegetable 

 matter (humus) of the soil the incrustation is dark brown or black, 

 hence the name. Water standing in pools on soils impregnated with 

 sodium carbonate is invariably of a dark color resembling a strong 

 infusion of cofïee. 



Effects of Alkali on Plants. 

 The soil water of lands impregnated with alkali is a more or less 

 concentrated solution of these compounds. It is the soil moisture 



