ALKALI LANDS 217 



have the composition of a black alkali, consisting almost 

 wholly of sodium and potassium carbonate. The last analysis 

 refers to a salt of mixed character, extremely rich in 

 nitrates. 



The proportions in which the different salts occur at various 

 depths, and at various times, in alkali lands, do not appear 

 to have been as yet studied in relation to the known laws 

 of diffusion ; there is much however in many of the par- 

 ticulars noticed which seems to find its proper interpretation 

 in the different rates of movement belonging to different 

 salts, to which we have already called attention. Thus on 

 reviewing the analyses of the salts obtained from different 

 depths of soil in summer time, we almost always find a much 

 larger proportion of potassium salts, of chlorides, and of nitrates 

 in the salt obtained by extracting the soil near the surface, 

 than in the salt extracted at the same time from a depth of 

 3 feet. The alkali carbonates are, on the other hand, generally 

 far more abundant in the deeper soil. Now we have already 

 seen that potassium salts will move more quickly in a moist 

 medium than salts of sodium, and that chlorides and nitrates 

 are much more diffusible than sulphates and carbonates. 

 Again, in the California Station Report, 1892-3-4, 141, we 

 have analyses of the salts found at different points across an 

 alkali patch ; here we find the proportion of potassium salts 

 and of chlorides twice as great near the circumference as 

 at the centre, while the proportion of sodium carbonate is 

 greatest at the centre, and diminishes gradually towards the 

 edge. The sulphates do not in this case march with the 

 carbonates. Much light will probably be thrown on some 

 of the phenomena of alkali lands, by bearing in mind the 

 relative rates of movement of the various salts concerned. 



