ALKALI SOILS. 449 



AMOUNT AND COMPOSITION OF SALTS IN ALKALI SPOT FROM CENTER TO 

 CIRCUMFERENCE, 4 FEET APART, I FT. DEPTH. 



While the table shows an obvious irregularity in some of the data at 

 the eight-foot point, arising doubtless from an irregularity of surface or 

 of texture overlooked in taking the samples, we find a very remarkable 

 regularity of progression in the cases of potassium sulfate, sodium 

 chlorid, sodium carbonate and sodium phosphate in the other four 

 samples. The maxima of the " black alkali " and the soluble organic 

 matter (humus) coincide, as does that of the phosphate ; the total 

 mineral salts at the outer margin are only a little over half of what is 

 found at the center. This is natural, as owing to the deflocculating 

 effect of the black alkali, the center is nearly a foot lower than the 

 margin. The lowering of the nitrate-content at the outer margin is 

 obviously due to the luxuriant vegetation growing adjacent. 



Reactions betiveen the Carbonates, Chlorids and Sulfatcs of Alkalies 

 and Earths. That a soluble earth-salt, such as the sulfate or chlorid of 

 calcium, will react upon an alkaline carbonate solution so as to form an 

 alkali sulfate, and e.g. lime carbonate, is well known; the neutralization 

 of the sodic carbonate in the soil by means of gypsum, above referred 

 to, is based upon this reaction. It is not so well known that the latter 

 may be reversed, partly or wholly, by the presence of carbonic acid in 

 the solution of the soil. Although observed as early as 1824 by Brandes, 

 and again in 1859 by A. Miiller, this reaction is not mentioned in text- 

 books and attracted no attention as a source of naturally occurring 

 alkali carbonates which in the past have formed the basis of extensive 

 commerce from the Orient, until in iS8S, the writer together with Weber 

 29 



