136 DEPARTMENTAL REPORTS. 



THE EFFECT OF A SALT UPON THE SOLUBILITY OF ANOTHER SALT. 



The effect of readily soluble salts upon the less soluble mineral 

 components of the soil is obviously of the first importance in the 

 study of alkali and in the use of mineral fertilizers. Experience has 

 shown that lime sulphate, in the form of gypsum, and lime carbonate 

 are probably the" most important of the slightly soluble components 

 of the soil in arid regions. Therefore the first work has been done 

 upon these substances. 



The solubility of gypsum has been carefully studied in the pres- 

 ence of sodium chloride, magnesium chloride, calcium chloride, and 

 sodium sulphate, and in the presence of sodium chloride with calcium 

 carbonate simultaneously. The effect of these other substances upon 

 the amount of gypsum taken up was found to be very great, the solu- 

 bility in certain cases being increased nearly fourfold. 



In an analogous manner the solubility of calcium carbonate and 

 magnesium has been studied in solutions of more soluble salts, due 

 attention being given to the modifying action of the amount of car- 

 bon dioxide in the air. 



That the results of these investigations will have a technical value 

 other than for agricultural studies seems assured, and communications 

 have been received from some manufacturing concerns and chemical 

 engineers relative thereto. 



THE RELATION BETWEEN CARBONATES AND BICARBONATES IN ALKALI SOILS. 



In cooperation with the physical laboratory of the Division a very 

 important investigation was made of the equilibrium between carbon- 

 ates and bicarbonates in water solutions. For instance, in the valley of 

 the Sevier River, in Utah, where the soils are naturally provided with 

 a fairly good underdrainage and the total amount of the alkali in the 

 soil is low, the proportion of bicarbonates to carbonates found in the 

 soil is large. Seepage waters from the soil, when exposed to the air, 

 either evaporating in ponds of aerated in the rapids of the river, show 

 increasing amounts of normal carbonate as the aeration continues up 

 to certain definite and invariable limits for constant condition. In 

 other areas containing black alkali, as about Fresno, Cal. , where the 

 total amount of alkali in the soil is relatively larger, the proportion of 

 normal carbonates to bicarbonates is correspondingly greater, and the 

 former preponderate to such an extent as often to be the most promi- 

 nent characteristic of these soils. Since it has been made evident that 

 bicarbonates are much less harmful to vegetation than normal car- 

 bonates, the economic importance of any work which will throw light 

 upon the subject and aid in its control is self-evident. This work is 

 of value also in connection with the view, for which there seems to be 

 some ground, that basic elements that serve as plant food in the soil 

 solutions of humid regions are present mainly in the form of bicar- 

 bonates. 



It was shown that even in contact with air containing but a small 

 proportion of carbon dioxide, and all the more in contact with the soil 

 atmosphere, which normally contains a much larger proportion of car- 

 bon dioxide, a solution of a normal (caustic) carbonate must also con- 

 tain some of the corresponding bicarbonate. On the other hand, it 

 was shown that a solution of a bicarbonate under all conditions with 

 which one meets in nature must necessarily contain a definite propor- 

 tion of the normal carbonate. It was shown that in the case of the 

 lime salts, under the conditions in which natural waters occur, the 



