BUREAU OF SOILS. 483 



leached by water may be still further extracted when other salts are 

 added in solution in water has an important bearing upon the theory 

 and practice of plant growth and soil treatment in that the effects 

 produced by the addition of, for example, a nitrate may not be due 

 only to nitrate itself, a portion of the beneficial effect being due to 

 liberated phosphate. 



In connection with the work on fertilizers and fertilizer materials 

 which the division has undertaken, a thorough study has been made 

 of the phosphate deposits of Tennessee, Arkansas, and Kentucky. 

 The values of the different types of phosphate rock found in the 

 same and in different places have been properly correlated by a 

 large number of analyses. The methods of mining, the extent of 

 the operations, the cost of production, and the future outlook for 

 the industry have been carefully investigated and described. The 

 information thus acquired, combined with that already published by 

 the bureau, constitutes a very valuable addition to our knowledge 

 concerning the phosphate deposits of this country. A crystallo- 

 graphic and photographic study of the minerals spodiosite, brushite, 

 monetite, and artificial calcium phosphate compounds has been un- 

 dertaken, with the object of throwing light on the natural forma- 

 tion of these minerals. An investigation of the Otero Basin of 

 New Mexico has been made for possible deposits of potassium salts, 

 and a large amount of information acquired which will be of use in 

 extencHng the work to other parts of the country. 



In collaboration with the United States Geological Survey, an 

 examination has been made of 17 salt-producing plants distributed 

 through central New York, Michigan, and Pennsylvania, for the 

 purpose of obtaining information concerning the source of brines 

 and lake salt, their composition with special reference to their potash 

 content, and their treatment. All information thus obtained bears 

 on the problem of the occurrence of potash in brines and lake salts 

 and its possible extraction therefrom. With the same object in view, 

 a study is being made of the separation of potassium chlorides and 

 sulphates of calcium, magnesium, and sodium, the solubility of sodium 

 and potassium sulphate in the presence of each other, and the sepa- 

 ration of potassium and sodium salts by other methods. 



Work is being done on possible methods of separating potash from 

 feldspar and other silicates, and an investigation is also being made 

 concerning the chemical fixation of atmospheric nitrogen, both from 

 a scientific and technical standpoint. This work constitutes an eco- 

 nomic examination of the available sources of nitrogen for agri- 

 cultural purposes and is cognate with the work on phosphates and 

 potash. A survey of the occurrence of and distribution of potash- 

 bearing algae on the American coast has been started with particular 

 reference to their utilization as a source of potash supply. This 

 work on fertilizers and fertilizer materials has very large economic 

 possibilities to the American people. 



SOIL FERTILITY INVESTIGATIONS. 



There have appeared a niimber of reports from this laboratory 

 dealing with the nature and properties of soil organic matter or 

 humus, and in connection with these problems some far-reaching dis- 

 coveries have been made in soil investigations. During the past year 



