EXPERIMENT STATION BULLETINS. 291 



was employed and the soils were kept outdoors under natural conditions, 

 although in some soils more material went into solution when the moisture 

 content was 1 of soil to 0.7 of water than when the moisture content was at 

 optimum. There was a closer relationship on the whole between the solu- 

 bility factor and the state of fertility, or crop producing power of the soil 

 with the former than with the latter. 



When natural soils, previously washed, and with a moisture content of 

 1 of soil to 0.7 of water were kept at a temperature of 53°C their rate of 

 solubility was somewhat appreciably increased. In some soils, however, 

 solubility was very little, if any, affected by the high temperature. The 

 solubility of many soils even at this high temperature continued to increase 

 for a long time, even 60 days but usually became constant at the end of 

 about 30 daj's. 



At the ratio of 1 of soil to 5 of water the rate of solubility of natural soils 

 was also slow and the extent of solubility extremely small, the amount of 

 material that went into solution at this water content being only about half 

 as great as that at the water content of 1 of soil to 0.7 of water, although 

 an apparent equilibrium was attained at this high water content just as 

 with the lower water content. Soils having a ratio of 1 of soil to 5 of water 

 kept at 53°C showed a slight increase in the rate and extent of solubility. 

 The solubility product, however, was onlj^ about one-third as great as that 

 of similar soils kept at the same temperature but having a ratio of soil to 

 water of 1 to 0.7, while an apparent equilibrium was attained in the high 

 ratio just as in the small ratio. 



The results of experiments wherein were used a ratio of 1 of soil to 5 of 

 water were held to indicate very strongly that the concentration of the soil 

 solution depends upon the relative masses of the soil and water and that the 

 soil does not possess a definite solubility, as definite compounds do. The 

 amount of material that goes into solution seems to increase as the ratio of 

 soil to water is increased up to about the optimum moisture content, and 

 then it decreases. 



OBJECT OP I'RESENT INVESTIGATION 



Since soils are composed of a complex and heterogeneous mass, and the 

 number and variety of factors operating being very great, unknown and 

 uncontrollable, it is extremely difficult, if not impossible, to explain always 

 the results obtained, or to assign them to any particular factor or cause. 

 Many times such experimental results are at best very empirical. 



In order, therefore, to obtain more definite, and if possible, more abso- 

 lute information on the solubility of soils, it was deemed advisable and nec- 

 essary to repeat the general investigation of the rate and extent of solubility 

 of soils, with rocks and rock forming minerals. It was thought and reasoned 

 that since the rocks and minerals are more definite compounds, or at least 

 to a considerable degree less complex than the soils, their results may be 

 of great value and help in checking up, interpreting and explaining those 

 obtained with soils. Accordingly, the rate and extent of solubility of a 

 large number of rocks and minerals were measured, an attempt being made 

 to include in the list the most common type of soil-forming rocks and min- 

 erals. 



METHOD EMTLOYED AND MODE OF PROCEDURE 



The method employed was the freezing point (2). The general procedure 

 consisted of first grinding the rocks and minerals to fine powder so it could 



