SOILS- — FERTILTZEES. 819 



these percentages varying in the case of the calcareous soil from 5.07 per cent 

 with potatoes to 11.3 per cent with horse beans, and in case of the peaty soil 

 from 32.3 per cent with oats to 43.6 per cent with wheat. 



"Another point which this investigation has brought out in a striking way is 

 the 'hysteresis' observable in the volume change when a soil is alternately 

 wetted and dried out. This process results in a natural paclving of the soil 

 and is seriously detrimental to the maintenance of good tilth if the extremes 

 of moisture content reached are wide apart." 



The action of water and aqueous solutions upon soil carbonates, F. K. Cam- 

 eron and J. M, Bell (U. S. Dept. Agr., Bur. Soils BuL Jf9, pp. 6.'/, figs. 5). — This 

 bulletin reviews the literature of investigations on the solubility of carbon 

 dioxid, lime, calcium carbonate, magnesia, and magnesium carbonate in water 

 and aqueous solutions of various kinds. It includes investigations previously 

 reported by the Bureau of Soils (E. S. R., 13, p. 428; 14, p. 524; IS, p. 117; and 

 19, p. 221) as well as others here published for the first time. 



The following are in brief the general conclusions drawn from the work : The 

 solubility of carbon dioxid in salt solutions is less than in an equal volume of 

 water. The solubility of the dioxid in water is increased by addition of nitric 

 acid, in sulphuric acid is decreased by the addition of water, and in water is 

 decreased by the addition of sulphuric acid. Consequently there is a mixture 

 of sulphuric acid and water which dissolves a minimum quantity of carbon 

 dioxid. " The more concentrated the solutions are, the less carbon dioxid is 

 absorbed. The solubility iu solutions of strontium chlorid is between that in 

 calcium and barium chlorids. The quantity of carbon dioxid absorbed becomes 

 less as the temperature increases. The solubility is less in sulphate solutions 

 than in chlorid solutions, and less in chlorid solutions than in nitrate solutions. 

 Solutions of sodium salts absorb carbon dioxid less readily than solutions of 

 similar potassium salts, and solutions of ammonium salts are better solvents 

 than solutions of either sodium or potassium salts." 



The apparent solubility of lime in aqueous solutions depends largely on its 

 origin, and, therefore, on the impurities it contains. At 0° C. it is approxi- 

 mately twice that at 100° C, the temperature solubility curve approximating a 

 straight line. The solubility iu dilute solutions of sodium, potassium, and 

 ammonium chlorids is greater than in pure water. The solubility curves for 

 solutions of sodium and potassium chlorids have maximum points, an;l the 

 Rolubility is less in saturated solutions tlian in pure water. 



" The solubility of lime in very dilute solutions of calcium chlorid seems tt» 

 be less than in pure water, but as the concentration increases the solubility is 

 raised much above that in pure water, es[)ecially at higher temperatures. 



" At lower temperatures and iu the more concentrated solutions of calcium 

 chlorid the stable solid phase is calcium oxychlorid. 



" The presence of other hydroxids depresses markedly the solubility of lime. 



"The presence of gypsum does not appreciably affect the solubility of lime. 



" In contact with very dilute solutions of calcium nitrate, lime passes into 

 solution as such, the solubility increasing with concentration of nitrate; at 

 higher concentrations the stable solid is one of a series of solid solutions, the 

 content of lime still increasing with increase of nitrate; at still higher concen- 

 trations the stable solid is a basic nitrate of definite composition, and the con- 

 centration of lime in solution falls with increase of nitrate; finally, at very 

 high concentrations the neutral nitrate separates as a solid phase. 



" In solutions of glycerol or mannite the solubility of lime is increased mark- 

 edly with increase of concenti'ation of the carbohydrate. 



■' When lime is brought into contact with sugar solutions the ratio of lime 

 to sugar iu the solid varies continuously with the composition of the solution. 



