152 EXPEUIMENTS WITH PLANTS 



It may also be softened by adding more lime (about 

 one pint of lime-water to ten pints of hard water). 

 Waters which readily redden litmus contain much lime. 



In addition to being itself a food, lime sets free 

 potash in soluble condition from the insoluble com- 

 pounds in which it is held, and increases the power of 

 the soil to "fix" potash and phosphoric acid; lime 

 greatly hastens the decomposition of humus and ma- 

 nure, sweetens the sour soil by combining with acids 

 and destroys many injurious insects and fungi. It 

 improves the texture of the soil by flocculating clay. 

 This may easily be shown by rubbing up clay in water 

 and adding a little of this turbid water to lime-water 

 (use distilled or rain-water as a control) . We may also 

 mix burnt lime with clay and observe the effect on the 

 mass when it hardens. 



How may potash be supplied to the soil ? Wood ashes 

 contain large quantities of potash and constitute the 

 best potash fertilizers. "Muriate" of potash (potas- 

 sium chloride) and sulphate of potash are also used. 

 Gypsum and lime set free soluble potash in the soil 

 from insoluble compounds, as does also common salt. 

 Crops may be, therefore, supplied with potash by ap- 

 plying lime or gypsum to the soil, where the soil con- 

 tains sufficient insoluble potash. 



Fertilizers which dissolve quickly when applied to 

 the soil are much superior to those which decompose 

 slowly (unless the cost is too great), since they give 



