THE SOIL AND ITS IMPROVEMENT 95 



6. Testing for Phosphoric Acid. — Put a little finely ground 

 phosphate rock in a glass of water to see if it will dissolve. In like 

 manner try a little ground bone in another glass. To see if any is 

 dissolved), pour in a little clear lime water. If any phosphate is 

 dissolved, the lime water will cause a white cloudy appearance. 



The question naturally arises: "Will rain dissolve bone 

 and phosphate rock when they are in the soil ? " Plant-foods 

 which do not dissolve somewhat when treated with water or 

 very weak acid are considered insoluble and are not readily 

 available for use by plants. Common, phosphate rock is 

 found upon the market at a price very much lower than acid 

 phosphate. It is used for field crops rather than for gardens, 

 as it has a less stimulating effect. It contains about twice 

 as much phosphorus per ton as acid phosphate. A common 

 name of phosphate rock is " floats." It should be ground 

 very fine before applying to soils. 



Potash is more commonly found in moist soils. Sandy soils 

 and those which have been farmed for a long time are most 

 deficient in it. AVood ashes contain much potash and are good 

 as fertilizer to use on gardens. The largest source of potash 

 is in the form of mineral salts, found in some parts of Ger- 

 many. These may be ground fine and placed directly on the 

 soil. More commonly perhaps they are refined or concen- 

 \trated. The two main commercial forms of the rich potash 

 ^alts are muriate of potash, containing fifty per cent of potash, 

 and sulfate of potash, containing about forty-eight per cent 

 of potash. These forms are soluble in water and easily 

 absorbed by plants. 



7. Wood Ashes as Plant-food. — Place a peck or more of wood 

 ashes in a vessel with a hole in the bottom. A leaky pail will serve 

 the purpose. Pour over the ashes enough water to show above the 

 top. Stir them a little with a stick, if possible. Catch the water 

 which runs through below, in a pan or other vessel. Examine this 

 water closely. Test it with the litmus paper mentioned in a pre- 

 ceding exercise. It turns litmus blue, and is alkali. Between the 

 fingers it feels soapy. It is really " lye water." 



