1 6 AGRICULTURE. 



CHAPTER IV. 



THE PLANT AND THE SOIL. 



THE POWER OF WATER TO DISSOLVE SUBSTANCES. If 

 we drop a little common salt into a glass of water, it will 

 disappear from sight ; but if we taste the water we find that it 

 is salty the salt has been dissolved in the water. If we pour 

 out the salty water into a saucer, and set it in a warm place, 

 the water will gradually become less and less, and we shall 

 soon see the white salt reappear as a fine white crust. We 

 know now that salt is soluble in water. If we keep on adding 

 salt to the water in the glass we shall find that after a while no 

 more salt will be dissolved, but what we add will remain un- 

 dissolved in the bottom of the glass. We conclude, therefore, 

 that the water can dissolve a certain amount of salt and no 

 more that there is a limit to the power of the water to dissolve 

 the salt. We can make the same trial or experiment with 

 other substances, such as sugar, saltpetre, etc. 



But all substances are not soluble. If we place some sand 

 in the glass of water it will not dissolve. If we stir up some 

 road dust in a glass of clean water, the water will at once be- 

 come dirty ; but after a while the dirt will settle and the water 

 clear up. Sometimes when we examine salt by putting a little 

 in water we find a small quantity of hard, gritty substance set- 

 tling at the bottom undissolved this is not salt, but an impurity 

 in the salt. If there were any sand in the sugar it would not 

 dissolve. A nail will not dissolve in the water, though it can 

 be more or less dissolved if there is a little acid in the water. 

 If we take a handful of hardwood ashes and stir them up in a 

 bowl of water, a large portion will settle to the bottom undia 



