270 NATURE STUDY AND AGRICULTURE 



paper. What is your conclusion as to the effect of an acid 

 on litmus paper? 



Test for Alkali. — Place a piece of the red litmus paper 

 that you used in an acid in a weak solution of potash and 

 water. What change in color takes place? From this 

 you may draw the conclusion that litmus paper is red in 

 acids and blue in alkalies. Try other substances: sweet 

 milk, sour milk, ammonia, lime water. 



Test for Salt. — Fill a glass half full of weak vinegar 

 and slowly add to it limewater. Test at intervals with 

 litmus paper. When the litmus paper does not change 

 color it shows that the solution has become neutral. It is 

 neither acid nor alkali, but a salt. 



Make a weak solution of nitric acid, and add to this a 

 solution of caustic potash until the litmus paper shows 

 that the solution is neutral. You now have a salt known as 

 potassium nitrate or saltpeter. You can get the nitrate 

 by evaporating the water. 



It is in the form of nitrates that most of the nitrogen 

 that plants use is obtained. There is plenty of nitrogen 

 in the air, but plants cannot use this. They must get all 

 their nitrogen from the soil. 



Soils may contain more acids than are good for plants. 

 We may test soils for acidity and alkalinity just as we tested 

 other things. 



Boil a sample of soil to be tested in a small quantity of 

 water. Let it settle, and when perfectly clear pour off the 

 liquid into a white dish and test with litmus paper. You 

 may have to leave the paper in for some time. If the paper 

 turns red, what is your conclusion in regard to the soil? 

 If blue ? If there is no change of color ? 



