MANUAL OF GENEEAL AGRICULTURE. 21 



ing upon apparent specific gravity? 3. The apparent 

 specific gravity of soils in the field may be taken as an 

 indication of the tilth of soils. Why? 



PART II CHEMICAL PROPERTIES OF SOILS. 

 SOIL ANALYSIS. 



If you have taFen or are now taking chemistry pro- 

 ceed at once with Exercise 20. If you have not studied 

 chemistry, obtain some chemistry manual and perform the 

 following experiments, as therein described: 



(1) Preparation of Oxygen. 



(2) Preparation of Hydrogen. 



(3) Preparation of Carbon dioxid. 



(4) Preparation of Nitrogen. 



The teacher should give a demonstration on labora- 

 tory manipulation to students unfamiliar with chemistry. 

 See any chemistry manual. 



20. ACIDS, ALKALIS, AND SALTS. 



Materials: Sulphuric acid, nitric acid, vinegar, red 

 and blue litmus paper, any fruit at hand, sodium and pot- 

 assium hydroxid, hydrochloric acid, evaporating dish. 



(a) Illustration and test for acids: Add a few 

 drops of sulphuric acid to half a tumbler of water. Add 

 drop by drop, tasting each time until the flavor can be 

 distinguished. Do the same with nitric acid. 



Compare the taste of each with that of vinegar. Put 

 red and blue litmus paper into the three substances used 

 above. Result? This is a sure test for acids. Test the 

 juice of any fruit at hand. Result? 



(b) Illustrations and test for alkalis. Dissolve a 

 small piece of sodium hydroxid (caustic soda) and another 

 small piece of potassium hydroxid (caustic potash), each 

 in about 20 cc. of water. How does each solution feel? 

 Test with both kinds of litmus paper. Result? 



Dip your finger into each solution and cautiously 

 taste. This bitter taste, soapy feeling, and alkalin reac- 

 tion, are the most characteristic properties of alkalis. 



