100 APPENDIX. 



By long exposure to the air and weather, much of the 

 most valuable portion of the organic part of the manure 

 escapes into the atmosphere, and another considerable 

 portion is washed away and carried off. From these 

 causes the soil is deprived of much of the most valuable 

 and fertilizing portion of the manure, and hence the 

 crops are also hindered in their growth and perfection. 

 The intelligent farmer will, therefore, protect his manure 

 from these sources of loss ; and he will be also enabled, 

 by reference to the tables already given, to supply an 

 additional quantity of those substances which the land 

 may need, in order to insure the best and most profit- 

 able crops. 



30. In the progress of this work we have had occasion 

 to refer to certain elementary bodies, or substances, 

 whose combinations make up the organic part of plants. 

 These elementary bodies are chemically expressed by 

 definite characters, or symbols, and, as their use is uni- 

 versally adopted, we have subjoined the symbols of all 

 the principal substances to which reference has been 

 made. 



31. In addition to the symbol, a numeral will be 

 noticed, called the EQUIVALENT, which means the com- 

 bining number. Thus the symbol of Oxygen is O its 

 equivalent, or combining number, 8 ; the symbol of 

 Nitrogen is N its equivalent, 14.15. 



32. Bodies, in forming chemical combinations, unite 

 in certain fixed or definite proportions, and these com- 



