AND AGRICULTURE* 67 



or three times, before use. Fish ought never to 

 be exposed on the surface of the ground ; their 

 exhalations, during decomposition, are very offen- 

 sive, and prejudicial to health. 



Amongst mineral manures, the most valuable 

 are nitrate of soda, sulphate of soda (common 

 glauber salts), sulphate of lime (gypsum), kelp, 

 wood-ashes (potash), and lime. 



Nitrate of soda is a white, saline (salt-like) 

 substance, found as an abundant natural product 

 in some parts of Peru. It is usefully applied, 

 as a top-dressing, to grass lands and young grain 

 crops. (See Appendix, 24.) 



It contains nitric acid and soda ; fifty-four 

 pounds of nitric acid and thirty-one pounds of- 

 soda form eighty-five pounds of nitrate of soda. 



Nitric acid is an intensely sour and corrosive 

 fluid, commonly known as aquafortis. It con- 

 sists of two gases, nitrogen and oxygen ; four- 

 teen pounds of nitrogen and forty pounds of oxy- 

 gen make fifty-four pounds of nitric acid. Thus 



Questions. Why should not fish be exposed on the sur- 

 face of the ground ? What are the most valuable mineral 

 manures ? Where is nitrate of soda found naturally ? Of 

 what is it composed ? What is nitric acid ? Of what com 

 posed ? In what proportions ? 



