CHEMISTRY. 5o 



catcd as to their relation in composition to the simple bodies. 

 Such, only, of these bodies will be described, as are necessary 

 to be known in their relations to Agricultural Science. 



ACIDS. 



Acids are chemical compounds whioh are capable of uniting 

 in different proportions with alkalies, to form a third class 

 called salts : by this union the properties of both the acids and 

 alkalies are destroyed, or neutralized. Most acids have a sour 

 taste, there are, however, some exceptions: they change 

 vegetable blues to red ; they are electro-negative, and there- 

 fore have a strong affinity for the electro-positive compounds, 

 such as alkalies, alkaline earths and oxides. Nearly all of 

 them contain oxygen; when the oxygen is not present, it is 

 replaced by hydrogen: they are therefore called by some 

 writers, oxacids and hydracids. 



Acids are divided again into mineral and vegetable; the 

 mineral are, nitric, sulphuric, muriatic, &c. : the vegetable acids 

 are very numerous, acetic, citric and tartaric are examples. 

 Most vegetable acids contain both oxygen and hydrogen. The 

 mineral acids are heavier than water, exceedingly caustic and 

 corrosive, destroying both animal and vegetable textures. 

 Some acids are in a fluid, and others in a dry, solid or crys- 

 taline form. They unite with water in all proportions. They 

 absorb water from the atmosphere, if exposed, and become 

 weaker in strength, diminished in weight, and increased in 

 bulk. 



ALKALIES. 



Alkalies are a class of bodies possessing properties opposite 

 to those of acids, having a strong affinity for, and uniting with 

 them in different proportions, to form salts, as before stated. 

 They are incombustible, caustic and acrid, very soluble in 

 water, and change vegetable blues and red to green, and yellow 

 to brown, in fact they destroy or change the vegetable colors 



