Qb AGRICULTURAL CHEMISTRY. 



to be learned of its various and vastly important offi- 

 ces in agriculture. We will enlarge on this subject at 

 another time. 



53. Protoxide of Iron (FeO) is a compound existing 

 abundantly in many wet, marshy soils. It is largely 

 soluble in water, and when so dissolved is injurious to 

 vegetation, often preventing the growth of any thing 

 save a little wiry, sour grass, which contains little or no 

 nourishment. If such land be thoroughly drained, a 

 large proportion of this oxide is taken off with the 

 water; and what remains may be neutralized by 

 ploughing and thus exposing it to the air ; it takes an- 

 other dose of oxygen, and becomes the red oxide or 

 sesquioxide of iron, which is rather beneficial than 

 hurtful td plants. The farmer may generally know 

 whether his low lands are troubled with the protoxide 

 of iron, by observing the water which flows from them. 

 If impregnated with this oxide, it will generally show 

 a film on its surface, often reflecting the colors of the 

 rainbow. If this film be very thin, it reflects the yel- 

 low ray ; if a little thicker, the red or brown ; and if 

 still thicker, the blue or violet. All these colors are 

 sometimes reflected from neighboring points on the 

 surface, which gives a sort of iris, or rainbow cast. 

 The explanation is thus : — the protoxide of iron comes 

 from the ground dissolved in water. On exposure to 

 the air, it takes more oxygen and becomes the red or 

 sesquioxide. This not being soluble in water, floats 

 awhile on the surface, forming a film, varying in thick- 

 ness, and, as before explained, in color, till at length 

 it sinks to the bottom, giving the channel a soft of 



