Oxidation of Iron in Soils. 439 



Silica 68* 



Alumina ........ IS** 



Protoxide of iron 5* 



Carbonate of lime 6*4 



Sulphate of lime I'l 



Salts of potash and soda ... '5 



Organic matter 6*3 



Moisture "3 



Phosphate of lime, a trace . . 



100- 

 The last example is one of what is termed a virgin soil ; it 

 was sent to me from Yorkshire, and with it some experiments 

 1 shall afterwards detail, were made. Mr. Smith of Deanston, 

 was kind enough to inform me that he considered it to be a 

 soil of good quality, and the gentleman from whose estate it 

 came, that it had been brought under very good cultivation. 

 My friend Mr. Howard analysed it, and found it to consist of 



Silica 72-4 



Alumina 12* 



Sulphate of lime '4 



Protoxide of iron 5*1 



Salts of potash and soda ... •? 

 Organic matter ...... 7*4 



Moisture 2* 



100- 

 Trusting that these results sufficiently prove the statement 

 I have made, that the lower degree of oxidation of iron in soils 

 is not injurious to vegetation, 1 shall proceed to consider the 

 cause, notwithstanding the tendency of iron in the lower state 

 of oxidizement to pass to the higher, when exposed to air and 

 moisture, of its remaining unchanged. This fact may, I think, 

 be accounted for, by the carbon of the organic matter or 

 humus converting, by its affinity for oxygen, the peroxide into 

 protoxide, itself becoming carbonic acid ; and that the oxygen 

 of the air having a greater tendency to combine with the car- 

 bon of the humus than to convert protoxide into peroxide of 

 iron, the former is left unchanged. 



In order to prove whether this idea was borne out by fact, 

 1 passed by an arrangement I shall presently describe — a 

 gentle current of air for three days over about 200 grains of 

 the soil I have last mentioned as having been analysed ; it 

 was operated on as when brought to me, and contained 18'5 

 per cent, of water. From the 200 grains I obtained six grains 

 of carbonic acid, equal to a loss of 1*63 grain of carbon; and 

 on examination I found the degree of oxidation of the iron to 

 have remained the same. 



