Mr. R. Phillips, juu. on the state of Iron in Soils. 437 



3. What is the proportional effect of looking through the 

 four-inch focus lens, and looking simply along a black line, 

 some three feet long? For example, if looking through the 

 slits and lens, an eye can make the lines cross at two inches 

 and at four inches, and at any intermediate distance, what is 

 the real average focus of that eye? 



To use a homely but forcible comparison, I would say. Dr. 

 Young, being himself" in the ship of science," seems to expect 

 that " the disciple can arrive there without a boat.*' A few 

 lucid paragraphs would furnish the boats on this occasion, and 

 oblige, 



Gentlemen, yours, &c. 



E. D. 



LXIII. 0« the State of Oxidation of Iron in Soils. 

 By Richard Phillips, Jun.* 



TJAVING for some time past directed my attention to the 

 ^^ analysis of soils, I have been somewhat surprised at the 

 remark I have met with in the works on Agricultural Che- 

 mistry of Prof. Johnston and others, that the lowest state of 

 oxidation of iron or the protoxide is when occurring in soils 

 injurious to vegetation ; my own experience having led me 

 to the conclusion, that although it is not necessary to the fer- 

 tility of a soil that it should exist in that state, nevertheless, 

 that in all soils rich in humus it is so found. The grounds 

 on which the statement I have alluded to has been brought 

 forward, are the following: — Bog earths have been found to 

 be unfit for vegetation ; and the drainage water from them, 

 when used for the purposes of irrigation, to be poisonous to 

 plants. Now in these earths the iron exists as protoxide, and 

 as there is much carbonic acid formed in them by the action 

 of the oxygen of the atmosphere on the carbon of the large 

 amount of humus they contain, the protoxide of iron, being 

 soluble in this acid, is thus carried away by the drainage water. 

 From the numerous examples I have had brought before me 

 in the laboratory, I have selected the following six analyses as 

 well illustrative of the fact I have before alluded to, that in 

 most rich soils the iron is found principally in the lower state 

 of oxidation. 



The first two are analyses of the soil and subsoil of some of 

 the best wheat land in the Lothians. The soils were brought 

 from thence by my friend Mr. Wilson, and analysed by him ; 

 in the soil he found the iron to be protoxide, whilst in the 

 subsoil it existed as peroxide, 



* Read before the Pharmaceutical Society, April 9, 1845. 



