414 SALTS OF IRON IN SOIL. 



degree. Yet it was and always had been sterile, and, as my ex- 

 perience now concurred with that of my older friend in showing, it 

 could not be either durably or profitably enriched by putrescent 

 manures. Could it be possible that the sulphate of iron (copperas) 

 which Davy found in this soil, and which he evidently spoke pf as 

 a rare example of peculiar constitution, could exist in nineteen- 

 twentieths of all the lands of lower Virginia ? This could scarcely 

 be j and yet, in despair of finding other causes, I set about search- 

 ing for this one. 



It was not difficult, even for a reader so little instructed in 

 chemistry, to apply the test for copperas. It was only necessary 

 to let a specimen of the suspected soil remain soaking in pure 

 water, until any copperas, if present, would be dissolved ; then to 

 separate the fluid by pouring off and filtration, and then to add to 

 the fluid some of the infusion of nut-galls. If copperas had been 

 held in solution, the mixture would produce a true ink, of which 

 the smallest proportion would be made visible in the before per- 

 fectly transparent water. But all these first attempts were fruit- 

 less, and I was obliged to conclude that the great defect, or impedi- 

 ment to improvement, in most of our soils, was not the presence 

 of the salts of iron. But though not a salt, of which one of the 

 component parts was an acid, might not the poisonous quality be a 

 pure or uncombined acid ? This question was raised in my mind, 

 and the readiness produced to suppose the affirmative to be true, by 

 several circumstances. These were, 1st. That certain plants known 

 to contain acid, as sheep-sorrel and pine, preferred these soils, and 

 indeed were almost confined to them, and grew there with luxuri- 

 ance and vigour proportioned to the unfitness of the land for pro- 

 ducing cultivated crops. 2d. That of all the soils supposed to be 

 acid which I examined by chemical tests, not one contained any 

 calcareous earth.* 3d. That the small proportion of my land, and 

 of all within the range of my observation, which was shelly, and of 

 course calcareous, was entirely free from pine and sorrel, and more- 

 over was as remarkable for great and lasting fertility, as the lands 

 supposed to be acid for the reverse qualities. Shells, or lime, 

 would necessarily combine with, and destroy, all the previous pro- 

 perties of any acid placed in contact; and therefore, if acid were 

 present universally, and acting as a poison to cultivated plants, it 

 seemed plain enough why the shelly lands were free from this bad 



* I was not then aware of the important and novel fact which I after- 

 wards ascertained and established, and which is now fully received (with 

 very slight acknowledgment of its source) by the geologists of this country, 

 that almost all the soils on the Atlantic slope of this country, and even including 

 nearly all limestone soils, are also entirely destitute of carbonate of lime, 

 though that ingredient seems nearly if not quite universal in all the best 

 soils of England and the continent of Europe. 



