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Some very interesting documents upon the use 
of sulphate of iron or green vitriol, which is a salt 
produced from peat in Bedfordshire, have been laid 
before the Board by Dr. Pearson ; and I have 
witnessed the fertilizing effects of a ferruginous 
water used for irrigating a grass meadow made by 
the Duke of Manchester, at Priestley Bog, near 
Woburn, an account of the produce of which has 
been published by the Board of Agriculture. I 
have no doubt that the peat salt and the vitriolic 
water acted chiefly by producing gypsum. 
The soils on which both are efficacious are cal- 
careous ; and sulphate of iron is decomposed by 
the carbonate of lime in such soils. The sulphate 
of iron consists of sulphuric acid and oxide of iron, 
and is an acid and a very soluble salt : when a 
solution of it is mixed with carbonate of lime, the 
sulphuric acid quits the oxide of iron to unite to 
the lime, and the compounds produced are insipid 
and comparatively insoluble. 
I collected some of the deposition from the fer- 
ruginous water on the soil in Priestley meadow. 
I found it consisted of gypsum, carbonate of iron, 
and insoluble sulphate of iron. The principal 
grasses in Priestley meadow are, meadow fox-tail, 
cock’s-foot, meadow fescue, florin, and sweet- 
scented vernal grass. I have examined the ashes 
of three of these grasses, meadow fox-tail, cock’s- 
foot, and florin. They contained a considerable 
proportion of gypsum. 
Vitriolic impregnations in soils where there is 
no calcareous matter, as in a soil from Lincoln- 
shire, to which I referred in the Fourth Lecture, 
