212 ^'SE OF GREEN V1TKIOL 



tilizing effcdt of fulphate of iron, unlefs by fuch contravening 

 evidence the quantity ftated 1o be ufed exceed fifty bufhels per 

 acre; it being an eflablifhed facl, that in certain proportions 

 this metallic fait is a poifon to plants. 



This difcovery of Mr. Willaume will, I think, give new 

 light, fo as to explain fully the rationale of the improvement 

 of land by the burnt earth and afhes from paring and burning. 

 It is ufual to account for the effects of this procefs, by refer- 

 ring to fuppofed alkaline or other {alts ; but of thefe there is no 

 evidence, nay, on trial I have not detected them, or at leaft 

 not in any efficient quantity ; but this I know, that fuch earth 

 and afhes contain oxide of iron, and as I fufpeft of munganefe ; 

 which from the analyfis, and the effect of fait of peat, muft 

 now be admitted into the clafs of manures. This very com- 

 munication of Mr. Willaume, affords evidence of the truth of 

 this conjecture, for the allies of the peat which afford the fait 

 " have been long known as a manure, and the demand is on 

 the increafe :" of courfe, thefe afhes contain an unulualquan~ 

 tity of oxide of iron. A confequence of this reafoning is, 

 that the burnt earth of foils will, ceteris paribus, fertilize in 

 proportion to the oxide of iron it contains. Accordingly the 

 afhes of the peat, (ays Mr. Willaume, have a furprifing ef- 

 fect, they " will double or treble a crop of any new-fown 

 grafs, fuch as trefoil, Sec." they are fo beneficial, that in fpite 

 of the expence they are carried in bags by higlers to great dis- 

 tances. It would be extending this paper beyond the propofed 

 limits, to reafon at a greater length, and to make a further in- 

 duction of fads: therefore I will clofe with afferting, that the 

 more I contemplate the facts in Mr. Willaume's letter, the 

 more evidence f perceive for the truth, that metallic falts, and 

 metallic oxides in general, and falts and oxides of iron in par- 

 ticular, are manures, if applied in proper doles. 

 It is confidered I do not think it is within the defign of this paper to make 

 aseffettiveupon obfervations on the anfwers to the 2d, 3d, 4th, 5th, and 6tf\ 

 plea^condi- "queries, except, once for all denting that it may be under- 

 ments orfcafoii- flood, that I confider the fait of peat and the afhes of peat, as 

 operating in promoting vegetation analogous to feafoning, or 

 condiments taken with the food of animals ; that is, analogous 

 to muftard, cinnamon, ginger, &c. which are not of them- 

 felves at all or necefTarily nutritious, but contribute to render 

 other things nutritious, by exciting the action of the ftomach 



and 



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