tions would be different in the same ftone, from what they would be if tried before calcination as lime wants its fixed air, &c. which it had when in the state of lime-ftone. But, as the lime is more liable to be varied by accidental circumftances, it is best to try the experiment with lime-ftone.

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$14.

It is, in general, believed, that the lime made of the hardest lime-ftone is stronger, as it is called, by which is meant more powerfully efficacious as a manure, than that which is made from materials of a fofter nature. Hence it is, in general, afferted, that lime made chalk from is much weaker, as a manure, than that which is made from harder lime-ftones bus w

Nothing, however, can be more erro neous than this hypothefis. In the former part of this Effay, I have had occafion to explain pretty fully what is the real difference between chalk and lime-ftone-and nothing can be more certain, than that the lime made of chalk is purer than that made from almost any lime-ftone-and contains a much larger proportion of calcareous matter;on which account it must be more efficacious as a manure than any of these more impure kinds of lime.

The hardest lime-ftone that I know is that belonging to Mr. Galley at Sunderland. -Its external appearance rather resembles flint than lime-ftone; and I have known i it shaped into flints for guns, and used as fuch with fuccefs-yet the lime made of this exceeding hard flone is as light, as white, and as foft to the touch, as the pureft chalk-lime.-It differs not from that in any relpect-infomuch, that I defy the great

eft

eft connoiffeur in these matters to diftinguish between it and the pureft chalk-lime, when perfectly calcined, by any other means than by the pieces of flint that are fo often met with among chalk-lime.

And from this lime, obtained from these very hard ftones, as perfect chalk may be artificially made, by the fimple procefs described p. 363. as was ever obtained from any quarry in England.

From thefe confiderations, therefore, I am obliged to conclude, contrary to the common opinion, that chalk-lime is, almost in all cafes, more efficacious, as a manure, than any lime obtained from lime-ftone, in equal quantities-as it is extremely rare to meet with a lime-ftone that contains near fuch a large proportion of calcareous matter; on which account it ought always to be preferred by the farmer, where both can be had at the fame price.

§ 15.

We know little certain about the mode in which lime operates, excepting that it acts merely in confequence of its being mixed with the foil in fubftance.-If a heap of lime fhall have lain ever fo long upon one fpot, and be afterwards carried clean away from it, fo that none of the particles of the lime remain to be mixed with the foil-that fpot will not be richer, or carry more luxuriant crops, than the places around it-which, every one knows, is not the cafe with regard to dung.

Again-if lime be fpread upon the furface of the foil, and allowed to remain there without being ploughed in, its effects will scarcely be perceived for several years, till it has had time gradually to fink through the fward and mix with the foil; after which

its

its effects begin to be perceived-although much less fenfibly, than if the fame quantity of lime had been intimately mixed with the foil, by means of the plough and har

row.

I am no ftranger to the improvements that have been made in Derbyshire, by means of lime without the plough; but this is no exception to what I have faid.-The effects are flow, though certain. Thofe

who inhabit countries that admit of the plough, are often advised to lay lime upon the grafs, and are made to believe, that their pasture will be inftantly mended by it, nearly in the fame perceptible manner as if it had been dunged. This I myself have tried, and have feen it tried by others—but always found that the grafs, for the first year, was rather hurt than benefited by it; nor was it fo much improved in fucceeding years as if the fame quantity of lime had been applied and intimately mixed with the foil.

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