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§ I2

That the farmer may have under his eye at one time the several criteria of the purity of lime that have been enumerated, in different places of this Essay, I chuse to mention. them here all at one time.—If he is attentive to remark these peculiarities, he needs be very little sollicitous about examining the qualities of his lime by any more minute and troublesome trials.—They are as under:

If the lime-stone loses much of its weight in calcination, and the lime-shells are extremely light;—if the shells require a very large proportion of water to flake them fully; ^-if it is long before they begin to fall;— if the lime-stone is not apt to run (or be vitrified) in the operation of burning ;—if it falls entirely when it gets a sufficient quantity of water after it has been properly calcined; ned ;—if it swells very much in flaking, and if the lime is light, fine to the touch, and of a pure white; he may be satisfied that it is extremely good, and may use it in preference to any other lime that is inferior to it in any of these respects.

These rules are perfectly sufficient to decide as to the comparative value of any two' kinds of lime that may be opposed to one another, and may be relied upon with certainty.

§ 12.

But, such as may discover a hew quarry of lime-!tone, and who1 wish to ascercaih with certainty its real value, before they put themselves to any expence about it, Will do well to employ the following more accurate,' and, in that casse, more easy analysis.

As which had been previously dried, and reduced to powder.—After each addition, suffer the violent effervescence, or 'ebullition, that will ensue, to abate before more is added.—When the whole of the powder is put to the acid, and the effervescence entirely subsided, stir it about several times with a piece of tobacco-pipe, and allow it to re-*main for some time, that the acid may act: upon every particle of the matter, and thoroughly dissolve it. And, to be certain that there has not been too little acid, put a few drops of fresh acid to the solution, which Will excite a fresh effervescence, if the vvh \q is hot fully dissolved.—When no change is produced by this addition, it is a certain proof that the whole is already dissolved.

Take

it assumes almost a colourless transparency, with a very faint tinge of yellow.

When they are thus prepared, either of these acids may be used indiscriminately for this experiment, as they are equally proper.

Take then a piece of filtring paper, thoroughly dry, the weight of which is also known—fold it properly, and put it in a glass funnel—pour the whole of the solution, with the matter that may. have subsided, into the funnel, and allow jt to nitre through the paper slowly.—When the fluid part has thus drained off, fill up the filtre again with pure water, to wash off the whole of the saline parts from the residuum *.—-Add water in this manner till it comes off without any saline taste—suffer it then to drop off entirely;—dry it thoroughly —and weigh the paper with its contents.-?The difference between which, and what the powder and paper were at the beginning, is the whole weight of the calcareous matter; so that its proportion to the whole mass is perfectly ascertained.

In this manner, I have examined a great many different kinds of lime-stone, and have found them vary in all degrees of purity

* The matter that remains undiffolyed.

yity, from such as were entirely soluble in acids, as sugar or salt is in water, to others that contained only one twelfth of their weight of soluble matter, and eleven twelfths of sand.—The ordinary kinds of limestone contain from one third to two thirds of their weight of sand.—-Hard chalk is usually- a pure calcareous earth soluble in acids: —And some forts of lime-stone may be met with that are equally pure ;—but these are rare. The only extensive lime-quarries of such a pure lime-stone that I have met with are at S.underland, in the county of Durham, where there are several quarries of exceeding fine lime-stone; the best of which belongs just now to Mr James Galley of that place—There are some quarries farther up the river Were, the stone of which is of a much inferior quality.

Were all the stones in the fame quarry equaily pure, the above would be a perfect

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