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ned;-if it fwells very much in flaking, and if the lime is light, fine to the touch, and of a pure white; he may be fatisfied that it is extremely good, and may use it in preference to any other lime that is inferior to it in any of thefe refpects.

Thefe rules are perfectly fufficient 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.

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But, fuch as may difcover a new quarry of lime-tone, and who wish to afcercain' 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 cafe, more eafy analyfis.

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which had been previously dried, and reduced to powder.-After each addition, fuffer the violent effervefcence, or ebullition, that will enfue, to abate before more is added. When the whole of the powder is put to the acid, and the effervefcence entirely fubfided, ftir it about feveral times with a piece of tobacco-pipe, and allow it to remain for fome time, that the acid may act upon every particle of the matter, and thoroughly diffolve it. And, to be certain that there has not been too little acid, put a few drops of fresh acid to the folution, which will excite a fresh effervefcence, if the whole is not fully diffolved.-When no change is produced by this addition, it is a certain proof that the whole is already diffolved.

Take

it affumes almoft a colourlefs tranfparency, with a very faint tinge of yellow.

When they are thus prepared, either of these acids may be used indifcriminately 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 glafs funnel pour the whole of the folution, with the matter that may have fubfided, into the funnel, and allow it to filtre through the paper flowly.-When the fluid part has thus drained off, fill up the filtre again with pure water, to wash off the whole of the faline parts from the reftduum *.-Add water in this manner till it comes off without any faline tafte-fuffer 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; fo that its proportion to the whole mafs is perfectly ascertained.

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

The matter that remains undiffolved.

rity,

rity, from fuch as were entirely foluble in acids, as fugar or falt is in water, to others that contained only one twelfth of their weight of foluble matter, and eleven twelfths

of fand. The ordinary kinds of limeftone contain from one third to two thirds of their weight of sand. Hard chalk is usually a pure calcareous earth foluble in acids: -And fome forts of lime-ftone may be met with that are equally pure ;-but these are rare. The only extenfive lime-quarries of fuch a pure lime-ftone that I have met with are at Sunderland, in the county of Durham, where there are feveral quarries of exceeding fine lime-ftone; the beft of which belongs just now to Mr James Galley of that place-There are fome quarries farther

up

the river WERE, the ftone of which is of a much inferior quality,

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

and

and unexceptionable method of ascertaining

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the purity of any lime-ftone: But it often

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happens, that, in a quarry of the very worst quality, there are fone pieces found that confift of pure fpat, that are entirely free of any mixture of fand; and, in other quarries of a better fort, there are often fmall veins of an impure fort of ftone mixed through the rock; fo that, if either of these thould chance to be picked out as à fpecimen for trial, the refult would not be just.

To avoid falling into this mistake, any one who wishes to make an accurate analyfis of any new discovered lime-ftone, will do well to take eight or ten ftonés from different parts of the quarry, that afe fomewhat different in appearance from one another; and, having taken a chip from each, pound the whole together, to afford a proper fubject for the experiment.

The fame experiment might be tried With lime but it is evident, the propor

tions

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