Loriot, that he fo pompously describes, yet it may happen, that, if circumftances accidentally concur to that end, a very perfect mortar may be obtained by following his directions. For, if the flaked lime that fhall be

adds, that, for plafter, it is better than new; because it is not so subject to crack in the work. "Intrita quoque quo vetuftior, eo melior ideo nulla tectoria eorum rimae foedavere."

·

Monfieur Loriot quotes this paffage, and contends, that calcis fine ferrumine fuo means merely flaked lime, in oppofition to his favourite powdered limefhells.What reafon he has to think fo, the reader is left to judge. It is to be obferved, however, that Monfieur Loriot does not confine the use of his cement to making mortar-Like thofe medicines that cure all diseases, it is equally proper for plaster; and indeed it is as a plaster he chiefly recommends it. There can be no doubt, however, from the au thorities above quoted, that the antients were as great ftrangers to the use of it in this fenfe as the moderns.

A

be employed has not had time to become in a great measure effete; if the unflaked fhells that are to be pounded have been perfectly calcined; if the lime-stone has been of a fandy fort of itself;-if the fand added to it has been of a proper kind, and in due proportion; and if these materials be carefully mixed before they are applied, there can be no doubt but the mortar would be very good: So that it may sometimes happen, that those who follow the practice recommended. by him, in making mortar for ordinary uses, may be lucky enough to fucceed to their wish. But, as these favourable circumstances may not chance to occur in other cafes, they may be as far from their purpose as they poffibly could be.

That gentleman, with his ufual want of accuracy, takes no notice of any of thefe circumstances. He only recommends that powdered quick-lime, by which he means pounded lime-fhells, be mixed up

with common mortar made of old flaked lime in certain proportions. He does not

give the smalleft hint as to the flate of old flaked-lime to be used as common mortar; but seems to think it a matter of no moment, whether it shall have been fo long flaked as to be perfectly effete, or the reverfe; he does not, indeed, feem to know any thing about that peculiarity of lime diftinguished by that term.

But, independent of that circumftance, the practice he recommends is much worse in other respects than that usually followed in modern times, either for making plafter or cement,-efpecially the firft. For, in the ordinary operation of flaking, those limeshells that are not enough burnt, have some chance of being rejected when the lime is fifted; whereas, in this method of pounding the whole promifcuously, thefe will be mixed with the others; and therefore it may be expected that fome of the particles will remain

remain unflaked for a very long time, which will be in danger of difuniting and bliftering the work long after it is put up.

§ 29.

Authors almoft univerfally agree in afferting, that the hardest lime-ftone affords a lime that will confolidate into the firmeft cement; and hence it has been in general concluded, that lime made of chalk affords a much weaker cement than what is made of marble or lime-ftone.

It appears, however, from the foregoing obfervations, that, if ever this be the cafe, it is only incidentally, and not necessarily so.

Lime made of pure chalk differs not in the leaft from lime made of pure marble.-Both confift of a fine impalpable powder, without any mixture of extraneous matter;-and, if they have been equally calcined, are possesZ z

fed

fed of the fame chemical qualities in every refpect. Indeed, nothing is more easy than to form artificial chalk from pure lime-ftone, as I have more than once experienced, which the reader may alfo do, by following the directions in the margin*, if his curiofity prompts him to it.

And

* In flaking lime composed of pure lime-stone, it will be observed, that the pieces fall into powder much more flowly than when the lime-ftone has contained any fand in it.

If a great quantity of water be fucceffively poured upon a large heap of these pure lime-fhells, without ftirring them, and if it be allowed to lie fome time afterwards, it will be found, on opening the heap, that fome pieces of lime-fhells have only expanded confiderably in bulk by the operation of flaking, without being crumbled down to a powderThefe pieces, if allowed to remain in a close place, where they are not exposed to the viciffitudes of the weather, will fill retain their form, and, as they gradually abforb their air, they acquire a fort of firmnefs of confiftence, and in time become chalk, in

every