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sizes are marked 90, 80, &c. without any intermediatenumbers between the tens. All these are half an inchor more narrower one than the other, though not withany exact regularity in the diminution of the sizes, or inthe dimensions of the pots of one number. Those of 90 or100, with a hoop and rings adapted to them, will receivesand-pots, stills, &c. large enough for the purposes ofthe apothecary : but furnaces for experimental pursuitsbeing the present object, it is sufficient here to havegiven a hint of this application of them.

It is expedient likewise, in a well-appointed elaboratory,to have some furnaces of a different construction as wellas of different magnitudes, set apart for particular uses,especially for those which demand great vehemence orcontinuance of fire.

In all cafes where vehement fire is to be continued forany considerable length of time, the furnace may bestrengthened by inserting one of the crucibles into anotherof a larger size. Some of the thick bottom part of theinner crucible is to be sawed off, and the remainderrounded with a rasp, that its surface may in some measurecorrespond to the cavity of the outer one; and the mouthof this last is to be widened, if it does not sufficientlyadmit the wide part of the other, by rasping off a littlefrom its inside all round the converging edge. Any cru-cible may thus be made to fit conveniently into the secondsize above it; that of number 60 into 80, 70 into 90,and 80 into 100. Such vacuity, as may remain betweenthe two, is to be filled with dry sand dropt in at the sides;or rather with staked lime, or fine sifted wood-affies,diluted with so much water as will render them of a dueconsistence for being poured in. This mixture soon sets,without shrinking considerably, and without growing hard

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