[ *5 I

admits the air, or of the pipe or chimney which car-ries it off.

It appears from the foregoing account, that two blacklead crucibles, fitted up in a manner which any commonworkman can easily execute, with a few additional parts aseasily procurable, are sufficient for forming almost any kindof furnace which experimental enquiries have occasionfor; and that they not only unite, like the different partsof other portable furnaces, into one furnace, but likewise,for sundry uses, form two distinct ones. It will be ex-tremely convenient to have a third crucible prepared inthe fame manner: in which cafe, as no operation requiresmore than two ; whatever kind of furnace is required forone operation, there will always be at least one left atliberty for another ; so that two very different kinds ofexperiments may thus be going on at the fame time,without hindrance, and without interfering one withanother.

For enquiries of any considerable extent or multiplicity,it is necessary to be provided with several of these crucibles;and though, for general use, we have given the preferenceto those marked 60 on the bottoms, yet other sizes maybe occasionally employed, and have their advantages forparticular purposes : much smaller ones, down as far asnumber 20, will make, for some uses, very convenientfurnaces. Those of number 60 may be considered as themean size : they are as large as arc wanted, in experimen-tal practice, for a capella or bath ; and they are thesmallest, and most manageable, that will answer effectuallyas a wind furnace or blast furnace for strong fire. Thelargest black lead crucibles are marked 100 : their internalheight is about thirteen inches and a half, and their internalwidth at the mouth ten inches and a half. The next

sizes