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mine the most proper construction of the two crucibles, foradapting them to different purposes, separately or combined.

The black lead crucibles of that size, which has thenumber 60 marked on the bottom, I have found to be thebest suited for the general uses of furnaces: their perpen-dicular height, in the inside, is about twelve inches;their width at the mouth somewhat less than eight inches,and about the middle of their height six and a half.These vessels I have fitted up in different methods, andfound the following construction to be in general the mostcommodious.

Each crucible has its mouth ground smooth and flat,upon a stone, with a little sand; and a round hole sawedin its bottom with the common compass saw of thecarpenters. In the side, a little above the bottom,another round hole is made; and opposite to this, asquare one; above which is cut a larger square one.The places of these apertures, and their comparativesizes, are represented in the annexed plates; in which allthe figures are drawn to one scale, to prevent the necessityof embarassing the description with an account of theparticular dimensions of the several parts.

All the apertures are fitted with stoppers, cut out ofpieces of broken crucibles, which are easily procurable atthose places where the pots themselves are fold. Thesquare apertures are made, at each of their sides, a littlenarrower internally than externally, by which means thestoppers^ though their surface lies equal with that of theoutside of the pot, are prevented from being puffed inwards:this flope is made on the sides, and not on the top orbottom, that the stoppers may not be liable to fall outwhen the pot stands on either end. The round ones arein little danger of falling out, being made to sit close, by

B 2 grinding