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grinding them into the apertures. The stoppers are con-veniently taken out and put in by means of a kind offork, each stopper being furnished with two small holesfor introducing the points: these holes are made atthe fame distance from one another, in all the stoppersof both the crucibles, so that the fame instrument servesfor them all: a springiness in its legs accommodates itto small inequalities. The bottom stopper is bettermanaged by the hand or tongs; a circular cavity beingcut in it, so as to leave a knob for that purpose in themiddle.

The grate consists of an iron ring, with cross bars fixedin it: the thickness or depth of the bars is considerablygreater than their width, that they may have sufficientstrength, and that the spaces between them may be asgreat as possible: the ring is formed of a bar, of thefame dimensions, turned round. Three of these grates,of different widths, are required for different uses:ode, of such a size, that it may rest against the con-verging sides of the pot, in the lower narrow part,just above the lowermost square hole; another, so largethat it may enter no further than nearly to the top of theuppermost hole; and the third, of the same width withthe outside of the mouth of the crucible. One grate of thesmaller size is necessary for each of the furnaces; but oneof each of the other two sizes is sufficient for both furnaces;those operations which require either of these grates,requiring at the fame time both the pots. For moreeffectually keeping the lower and middle grates in theirplaces, either grooves are cut for their edges to rest upon,all round the pot; or three notches are made, for each,at equal distances, in the pot, and corresponding knobsor pins on the circumference of the grate; which pins arerivetted into the ring. This last method is the most

eligible.