[ 5 6 ? 1

too interesting to be patted over, in this history, withoutbeing verified by further trials.

14. Having at hand: a wind furnace, formed of a mixtureof Sturbridge clay and powdered glass-house pots, securedby iron hoops on the outsi.de, about two feet high from thegrate to the top of the dome, fourteen inches wide in themiddle and ten inches, at the grate, with a chimney ofnearly half the diameter of the grate and fourteen feet high;I first made trial of this furnace, and found its effect: tobe such, that there was no occasion to have recourse toany other. I fitted into it a muffle, in the manner de-scribed' by the. ingenious author in a memoir on die vitre-fication of clay with chalk, formed of the same composi-tion with the furnace,, two inches high, three inches wide,of such length as to reach across the furnace, supported atthe height of five inches above the grate by a brick offire-standing clay, which was cut Hoping downwards so asto cover as little as possible of the grate.

15. A large cupel having been kept red hot in the muf-fle about an hour; two ounces of lead were put in, andone ounce of the picked grains of platina dropt into themelted lead. The fire being raised with coaked pitcoal toits greatest vehemence, the whole internal part of themuffle appeared of a dazzling brightness, and the cupelcould not be distinguished, till cold air was suffered to passthrough by keeping the door open for some time, whichwas done frequently, to promote the scorification or dissi-pation of the lead. In this state the heat was continued,,untill, in five or six hours, penetrated by the vitrescentcinder of the coal, the muffle begun to fail: all its backpart, and some of the internal part of the furnace, melted,forming partly irregular vitreous lumps, and partly run-ing down through the grate in large drops of black hard.gla&.. The cupel was hard, yellowisli white, and semi-

transparent,.