III. EXPERIMENTS

Of the conversion of Glass Vessels intoPorcelain, and for establishing the prin-ciples of the art.

H AVING many years ago distilled some woodsoot, with a strong fire, in a green glass retortset in sand, I observed great part of the bottom ofthe retort, after the operation, to be remarkably changed :it was quite opake, of a black colour on the inside wherethe foot had been in contact; with it, and whitish on theoutside where it rested upon the sand : it had no longerthe brittleness of glass, but broke with difficulty like thebetter kinds of stone ware : its internal substance waswhite like porcelain ; and not of a glassy smoothness, butof a fine fibrous texture.

This singular change, in a body suposed so little sus-ceptible of alteration, was attributed to the vapours ofthe foot having penetrated into the substance of the glass :sundry pieces of the fame kind of glass were thereforeintermixed with another quantity of foot, in an iron pot,to which was adapted a head with a receiver, and thedistillation conducted in the usual manner, till nothingmore could be forced out from the foot in a strong fire :on examining the pieces of glass, some, in the middle ofthe matter, seemed scarcely at all altered ; others, aboutthe sides and bottom of the pot, were changed in partnearly in the fame manner as the bottom of the retorthad been.

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