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securing the lower ends in a bed of luting : the cruciblesbeing closely covered, and exposed to the seme degrees ofheat as in the preceding experiments, the glass underwentthe seme changes as if it had been surrounded with send ;with only this difference, that the changes happened muchmore slowly ; and that the pieces of glass having no solidmatter to support them at the sides, many of them, madesoft by the heat, had failed and bent downwards. It seemsmanifest from this experiment, that the send or othermaterials are of use only for expediting the process, andaffording a support to the vessel; and that they are entirelyinessential to the porcelain itself.

There are other facts which seem to strew, that theglass, instead of receiving any new ingredient in its con-version, loses a part of one of its own, at least in the lat-ter stages of the process. In the cementation with send,the send near the surface of the glass, as already observedin the preceding part of this essay, was commonly foundto cake together ; a presumption that it had imbibed someof the saline matter of the glass, for send of itself isnever found to cohere by heat. When fresh pieces ofglass were cemented repeatedly with the seme send, thesend actually begun to melt, and covered the surface ofthe glass, or of the porcelain resulting from it, to a con-siderable thickness, with a semivitreous coat, which ad-hered so strongly as not to be separated by a blow.When the baking of one piece of glass was long continued,it became friable and porous, the adjacent send concretingat the fame time into a mass scarcely to be dstinguifhedfrom it.

From these observations I apprehend it may be con-cluded, that a part of the alkaline salt of the glass exudesby the heat, and is imbibed by the surrounding matters;and that by a long continuance of the baking, so much5 of