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This change of glass has doubtless happened often,without being attended to. Neumann is the first writerby whom I find it taken notice of: in distilling milk ina glass retort, he observed that the bottom of the vesselacquired the appearance of porcelain, which he attributesto the sine white earthy matter of the milk forced into theglass by the heat.

M. de Reaumur was led to the same discovery by analo-gical reasoning, as I have already mentioned in the noteson Neumann’s chemical works, where a further accountof this affair is promised. Reaumur, having had largeexperience of the effects of inflammable and earthy bodieson iron, by baking, in the conversion of forged iron intosteel, and in the softening of cast iron, applied the sameprocess to common glass, and thus discovered the newporcelain, which he calls porcelain by transmutation,porcelain by revivification, or porcelain of glass. Theglass was cemented, or baked, in crucibles, first with thefoot, powdered charcoal, and other substances employedin the experiments on iron : it became opake, externallydark-coloured or black, but internally of a fine whitecolour. Other materials were then made trial of, in hopesthat some one might be found, which should occasion thesurface to be as white as the internal part: among thesubstances tried in this view, of which he gives no parti-cular account, he judged white sand and plaster-of-paris,or rather a mixture of the two, to answer the best. Hedirects vessels of common green glass to be filled and sur-rounded with this mixture, in large crucibles or cement-ing pots, such as are commonly used for the baking ofearthen wares; the crucibles to be covered and luted,and set in a potter’s furnace : the fame sire, which bakesthe common wares, changes the glass vessels into vessels ofthe new porcelain. He observes, that this porcelain may

be