23. _Stone ware._--The materials of this ware, as well as the mode of preparing them, differ but little from those of the common and better kinds of earthen wares. The clays, however, which contain but little or no oxyde of iron are chosen, since this substance would cause the ware to melt and warp, before a sufficient degree of heat could be applied to give it the requisite hardness. 24. The glazing is formed by a vitrification of the surface of the vessels, caused by the action of common salt thrown into the kiln, when it has been raised to its greatest heat. This glazing is more perfect than that on ordinary earthen wares, being insoluble by most chemical agents. It is hardly necessary to remark that this method of glazing precludes the use of saggers. 25. _Porcelain._--This ware exceeds every other kind in the delicacy of its texture, and is peculiarly distinguished by a beautiful semi-transparency, which is conspicuous when held against the light. In China, it is made chiefly of two kinds of earth; one of which is denominated _petuntze_, and the other _kaolin_; but both are varieties of feldspar, found in the mountains, in different localities. They are brought to the manufactories from a distance in the form of bricks; the materials, as taken from the mines, having been reduced to an impalpable powder in mortars, either by the labor of men or by water-power. 26. These materials are combined in different proportions in the manufacture, according to the quality of the proposed ware. In the best kind, equal quantities are used; but for those of inferior quality, a greater proportion of petuntze is employed. The translucency so much admired in porcelain, or _tseki_, as the Chinese call it, is owing to the petuntze, which, in burning, partially melts, and envelops the infusible kaolin. 27. It is not known who was the inventor of porcelain, as the Chinese annals are silent with regard to this point; nor do we know more of the date at which the manufacture was commenced. It is certain, however, that it must have been before the fifth century of the Christian era. Since this ware has been known to Europeans, it has been manufactured chiefly, and in the greatest perfection, in the large and populous village of King-te-ching. 28. Porcelain was first brought to Europe from Japan and China, and for a long time its materials and mode of manufacture remained a secret, in spite of the efforts of the Jesuit missionaries, who resided in those countries. At length, in 1712, Father Entrecolles sent home to France, specimens of petuntze and kaolin, together with a summary description of the process of the manufacture. 29. Shortly after this important event had transpired, it was discovered that materials nearly of the same kind existed in abundance in various parts of Europe. The manufacture of porcelain was, therefore, soon commenced in several places; and it has since been successfully carried on.