glass chamber to apply more closely. These covers are three wrought-iron plates, each ¼th of an inch in thickness and 16 inches long; but their widths vary, and are 7, 10, and 12 inches. The e put side by side cover the mouth of the chamber, but, varied in juxtaposition, allow of more or less of the chamber being opened at once, according to whatever the experiment may require; each has a short solid handle fixed to the middle of the upper surface.
Besides the iron covers, there are a set of earthenware covers, consisting of six square tiles each 1⅜ inch thick (62). These are notched to receive the handles of the iron covers, and being put together over them, constitute a covering of earthenware, which very importantly assists in retaining the heat.
The tiles and brick used in the annealing process (89) are the ordinary dry varieties, with some pieces of various sizes, to allow of the close adjustment of the whole.
The earthenware supporting blocks (57) required for the arrangement and support of the platinum tray, should be formed out of some kind of Hat unglazed ware containing as little iron as possible, and should be of various thicknesses, sizes, and forms, although parallelepiped's are the most usual. They should not be of such substance as is liable to fly or send off anything when heated; and when any portion of glass adheres to them, it should either be cleared off or the piece thrown away. The Cornish tile before described (52. 53) is excellent for this use, and may be sawn, rasped or ground into any shape required.
The glass-covers (60, &c.) that have yet been used were merely inverted evaporating basins. They answer the required purpose exceedingly well, except that, when large, they are too strong, too heavy, and too deep. Some covers for the purpose are therefore in progress, and as they only have to support their own weight and hold together, they are to be thin. The covers should be of very refractory and highly baked ware; it may be desirable to have them very slightly glazed, to keep them clean, and prevent the absorption of any substance which might send off vapours injurious to the glass.
The fire tools required for this furnace will suggest themselves. Amongst the rest should be a pair of tongs which will readily lay hold either of the earthenware tile or the iron covers;
