FURNACE 



519 



1009 



1010 



9. A circular cover or domo (fig. 1009) flanged at the bottom, and having a knob or 

 handle at the top. It is pierced with twenty-four holes of a quarter of an inch in 

 diameter, arranged in two rows near the bottom. This dome, 



when of small size, is made of plumbago; when large, of 

 firo-clay. 



10. Plumbago crucibles made with a solid overhanging rim, 

 the use of which is to suspend the crucibles over the gas- 

 burner, by means of the cylinders Nos. 5 and 6. When the 

 crucibles are too small to fit the cylinders, the flat-plate No. 7, 

 is filed to fit the crucible, and is then placed on the cylinder, 

 to whose diameter it is adapted. 



Besides these pieces of fire-clay and plumbago, it_ is necessary to be provided with 

 a strong iron tripod, to sustain the furnace ; an iron pan, in which to place the 

 furnace ; and a quantity of gravel, or rounded flints, not less than half an inch, nor more 

 than one inch in diameter. These pebbles form an essential part of the gas-furnace. 



Other forms of Griffin's gas-furnace will be found fully described in "Watts's 

 ' Dictionary of Chemistry.' See also Mr. Griffin's description of a gas-furnace for 

 attaining a white heat without the aid of a blowing-machine, in Journ. of Chemical 

 Soc., 1870, p. 280. 



Mr. George Gore has patented a gas-furnace of great power, which he thus 

 describes (Jig, 1010): A is a cylinder of fire-clay about nine inches high and 

 six inches diameter, open at both ends, with a 

 hole in its side near the bottom to lead into the 

 chimney ; it is covered by a moveable plate of fire- 

 clay, B, with a hole in its centre for introduction 

 or removal of the crucible, &c. ; this hole is closed 

 by a perforated plug of clay, c, for access to the 

 contents of the crucible, and that again is closed by 

 another clay stopper D. E is a chimney of sheet 

 iron about five or six feet high, kept upright by a 

 ring of iron, F, attached to the top of the furnace. 

 The fire-clay cylinder is enclosed in a sheet-iron 

 casing with a bottom of iron, to which are fixed 

 three iron legs, G. An iron tube H, with a prolon- 

 gation i, supports by means of the screw, j, the 

 burner K, and its tube L, which is open at both ends. 

 Gas is supplied to the burner by means of the tag, M, 

 which has a small index, N, attached to it for 

 assistance in adjusting the gas. ' Inside the larger 

 cylinder is another fire-clay cylinder or cupola, o, 

 with open ends, and with three projections of fire- 

 clay, P, for supporting the crucible, Q; it is kept 

 steady by means of three fire-clay marbles, E. The 

 gas-burner is a thin metal cylinder, deeply corru- 

 gated at its upper end, with the corrugations dimi- 

 nishing to nothing at its lower end. 



The action of this furnace is as follows : Gas is 

 admitted to the open tube, L, by the tap, M ; it there 

 mixes with air to form a nearly explosive mixture, 

 which ascends through the burner, and burns in the 

 clay cylinder, o, being supplied with the remainder 

 of air necessary to complete combustion through the tube H, to the outer surface of 

 the flame, by means of the spaces between the corrugations. The flame and products 

 of combustion pass up through the cylinder o, and then downwards outside it to the 

 chimney, the focus of greatest heat being at o. 



It is important in using this furnace that the burner is placed quite in the centre 

 of the bottom of the tube o ; also that a crucible of not too large or not too small 

 dimensions be selected. The most suitable way of supporting a smaller crucible is 

 by placing it in a larger one that has had its upper parts broken off. If desirable, a 

 little clay luting may be placed round the top edge of the iron casing to exclude air 

 entering between it and the cylinder ; also a little thin clay luting upon the part of 

 the bottom of the furnace where the inner cylinder, o, rests. 



In lighting the furnace, the plugs c and D are removed, a light held inside the 

 opening, and the gas turned on full. Should the flame blow down to the bottom of 

 the tube, L, on lighting (which, however, rarely occurs unless the furnace is already 

 hot), the gas must be turned ofl^ and the bottom of L momentarily closed whilst 

 lighting the gas as before. Should the flame not burn down to the burner, but only 



