Electrochemical and metallurgical industry . ccur unless the substance had begun to fuse. It is now known that certain forms of carbon increasegreatly in apparent volume when converted into graphite. An interesting experiment was made with a carbon rodwhich passed through a clay crucible filled with sand. Thecurrent was passed through the rod which fused and volatil-ized. I obtained a sort of very hard fulgurite (lightning-tube) the interior of which was lined with smoky-quartz; theinner diameter of this tube was at least ten times that of thecarbon. Mr. Elihu Thomson lias recently obtained a
Electrochemical and metallurgical industry . ccur unless the substance had begun to fuse. It is now known that certain forms of carbon increasegreatly in apparent volume when converted into graphite. An interesting experiment was made with a carbon rodwhich passed through a clay crucible filled with sand. Thecurrent was passed through the rod which fused and volatil-ized. I obtained a sort of very hard fulgurite (lightning-tube) the interior of which was lined with smoky-quartz; theinner diameter of this tube was at least ten times that of thecarbon. Mr. Elihu Thomson lias recently obtained a patent for mak-ing quartz tubes in this manner. Despretz also made several experiments on the effect ofheat on diamond. For this purpose he used a tube furnacewhich he made by connecting the carbon terminals with acarbon tube in which the diamonds were placed. Despretzpaper may be found in Comptes Rendus No. 25, T XXIX,1849. This furnace, designed by Despretz, may be looked upon asthe progenitor of the furnace known as the Borchers t\pe. An. FIG. I.—DI.\GK.\M OF liOKCHERS FURN.\CE. illustration of the Borchers furnace is given in Fig. i. Tiand T2 are heavy carbon terminals which are connected elec-trically by the resistor R. The connections between the re-sistor and the terminals may be made by drilling holes in theterminals and packing with graphite, Gi and G2, as shown inthe figure. The connections to the source of current aremade at Hi and H2. The material to be heated surroundsthe resistor R, and the furnace is covered by the bricks to Borchers, all oxides may be reduced in this fur-nace. The data given by Borchers for this furnace are as follows: An electromotive force of to is necessary todrive a current of i ampere through i mm. of a carbon pen-cil at the temperatures of these experiments, with a currentdensity of 6 to 10 amperes per sq. mm. of sectional area. This would give a resistivity of to ohm, whichis somewhat higher than req
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