496 REPORT — 1882. 



lime, is made the positive electrode of the arc, while a carbon rod, passed into 

 another perforation in the lime so as to meet the tube in the middle of the block, 

 is made the negative electrode, the tube becomes gradually heated up, and in the 

 direct line of the tube the metallic lines are seen bright because there is no back- 

 ground, but against the hot walls of the tube the same lines are seen reversed. 

 The effects of gradually increasing temperature were traced as the tube was 

 gradually heated. VI. Occasionally a double reversal of lines occurs, and a photo- 

 graph was exhibited showing an expansion of the magnesium lines, between K and L, 

 which extended so far as to produce reversal of the most refrangible two of the 

 cyanogen bands, the magnesium producing also a broad absorption band, against 

 which the magnesium triplet was seen bright and sharp. This seems due to the 

 less dense, but intensely heated, magnesium vapours, pushed forward up the tube 

 by the sudden burst of dense vapour evolved on dropping a fresh piece of magne- 

 sium into the arc. 



4. On the Electric Furnace. 

 By Dr. C. W. Siemens, F.B.S., and Professor A. K. Huntington. 



The electric furnace has previously been described in the Journal of the Society 

 of Telegraph Engineers, June, 1880. It has since been found advisable to sur- 

 round the furnace with a coil. By this means the direction of the arc can be 

 regulated at will, and the tendency which it has to fly to the sides of the crucible 

 be checked. 



The electrodes may be of such carbon as is used in electric lighting or of any 

 other convenient conducting substance. They may, if desired, be cooled by circu- 

 latino- water through or round them, or by exposing them as far as possible to the 

 air. For example, in one experiment a ^in. nickel positive pole was employed, 

 the lower end being inserted into a solid rod of copper about 1 in. square by 6 in. 

 long. With this pole, no other means of keeping it cool being adopted, 1 lb. of 

 grain nickel was fused in a clay crucible and poured in eight minutes, starting 

 with all cold. The electrode was but little attacked, and no leakage occurred. 



There are two great advantages possessed by the electric furnace, viz., that the 

 temperature attainable is practically only limited by the refractoriness of the 

 materials of which the furnace is constructed, and that the heat is developed im- 

 mediately in the material to be fused, instead of first having to pass through the 

 containing vessel. The temperature to be obtained by the use of fuel is limited 

 by dissociation. Deville has shown that carbonic acid undergoes dissociation at 

 the ordinary atmospheric pressure at about 2,GO0° Cent. = 4,700° Fahr. 



In the experiments made by the authors, five D-2 machines driven by a Mar- 

 shall's 12-horse power engine were employed : one being used as an exciter. The 

 current ranged between 250 and 300 amperes. The most refractory clay crucibles 

 supplied by the Patent Plumbago Crucible Company were invariably cut through 

 in a few minutes, and, except for experiments of short duration, were useless. 

 Plumbago crucibles stood exceedingly well. Obviously, however, they could not 

 be employed for all purposes, owing to their tendency to cause carburisation of the 

 metal experimented with. In some experiments the fusion of metal was effected 

 in a bed of lime, sand, or electric light carbon-dust. The latter is a very bad 

 conductor, and, as in the case of lime and sand, aUows the- arc when once formed 

 to maintain a passage through it to the metal beneath. 



Wrought Iron. — Six pounds of wrought iron were kept under the action of 

 the arc for twenty minutes, and the metal then poured into a mould. It was 

 fouud to be crystalline, and could not be forged. This is the result which has 

 always been obtained when iron, nickel, or cobalt have been fused. Although the 

 remedy, viz., the addition of a little manganese just before pouring, is well known, 

 the cause remains still imexplained. 



Steel. — As much as 20 lbs. of steel files have been melted in one charge, the 

 time required being about one hour, starting with the furnace hot. With such 

 large quantities the metal has invariably been full of blowholes. 



