Feb. lo, 1881] 



NA JURE 



)53 



inically than by the use of Sir Humphry Pavy's gigantic 

 battery, and Messrs. Huggins, Lockyer, I.lveing, and other 

 physicists have taken advantage of the comparatively new 

 method to advance astronomical and chemical research with 

 the aid of spectrum analysis. 



My object is now to show that the heat of the electric arc is 

 not only available within a focus or extremely contracted space, 

 but that it is capable of producing such larger eflects as will 

 render it useful in the arts for fusing platinum, iridium, steel, 

 or iron, or for eftecting such reactions or decompositions as 

 require for their accomplishment an intense deq;ree of heat, 

 coupled with freedom from such disturMng influences as are 

 inseparable from a furnace worked by the combustion of car- 

 bonaceous material. 



The apparatus nhich I employ to effect the electro-fusion of 

 such material as iron or platinnm is represented in the 

 drawing. It consists of an ordinary crucible of plumbago 

 or other highly refractory material, placed in a metallic jacket 

 or outer casing, the intervening space being tilled up with 

 pounded charcoal or other bad conductor of heat. A hole is 

 pierced through the bottom of the crucible for the admission of 

 a rod of iron, platinum, or dense carbon, such as is used in 

 electric illumination. The cover of the crucible is also pierced 

 for the reception of the negative electrode, by preference a 

 cylinder of compressed carbon of comparatively large dimen- 

 sions. At one end of a beam, supported at its centre, is .sus- 

 pended the negative electrode by means of a strip of copper, or 

 other good conductor of electricity, the other end of the beam 

 being attached to a hollow cylinder of soft iron free to move 

 vertically within a solenoid coil of wire, presenting a total resist- 

 ance of about 50 units or ohms. By means of a sliding weight 

 the preponderance of the beam in the direction of the solenoid 

 can be varied so as to balance the magnetic force with which the 

 hollow iron cylinder is drawn into the coil. One end of the 

 solenoid coil is connected with the positive and the other with 

 the negative pole of the electric arc, and, being a coil of high 

 resistance, its attractive force on the iron cylinder is proportional 

 to the electromotive force between the two electrodes, or, in 

 other words, to the electrical resi-tance of the arc itself. 



The resi^tance of the arc was determined and fixed, at well 

 within the limits of the source of power, by sliding the weight 

 upon the bsam. If the resistance of the arc should increase from 

 any cause the current passing through the solenoid would gain in 

 strength, and the magnetic force overcoming the counteracting 

 weight would cause the negative electrode to descend deejier 

 into the crucible ; whereas, if the resistance of the arc should 

 fall below tlie desired limit, the weight would drive back the 

 iron cylinder within the c nls, and the length of the arc would 

 increase, until the balance between the forces engaged had been 

 re-establi-hed. 



Experiments with long solenoid coils have shown that the 

 attractive force exerted upon the iron cylinder is subject only to 

 slight variation within a range of several inches, which circum- 

 stance allows of a working range to that extent of nearly uniform 

 action on the electric arc. 



This automatic adjustment of the arc is of great importance 

 to the attainment of advantageous results in the process of 

 electric fusion ; without it the resistance of the arc would 

 rapidly diminish with increase of temperature of the heated 

 atmosphere within the crucible, and heat would be developed in 

 the dynamo-electric machine to the prejudice of the electric 

 furnace. The sudden sinking or change in electrical resistance 

 of the material undergoing fusion would, on the other hand, 

 cause sudden increase in the resistance of the arc, with a 

 likelihood of its extinction, if such self-adjusting action did not 

 take place. 



Another important element of success in electric fusion con- 

 sists in constituting the material to be fused the positive pole of 

 the electric arc. It is well known that it is at the positive pole 

 that the heat is principally developed, and fusion of the material 

 constituting the positive pole takes place even before the crucible 

 itself is heated up to the same degree. This principle of action 

 is of course applicable only to the melting of metals and other 

 electrical conductors, such as metallic oxides, which constitute 

 the materials generally operated upon in metallurgical pro- 

 cesses. In operating upon non-conductive earth or upon streams 

 of gases it becomes necessary to provide a non-destructible 

 positive pole, such as is supplied by the use of a pole of fused 

 platinum, or iridium, or by a plumbago crucible. In working 

 the electric furnace some time is taken up in the first instance 



in raising the temperature of the crucible to a consider.able 

 degree, but it is surprising how rapidly an accumulation of lieat 

 takes place. In using a pair of dynomo-machines cajiable of 

 producing 70 webers of current with an expenditure of 7-hoi-sc 

 power, and which, when used for purposes of illumination, 

 produce a light of 12,000 candles, a crucible of about S inches 

 in depth, immersed in a non-conductive material, has its tem- 

 perature raised to a white heat in fifteen minutes, and 4 lbs. 

 of steel are fu<cd within another fifteen minutes, successive 

 fusions being effected in somen hat diminishing intervals of 

 time. The process can be carried on on a still larger scale by 

 increasing the power of the dynamo-machines and the size of the 

 crucibles. 



The purely chemical reaction intended to be carried into effect 

 within the crucible might be interfered with through the detach- 

 ment of panicles from the dense carbon used for the negative 

 pole, although its consumption within a neutr.al atmos]ihere is 

 exceedingly slow. To prevent this I have used, both in this con- 

 nection and also in the construction of electric lamps, a water 

 pole, or tube of copper, through w hich a current of water circu- 

 lates, so that it yields no substance to the arc. It consists simply 

 of a stout copper cylinder closed at the lower end, having an 

 inner tube penetrating to near the bottom for the passage of a 

 current of w ater into the cylinder, which water enters and' is dis- 

 charged by means of flexible india-rubber tubing. This tubing 

 being of non-conductive material, and its sectional area smali, 

 the escape of current from the pole to the reservoir is so slight 

 that it may be neglected. On the other hand some loss of heat 

 is incurred, through conduction, with the use of the water pole, 

 but this loss diminishes with the increasing heat of the furnace, 

 inasmuch as the arc becomes longer, and the pole is retired more 

 and more into the crucible cover. 



In the ex|ierin\ents which I shall now place before you the 

 current which has su)iplied the one electric lamp in the centre of 

 the hall will be diverted by means of a commutator through the 

 electric furnace. After it has been active for five minutes to 

 warm the crucible, I shall charge it with S lbs. of broken steel 

 files, which I shall endeavour to melt and ponr out into an ingot 

 mould before your eyes. 



By some obvious modifications of this electric furnace it can 

 be made available for a variety of other purposes where intense 

 heat is required combined with immunity from disturbing 

 chemical actions. By piercing a number of radial holes 

 through the sides of the chamber, and introducing the ends of 

 wires through the same, an excellent means is provided of 

 heating those wire ends very rapidly, without burning them, 

 for the purpose ofwelding them together. The electrical furnace 

 will also be found useful, I believe, in the hands of the chemist 

 to effect those high temperature reactions between gaseous 

 bodies which require the employment of temperatures far 

 exceeding the hitherto available limits, and will thus increase 

 the area of available reactions at his disposal for the attainment 

 of either scientific or practical ends. 



I have endeavoured to compress within the limited space of 

 a single lecture, subject matter that might occupy the close 

 attention of the student for weeks or months, and I may there- 

 fore be j)ardoncd if I have failed to convey to you more than a 

 very rough outline of what may be accomplished by the judicious 

 use of gaseous fuel, and of the electric current, as heating 

 agents. The one purpose that has been foremost in my mind 

 in preparing this lecture, has been to make war npon the 

 smoky chimney, which, so far from being a necessity under any 

 circumstances whatever, should be regarded only as a remnant 

 of that stage of our industrial and social progress which satis- 

 fied with the attainment of certain ends, could afford to neglect 

 the economical and sanitary conditions under which those ends 

 were accomplished. 



The Exhibition which has lately been held in this city of 

 appliances for heating and illuminating by means of gas and 

 electricity, in which your President, my esteemed friend, Sir 

 William Thomson, took so prominent a part, as he does in 

 everything tending towards the advancement of human know- 

 ledge anil well-being — proves how deep is the interest felt 

 amongst you in those very questions with which I have had to 

 deal this evening. 



And so I thought you might not be disinclined to give 

 attention once more to a particular view of the question, which 

 happens to be the result of the independent labour of one who 

 may claim at any rate to have given a life-long attention to 

 the subject. 



