222 THE SCIENTIFIC PAPERS OF 



3bo estimated at from 2,500 to 2,800 C. But long before this 

 extreme poiiit has been reached, combustion becomes so sluggish 

 that the losses of heat by radiation balance the production by 

 combustion, and thus prevent further increase of temperature. 



It is to the electric arc, therefore, that we must look for the 

 attainment of a temperature exceeding the point of dissociation of 

 products of combustion, and indeed evidence is not wanting to 

 prove the early application of the electric arc to produce effects 

 due to extreme elevation of temperature. As early as the year 

 1 807, Sir Humphrey Davy succeeded in decomposing potash by 

 means of an electric current from a Wollaston battery of 400 

 elements ; and in 1810 the same philosopher surprised the members 

 of the Royal Institution by the brilliancy of the electric arc 

 produced between carbon points through the same agency. 



Magneto-electric and dynamo-electric currents enable us to 

 produce the electric arc? more readily and economically than was 

 the case at the time of Sir Humphrey Davy, and this compara- 

 tively new method has been taken advantage of by Messrs. 

 Huggins, Lockyer, and other physicists, to advance astronomical 

 .and chemical research by the aid of spectrum analysis. Professor 

 Dewar quite recently, in experimenting with the dynamo-electric 

 current, has shown that in his lime tube or crucible several of the 

 metals assume the gaseous condition, as demonstrated by the re- 

 versal of the lines in his spectrum, thus proving that the tempera- 

 ture attained was not much inferior to that of the sun.' 



My present object is to show that the electric arc is not only 

 capable of producing a very high temperature within a focus or 

 extremely contracted space, but also such larger effects, with com- 

 paratively moderate expenditure of energy, as will render it useful 

 in the arts for fusing platinum, iridium, steel, or iron, or for 

 effecting such reactions or decompositions as require for their 

 accomplishment an intense degree of heat, coupled with freedom 

 from such disturbing influences as are inseparable from a furnace- 

 worked by the combustion of carbonaceous material. 



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

 such material as iron or platinum is represented in the accompany- 

 ing drawing, Plate 20. (This diagram was explained in full 

 detail to the meeting.) It consists of an ordinary crucible, a, of 

 plumbago or other highly refractory material, placed in a metallic 



