258 THE ADDRESSES, LECTURES, ETC., OF 



I now approach another and the last portion of my address, the 

 attainment of very intense degrees of heat either for effecting 

 fusion or chemical decomposition. Although by means of the 

 combustion of either solid or gaseous fuel heats are produced 

 which suffice for all ordinary purposes, there is a limit imposed 

 upon the degree of temperature attainable by any furnace depend- 

 ing upon combustion. It has been shown by Bunsen and by 

 St. Claire Deville, that at certain temperatures the chemical affinity 

 between oxygen on the one hand and carbon and hydrogen on the 

 other absolutely ceases, and that if the products of combustion 

 C0 a and H a O be exposed to such a degree of temperature they 

 would fall to pieces into their constituent elements. This point 

 of dissociation, as it is called, is influenced by pressure, but has 

 been found for C0 a under atmospheric pressure to be 2600 C. 

 (or 4700 Fahr.). But long before this extreme point has been 

 arrived at, combustion is greatly retarded and the limit is reached 

 when the losses of heat by radiation from the furnace balance its 

 production by combustion. 



To electricity we must look for the attainment of a tempera- 

 ture above that of dissociation, and we have evidence of the 

 early application of the electric arc to such a purpose. In 1807 

 Sir Humphrey Davy succeeded in decomposing potash by means 

 of an electric current from a "Wollaston battery of 400 elements, 

 and in 1810 he surprised the members of the Eoyal Institution 

 by the brilliant electric arc produced between carbon points 

 through the same agency. 



Magneto-electric and dynamo-electric currents allow of the 

 production of the electric arc much more readily and economically 

 than by the use of Sir Humphrey Davy's gigantic battery, and 

 Messrs. Huggins, Lockyer, Liveing, 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 effects 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 



