1882.] 



On an Arrangement of the Electric Arc, 8fC % 



119 



But although these experiments seem to lead to this conclusion, 

 more extended researches with other gases of the same nature, using 

 the same precautions, will have to be made, before the real form of 

 the curve can be ascertained. 



This investigation has been carried out in the Laboratory of the 

 Royal Institution. 



X. " On an Arrangement of the Electric Arc for the Study 

 of the Radiation of Vapours, together with Preliminary 

 Results." By G. D. Liveixg, M.A., F.R.S., Professor of 

 Chemistry, and J. Dewar, M.A., F.R.S-, Jacksonian Pro- 

 fessor, University of Cambridge. Received June 8, 1882. 



In previous papers* we have described various devices for facilitat- 

 ing the study of the reversal of the lines of metallic vapour. The 

 first series of observations were made by examining the spectrum of 

 the interior of iron or porcelain tubes filled with vapour and heated 

 to the highest temperature of a coke furnace, the subsequent series 

 being eye or photographic records of the radiation of the electric arc 

 surrounded by metallic vapour in the middle of blocks or tubes of 

 lime or magnesia. 



By inclosing the arc in a crucible of lime or magnesia we have 

 found its steadiness very greatly increased, and the mass of metallic 

 vapour which can be maintained at a temperature approaching to 

 that of the arc much enlarged, but it cannot be said that that tem- 

 perature is at all under control, and the walls of the crucible are 

 almost always cooler than the contents. By the arrangement we have 

 now to describe we are able to make observations through a long 

 range of temperature, as the temperature rises and as it falls, and so 

 to trace the influence of temperature in many cases in which the 

 extent of that influence was before doubtful. The temperature 

 attainable is doubtless far below that of the arc, but still it is quite 

 sufficient to maintain iron and aluminium in the state of vapour, and 

 show the reversal of the lines of these elements with singular sharp- 

 ness. The temperature of the interior is sufficiently high to transform 

 the diamond into coke, even in a current of hydrogen, and the result 

 may be taken as proving that the temperature is above that of the 

 oxyhydrogen flame. 



The apparatus employed is thus constructed : A rod of carbon, a in 

 the figure, 15 millims. in diameter, perforated down its axis with a 

 cylindrical hole 4 millims. in diameter, is passed through a hole in a lime 



* " Proc. Roy. Soc," " On the Reversal of the Lines of Metallic Vapours,'' 

 vols. 28, 29, 32. 



