1879. J on S})cctro8Cop{c Investigation. 205 



spectra in the caso of antimony, phosphorus (?), sulphur, and arsenic 

 (probably). " As the temperature employed for the volatilization 

 of the metals did not exceed bright redness, or that at which cast 

 iron readily melts, the range of metals examined was necessarily 

 limited ; and in order to extend these observations to the less fusible 

 metals, as well as to ascertain whether the spectra of those vola- 

 tilized at the lower temperature would be modified by the application 

 of a greater degree of heat," a now series of experiments were 

 undertaken by Lockyer and Koberts, in which the combined action 

 of a charcoal furnace and the oxy-hydrogen blowpipe was employed. 

 A lime crucible after the form of Stas was used to replace the iron 

 tube. By this means they obtained still no new reversal of a metallic 

 line, but they observed channellcd-space spectra in the cases of silver, 

 manganese, chromium, and bismuth. They observed, however, that 

 the metal thallium gave the characteristic bright green line, the light 

 of the arc not being reversed. 



In the above-mentioned experiments, the coolness of the ends of 

 the tube, which acted as condensers of the metallic vapours, and the 

 continual change of density and temperature necessarily produced by 

 the maintenance of a current of hydrogen through the tube, appear 

 to account for the failure in observing reversals. 



The following facts have been acquired during the course of a 

 long series of conjoint experiments with my distinguished colleague, 

 Professor Liveing, of Cambridge.* 



In order to examine the reversal of the spectra of metallic vapours, 

 it is more satisfactory to observe the absorptive effect j)roduced on 

 the continuous spectrum emitted by the sides and end of the tube in 

 wliich the volatilization takes place. For this purj)ose it is convenient 

 to use iron tubes about half an inch in internal diameter, and about 

 27 inches long, closed at one end, thoroughly cleaned inside, and 

 coated on the outside with borax, or with a mixture of plumbago and 

 fireclay. These tubes are inserted in a nearly vertical position in a 

 furnace fed with Welsh coal, which will heat about 10 inches of the 

 tube to about a welding heat, and observations are made through the 

 upper oi)en end of the tube, either with or without a cover of glass 

 or mica. To exclude oxygen, and avoid as much as possible variations 

 of temperature, hydrogen is introduced in a gentle stream by a narrow 

 tube into the upper part only of the iron tube, so that the hydrogen 

 floats on the surface of the metallic vapour without producing convec- 

 tion currents in it. By varying the length of the small tube con- 

 veying the hydrogen, the height in the tube to which the metallic 

 vapour reaches may be regulated. Thus dillereut depths of metallic 

 vajDour may be maintained at a comparatively constant temperature 

 for considerable periods of time. The general plan of the apparatus 

 is given in Plate I. (at the end of the paper). 



" On the Reversal of the Lines of MetalUc Vapours," Nos. I., II., III., IV., V., 

 VI., 'Proc. Key. See.,' 1878-1870. 



