﻿654 



Mr. St. Landau-Ziemecki on the Emission 



heated, showed the ordinary band spectrum. The temperature 

 being raised to 960°-1000° C, the conditions o£ the electric 

 excitation remaining the same, a new line spectrum replaced 

 the band spectrum. The appearance of that spectrum is 

 quite different from the appearance of the spectrum obtained 

 in a narrow tube with condensed discharges. It consists of 

 relatively few lines; two lines in the ultra-violet are especially 

 strong and characteristic ; the others are faint. 



Some details of the experiments may now be given. The 

 iodine was introduced into the tube by sublimation in the 

 following way. Pure iodine of commerce (Kahlbaum) was 

 re-sublimated in vacuo; the crystals were then put into the 

 glass tube R a (fig. 2), which was to the right connected with 

 the mercury Gaede pump and to the left with the quartz 

 apparatus. Quartz and glass were joined together with 



Fig. 2. 



ground surfaces ; sealing-wax made that joint perfectly 

 tight (W, fig. 2); The apparatus was exhausted during two 

 hours. During that time the U-tube was immersed in solid 

 C0 2 to prevent the iodine vapour from penetrating into the 

 pump ; at the same time the quartz part of the apparatus, 

 which was previously chemically cleaned, was now heated in 

 the most energetic manner with a Bunsen burner and finally 

 with a blow-pipe. The apparatus was then cut away from 

 the pump at P 1? and the iodine sublimated from R x to R 2 , 

 this part being immersed in liquid air. After some hours, 

 R 3 was in turn immersed in liquid air, and a crust of iodine 

 crystals was formed there. Every precaution against con- 

 tamination having been taken, the quartz part of the 

 apparatus was again put in communication with the pump, 

 and after an exhaustion of half-an-hour ; s duration the quartz 

 apparatus with the iodine crystals at R 3 was cut away from 

 the pump at P 2 . The Geissler tube obtained was put in the 

 electric oven shown in fig. 1, and finally bent with the coal- 

 gas oxygen flame in the desired manner. The tube was 

 provided with external electrodes formed by tinfoil cemented 

 to the quartz with a mixture of graphite powder and water. 



