of the Metals developed by Exploding Gases. 163 



in an iron tube shown in section in fig. 1, half an inch in 

 diameter, fitted at the end with a thick glass plate (a), held on 

 by a screw- cap (c) and made tight with leaden washers. 

 Small lateral tubes (d d), at right angles to the main tube, were 

 brazed into it near the two ends, for the purpose of connect- 

 ing it with the air-pump, admitting the gases, and firing 

 them. For this last purpose a platinum wire (b) fused into 

 glass was cemented into the small tube, so that an electric 

 spark could be passed from the wire to the side of the small 

 tube when the gases were to be exploded. 



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a ik 



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To bring out the lithium lines, a small quantity of lithium 

 carbonate in fine powder was blown into the tube before the 

 cap with glass plate was screwed on. Powder was used 

 because we supposed that it must be loose dust which would 

 be lighted up by the explosion. The lithium lines came 

 out bright enough, and it was unnecessary to put in any more 

 lithium for any number of explosions. The tube was of 

 course quite wet after the first explosion from the water 

 formed, but the lithium lines were none the less strong. 

 Indeed, after the tube had been very thoroughly washed out, the 

 lithium lines continued to be visible at each explosion, though 

 less brightly than at first. A good deal of continuous spec- 

 trum accompanies the flash which, from the overlapping of 

 spectra of different orders, makes observations difficult, so a 

 screen of red glass was used to cut this off when the lithium 

 red line was under observation. In any case, however, close 

 observation of the flashes is very trying, from the suddenness 

 with which the illumination appears and the briefness of its 

 duration. At first we compared the lithium line given by the 

 flash of the exploding gases with that produced by the flame 

 of a small Bunsen burner in which a bead of fused lithium 

 carbonate was held, both being in the field at once. While 

 the flame-line was sharply defined, the flash-line had a different 



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