of the Metals developed by Exploding Gases. 167 



ascribed to the oxide of copper. The green line of copper 

 had been observed in the flash before the copper lining was 

 put into the tube; and we concluded that the copper was de- 

 rived from the brass with which the small lateral tubes were 

 fastened into the large tube, or that the iron of the tube con- 

 tained a little copper. When the leaden lining was used, only 

 one visible line of lead was developed, and that was the strong 

 violet line, but two ultra-violet lines between M and N were 

 strongly depicted on the photographic plates. The violet line 

 of lead had also been observed in many of the photographs 

 taken before the leaden lining was introduced. This we 

 ascribed to the leaden washers used to make the glass or 

 quartz plates air-tight. The line was greatly increased in 

 strength by the leaden lining. The zinc lining gave no 

 visible line at all, notwithstanding the easy volatility of the 

 metal; and in the ultra-violet it gave only a very doubtful 

 impression of one of the lines near P. The cadmium, alumi- 

 nium, and tin linings gave no lines at all. Zinc dust put 

 into the tube gave no zinc lines, merely increased the conti- 

 nuous spectrum, and speedily rendered the quartz end opaque. 



A clean wire of magnesium put into the tube gave the b 

 group of lines, but no other line. No trace of the blue line, 

 so conspicuous in the flame of burning magnesium, nor of the 

 triplets near L and S, nor of the very strong line, the strongest 

 of all in the arc, at wave-length 2852. b x and b 2 were well 

 seen; but as b± is an iron line, as well as a magnesium line, 

 and the iron line was visible in the flash before the magne- 

 sium wire was introduced, we cannot be sure whether the 

 magnesium line, as well as the iron line, was present in the 

 flash. Magnesia did not develop any line at all; merely 

 augmented the continuous spectrum. 



Compounds of sodium, such as the carbonate and chloride, 

 introduced in powder gave the ultra-violet line between P 

 and Q strongly, frequently reversed ; but no other line except 

 of course D. Potassium compounds developed, often reversed, 

 the pair of violet lines, and also the ultra-violet pair near 0, 

 but no others. 



A strip of silver developed two ultra-violet lines, one on 

 either side of P; but we could not detect in the flash the well- 

 known green lines of that metal. When powder of silver 

 oxalate was introduced, the yellowish-green line (w.l. 5464) 

 was seen at the first explosion but not afterwards. As silver 

 oxalate is itself an explosive compound, decomposing with an 

 evolution of heat, it is reasonable to ascribe the appearance of 

 this line at the first explosion to the extra temperature so 

 engendered. 



