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bands of the spectrum, the position of which is measured), we get a 

 new kind of chemical analysis. In this way only we may ascertain 

 the residual contents of the exhausted tubes, and the changes they 

 undergo, either suddenly by the discharge, or gradually afterwards. 

 Thus, for instance, a spectrum-tube in which traces of vapour of 

 sulphuretted carbon were enclosed, presented most unexpectedly the 

 combined spectra of hydrogen and oxide of carbon. Hence we con- 

 clude that there remained also within the tube some traces of vapour 

 of water, which was decomposed as well as the sulphuretted carbon. 

 Traces of sulphur were deposited on the interior surface of the tube, 

 while oxide of carbon and hydrogen remained within it. 



Nearly all examined combinations of hydrogen with metals, with 

 chlorine, &c., were almost instantly decomposed. The spectrum of 

 hydrochloric acid was found to be the combined one of hydrogen and 

 chlorine. Sulphur and arsenic were deposited from their combi- 

 nations with hydrogen, the former constituting fine dendrites, the 

 latter well-defined large bands : the spectrum in both cases was that 

 of pure hydrogen. Seleniated hydrogen showed within the capillary 

 tube a fine yellow tint, but this tint was converted during the passage 

 of the discharge into a brilliant red one ; the change of colour started 

 from one of the extremities of the capillary tube, and reached the 

 other one after a few seconds. The spectrum observed during this 

 change of colour was in the first moment a most distinct one, showing, 

 for instance, between H/3 and Hy two similar systems of two brilliant 

 blue bands separated by a black one about double as large ; but this 

 spectrum entirely disappeared, as in dissolving views, being by and 

 by replaced by the spectrum of hydrogen. A few minutes after the 

 discharge was stopped the red colour turned again into the primitive 

 yellow one, the gas decomposed by the discharge having been re- 

 composed again. Thus the same experiment could be repeated any 

 number of times. 



[Similar chemical effects were ascertained in a different way in the 

 case of sulphurous acid, which, if included within a larger tube, shows 

 a fine stratification of narrow .violet bands. When the discharge 

 passes during several minutes, the stratification is altogether 

 changed, the narrow violet bands being transformed into the large 

 clouds of the best Torricellian vacuum tubes. The primitive condi- 

 tion of the gas is restored by heating the electrodes ; but in every 



