ADDENDA on SPECIF. ANALYSIS. JUXDULATORy FORCES. L I G H T. 



167 



the lens. The prism can be turned round its own axis 

 by the lever, d, and the tube, A, can be adjusted so as 

 to vary the angle with the brass tube, e; a small reflect- 

 ing prism is, when necessary, placed so as to cover half 

 the slit, s, and to reflect light from a second source so as 

 to form a second spectrum on the plate, as in Steinheil's 

 apparatus. 



" If the prism be so adjusted as to throw the solar rays 

 reflected from a heliostat upon the screen of the camera, 

 the wires which transmit the sparks from a Rhurnkorff 's 

 coil are placed in front of the uncovered portion of the 

 slit, and the two spectra are simultaneously impressed. 

 The solar beam is easily intercepted at the proper time 

 by means of a small screen, and the electric spectrum is 

 allowed to continue its action for two, three, or six mi- 

 iiutes, as may be necessary. 



"Although with each of the metals including pla- 

 tina, gold, silver, copper, iron, bismuth, cadmium, zinc, alu- 

 minum, magnesium when 

 the spark was taken in air, 

 decided photographs were 

 obtained, it appeared that 

 in each case the impressed 

 spectrum was very nearly 

 the same, proving that the 

 lines produced were not 



Platina and Solar Spectra. 

 those which were characteristic of the metal, but that 



they were the lines due to the incandescence of the air. 

 These bright lines, it ia important to observe, do not 

 correspond to any black lines in the solar spectrum, ap- 

 parently indicating the absence of nitrogen in the solar 



lere. 



"The peculiar lines of the metal seem to be chiefly con- 

 fined to the visible portion of the spectrum, and these 

 have little or no photographic power. 



" Metallic Spectra, thawing Correiponding Band*. 

 Fig. 163. Gold Spectrum. 



HI Mill! 



. . . 



Fig. 161. SUrer Spectrum. 





Fig. 1M. Copper and Solar Spectra. I 



H k 

 Fig. 160. Iron Spectrum. 



"This was singularly exemplified by repeating the 

 experiments upon the game metal in air, and in a con- 

 tinuous current of pure hydrogen. In these experiments 

 Fig. los. two iron or platina wires were 



I sealed into a bulb blown upon a 

 long narrow tube wliich conveyed 

 the gas under trial. Under these 

 circumstances, for example, iron 

 Iron Spectrum In Hydrogen, g^^ fa hydrogen a spectrum in 

 wliich a bright orange and a strong green band were 

 visible, besides a few faint lines in the blue. Although 

 the light produced by the action of the coil was allowed 

 to fall for ten minutes upon a sensitive collodion surface, 

 f Fociu ratbcr shorter than that of other photographs. 



Fig. 169. 



Fliilina Spectrum in Hydrogen. 



scarcely a trace of any action was perceiv ed (Fig. 168) ; 

 whilst in five minutes in the air, a powerful impression 

 with numerous bauds was obtained (Fig. 166). 



" Similar results were obtained with platina (Figs. 109 

 and 162). When carbonic 

 acid was substituted for 

 hydrogen, maintaining a 

 continuous current of 

 the pure gas during the 

 whole experiment, the 

 effect upon the sensitive 

 plate was scarcely more marked. 



" No photographic impression was obtained in ten 

 minutes of the brilliant red line produced by sending 

 the discharge of Rhumkorff's coil through one of 

 (K-issler's hyd"ogen vacua. 



"Fig. 170 shows a copy of the photographic spectrum 

 produced by the violet line of light obtained from one of 

 Fig. i;o. Oeissler's nitrogen vacua. 



The lines produced by the 

 different metals which are 

 characteristic of them, are 

 best displayed by using, as 



Nitrogen Vacuum Spectru n. AVheatstone did originally, 

 somewhat feeble electrical discharges. When, for in- 

 stance, the Leyden jar is introduced into the secondary 

 current of the Rhuinkorff 's coil, as practised by Grove, 

 the light is principally produced, as Alter and Angstrom 

 have shown, by the ignition of the atmospheric air, and 

 particularly by the nitrogen. The spectrum will appear 

 to be filled with brilliant lines, which are nearly the 

 same, whatever electrodes are used ; but if the Leyden 

 jar be removed, the characteristic bands of the metals 

 may be distinctly seen. Those of irou are only well seen 

 when the metal is red-hot, but not actually burning. 



"Most of the metals give, as was remarked by Masson, 

 a feeble continuous spectrum streaked by bright bauds 

 of varying intensity ; and this sombre ground is not due 

 to the ignition of the electrodes, as may be at once seen 

 by the iustaut change presented in the appearance of the 

 spectrum, if one of the electrodes does become iiicau- 

 dtsccnt. 



" It was early remarked by Mr. Talbot, that, in the 

 ipectra of coloured flames, the nature of the acid did not 

 influence the position of the bright lines of the spectrum, 

 which he found was dependent upon the metal employed ; 

 and this remark has been confirmed by all subsequent 

 observers. 



" But the case is very different in the absorption bands 

 produced by the vapours of coloured bodies. There the 

 nature of both constituents of the compound is essen- 

 tially connected with the production of absorption bands. 

 Chlorine combined with hydrogen gives no bauds by 

 absorption in any moderate thickness. 



" Chlorous acid and peroxide of chlorine both produce 

 the same set of bands ; while hypochlorous acid, although 

 a strongly coloured vapour, and containing the same 

 elements, oxygen and chlorine, produces no absorption 

 bands. Again, the brownish-red vapours of percliloride 

 of iron produce no absorption bands ; but iron, when 

 converted into vapour in a flame, gives out bands which 

 are independent of the form in which it occurs com- 

 bined. 



"These anomalies appear, however, to admit of an 

 easy explanation, if we suppose that in every case the 

 compound is decomposed in the flame, either simply by 

 the high temperature, just as Grove has shown that water 

 is. In other <-ases of the production of bright lines by 

 the introduction of a metallic salt into the flame of 

 burning bodies, the reducing influence of the hydrogen, 

 and other combustible constituents of the burning body, 

 would decompose the salt, liberating the metal, which, 

 aftei producing its characteristic lines, would immediately 

 become oxidised, and be carried off in the ascending 

 current. In the voltaic arc this decomposition must of 

 necessity take place by electrolytic action. 



" The compound gases, protoxide and deutoxide of 

 nitrogen, give, when electrified, the same series of bright 

 bands as Pliicker has shown, which their constituents 



