SPECTROSCOPIC SPECTRA. 503 



flame ; in the Bunsen flame it is scarcely seen. This blue 

 strontium line is really single, and appears so even in 

 larger spectroscopes, but the red band resolves itself 

 when the dispersion is greater into a number of lines of 

 various shades of red. The bands of the barium 

 spectrum show a similar behaviour. Barium chloride, 

 very suitable for the experiments, may be bought at 

 any chemist's. Strontium chloride, the corresponding 

 strontium compound, is not so easily obtained, but stron- 

 tium nitrate may be substituted, which, on account of 

 its use in making red fireworks, may be readily bought. 

 A very small quantity of it is taken up by the wire, and 

 moistened with hydrochloric acid if the flame ceases to 

 be coloured. 



The various compounds of one and the same sub- 

 stance are not volatilised with equal readiness ; the more 

 volatile compound is in general the best for the purpose 

 of spectrum analysis. Besides the six substances above- 

 mentioned only a few more, and those comparatively 

 rare, can be volatilised in the flame of burning hydrogen ; 

 but many other substances, for example, most metals, 

 may be brought to the state of ' incandescent,' that is 

 luminous, vapour by the heat of a powerful electric spark. 

 Many others again for example,hydrogen itself-^-which 

 are already in a gaseous state, require the heat of the 

 electric spark in order to be raised to the high tempe- 

 rature at which the light emitted by them is easily per- 

 ceptible. Every substance, which by any means what- 

 ever is brought to the state of vapour (or of a gas), gives 

 out its own spectrum, consisting of definite lines by 

 means of which it may be recognised and distinguished 

 from other substances. 



