SECT. iv. SPECTRA OF COLOURED FLAMES. 133 



perfectly pure homogeneous yellow; potash gives a violet 

 light, strontia red, baryta green. The colour is given 

 out by the glowing atoms of the vaporized metals 

 sodium, potassium, strontium, and barium in a state of 

 violent ignition ; for as the salt and its metal give the 

 same colour and the same spectrum when ignited, it is 

 evident that the colour is independent of the oxygen of 

 the alkali. 



Sir David Brewster appears to have been the first who 

 analysed coloured light with a prism ; and in 1822 Sir < 

 John Herschel, besides having made a series of obser- ) 

 vations on coloured flames, had determined the spectra 

 of the muriates of strontia and lime, the ehlorides and 

 nitrate of copper and boracic acid ; and observes that 

 ' the colours thus communicated by different bases to 

 flame afford, in many cases, a ready and neat way of 

 detecting extremely minute quantities of them.' 6 



The same opinion was afterwards formed by Mr. Fox 

 Talbot, who after many experiments on metallic salts, 

 says in his paper, 7 that a glance at the prismatic spectrum 

 of a flame may show it to contain substances which it 

 would otherwise require a laborious chemical analysis to 

 effect. In that paper this gentleman noticed that the 

 glowing salts of lithium and strontium give a crimson or 

 red colour to flame so exactly of the same tint that if these 

 metals were in combination it would be impossible to 

 decide to which metal the colour is due. But when he 

 passed their respective lights through a prism, he found 

 that the bright lines on their spectra are entirely dif- 

 ferent. * The stf ontia flame,' he observes, ' exhibits a 

 great number of red rays well separated from each 

 other by dark intervals, not to mention an orange, 

 and a very definite bright blue ray. The lithia 



6 This prediction, made in his Treatise on Light published in 1826, has 

 been completely fulfilled by the discovery of four new metals by spectrum 

 analysis. 



7 Phil. Mag. Tol. iv. 1834, p. 114. 



