132 Prof. Arthur Sinithells on the 



Salts of the Alkalis. 



Salts of the alkalis (and, so far as I have examined them, of 

 the alkaline earths), when introduced into the separator by 

 means of the spray, impart their characteristic tint and 

 spectrum to each cone, but as the inner cone has a much 

 higher average temperature than the outer one it acquires by 

 far the brighter tint. 



These facts may be exhibited in a very striking way as 

 follows : — A mixed solution of cupric chloride and lithium 

 chloride is introduced into the sprayer feeding a separator with 

 air ; if the gas-supply be in excess, the undivided flame shows 

 a mixed colour due to the copper and lithium salts ; but if 

 now the gas-supply be diminished and the cones allowed to 

 separate, the inner cone appears bright crimson and the 

 outer one only green. The explanation of this is very simple: 

 the colour proper to the copper salt is, as we have seen, deve- 

 loped only in the outer cone, that due to the lithium salt in 

 both cones ; but in the upper one it is so faint as to be 

 entirely masked by the green of the copper salt. 



Concl 



usions. 



The experiments recorded in this paper afford some evi- 

 dence as to the validity of the view of the origin of flame- 

 spectra advocated by Pringsheim. If, as he concludes, the 

 flame-spectra commonly attributed to the alkali metals are a 

 direct consequence of chemical processes occurring in the 

 flame, the same is presumably true for the spectra of chemical 

 compounds such as those of copper and gold. As a matter 

 of fact chemical changes do accompany the production of the 

 spectra dealt with in this paper. Thus when cupric chloride 

 is introduced into the flame, we have the formation of cuprous 

 chloride and of cuprous oxide. The case of gold chloride is 

 more important. In the case of this salt the spectrum is 

 only developed when a large excess of chlorine or of hydro- 

 chloric acid and air are present ; in their absence a consider- 

 able quantity of a spray or dust of the salt may be passed 

 through the flame without giving any spectrum. The gold 

 chloride, in fact, can only be maintained at a temperature 

 sufficient to develop its spectrum when it is surrounded by 

 an atmosphere either of chlorine or of an equivalent mixture 

 of hydrochloric acid and oxygen. The gold-chloride mole- 

 cules, however, must not be regarded as remaining intact 

 under these circumstances, for where a dissociable salt appears 

 to be maintained in the undissociated state, through the 

 presence of an excess of one of the products of dissociation, 



