Luminosity of Gases. 127 



effects, and to determine if possible to what definite compound 

 each particular effect was due. 



The effect of introducing a bead of cupric chloride into a 

 Bunsen-flame has been carefully described by Lecoq de 

 Boisbaudran {Spectres Lumineux,^. 156). As already stated, 

 he distinguished four cases, but of these we need only take the 

 first, in which a large quantity of salt is used. The salt first 

 melts, and then in a few moments is seen to be surrounded 

 by a brilliant patch of yellow, like a piece of ordinary candle- 

 flame ; the exterior parts of this patch are reddish (again 

 resembling carbon luminosity). Outside the yellow a bright 

 blue colour appears, and outside this the flame is coloured 

 green. The yellow luminosity is of short duration, the blue 

 lasts longer, but soon the only tint remaining is the green. 



These three effects were so local and distinct that it seemed 

 possible to collect the substances to which they were due, 

 and this was done by holding in the flame glass or porcelain 

 basins filled with water. The deposit obtained in this way 

 from the yellow part of the flame was red in colour, it trans- 

 mitted greenish light, it could be burnished, it dissolved in 

 nitric acid with evolution of red fumes, and in fact answered 

 in every respect to metallic copper. The yellow luminosity 

 observed with a large quantity of cupric chloride in a Bunsen- 

 flame must, therefore, be attributed to the liberation and 

 incandescence of minute particles of solid copper. 



The deposit obtained from the blue part of the flame was 

 of a very pale yellow colour when freshly formed. On 

 standing or by breathing upon it, the film absorbed moisture 

 and became quite w r hite : it answered in all its properties to 

 cuprous chloride containing a little of the cupric salt. 



The green part of the flame produced a deposit which was 

 almost black and corresponded in appearance and chemical 

 properties to cupric oxide. As the film was very thin, the 

 possibility of it having been originally cuprous oxide and 

 having subsequently oxidized was not excluded. 



From these experiments it is obvious that the three distinct 

 colour-effects noticeable wdien cupric chloride is introduced 

 into a Bunsen-flame correspond to three different substances, 

 viz., metallic copper, cuprous chloride, and an oxide of copper. 



It is highly improbable from a chemical point of view that 

 cupric chloride when introduced into a flame should afford a 

 spectrum. The easy decomposability of this salt and the 

 stability of cuprous chloride (wdiich is volatilizable without 

 change) would lead one to anticipate the decomposition of 

 CuCl 2 into Cu 2 Cl 2 and Cl 2 long before there could be any 

 question of incandescence. That this is the case can be 



