Luminosity of Gases. 125 



respectively to cuprous chloride, cuprous or cupric oxide, and 

 metallic copper. The spectrum previously attributed by him 

 to metallic copper was now ascribed to one of the oxides of 

 copper, and the chloride spectrum, though not particularized 

 in the text, is indicated on the map as being due to cuprous 

 chloride only. 



In 1865 Diacon published {Ann. Chim. Phys. [4] vi. 

 p. 1, 1865) a paper on " The Influence of the Electro- 

 negative Elements on the Spectra of Metals,''' in which he 

 maps and describes the spectrum of cupric chloride as pro- 

 duced in a coal-gas flame. He mentions that the spectrum is 

 due to the superposition of the spectra of oxide and chloride. 

 Lecoq de Boisbaudran, in his Spectres Lumineux (1874), 

 gives a map of the spectrum obtained from copper chloride 

 when the salt is introduced into a Bunsen-flame. In describ- 

 ing this map Lecoq de Boisbaudran distinguishes four cases 

 in the use of copper chloride for the production of spectra, 

 according to the quantity of salt employed and the length of 

 time it is held in the flame. The particular case mapped is 

 apparently given by the author as the one in which the normal 

 spectrum of cupric chloride is obtained. 



When in using the separator the spray of a dilute solution 

 of cupric chloride is supplied with the air, the outer cone 

 assumes a bright green colour ; the lower cone is unaffected 

 so far as the eye can judge (as soon as all air has been 

 removed by diffusion from the space between the tubes), and 

 nothing but the " candle " spectrum is seen in the spectro- 

 scope. If now a piece of asbestos soaked in hydrochloric 

 acid be introduced into the upper cone, the green colour is 

 replaced by a vivid blue. The same effect is obtained by 

 introducing hydrochloric-acid gas with the gas-supply by 

 means of the saturator. If the solution of copper chloride be 

 replaced by one of copper sulphate or nitrate, similar effects 

 are obtained. When these flames are examined by means of 

 the spectroscope, the sulphate and nitrate of copper are seen 

 to produce exactly the same result. The dilute solution of 

 CuCl 2 alone gives a spectrum containing the same lines and 

 bands as the nitrate and sulphate with the addition of other 

 faint bands. When hydrochloric acid is supplied, the blue 

 flame obtained gives a spectrum in which the lines and bands 

 common to the sulphate and nitrate are very faint, whilst the 

 additional lines just referred to as pertaining to the CuCl 2 

 flame are greatly intensified, and new lines also make their 

 appearance. Using cold hydrochloric acid, it is impossible 

 to entirely quench those lines which are found in the simple 

 sulphate and nitrate spectra. But if the hydrochloric-acid 



