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Profs. G. D. Liveing and J. Dewar. [Dec. 21, 



the spectrum of hydrocarbon flames is seen, and it increases in bril- 

 liance as the pressure of the gas is increased up to ten atmospheres, 

 and continues bright at still higher pressures so far as we have ob- 

 served, that is, up to twenty atmospheres. The spark without con- 

 denser in carbonic oxide at atmospheric pressure, shows both the 

 spectrum of carbonic oxide and that of the hydrocarbon flame ; and 

 as the pressure of the gas is increased, the former spectrum grows 

 fainter, while the latter grows brighter, no jar being used. The line 

 spectrum of carbon is also visible. At the higher pressures the flame 

 spectrum predominates and is very strong. The observations were 

 carried up to a pressure of twenty-two and a half atmospheres. On 

 letting down the pressure, the same phenomena occur in the reverse 

 order. All the parts of the flame spectrum, as seen in a Bunsen burner,, 

 are increased in intensity as the pressure is increased. The fact that 

 the effects of high pressure are so similar to those produced by the use 

 of a condenser at lower pressures, seems to point to high temperature 

 as the cause of those effects. But against this, we have the fact that 

 at reduced pressure we get in carbonic oxide, the carbonic oxide 

 spectrum and the line spectra of carbon and oxygen simultaneously, 

 without that of the hydrocarbon flame. As we cannot doubt that a 

 very high temperature is required to give the line spectrum of carbon, 

 we must suppose that reduced pressure is unfavourable to the stability 

 of the molecular combination, whatever it be, which gives the hydro- 

 carbon flame spectrum. Wesendonek has remarked (loc. cit.) that 

 in carbonic acid at pressures too low for the flame spectrum to be 

 developed without a jar, it is only in the narrow part of the tube that 

 the use of a jar brings out that spectrum. It would appear, therefore, 

 that the constraint, due to the confined space in which the discharge 

 occurs, has the same effect, in regard to the stability of the combination 

 producing the spectrum in question, as increase of pressure. 



Cyanogen Flame Spectrum. 



Our former observations " On the Flame Spectrum of Cyanogen 

 Burning in Air " were made on cyanogen gas, prepared from well-dried 

 mercury cyanide, which was passed over phosphoric anhydride, and 

 burnt from a platinum jet fused into the end of the tube. We ob 

 served what Plucker and Hittorf had noted, that the hydrocarbon 

 bands were almost entirely absent, only the brightest green band was 

 seen, and that faintly. When gaseous cyanogen is liquefied by the 

 direct pressure of the gas, the researches of Gore (" Proc. Roy. Soc," 

 vol. 20, p. 68) have shown that it is apt to be contaminated with 

 a brownish, treacley liquid, which probably arises from the imperfectly 

 purified or dried cyanide of mercury. In order to obtain pure cyanogen 

 we have prepared quantities of liquid cyanogen, not by compression, 

 but by passing the already cooled gas into tubes placed in a carbonic 



