506 



Profs. Liveing and Dewar. 



[June 10, 



sensitive one for nitrocarbon compounds, but that cyanogen is far more 

 permanent under the electric discharge when mixed with a large bulk of 

 hydrogen than when the discharge is passed through cyanogen alone. 



In all the foregoing experiments the bands which Angstrom and 

 Thalen ascribe to hydrocarbons were always more or less plainly seen ; 

 and we have come to the conclusion that much more care than has 

 generally been thought necessary is needed if the last traces of 

 hydrogen and its compounds are to be removed from spectral tubes. 

 Indeed, we do not think that all water can be removed from apparatus 

 and reagents which do not admit of being heated to redness. To 

 illustrate this, we may mention one or two experiments. 



Into the bulb of a sparking tube similar in form to that of fig. 4, 

 but rather longer, some loose phosphoric anhydride was introduced and 

 then some well dried and redistilled carbon bisulphide. The end of 

 the tube having then been drawn out the carbon bisulphide was boiled 

 out in an oil-bath at a temperature of 200° C, and the tube sealed off. 

 On passing the spark without condenser the hydrocarbon bands were 

 discernible, and on putting on the condenser the hydrogen line C came 

 out plainly and was identified by comparison with an ordinary vacuum 

 tube containing hydrogen. One would have supposed that the phos- 

 phoric anhydride would have retained all the moisture, and that there 

 could be no other source of hydrogen in the tube. 



In another experiment a mixture of carbonate of sodium and boric 

 anhydride, previously to admixture heated red hot, was introduced into 

 one end of a piece of combustion tube, near the other end of which wires 

 had been sealed, and the open end drawn out ; the mixture was then 

 heated, and when it was judged that all the air was expelled, the tube 

 was sealed off at atmospheric pressure. On passing sparks through it 

 carbonic oxide bands and oxygen lines could be seen, but no hydrogen, 

 hydrocarbon, or nitrocarbon bands could be detected. It appears, 

 therefore, that the application of a red heat is likely to prove a more 

 effectual means of getting rid of moisture than the use of any desic- 

 cating agent. 



The first point we have had before us in these investigations is 

 whether the groups of shaded bands seen in the more refrangible part 

 of the spectrum of a cyanogen flame, of which the three which can be 

 detected by the eye are defined by us in our previous paper on this 

 subject by their wave-lengths (4600 to 4502, 4220 to 4158, and 3883 to 

 3850), are due to the vapour of carbon uncombined, or, as we con- 

 clude, to a compound of carbon with nitrogen. 



Now, the evidence that carbon uncombined can take the state of 

 vapour at the temperature of the electric arc is at present very imper- 

 fect. Carbon shows at such temperatures only incipient fusion, if so 

 much as that, and that carbon uncombined should be vaporised at the 

 far lower temperature of the flame of cyanogen is so incredible an 



