Oct. 28, 1S80] 



NA TURE 



621 



: f the hottest known, from the large amount of heat evolved in 

 lie decomposition of cyanogen and nitric oxide, namely, 41,000 

 ind 43,300 units respectively. There is in the case of cyanogen, 

 s in the case of so many other substances, a difference iu the 

 ilative intensities of the different parts of the spectrum of the 

 ame at different temperatures, but no other change of character, 

 la the upper part of the flame where much or all of the cyanogen 

 [j oxidised or decomposed the spectrum is continuous, but at the 

 >ase of the flame \vhere it is issuing from tlie nozzle the cyanogen 

 lands are always seen both when the cyanogen is burning in 

 I'Xygen and when it is burning in nitric oxide. This is what we 

 liould anticipate, provided intermediate, and not the final, 

 i^ompounds are the active sources of the banded spectrum. 



Each of the five sets of bands shown in the diagram is attended 

 >n its more refranjible side by a series of rhythmical lines 



Extending to a considerable distance, not shown in the diagram, 

 lUt easily seen in the photographs. 



Coal gas burning in oxygen gives no bands above that near G 

 within the range of the diagram. Fig. i ; but beyond this 

 |] ihotographs show a spectrum of a character quite different from 

 that at the less refrangible end, which the authors have traced to 

 Ije due to water and described elsewhere {Proc. R. S., No. 205). 



The authors then describe experiments with carbon tetra- 

 ichloride, conducted with great care and numerous repetitions 

 because of the prominence given to an experiment with this 

 compound by Mr. Lockyer in a recent "Note on the Spectrum 

 kif Carbon," and because their results in every case difter from 

 those which he obtained. 



The form of sparldng tube employed w'as similar to that used 

 |l;y Salet. This was attached by thick rubber tubing to a 

 straight glass lube of which one half, about 6 inches long, was 

 ailled with phosphoric anhydride, and the other half with small 

 fragments of soda-lime to prevent any chlorine from the decom- 

 .posiiion of the tetrachloride by the spark from reaching the 

 Hprengel pump. The tetrachloride used had been fractionated 

 Rintil it had a constant boiling point of 77° C. Sufficient of it 

 ".vas introduced into the sparking tube to fill nearly one quarter 

 of the bulb at the end, and the whole interior of the tube 

 Ithoroughly wetted with it in order to facilitate the removal "of 

 Uie last traces of air. 



When the tube containing the tetrachloride had been so far 

 exhausted that little but condensible vapours were pumped out, 

 the bulb was heated so as to fill the apparatus with vapour of 

 tetrachloride, the pump still going, and this was repeated as long 

 as any incoudensible gas was extracted. Sparks were then 

 passed through the tube for a short time, the pump still being kept 

 going. After a short time it was unnecessary to keep the pump 

 going, as all the chlorine, produced by decomposition of the 

 tetachloride was absorbed by the soda-lime. On now examining 

 the spectrum, no trace of any of the cyanogen bands could be 

 detected, either by the eye or by photography, however the 

 ;park might be varied. The violet lines of chlorine described 

 by Salet were more or less visible, coming out brightly when a 

 condenser w'as used. Several tubes were treated in this way, 

 and many photographs taken, but always with the same result ; 

 no trace appeared of either the seven blue, the six violet, the five 

 idtra-violet, or of the still more refrangible bands of the cyanogen 

 flame. It is true that all the photographs showed three lines in 

 the ultra-violet, but these do not at all closely resemble the 

 cyanogen bands, they are not shaded like them. The least 

 refrangible of the three is coincident witli the middle maximum 

 in the ultra-violet set of five bands, but the other two do not 

 coincide with other of these maxima. When a condenser is 

 used, these three lines come out with much greater intensity, and 

 two other triplets appear on the more refrangible side, as well 

 as other lines. 



The general character of the violet part of the spectrum of the 

 spark in carbon tetrachloride taken without a condenser, but not 

 the exact position to scale of w^ave-lengths of all the lines, is shown 

 in Fig. 2. Fig. 3 shows the brightest of the additional lines 

 which come out with the use of a condenser. Photographs of 

 sparks taken in hydrochloric acid showed a precisely similar 

 group of ultra-violet lines, so that there is no doubt that the 

 three lines which the photographs show near the place of the 

 ultra-violet cyanogen bands are due to chlorine. 



Repeated trials iu which the arrangements were varied having 

 shown that pure carbon chloride, if free from nitrogen, does not 

 give any of the bands ascribed to compounds of carbon with 

 nitrogen, the next step was to determine whether the addition of 

 nitrogen would bring them out, and if so what quantity of 



nitrogen would make them visible. For this purpose the binding 

 of the rubber tube connecting to the pump a sparking tube con- 

 taining tetrachloride and found to give no cyanogen bands, was 

 loosened, and, after letting in very little air, immediately closed 

 again. On now passing the spark the six violet bands at once 

 appeared, and the seven blue bands also were in a short time 

 well seen. 



After trying some other experiments of a similar kind which 

 indicated that a very small r|uantity of nitrogen was sufficient to 

 develop the cyanogen bands in one of these tubes, a minute frag- 

 ment of bichromate of ammonia, carefully weighed and wrapped 

 in platinum foil, was introduced into the neck of one of the 



