1881.] on the Origin and Identify of Spectra. 681 



" I beg pcrmissiou, therefore, in the meantime, to submit to the 

 notice of the Society an experiment with a tube containing QC\^* 

 which, I tliink, establishes the conclusions arrived at by prior 

 investigators. And I may add that it is the more important to 

 settle the question, as Messrs. Liveing and Dewar have already based 

 upon their conclusions theoretical views of a kind which appear to 

 me calculated to mislead, and which I consider to have long been 

 shown to be erroneous." The following experiments have been made 

 to test the accuracy of our previous work, and to confirm or disprove 

 Mr. Lockyer's views. 



The form of sparking tube employed was similar to that used by 

 Salet. This was attached by thick rubber tubing to a straight glass 

 tube of which one half, about 6 inches long, was filled with phosphoric 

 anhydride, and the other half with small fragments of soda-lime to 

 prevent any chlorine from the decomposition of the tetiachloride by 

 the sj^ark from reaching the SjDrengel pump. The tetrachloride used 

 had been prej^ared in our own laboratory, and fractionated until it 

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

 into the sparking tube to fill nearly one quarter of the bulb at the 

 end, and the whole interior of the tube thoroughly wetted with it in 

 order to facilitate the removal of the last traces of air. 



When the tube containing the tetrachloride had been so far ex- 

 hausted that little but condensible vapours were pumped out, the 

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

 chloride, the pump still going, and tliis was repeated as long as any 

 incondensible 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 tetrachloride was absorbed 

 by the soda-lime. On now examining the spectrum, no trace of any 

 of the bands we ascribe to nitrocarbons could be detected, either by 

 the eye or by photograj^hy, however the spark might be varied. The 

 violet lines of chlorine described by Salet were more or less visible, 

 coming out brightly when a condenser was used. Several tubes were 

 treated in this way, and many j^hotographs taken, but always with 

 the same result ; no trace appeared of either the seven blue, the six 

 violet, the five ultra-violet, or of the still more refrangible bands of 

 the cyanogen flame. All the pliotographs showed three lines in the 

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

 as they are not shaded. The least refrangible of the three is nearly 

 coincident with the middle maximum in the ultra-violet set of five 

 bands, but the other two do not coincide with any 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 refran- 

 gible side, as well as other lines. In order to compare the positions 

 of these lines with the cyanogen bands, we have taken several 



* Carbon tetrachloride. 



