500 



Profs. Liveing and Dewar. 



[June 10, 



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 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 photo- 

 graphy, 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 photographs 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. It 

 is true that all the photographs showed three lines in the ultra-violet, 

 but these do not at all closely resemble the nifcrocarbon bands, they 

 are not shaded like the nitrocarbon bands. The least refrangible of 

 the three is coincident with 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. In order to compare the 

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

 photographs of the spark in tetrachloride simultaneously with a cyano- 

 gen flame, the latter being thrown in by reflexion in the usual way. 

 Wratten and Wainwright's instantaneous dry plates were used, and 

 gave a strong picture of the cyanogen flame after three seconds' ex- 

 posure, but in order to ensure getting a picture of all the lines which 

 the spark could produce, we gave an exposure of three minutes to the 

 spark. Not one of many photographs so taken showed any traces of 

 the cyanogen bands. The general character of the violet part of the 

 spectrum of the spark in carbon tetrachloride taken without a con- 

 denser, but not the exact position to scale of wave-lengths of all the 

 lines, is shown in Diagram 1, fig. 2. Fig. 3 of the same diagram 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 we have no 

 doubt that the three lines which our photographs show amongst the 

 five ultra-violet nitrocarbon bands are due to chlorine. 



A bulb tube was next partly filled with tetrachloride, the en d drawn 

 out to a long narrow neck, and the tetrachloride boiled out in an oil- 

 bath (150° C.) so as to expel all air, and the tube sealed off. This 

 tube likewise showed no nitrocarbon bands. 



