102 Mr. W. M. Watts on the Spectra of Carbon. 



rature 2250° C.) gives the D lines only. It melts gold but not 

 platinum. 



We may therefore employ the line Na /3 as a test of tempera- 

 ture indicating a temperature at least 2000° C. 



Certain lines of the lithium spectrum may be employed for 

 the same purpose. In the Bunsen burner, a bead of lithium- 

 chloride gives a spectrum of one red line whose wave-length is 

 about 6684. The flame of coal-gas fed by a jet of air shows, 

 besides the red line, an orange line whose wave-length is about 

 6107. In the flame of coal-gas and oxygen a blue line (4605) 

 is added; and in the electric arc a fourth line (4921) becomes 

 visible. All these lines can be obtained by means of lithium- 

 chlorate in the Bunsen-flame. 



A vacuum-tube containing coal-gas gives the same spectrum 

 as if carbonic oxide or olefiant gas were employed, viz. the spec- 

 trum C II. This experiment was repeated with a coal-gas tube 

 containing pieces of metallic sodium. At first the spectrum was 

 that of carbon, as previously described ; but as the tube became 

 heated by the continued discharge, the line Na /3 came out fol- 

 lowed by the lines 7, 8, and e, and the carbon-lines faded away 

 till ultimately the sodium-spectrum of five lines alone remained. 

 During this change the carbon-lines and the sodium-lines were seen 

 together ; and as the temperature to which the sodium-vapour 

 was heated cannot be supposed to be different from that to which 

 the carbon-vapour was heated, it follows that the spectrum C II. 

 may be produced by carbon heated above 2000° C. 



It is to be observed also that this spectrum may be produced 

 by carbon heated not much above 2000° C, since it was obtained 

 together with C /3 and without C 7, which comes out under 

 3000° C. 



Carbon-spectrum No. I. is given by the blue cone of the 

 Bunsen flame, the temperature of which cannot be much above 

 1500° C, and is certainly less than 2000° C. ; and the same 

 spectrum (with the addition of two new groups of lines, fand 6) 

 is obtained at all temperatures up to that of the cyanogen-flame 

 in oxygen, or probably 10,000° C. We have thus two quite dif- 

 ferent spectra, each of which has been shown to be due to carbon 

 itself, and not to any compound of carbon, which are proved to 

 be obtainable at the same temperature. In the case of the six dif- 

 ferent spectra of hydrogen described by Wiillner*, which are all 

 obtained by the electric discharge in gas at different pressures, 

 w r e may suppose the differences to be due to difference of tempe- 

 rature ; but in the case of the carbon-spectra we are forced to 

 some other explanation. It is worthy of remark that, while the 

 spectrum C II. is obtained only by the use of electricity, the 

 * Pogg. Ann. vol. cxxxvii. p. 337. [Phil. Mag. May 1870, p. 366.] 



