APPENDIX III. 



EMISSION SPECTRUM OF BURNING CARBON BISULPHIDE AND 

 CORRECTIONS TO THE WORK OF JULIUS. 1 



It is becoming more and more a recognized fact that the infra-red 

 spectrum is the seat of great disturbances which can be attributed to 

 well-known groups of chemical atoms or "ions." The pioneers in this 

 field of investigation were Angstrom and Julius. Their interest in the 

 subject dates back to the time when rock salt first became recognized as 

 a means for producing the heat spectrum. The dispersion of rock salt 

 was then undetermined beyond 5 /u, and in order to express their emis- 

 sion and absorption bands in wave-lengths they adopted a tentative 

 method of extrapolation, which, since then, has been found to be erro- 

 neous. In the meantime, data on infra-red spectra have continued to 

 accumulate, which are often in violent disagreement. For example, 

 CS 2 is variously quoted as having an absorption band at 6.7 to 8.4 ju, 

 while the true value is about 6.8 p. 



During the past few years the writer has attempted to determine the 

 values of the maxima of absorption and emission as accurately as pos- 

 sible in absolute value of wave-lengths, and thus bring a little harmony 

 out of this chaos. This means repeating part of the work of others in 

 order to get a check upon the extrapolation. One of the most interest- 

 ing pieces of work of this type is that of Julius, who found the emission 

 spectrum of gases during combustion. It contains a very considerable 

 amount of careful work, certain parts of which appear to have gone 

 quite unnoticed by later investigators. It is of no little interest, for it 

 contains evidence of emission bands farther in the infra-red than subse- 

 quent work, along other lines, has been able to show. These bands 

 belong to the acid elements and appear at low temperatures, i. c., they 

 do not appear in spark (and arc ?) spectra. This is just the opposite 

 of what the writer found for the basic elements (metals) in which no 

 emission bands were found beyond 2. p. Perhaps this may eventually 

 give us some clue to the mechanism of radiation. We have two sharp 

 distinctions between the acid and the basic elements. The metals have 

 selective absorption in the short wave-lengths, are opaque to infra-red 

 rays, and no emission lines have been found beyond 2 /*. In fact, accord- 

 ing to Pfliiger's work, the maximum of the emitted energy lies in the 

 short wave-lengths beyond the visible spectrum. On the other hand, the 

 acid elements have selective absorption bands throughout the spectrum 

 and have emission lines extending far into the infra-red, which gen- 

 erally coincide with the marked absorption bands. The question of the 



'Julius: Licht- und Warmestrahlung Verbrannter Case., Berlin, 1890. 

 118 



