APPENDIX VII. 



CORRECTION TO TH15 WORK OP JULIUS.^ 



At the time when Julius found the absorption spectra of some 20 

 compounds the dispersion of rock salt beyond 5 fx was unknown. Lang- 

 ley's (loc. cit.) dispersion curve extended to 5 /x, at which point it 

 became practically a straight line, and, since he had penetrated the 

 infra-red beyond this point, he naturally desired to know how far he 

 had explored the spectrum, expressed in wave-lengths. To do this he 

 tentatively extrapolated the dispersion curve in a straight line beyond 

 5 fi. Julius, with apparently less hesitation, has applied this extrapo- 

 lation to his work, which appeared about the same time, and has given a 

 table of wave-lengths of the absorption bands. As is well known now, 

 the dispersion curve suddenly becomes curved beyond 5 fi, and conse- 

 quently all the succeeding wave-lengths thus found are too large. 



All but seven of the compounds studied by him are recorded in this 

 work. The remaining seven were not examined, and to make the com- 

 parison complete the corrected values of the absorption bands of five 

 of the most important ones are given in the following table. The cor- 

 rection was made by drawing a straight line from 5 /*. The position of 

 this line was determined from the dispersion curve by comparing the 

 values of the maxima of compounds studied by both of us. For exam- 

 ple, for CoHgSH the band at 7.1 /^ on the dispersion curve was found at 

 a point above it (at 8.6 /a), while the 10.26 ju, band on the curve lies still 

 farther from the curve (at 16.5 /a). The maxima of numerous com- 

 pounds thus located lay quite close to the straight line drawn through 

 them, so that with few exceptions the difference in the values of the 

 maxima, as found by both observers, usually amounts to only from 0.02 

 to 0.05 fj-, depending upon the sharpness of the band. 



Compounds. 



PCI3... 

 CHBrs. 

 SiCU. . , 

 SiKCls 

 S2C2I. . . 



10.08 

 6.426 

 6.1 b 

 6.0 

 6.45 



o > 

 o 



7.840* 



5.82 

 5-64 



5-57 

 5-85 



12.4 



8.6 



6.8 

 II. 15 



9.656 



8.82 



7-1 

 6.1 

 8.27 

 7-63 



14.1 

 10.05a 

 II. I b 

 13.0 a 

 II. 8 



9.44 



7.82 

 8.27 

 9.04 

 8.58 



16.] 



12.7a 



13.06 



14.96 



12.9 



O > 

 V 



10.13a 



8.95 

 9.04 



9-74 

 9.0 



14.1 6 

 14.856 



14.056 



g.44 

 9-7 



g.42 



16.26 



10.16 



*Depth of bands is indicated by the letters a and 6, where a refers to the deepest band. 



ijulius: Verhandl. d. Kon. Akad. v. Wetensch. Amsterdam., Deel. I, Nr. i, 1892. 



Beiblatter, 17, p. 34. 



135 



