APPENDIX II. 



ADDITIONAL DATA. 



\s this work goes to press the experiments on selective reflection by 

 Pfund 1 has appeared, and since it contains considerable new data it is 

 added for the sake of completeness. In fact, sulphuric acid was not 

 thoroughly examined by the writer when he learned that another was 

 working in the same field, although the examination of the sulphates 

 demanded it. The sulphates given in the appended table furnish addi- 

 tional evidence of the presence of bands due to the SO 4 ion. Further- 

 more, the nitrates have a band at 7.45 p which the writer found in 

 several nitro derivatives 2 of benzine. He was uncertain, however, 

 whether it was caused by the NO, group or "ion." In the same man- 

 ner, the 7.4 fj. and 9 ^ reflection bands of nitroso dimethyl aniline coincide 

 with the bands found by transmission at 7.4 and 8.9 p. The transmission 

 curve is very low, and probably most of the bands observed are really 

 due to selective reflection. Again, glycerin has a reflection band at 9.7 /x, 

 which is one of the characteristic bands of the alcohols as found by 

 transmission. No doubt the large absorption bands found by the writer 

 in ethyl succinate from 7 to 8 /*, in cyanine at 6.6 and 13.2^, and in 

 methyl salicylate at 7 to 9 p,, are really due to selective reflection, but 

 this material was not at hand when the present reflection work was 

 done. In fact, it is what one would expect to find for such large bands, 

 although there are no data to indicate the necessary size of the extinc- 

 tion coefficient to cause selective reflection. His interesting experiments 

 showing that a substance in a liquid and in a solid state has the same 

 absorption (reflection) maxima is further proof of what the writer 

 found for the absorption bands of several carbohydrates, such as thymol, 

 paraffin, stearic acid, phenol, and menthol at 3 p., and is, of course, to be 

 expected so long as the "physical molecule" is unchanged, as announced 

 long ago by Stenger. Of more importance are his experiments with 

 sulphuric acid, in which several bands disappear on dilution, which 

 may help clear up a similar case observed by Kriiss in the visible spec- 

 trum. His reflection curves for fuming sulphuric acid show maxima at 

 7.25, 8.6, and 10.35^, while the writer found absorption maxima at 7.4, 

 8.7, and 10.37 A* f r sulphur dioxide (SO 2 ). This is an extraordinary 

 coincidence which, it is true, is apparently not very close for the first 



1 Pfund : Astrophys. Jour., 24, p. 19, 1906. 

 1 Investigations of Infra-Red Spectra, vol. i, p. 86. 

 116 



