i 7 8 



SELECTIVE REFLECTION BANDS. 



reflection maxima of the bands at 11.5 and 14.5 /x against the atomic 



weight of the base. From this it will be seen that the rate of shift of the 



band with increase in atomic weight of the base is greater for the bands at 



1 1.5 and 14.5 pt than for those at 6.6 and 7.0^, just as was found for the 



bands of the sulphates at 4.6 /ji, at 6.2 to 6.6 ft, and at 8.2 to 9.3 / (see 



figs. 44 and 45). 



Table X. 



Substance. 



Magnesite . . . 



Calcite 



Aragonite. . . . 

 Rhodochrosite 



Siderite 



Smithsonite . 

 Strontianite . 

 Witherite . . . 

 Cerussite .... 



Chemical 

 composition. 



MgC0 3 



CaCOs 



CaCOs 



MnCOs 



FeCOs 



ZnCOs 



SrC0 3 



BaC0 3 



PbCOa 



Atomic 



weight of 



base. 



24.2 

 39-7 

 39-7 

 54-6 



55-5 



64.9 



86.9 



136.4 



205.4 



Reflection maxima. 



Band i. 



6.5 M 



6.6 



6.65 



6.63 



6.60 



6.7 



6.76 



6.86 



7.2 



Band 2. 



Band 3. 



11. 2 M 

 II.31 



"55 



11.47 + 



11.47- 



11.38 



11.56 



11.60 



11.94 



T 3-9/* 



14.2 



14.2 

 14.0 



13-9- 



13.6 



14-37 



14-5 



14.8 



By arbitrarily selecting KN0 3 and AgN0 3 from the nitrates, Morse 

 found the line drawn through the maxima of the reflection bands was 

 "approximately parallel" to those of the carbonates (see fig. 43). More- 

 over, the line drawn through the maxima of the sulphates, at 8.6 to 9 //, 

 is also closely parallel with those of the carbonates. From this he was 

 led to suspect that the shift of the band with increase in the atomic weight 

 of the base is of the same order of magnitude in carbonates, nitrates, and 

 sulphates. If the data had been plotted to a larger scale, as the accuracy 

 of the values of the maxima seem to permit, then the lines would not even 

 be approximately parallel, as will be noticed in figs. 43 and 44. 



After examining the reflection and transmission spectra, one or both, 

 of over 300 substances, the observations lying in the region of the spectrum 

 from 0.5 to 30 + /*, I have found that it is an easy matter to work out all 

 sorts of fantastic relations, only to learn, after gathering more data, that 

 the whole thing was an illusion. For this reason it seems to me that the 

 linear relation between the weight of the element, combined with equal 

 amounts of oxygen in the acid radical found by Morse by arbitrarily 

 selecting maxima of reflection bands, is misleading. From the earliest 

 work of Abney and Festing to the latest (theoretical) work of Einstein, it 

 has been generally accepted that oxygen is the active element in causing 

 (at least in " sharpening ") certain bands, just as sulphur has been found 

 quite inactive. The great groups of chemically related compounds have 

 been found to have similar absorption and reflection spectra, but no sim- 

 ple relation could be established between the spectra of the groups of 

 compounds. The present simple relation results from selecting particular 

 reflection bands found in certain carbonates, nitrates, sulphates, and sili- 



