JOO INFRA-RED REFLECTION SPECTRA. 



in solution. Stenger 1 found that it is only when a change in the aggre- 

 gation conditions or in the solving process is accompanied by a change 

 in the physical molecule that a change occurs in the absorption spec- 

 trum. One would expect similar conditions in the infra-red. In 

 Appendix IV of the first volume of this investigation a preliminary 

 examination was made of the transmission of several solids in solution, 

 and it was shown that the method is feasible for infra-red work. The 

 present examination by reflection is only preliminary, and was under- 

 taken primarily to learn whether possibly some of the sulphates, which 

 in the solid state have a single sharp maximum at 9.1 /A, really have 

 several bands, say at 8.6 and 9.6 /x, which for some unexplained reason 

 are merged into one. (There seems to be no reason why the sulphates 



^ 



Spectrometer slit "/X Plane mirror 



(Vertical) ir> i '[j -f 



' ^ // i ' 



ILjA-^-iJ) Vessel for liquids 



\ 'wgTin itirriS and position of 

 I comparison mirror 



\ I 



\ I 

 \ i 

 \ 

 \ t 



i.'srnst heater 



FIG. 83. Arrangement of apparatus for reflection from solutions. 



of Cd, Co, Ni, and Cu should have a single band, while those of Ba, Sr, 

 and Mg should have several bands.) Of course one would hardly 

 expect this to be the case, but preconceived ideas are often deceptive. 

 The constantly recurring bands of the sulphates at 4.5 to 4.6 /* and 



9.05 to 9.2 fj, reminds one of similar conditions in compounds containing 

 CH 3 groups. The adjustment of the apparatus is shown in fig. 83. 

 On account of the difficulty of adjusting the liquid to the level of the 

 silver comparison surface no attempt was made to obtain the absolute 

 reflecting power accurately. 



SULPHURIC ACID (H = SO 4 ). 

 (Concentrated. Fig. 84.) 



This substance was not examined for various concentrations, as 

 explained in Appendix II. 



The maxima occur at 8.6, 9.55, 10.42, and 11.35 /x. The fact that the 



8.6 [ji and 9.52 /x, band of H 2 SO 4 occurs in the hydrous and anhydrous 



1 Stenger: Ann. der Phys. (3), 33, p. 578, 1888. 



