62 INFRA-RED ABSORPTION SPECTRA. 



in its stead is a large band at 10.5 jx. It will thus be seen that the three 

 large bands of CH3I occur in slightly shifted positions in CgHgl, and, 

 in addition to this, they are also more prominent in the latter. The bands 

 from 3-4/* to 6/* are more prominent in this compound, while beyond 

 12 fx several new ones occur. As a whole there are a greater number 

 of transmission minima in C2H5I than in CH3I, which is to be expected, 

 if absorption depends upon the groups of atoms in the molecule. The 

 14 /x band is overshadowed by the one at 13.6/1,. With the 0.05 mm. 

 film, the band at 7.15 /a occurs at 7.06)11, the side's appearing unsymmet- 

 rical. In photographic spectra such examples of the blurring of the 

 band is of frequent occurrence. As with other compounds, no shifting 

 of absorption bands could be detected. 



Ethyi^ Alcohol (Absolute). C2H5OH. (Fig. 38.) 

 As already mentioned, a number of alcohols have been examined by 

 Julius and found to become suddenly opaque at 7 fx, due to thickness 

 of the cell of 0.2 mm. The curves (fig. 38) explain this, as will be 

 noticed in the great opacity which extends from 7 to 10 /x, beyond which 

 there is a transparent region at 10.5 ju., and again opacity beyond 13 /a. 



Puccianti^ has also examined this compound and several of the iodides 

 up to 2.5 fx. He found that all compounds in which carbon is directly 

 united with hydrogen showed absorption maxima at 1.71 /a. In the 

 above curve there is a slight depression at 1.6 jx, which represents the 

 band found by him, but, on account of the narrowness of the dispersion 

 in this region, no attempt has been made to adjust this disagreement. 

 This obliteration of the band is due entirely to the overlapping of the 

 slit, on account of narrow dispersion. The 3.45 ix band is broad for the 

 0.18 mm. cell, but appears complex for the 0.04 mm. cell. No doubt 

 the 7.3 IX band is likewise a composite of two or more bands, which 

 would be resolved with greater dispersion. The 5.95 fx band is only a 

 slight depression. The curve is of importance in showing the freedom 

 from water, which the alcohols so easily absorb. Ordinary ethyl alco- 

 hol and glycol were found to be opaque beyond 7 fx, using a thin film, 

 like the one above. At its best, however, alcohol is very opaque to 

 infra-red radiation, as seen in curve a, 0.18 mm., which is opaque at 

 6 IX, and continues thus. Curve h, 0.02 mm. thickness, was repeated, 

 using a new film to be certain that the transparency at 8.5 /x and 10.5 /x 

 is real. This sample had been treated with sodium and contained per- 

 haps about 0.4 per cent of water. There is quite a contrast between this 

 compound and the others considered in this group, all of which are much 



ipuccianti, loc. cit. 



