INVESTIGATION WITH A ROCK-SALT PRISM. 65 



This compound was studied in the vapor state, and also as a Hquid at 

 3.4 /i. No difference could be detected in the location of the 3.4 fx band 

 for the liquid and vapor phase. The acetone curve has a great similar- 

 ity to that of methyl acetate and methyl carbonate, especially at 4.75 /*, 

 5.75 [X, and 8 /i, but the great opacity and breadth of the absorption 

 bands prevents a minute study of them. The large spectrometer failed 

 to resolve the region at 3.3 jn, just as was found for the fatty acids at 7 jx, 

 and as Ransohoff found for the alcohols at 6 /x.. 



Methyl Carbonate. CO <q^J|'- (Fig. 47.) 



Like the preceding compound, methyl carbonate has an opaque 

 region, extending from 6 to 9 /t, but as a whole it is distinguished for 

 several sharp transmission minima. But few compounds have been 

 found that show such extraordinary variations in transparency and 

 opacity. The minimum at 12.65 l^ has a depth of 70 per cent. If this 

 sharpness and depth is due to the presence of oxygen, as mentioned in 

 discussing benzaldehyde, then the same is to be noticed here. The 3.5 /i 

 band is evidently complex. The 5.8 /i, band occurs strong and well 

 defined. The 8 ix band is to be noticed for the first time in considering 

 this group of compounds. This band is no doubt complex. 



CH2— COOC2H5 

 Ethyl Succinate. | (Fig. 48.) 



CHj— COOC2H5 

 As the structural formula shows, this compound is derived from 

 succinic acid, Co¥i^{COJA)2 (from amber), by replacing the H atom 

 by the C2H5 radical. The curve is conspicuous for its sharp transmis- 

 sion minima and a region of great opacity extending from 7 to 10 /x. 

 Other compounds, having great opacity in this region, have been 

 noticed. Eucalyptol is an excellent example for showing great opacity 

 followed by great transparency. But this compound is almost the only 

 one having a narrow opaque region, beginning abruptly at 7 /a and 

 ending just as abruptly at 10 /x, which is followed by a region of great 

 transparency, interspersed by deep, narrow transmission minima. The 

 5.85 IX band is large, which is unusual except in the fatty acids. 



These last four compounds were selected in order to learn the effect 

 of the different combinations of O and CH3 upon absorption spectra. 

 It will be noticed that the whole spectrum undergoes a change, except 

 the region at 3.4 fx, which is not seriously disturbed. 



COMPOUNDS CONTAINING SULPHUR. 



The sulphur compounds represent the earliest work on absorption 

 spectra, when the approximate coincidence of the absorption bands of 

 sulphur and carbon disulphide, at 1 1.7 /x, presented the question whether 



