Il6 INFRA-RED ABSORPTION SPECTRA. 



(6) The spectra of groups of compounds are similar, and are char- 

 acteristic of the grouping adopted by chemists, as found by Abney and 

 Festing. 



(7) Carbohydrates have a characteristic spectrum, with absorption 

 bands at 0.83 to 0.86 /*, 1.67 to 1.72 n, 3.25 to 3.43 fi, 6.75 to 6.86^, and 

 13.6 to 14 /i. The first large absorption band in carbohydrates occurs 

 in the region of 3.2 /a, which is in general followed by a transparent 

 region from 4 to 5 /a. The work of Puccianti, in which he found that 

 all carbohydrates have an absorption band at 1.71 /*, while benzene 

 derivatives have two additional bands, at 2.18 and 2,49 /a, respectively, 

 has been confirmed on 18 new compounds. The 1.7 /* band deserves 

 especial notice. 



(8) In addition to the characteristic carbohydrate spectrum, certain 

 bands in it occur in positions which are close harmonics, the maximum 

 wave-length of each succeeding band being twice the preceding. The 

 question whether this is merely a coincidence or whether it is an exact 

 relation is not fully determined. To decide this question a larger dis- 

 persion will be necessary, while the spectrum will have to be explored 

 to 27.6 /x for the next harmonic. In the same manner more pairs of 

 bands will have to be located in the ammonia spectrum, etc., in order 

 to show that the constant difference of the wave numbers found is not 

 merely a coincidence, hence, that there is a true spectral series present. 



(9) The three isomeric xylenes have banded, " channeled," spectra, 

 in which the most important line in each group lies farthest toward the 

 long wave-lengths, in the order ortho, meta, para. In other words, 

 the ortho, in which the CHg-groups are the closest together in the ben- 

 zene ring, has the " head " of each group of bands lying farther toward 

 the infra-red than are the heads of the corresponding bands of the meta 

 and para compounds. This seems to indicate a resonance of electric- 

 ally charged particles (CHg), whose capacity is increased, whose period 

 becomes slower, and, hence, whose maxima are shifted toward the longer 

 wave-lengths, with a decrease in the distance between the particles. 



( 10) In many compounds numerous bands are in coincidence, which 

 would no doubt be found in different positions when using a larger dis- 

 persion. Other bands, like the one at 3.25 fi in benzene, in benzalde- 

 hyde, and in pyridine, or the 3.43 jx and 6.86 /x found in aliphatic com- 

 pounds, seems to point to a specific group of atoms as their source, or 

 to some " ion " or " nucleus " common to them. 



The most marked example of this type is phenyl mustard oil, in which 

 the vibration characteristic of the mustard oils at 4.78 fi is superposed 

 upon the vibration of the benzene " nucleus " or " ion," which has its 

 maxima at 3.25 /a, 6.75 /a, etc. In some compounds there is evidence 



