DESCRIPTION OF APPARATUS AND METHODS. 3 1 



pounds containing CHs-groups, and, hence, ascribed it to this group. 

 As a standard for judging the effect of the OH radical in certain com- 

 pounds, the water bands found by Aschkinass^ at 3 /a and 6 fx were 

 selected. Ransohoft',^ in his study of several alcohols, had tacitly con- 

 cluded that the band at 3 )u, was due to the OH radical. Such conclu- 

 sions in regard to the CH3 and OH groups seemed contradictory to the 

 work of Angstrom and Palmer/ who found that the chlorine band at 

 4.28 fx does not occur in the six chlorine compounds investigated by 

 Julius. The latter had previously shown that the chemical atom lost 

 its identity in a compound, so that one can not foretell the absorption 

 spectrum of a compound from a knowledge of the spectra of the con- 

 stituent elements. 



In the detailed study of each compound the chemical properties will 

 constantly be noticed. In some cases it will be found that certain chem- 

 icall}' related compounds, especially groups like the fatty acids, or the 

 mustard oils, give similarly related absorption spectra, while others 

 which are unusually similar in their physical properties, e. g., benzene 

 and thiophene, show entirely different absorption spectra. In some 

 compounds we shall find the evidence of the effect of absorption as 

 being due to a definite group of atoms; in other compounds the evidence 

 points just as strongly in favor of the manner of bonding of the atoms, 

 while still other compounds show that both the groups of atoms and the 

 manner of bonding with other atoms, as well as the kind of atom, are 

 instrumental in causing absorption. 



^Aschkinass, loc. cit. ^Ransohoff, loc. cit. ^Angstrom & Palmer, loc. cit. 



