INVESTIGATION WITH A ROCK-SALT PRISM. 95 



the farther one penetrates the infra-red. But few substances show this 

 property. Examined with the large spectrometer, the complex 3 /j. 

 region shows a band at 2.9 fi and 3.43 /t, with a possible small one at 

 3.7 fi. The region at 5.9 fi is complex, showing three bands — at 5.8 /j., 

 6.0 fx and 6.2 fi, respectively, A small band is found at 6.45 ft. The 

 6.87 fx. band is found in many aliphatic compounds (at 6.86 p.), especially 

 the petroleum distillates and other compounds having CHo groups. It 

 is harmonic with the one at 3.43 fi. 



The lower curves represent work done before the arrangement was 

 devised whereby thin films could be vised. Time did not permit a 

 re-examination of the region from 7 to 12 /x with the small spectrometer. 

 From the unusual depth and narrowness of the bands found with the 

 large spectrometer it is quite evident that the presence of oxygen has 

 a great effect in sharpening the absorption bands, just as shown by 

 Abney and Festing.' This would have been more evident from 11 [x to 

 14 fi, using a thinner film. The sample of eucalyptol was quite pure, 

 having been prepared with the pinenes already mentioned. 



Terpineol. CioHisO. (Fig. 116.) 

 This compound is isomeric with eucalyptol. Just how pure it was 

 is difficult to say. It is supposed to be a solid, melting at 35°, and 

 having a mayflower odor. This compound was a viscous liquid, boiling 

 at 208°, obtained from Merck. The whole curve reminds one of euca- 

 lyptol, except that it is less transparent, when we compare the films, 

 which were 0.0 1 mm. thick. The opaque region from 7 to 8 /x, followed 

 by a greater transparency, is noticeable, as in the rest of the terpenes. 

 The absorption bands are not quite so sharp as for eucalyptol. The 

 large spectrometer resolves the double band at 3.2 /* into two bands. 

 Here the 3.43 ix band is not harmonic with the one at 6.95 [x, the latter 

 being shifted from its usual place at 6.86 /x. 



Menthol. C10H19OH. (Fig. 117.) 



This saturated secondary alcohol of the monocyclic camphors is the 

 chief constituent of peppermint oil. It melts at 42°, hence, after once 

 melted, could be kept in that condition before the spectrometer slit by 

 permitting the intense heat of the radiator to fall upon it. 



Only part of the spectrum of this compound was examined with the 

 large spectrometer, to learn the effect of the OH-group. Lack of time 

 did not permit an examination beyond 8 /x, using the small spectrometer. 



The spectrum examined is characteristic of the terpenes. The bands 

 at 3.45 fx and 6.9 /x (harmonic) occur as usual, as does also the one at 



^Abney & Festing, loc. cit. 



