INVESTIGATION WITH A ROCK-SALT PRISM. 93 



PiNENE. CioHie. (Figs. Ill and 112.) 



C^3 Pinene belongs to the complex " terpenes," con- 



^^^ ^ ^ ^^^ sisting of two rings. Nevertheless, when com- 



yC^ pared with limonene (CioHig), which is considered 



HjC^-^ C CHj ^ simpler compound, the difference is not very 



marked, except in the transparency. The number 

 of transmission minima is about the same, while the position of several 

 of them is changed. 



For the present work dextro- and laevo- pinene (CioHig; boil.pt., 

 I56°-I57°; rot. -(-8°.io and — 33°.62; thickness of cells, 0.07 mm. and 

 0.08 mm.) were used. Whether or not the optical activity manifests 

 itself in the transmission is not apparent from the curves. The differ- 

 ence in the transparency of the two substances can be accounted for 

 by the difference in thickness of the two films. One would next con- 

 sider the absorption bands. From the curves it will be seen that the 

 transmission minima coincide so closely that, as a whole, this single 

 comparison shows that the effect of the shape of the molecule, i. e., the 

 geometrical relation of the atoms in it, is not apparent. It is probably 

 what one would expect for unpolarized light. The two compounds 

 were examined because a more thorough exploration for absorption 

 bands was desired than that made on the dextro-pinene, so it seemed 

 interesting to try the laevo-pinene, with the aforesaid results. Unfor- 

 tunately, time did not permit an examination of the terpenes with the 

 large spectrometer. Only /-pinene was examined. No new bands were 

 found at 3.43 \x., showing that the absorption band integrated through by 

 the radiometer is fairly well resolved. This is quite a contrast to the 

 xylenes. The 6.1 /* band is resolved into three, while the one at 7.1 /a 

 consists of two bands. 



Pinene is viewed as a derivative of a combined hexa and tetra methyl- 

 ene ring. But we find no relations between its bands and those of 

 methylene and the methylene hydrocarbons from petroleum. 



Venice Turpentine. (Fig. 113.) 



Venice turpentine is a mixture of pinene, resin, etc. It is far more 

 transparent than pinene, and differs from it in that the 3.45 [x. band is 

 barely visible, while its greatest absorption occurs at 3.75 /u,. The 

 5.95 \i band is very sharp, as well as the one at 6.95 /n. From 7 ^ to 9 /* 

 it appears less complex than pinene, while beyond this point the trans- 

 mission minima agree well with those of pinene. 



Resin. C^HeoOi. (Fig. 114.) 

 Violin resin (colophonium), C44Heo04 (?), is residue from distilling 

 oil of turpentine. On account of its amorphous condition, it is easily 



