J2. INFRA-RED ABSORPTION SPECTRA. 



the other fatty acids is resolved into two bands, viz, 6.85 /x and 7.06 \i. 

 It would be of interest to learn whether the others are likewise double. 

 From experience gained at 3 /x, using the larger spectrometer, it appears 

 that a very much larger dispersion is necessary to decide this question. 



PETROLEUM DISTILLATES. 



Through the generosity of Prof. C. F. Mabery,^ of Case School of 

 Applied Science, who presented me with 25 samples of distillates from 

 Ohio, Pennsylvania, and California petroleum, I was able to examine 

 these most interesting oils. They belong to the paraffin (CnHgn+a)- 

 the methylene (CnHon), and the acetylene (CnH2n-2) series of hydro- 

 carbons. During the past seven years they had been fractionally dis- 

 tilled many times, some at least thirty times, and were in a high state 

 of purity. They differ considerably in specific heats, being lower in 

 the methylene hydrocarbons. " Whether^ this is due to greater com- 

 pactness in the methylene molecule or some quality of its ring structure, 

 it would be interesting to ascertain." 



These oils were examined with the hope of discovering a shift of the 

 absorption bands with increase in molecular weight. As will be noticed, 

 no such shift could be detected. Besides, all the compounds showed the 

 same absorption bands, differing, of course, in intensity in different 

 compounds. This is the same result that was obtained by Hartley and 

 Dobbie^ for the alkaloid solutions in the ultra-violet. 



The methylene series consists of a ring of CHg-groups, while the par- 

 affin and acetylene series consist of a chain of CHg and CHg groups. 

 Hence, if we had investigated these compounds with only a small spec- 

 trometer, it would appear that structure does not seriously affect absorp- 

 tion spectra. However, with the large spectrometer some of the com- 

 pounds showed small absorption bands in the transparent region from 

 4 to 6 fi, while others showed no bands whatever. One absorption cell 

 was used for quite a number of these compounds, and at the end of that 

 time the inside of the cell was as smooth as at the beginning, showing 

 that no water was present. 



Although the compounds, as a whole, have a great bearing on this 

 work, their discussion can be confined to a small space, since the curves 

 are so similar. By similarity here is meant in the location of the marked 

 absorption bands. 



^Mabery : Composition of Petroleum, Proc. Amer. Acad., 37, p. 565, 1902. 

 ^Mabery & Goldstein : Proc. Amer. Acad., 37, p. 540, 

 ^Hartley & Dobbie, loc. cit. 



