74 INFRA-RED ABSORPTION SPECTRA. 



parent because of the thinner films thus used. On account of evapora- 

 tion they could not contain any quantity of the liquids boiling at ioo°, 

 so that the absence of shifting can not be attributed to the presence of 

 hydrocarbons of lower boiling point. 



The different hydrocarbons studied, with their boiling points, are 

 given on page 73. The petroleum distillates are conspicuous for three 

 regions of absorption, at 3.43 ^t, 6.86 /t, and 13.8 /i. The spectra are 

 entirely different from those of the fatty acids, which have an addition 

 of two oxygen atoms. In the methylene series it is not known whether 

 the Ohio oils (C10H24 and C^Ji^^) have the same structure as that of the 

 California oils. 



The Pennsylvania oils (C.Ji^^ to Ca.H^g) are probably the same as 

 the Ohio oils. They occur with the solids of the paraffin series, and 

 were separated from them at —10° by filtering under pressure. The 

 impure paraffin series of distillates are a mixture of solid and liquid. 

 The solid was separated in a crude state by cooling and filtering ; it was 

 then purified by dissolving in ether and precipitating it from solution 

 by means of alcohol. 



The chlorine compounds, C.Jio^ CI [b. p. I30°-I35° (12 mm.)] 

 Ci.H^sCl [b. p. I45°-I50° (20 mm.)] and C^,U^, CI [b. p. i7oJ-i73j 

 (15 mm.)], were obtained from chlorinated oils boiling at 223°-224°, 

 at 240°, and at 189° (50 mm.), respectively. 



The band at 5.8 ju, seemed to vary in depth when examined at different 

 dates. This was thought to be due to the absorption of moisture, but 

 a subsequent examination, with the large spectrometer, of a specimen 

 which had stood over P2O5 for several weeks, and the same specimen 

 after it had been exposed to the moist air of the room, showed no differ- 

 ence in the absorption band, which was small. Since the samples 

 obtained were small, varying from a few drops to 2 cc, it was impossible 

 to distill them, so they were placed in wide-mouthed bottles containing 

 P2O5, and left there from several days to several weeks, depending upon 

 their tendency to evaporate. This drying made no difference on the 

 absorption spectra, and it was concluded that the oils were free from 



moisture. 



Hexane. CaHu. (Fig. 62.) 



This sample came from Kahlbaum, and is of importance here, since 

 it belongs to the same group of compounds as the petroleum distillates. 

 On account of its low boiling point, 69°, it had to be inclosed in a thicker 

 cell than the oils, hence it appears more opaque. Except for a new 

 band at 8.82 fi and a slight shift at 9.42 fi, the absorption spectrum is 

 the same as for the oils. This is a synthetic product, which fact adds 

 interest to the agreement of its absorption spectrum with the other com- 



