56 INFRA-RED ABSORPTION SPECTRA. 



of ethylene (C2H4), but not a single band is in common, just as was 

 found for CH^ and CCI4. 



The maximum at 6.4 /u, is closely harmonic with the one at 12,9 /x. 

 The sample of C2CI4 used was presented me by Dr. W. C. Geer, who 

 had prepared it with great care. Nevertheless the small bands at 8 /a 

 seem to indicate the presence of CCI4, which may have been formed in 

 the process of making of C2CI4. The latter is an intermediate product. 

 However, the absence of the 6.5 fi band and the presence of the 12.9 /a 

 band leaves the question of the presence of CCI4 somewhat in doubt. 

 This, however, does not interfere with the comparison of C2CI4 with 

 ethylene (C2H4). 



Ethylene Bromide. iCaHiBri. (Fig. 30.) 

 (From Bender and Hobein ; boiling point, 131°.) 



The absorption spectrum of this compound is of special importance 

 because the ethylene gas (C2H4) was made from it. The difference 

 between the two absorption curves of these two compounds is found 

 mostly in the general absorption. The C2H4 has a large triple band at 

 10.5 IX, where C2H4Br2 is quite transparent. The bands at 3.35 fi, 6.98 /i, 

 9.8 fi, 1 1.2 /A, and 13 ju, are found common to both compounds, although 

 they vary in intensity. The C2H4Bro boiled at the theoretical tempera- 

 ture, 131°, and must have been pure. The fact that so many bands are 

 in common with ethylene indicates that the addition of two Br atoms 

 has not had any great influence upon the original absorption bands, just 

 as the substitution of a Br atom in benzene has not changed the benzene 

 spectrum. Two pairs of bands at 8.0 //. and 8.44 /u,, and at ii.i4)U, and 

 12.0 |u, have a " common difference " of F= 66, which would indicate 

 that they belong to a spectral series. 



WATER AND ALCOHOL. 



Water. H-O-H. (Fig. 31.) 



This substance has been extensively studied by Julius,^ Paschen,^ 

 Aschkinass,^ and others, both as a vapor and as a liquid film — emission 

 and absorption spectra. The investigators do not quite agree in the 

 location of the maxima, although the work of each one, taken by itself, 

 appears consistent. All have found an extreme opacity to infra-red 

 radiation, so that the films of water had to be reduced to a few thou- 

 sandths of a millimeter in order to be able to study it at all. Were it 

 not for this property, water could be used as a solvent for studying sub- 



^Julius : VerhandL Kon. Akad., Amsterdam, 1892. 

 *Paschen : Ann. der Physik, 53, p. 334, 1894. 

 ^Aschkinass ; Ann. der Physik, 55, p. 431, 1895. 



