INVESTIGATION WITH A ROCK-SALT PRISM. 55 



few hours. The iodine band at 7.3 fx. could not be detected, although 

 special care was taken in the examination. This is due to the thinness 

 of the film and the weakness of the band. 



The 3.3 ^i band is very weak, due to the opacity of the crystalline 

 film. Julius^ found this same band very weak in bromoform (CHBrj). 

 It is a little stronger and shifted in the simpler CH compounds. 



Carbon Tetrachloride. CCU. (Fig. 28.) 



This compound is noted for the absence of large absorption bands up 

 to 6 n, as seems to be true of carbochlorates as distinguished from car- 

 bohydrates. Two small bands, at 2.9 /a and 4.45 fi, do not appear in 

 Julius's curves. The first deep maximum is at 6.5 /x. This band shows 

 a break in the curve for the small spectrometer, and was found to be 

 double, by using the large spectrometer, the maxima being at 6.45 /i, and 

 6.57 ft, respectively. The mean of these two is at 6.51 /i. Paschen^ 

 found this band at 6.45 /i. Thinking that it would be a good check 

 upon my work, the observations were repeated with the large spectro- 

 meter (curve xxxx ), with the result that two bands were found. 

 This is an excellent example of what may be expected if a large disper- 

 sion can ever be applied to the region at 3 )u, for some of the other com- 

 pounds. 



There are no further large absorption bands until we arrive at 13 /x. 

 Here a broad, deep band exists which is harmonic with the double band 

 at 6.5 II. 



Since the photographs of Abney and Festing^ show no lines for the 

 region up to 1.2 fx, and since Puccianti* found no bands up to 2.5 11, it 

 appears that the absence of bands up to 6/* is not due to the lack of 

 resolution of the fine lines, but is more likely due to their entire absence. 

 For this reason this compound ought to be an excellent solvent for 

 studying selective absorbing solids in solution. (See Appendix IV.) 



The great change introduced by substituting four CI atoms for four H 

 atoms is very evident by comparing this spectrum with that of methane 

 (CH4), which has only two large bands, at 3.3 /^ and y.y fi, respectively. 



Tetrachlorethyeene. C2CU. (Fig. 29.) 



As in carbon tetrachloride, this compound has no absorption bands 



until we arrive at 5.5 /a. The large band of CCI4 at 6.5 /a is entirely 



wanting, while the 12.9 /x band is present, but is narrower. At 8/x are 



two bands common to CCl^. This compound has some of the properties 



^Julius, loc. cit. ^Abney & Festing, loc. cit. 



"Paschen, loc. cit. *Puccianti, loc. cit. 



