solid Hydrocarbons found in Petroleum Distillates. 97 



If now we observe the absorptive action of these solutions in 

 the manner indicated in fig. 3, we shall find that the absorp- 

 tion-bands, like those of fluorescence, are displaced upwards in 

 the spectra of the solutions as compared with their position in 

 that of the solid. 



This will be illustrated by comparing fig. 9, which represents 



the absorption-spectrum of thallene dissolved in benzole, with 

 fig. 6, which is the absorption-spectrum of solid thallene. 



The absorption-bands of the solutions in benzole, chloroform, 

 and olive-oil do not appear to differ in any important degree ; 

 but in the etherial solution the bands are higher than in the 

 others. In the solution in turpentine the lower band especially 

 is exceedingly faint, so as to escape recognition entirely in the 

 method of observation employed in the other cases, even when 

 a pint bottle of solution was used; but when the tube of a 

 Duboscq saccharimeter was filled with this solution, this line 

 could be detected with a direct-vision spectroscope. 



In carbon-bisulphide solution a similar difficulty was encoun- 

 tered, so that in a preliminary publication T spoke of these bands 

 as not appearing ; but renewed observation has enabled me to 

 assure myself that in this solution all the bands exist, and at 

 lower points in the spectrum than in any of the other solutions 

 yet examined, the lowest one in particular occupying a point 

 even below that of the corresponding band in solid thallene. 

 There is also in this solution a decided general absorption of all 

 rays above F, which causes some special difficulty in measuring 

 the bands. 



In such cases as this the mode of observation to be next no- 

 ticed is specially efficient as a guide, indicating what we must 

 look for in each case. A similar displacement of bands by 

 change of solvent has been noticed by Hagenbach in the case 

 of soot, amide of phthalic acid, chlorophyl, purpurine, &c. (Pog- 

 gendorff's Annalen, 1872, vol. cxlvi. p. 533) ; and I have also 

 found it in a number of the uranium salts. 



When a pure spectrum is thrown on the side of a tank of 

 glass or quartz filled with the benzole solution, by the arrange- 

 ment of prism &c. indicated in fig. 4 we see, on looking down 



