316 EEPORT— 1880. 



As representatives of bodies with two doubly-linked adjacent atoms, 

 ethylene, amylene, and allyl-alcohol were examined : no absorption-bands 

 were seen. To ascertain tbe effect of treble-linking, two carbon atoms, 

 acetylene and valerylene, were examined : again, no absorption-bands 

 were apparent. 



It appears probable then that in no case do carbon atoms arranged in 

 an open chain give rise to absorption- bands. The arrangement of the H 

 and O atoms has not been found to affect the question. 



With hydrocarbons containing at least six atoms of caibon and their 

 derivatives there are three possible arrangements which admit of the 

 carbon atoms forming a closed chain : — 



(1) Three pairs of carbon atoms may be doubly-linked, as is assumed 

 to be the case in benzene ; 



(2) Two pairs may be doubly-linked ; 



(3) The six atoms may be singly-linked. 



There are reasons for representing oil of turpentine and terebene as 

 having two pairs of carbon atoms donbly-linked, and their nucleus formed 

 by a closed chain, which includes these two pairs of atoms. These bodies 

 exhibit no absorption-bands, from which Prof. Hartley concludes that 

 bodies containing a closed chain of carbon atoms, in which only two pairs 

 are doubly-linked, do not cause intermediate absorption. Again, the 

 constitutional formula of camphor may be based on a closed chain of 

 carbon atoms. It is found to be more diactinic than the terpenes, from 

 which it may be inferred that its atoms are less compactly united : a 

 state consistent with the theory of a singly-linked closed chain of atoms. 

 Camphoric acid agrees with camphor in this respect. From the foregoing 

 considerations it is surmised that no molecular arrangement of carbon 

 atoms causes selective absorption, unless three pairs are doubly-linked 

 together in a closed chain. 



The absorption-spectra of condensed benzene nuclei are next con- 

 sidered. 



It was expected, from the generally accepted views as to the con- 

 stitution of naphthalene and anthracene, that these substances would 

 cause a larger number of absorption-bands than benzene, and that the 

 bands would have greater intensity. A solution of naphthalene, however, 

 of 1 in 60,000 shows four absorption-bands, whereas six bands of ben- 

 zene, apparent at a dilution of between 1 in 700-800, have been entirely 

 eliminated at 1 in 2500. Therefore, although the number of bands is 

 not increased, the absorptive power is very considerably greater in the 

 case of naphthalene. 



Phenanthren, which is supposed to contain three benzene rings 

 arranged as follows, shows three strong absorption-bands with a solution 

 containing one in 4000 : — 



^C— C^ X'— c^ 



C'^ \c-c— c^ "^c 

 Anthracene, k I, i, I i, 



