86 Journal of the Mitchell Society [January 



auxochromes, CgHgNRa or C6H4OH groups. If the chromo- 

 phore is different or if, with the same chromophore the number 

 of CgHgNRo groups vary, or if the position of the auxochrome 

 varies in its relation to the fundamental element, the absorp- 

 tion curve is different. 



Hartley states as a rule, " all open chain hydrocarbons exert 

 a continuous absorption, the extent of which is dependent upon 

 the number of atoms in the molecule." Hydrogen is the most 

 colorless substance known, which fact Hartley explains by say- 

 ing that the rate of vibration of its atom or its molecule is the 

 most rapid of all elements. This may be attributed to the fact 

 that its mass it much less than that of any other element — 

 perhaps its rapid vibration may be due to the large amount of 

 energy associated with the molecule. That hydrocarbons are 

 the least colored of all carbon, compounds is due to the energy 

 of the hydrogen atoms beingcommimicated to the whole molecule. 

 This may account for hydrogenized matters becoming colorless. 

 The greater the proportion of hydrogen the faster the vibration. 

 JSTaturally the introduction of a heavier atom or group in place 

 of the hydrogen will lower the rate of vibration and bring the 

 absorption nearer the visible spectrum ; sufficient damping will 

 produce color. 



Armstrong has advanced the theory that the production of 

 color is dependent upon special modes of atomic arrangement, 

 and particularly on such modes as involve the existence of a 

 condition of strain in the resulting system due probably to the 

 peculiarities in the affinity relationships of the different con- 

 stituent elements of the system which prevent mutual neutrali- 

 tation of the affinities. The occurrence of color would then 

 more frequently than not be concomitant with a high degree of 

 reactivity, the colored compound being one of high potential 

 or slight stability. The dominant feature of the arrangement 

 is a comparison of the unsaturated hydrocarbons with the para- 

 ffins. The paraffins, which are singularly inert and all but col- 

 orless, contain carbon atoms united by single bonds. The un- 

 saturated hydrocarbons begin to manifest color in the regions 

 above and below the visible spectrum. These compounds are 



