Geological Society. 333 



Hence it is seen that the chemical rays reflected at different times 

 and hours not only possess quantitative but also qualitative differ- 

 ences, similar to the various coloured rays of the visible spectrum. 

 Had nature endowed us with the power of discriminating the chemi- 

 cal rays, as we do the visible ones, by impressions of varying colour, 

 we should see the rosy tints of morning pass in the course of the 

 day through all the gradations of colour until the warm evening 

 ones at length succeed. 



A long and continued series of observations must be made before 

 we are able to appreciate the influence which these qualitative differ- 

 ences in the chemical rays exert upon the photochemical pheno- 

 mena of vegetation. That this influence must be of the greatest 

 importance is evident from the varying effects produced in other 

 photochemical processes by differences in the solar light. We need 

 only mention in proof of this assertion, the fact, well known to all 

 photographers, that the amount of light, photometrically speaking, 

 gives no measure for the time in which a given photochemical 

 effect is produced, and that a less intense morning light is always 

 preferred for the preparation of pictures to a bright evening light. 



GEOLOGICAL SOCIETY. 



[Continued from p. 156.] 



January 20, 1858. — Major-Gen. Portlock, President, in the Chair. 



The following communications were read : — 



1. " On the Evolution of Ammonia from Volcanos." By Charles 

 Daubeny, M.D., F.R.S., F.G.S., &c. 



The author referred to the existence of a chemical compound of 

 titanium with nitrogen, known from the researches of Wohler and 

 Rose ; and pointed out in this paper its bearing on one part of the 

 theory of Volcanos, namely, the evolution of ammonia, and the con- 

 sequent presence of ammoniacal salts amongst the products of their 

 operations. Dr. Daubeny first commented on the hypotheses already 

 suggested by Bischoff' and Bunsen, to account for the volcanic pi-o- 

 duction of ammonia: viz. 1st, the decomposition of carbonaceous 

 or other organic substances ; 2ndly, the conversion, by the hot lava 

 overflowing the herbage, of the nitrogenized matter present in the 

 latter into ammonia, and the combination of this with the muriatic 

 acid in the lava giving rise to the sublimation of sal-ammoniac. To 

 both of these hypotheses the author pointed out serious objections. 

 He had himself proposed to account for the presence of ammonia in 

 volcanic outbursts by assuming that the gaseous hydrogen, although 

 incapable of combining with nitrogen under ordinary pressures, might 

 unite with it under that exercised upon it in the interior of the 

 earth : and he still believes this idea to be worthy of consideration, 

 though perhaps it is impracticable to secure by experiment the con- 

 ditions necessary for the chemical union of these two gases. 



The affinity, however, which certain metals possess for nitrogen 

 seems to afford more solid grounds on which to build a theory re- 

 specting the production of ammonia. Titanium has been found, 

 by MM. Wolilcr and St. Claire Devillc, to absorb nitrogen from the 



