1 62 Dr. Draper on the Decomposition of Carbonic Acid 



In its connexions with modern organic chemistry and phy- 

 siology the experiment of the decomposition of carbonic acid 

 by leaves assumes extraordinary interest. To no other single 

 experiment can the same importance be attached. When we 

 remember that this decomposition is the starting-point for 

 organization out of dead matter, that commencing with this 

 action of the leaf the series of organized atoms goes for- 

 ward in increasing complexity, and blood, and flesh, and cere- 

 bral matter are at its terminus, it is clear that unusual im- 

 portance belongs to precise views of -this the commencing 

 change. The beams of the sun are the authors of all organi- 

 zation. 



There is but one way by which the question can be finally 

 settled, and that is by conducting the experiment in the pris- 

 matic spectrum itself. When we consider the feebleness of 

 effect which takes place, by reason of the dispersion of the in- 

 cident beam through the action of the prism, and the great 

 loss of light through reflexion from its surface, it might ap- 

 pear a difficult operation to effect a determination in this way. 

 Encouraged, however, by the purity of the skies in America, 

 I made the trial and have met with complete success. 



Before entering on the experiments which I have to com- 

 municate, I cannot avoid once more impressively calling the 

 attention of chemists to the true character of those emanations 

 which are here designated " tithonic rays." It is not enough 

 that we admit the existence, throughout the spectrum, of dark 

 rays, possessing the power of bringing about chemical changes ; 

 it is not enough that we call them chemical rays ; there are 

 qualities of distinction appertaining to them which mark them 

 out as being specific in their kind, properties which they 

 possess totally distinct from those of light and heat. Their 

 title to the rank of a distinct imponderable agent is just as 

 perfect as that of light or heat. From heat they are to be 

 distinguished by incapacity for metallic conduction, and by 

 want of the power of expanding bodies ; from light by failing 

 to give any impression to the organ of vision. According to 

 the recognized rules of chemistry they ought to be received 

 as a fourth imponderable agent. 



It is not sufficient, as has been said, to call them "che- 

 mical rays." The term implies that the distinctive charac- 

 teristic pertaining to them is the power of changing the com- 

 position of bodies. But do not the rays of heat eminently 

 produce like changes? Are not half the decompositions in 

 chemistry brought about by the action of caloric? As respects 

 light, many instances are already known in which it produces 

 decompositions and combinations ; as will be presently shown, 



