474 Mr. Frederick Siemens [May 7, 



in most cases, much higher than generally admitted ; and that the 

 authorities I am about to refer to have omitted in almost all the 

 experiments they have made to take into proper consideration one 

 element which is liable to alter materially the results obtained by 

 them. This element is the surface, form^ and material of the apparatus 

 used for those experiments. 



In considering the question of dissociation, I propose to com- 

 mence with Deville, who first discovered and called attention to 

 the dissociation of gases at high temperatures. He made numerous 

 experiments with various gases, dissociating steam, carbonic acid, 

 and also carbonic oxide (in the latter case producing carbonic 

 acid and carbon), and fixed certain temperatures at which he found 

 that either complete or partial dissociation took place. Without 

 going into details I may mention that Deville required to use vessels 

 and tubes of definite dimensions, material, and structure, in order 

 to obtain the results stated. One experiment had to be made with a 

 porous tube, another required the use of a vessel with rough interior 

 surfaces, or containing some rough or smooth material. In this way 

 Deville arrived at a great variety of results, and although he does not 

 state that the rough surfaces, or porous tubes, or the solid material 

 placed inside the vessels which he employed, had any particular 

 influence on the temperature at which dissociation took place, yet 

 it would appear that he could not obtain his results without having 

 recourse to those means. Deville's results depended very much upon 

 the various kinds of surfaces he used in his experiments, if they were 

 not entirely brought about by them ; these experiments, moreover, 

 were of a very comjDlicated nature, so I propose to pass on to more 

 modern authorities whose experiments are of simpler character, and 

 less open to objection. 



The most important experiments, which modify those of Deville, 

 are due to Bunsen. Bunsen observed the dissociation of steam and 

 carbonic acid by employing small tubes filled with an explosive mix- 

 ture of these gases, to which suitable pressure gauges were attached. 

 On igniting the gaseous mixture explosion took place, and a high 

 momentary pressure was produced within the tube ; from the pressure 

 developed Bunsen calculated the temperature at which the explosion 

 took place, and found that it varied with the mixtures cmi)loyed. 

 He records the circumstance that only about one-third of the com- 

 bustible gases took part in the explosion, from which circumstance 

 he concluded that the temperature attained was the limit at which 

 combustion occurred. To prove this, Bunsen allowed the gases suf- 

 ficient time to cool, after which a second explosion was produced, and 

 oven a third explosion when time was allowed for the gases to cool 

 down again. Bunsen's theory seems very plausible, besides which 

 he obtains much higher temperatures for his limits of dissociation 

 than other physicists, so that I might have accepted the figures at 

 which ho arrives ; these arc for steam about 2100° C, and for car- 

 bonic acid about 3000' C. These temperatures arc i)robably higher 



