476 Mr. Frederick Siemens [May 7, 



From the temperatures tliiis obtained, in each case, the real 

 dissociation temperature, if no surfaces were present to influence the 

 result, might be approximately calculated. 



Bunsen's method of experimenting, according to my view of the 

 matter, should form the foundation of further research to determine the 

 dissociation temperatures of products of combustion. Even if means 

 were found for'eliminating the influence of surfaces, no known material 

 at our disposal could withstand the very high temperature to which 

 the vessels or tubes would be subjected if experiments were carried 

 out according to Deville's method. 



That the surfaces of highly heated vessels or tubes either pro- 

 duce, or tend to produce, dissociation, has been corroborated lately by 

 two Eussian experimentalists, Menschutkin and Kronowalow. These 

 gentlemen found that dissociation of carbonic acid and other gases 

 was much facilitated when the vessels used for the experiments were 

 filled with material offering rough surfaces, such as asbestos or broken 

 glass. 



My view of the theory of dissociation caused or influenced by 

 surfaces, may be given as follows : — Increase of temperature producing 

 expansion of gases will reduce the attractive tendency of the atoms 

 towards one another, or, in other words, diminish their chemical 

 affinity. In the same ratio as the temperature is increased the 

 repelling tendency of the atoms must increase also, until at last 

 decomposition, or what is called dissociation, takes place. This being 

 admitted, it will follow that the adhesive or condensing influence of 

 surfaces on the atoms of the gas, which action will increase at high 

 temperatures, will assist this decomposition by increasing the repel- 

 ling tendency of the atoms. 



Victor Meyer, who at first disjrated the accuracy of the results 

 obtained by the two physicists I have mentioned, ultimately accepted 

 them. This circumstance I was very j)leased to learn as their experi- 

 ments confirmed the results I arrived at in practical work with 

 furnaces. Thus the question may be considered nearly settled, the 

 more so as Meyer is himself a great authority in questions of dis- 

 sociation, having carried out many interesting experiments. Meyer, 

 for instance, proved dissociation by dropping melted platinum into 

 water, and finds that oxygen and hydrogen are evolved from the steam 

 produced. There can be no doubt on this point, but the question 

 arises whether heat is the sole agent that brings about the dissocia- 

 tion of steam in this case. In the first place the dissociating influence 

 of the highly heated surfaces of platinum on steam has to be taken 

 into consideration, and secondly the chemical affinity which platinum 

 has for oxygen, and still more for hydrogen. The same remarks 

 apply to Meyer's experiment of passing steam or carbonic acid through 

 heated platinum tubes, in which case he obtains only traces of dis- 

 sociation, the temjDerature beiug much lower. Other experiments 

 might bo mentioned; but none lead to a difibrcnt conception of the 

 question. 



