10 Dr. Schweigger on Prof. Duebereiner's 



development of electricity by the agency of points, in mixtures 

 of gases strongly opposed in electric polarity ? and this in a 

 greater degree proportionably to the tendency to development 

 of the electricities under ordinary circumstances, that is, the 

 further those gases are distant from each other in the electro- 

 chemical series, or the more powerful their inclination to com- 

 bine. But we are unacquainted with more strongly opposed 

 electro-chemical poles than oxygen and hydrogen, which are 

 the extreme links of a series formed by arranging all bodies 

 between the two wires of the Voltaic battery. 



But why does platinum contribute in so distinguished a 

 manner to this combination ? — Because it is best adapted for a 

 spongy mass, by its not melting in a common fire. The 

 metals nickel and palladium may be added to platinum with 

 regard to this latter aptitude. According to Dulong and The- 

 nard's observations, the "platinum in the spongy state strongly 

 calcined, loses the property of becoming incandescent; but in 

 this case, it causes the combination of the two gases slowly, 

 and without a very sensible raising of the temperature *:" which 

 is according to our theory, that if the points of the platinum 

 sponge are made to melt in consequence of a strong calcina- 

 tion, and by which they lose their angles, the experiment, which 

 is founded on the agency of points, will be less successful. 



Agreeably to this theory I had offered the supposition, that 

 platinum powder prepared by mechanical means would ope- 

 rate with still less energy ; and this is really the case. In the 

 same manner, a smooth and thin leaf of platinum does not 

 operate until it is crumpled ; which again shows the influence 

 of points. The experiments which the French chemists made on 

 the agency of some metals in the decomposition of ammonia, 

 are beautiful and ingenious. The observation, first made by 

 Thenard, is to be found at large in the former series of this 

 Journal (see band vii. p. 299, &c), and even at that time I 

 added an appendix, in order to explain this remarkable phae- 

 nomenon according to the laws of crystallo- electricity. In like 

 manner the observations of Gay-Lussac on the decomposition 

 of the vapour of prussic acid must be considered as support- 

 ing this theory (see band xvi. p. 14). MM. Dulong and 

 Thenard, at the conclusion of their memoir occasioned by the 

 ingenious experiment of Dcebereiner, express the supposition, 



worst conductor of heat. It is probable, however, that the ground of the 

 former property lies still deeper, and perhaps in this newly-discovered prin- 

 ciple. It may also be mentioned here, that M. Hildebrandt, in his Treatise 

 on light emanating from electrical points, attributes to platinum a great 

 power of exciting it. 



* Sec Phil. Mag. vol. Ixii. p. 284. 



that 



