118 ANNUAL OF SCIENTIFIC DISCOVERY. 



ductibility in metallic wires. The method which lie adopted in his experi- 

 ments is that known as the electrical bridge. The current of a Bunsen's 

 battery of six large cells was divided between the wire to be tested (a very 

 soft copper wire, O'O.j of an inch in diameter, covered Avith gutta-percha) and 

 another conductor, both being coA-ered with a delicate Rnhmkorff's galvano- 

 meter, so that the needle remained on the zero point. All contacts AA-ere 

 made invariable by solderings. No sensible effect being determined by the 

 pressure of nine atmospheres in a pierometer, a press Avas used to produce 

 compressions superior to four hundred atmospheres, consequently greater 

 than that experienced by an electric Avire immei'sed in the ocean at a depth 

 of 12,420 feet. The wire, besides its ordinary coating, Avas further protected 

 by tAvo coverings of thick gutta-percha placed betAA r een the steel plates Avhich 

 held it. The experiments haA-e shown : 1. That a pressure of thirty atmos- 

 pheres diminishes the electrical conducting power of a copper wire. 2. That 

 the effect increases with the pressure. 3. That the diminution is the same 

 for each compression, as long as the latter is constant. 4. That the primitive 

 conducting poAver is exactly restored when the pressure A'anishes altogether. 



ON THE CHEMICAL EFFECTS OF ELECTRIC DISCHARGES. 



Pliicker has published, in successive parts, the results of an elaborate and 

 very interesting investigation of electric discharges in tubes containing rare- 

 fied gases. For the details AVC must refer to the original papers, Avhich do 

 not admit of condensation, and content ourselves AA r ith giving, in the author's 

 OAvn words, the results, which are most interesting to chemists. 



1. Certain gases (oxygen, chlorine, bromine and A'apor of iodine) combine 

 more or less sloAvly Avith the platinum of the negative electrode, and the 

 resulting compounds are deposited upon the surrounding sides of the glass 

 tube. When the gases are pure, we approximate in this manner to a perfect 

 vacuum. 



2. Gases which are composed of two simple gases (A'apor of water, ammo- 

 nia, protoxide of nitrogen, deutoxide of nitrogen, nitrous acid), are imme- 

 diately separated into their components, and then remain unchanged, if they 

 do not (as ammonia) unite Avith the platinum. If one of the gases be oxy- 

 gen (as in steam and the different oxides of nitrogen), this gradually disap- 

 pears, and only the other gas remains. 



3. When the gases are composed of oxygen and a solid simple substance, 

 complete decomposition by the current takes place but slowly, the oxygen 

 going to the platinum of the negatiA'e electrode (sulphurous acid, carbonic 

 acid). Carbonic acid at first splits instantly into the lower gaseous oxide and 

 into free oxygen, which combines gradually Avith the platinum. Carbonic 

 oxide gas is then sloAvly decomposed by the combination of its oxygen with 

 the negative electrode. The results above mentioned AA r ere obtained by 

 means of the so-called Geissler's tubes, which are simply glass tubes of v&- 

 rious forms, containing rarefied gases, and provided Avith platinum Avires 

 fu<e;l into the glass. The electric currents were partly derived from the 

 electric machine, and partly from Ruhmkorff's apparatus. Finally, the re- 

 sults themselves are directly deduced from the prismatic analysis of the light 

 of the sintple and compound gases, the spectrum obtained bcin^r simple, or 

 composed of tAvo distinct and superposed spectra, according as the discharge 

 passes through a simple gas or a mixture of tAvo. Fogg. Ann., cv. 67. 

 SiUiman's Journal, 



