512 Mr. Grove on the Electro-chemical Polarity of Gases. 



alternations of oxidation and reduction were produced by inter- 

 ference in consequence of tlie discharge proceeding from suc- 

 cessive points of the terminal or terminals, a difference of effect 

 might be anticipated if the electricity passed from a point only, 

 and not from a line as was the casein Experiment 13. I there- 

 fore sealed a platinum wire g'^th of an inch in diameter into a 

 piece of glass tubing, and then ground the extremity to a flat 

 surface, so that the section only of the wire was exposed ; this 

 wire was placed opposite, and at 0"07 of an inch distance from 

 the polished silver plate, in a mixture of one volume of oxygen 

 with five volumes of hydrogen attenuated until the barometer 

 stood at half an inch ; discharges from the secondary coil were 

 then passed, the plate being positive, and a round dark spot of 

 oxide formed represented at fig. 8 ; the platinum sealed in glass 

 was then removed and the steel needle substituted for it, all else, 

 viz. plate, gas, barometer height, &c. being the same : the system 

 of rings represented at fig. 9 was now produced. 



Another experiment was made, directed to the same point : a 

 wire of copper 0*04 inch diameter, and a thread of glass of the 

 same diameter were attached by sealing-wax at their extremities 

 in a horizontal position 0025 of an inch from different parts of 

 a silver plate, being insulated from the silver by the wax inter- 

 posed at the extremities. The gaseous mixture and barometric 

 height being the same as in the last experiment, and the silver 

 plate made positive, when the platinum wire sealed in glass was 

 brought near the plate, and the discharges passed, a spot similar 

 to fig. 8 was formed ; but when the coated point of platinum 

 was brought over the copper wire at 0*02 inch distance, a figure 

 consisting of two separated semicircles was formed, having spots 

 in the bisection of the chords, as shown at fig. 10, the portion 

 between the spots and the semicircular line of oxide being of 

 polished silver. With the glass thread the effect was the same, 

 but produced with greater difficulty and not so well defined. 



In many repetitions of these experiments which I have made, 

 I have invariably produced the alternately polished and oxidated 

 rings from the bare wire, and have not procured them from the 

 coated wire, except to a very slight degree, and under certain 

 circumstances, which, as far as I could trace, were as follows : — 



1st. When the extremity of the wire was very near the plate, 

 so that it had a sensible magnitude with reference to the inter- 

 vening space, a slight formation of minute rings could be detected 

 at the commencement of the experiment. 



2nd. When the experiment was long continued, or when the 

 coated platinum wire had been used for previous experiments, a 

 set of rings, not consisting of an alternation of oxidated and 



