M. Viard on the Electro-chemical Deportment of Oxygen. 245 



galvanometers, I think that the presence of these substances, on 

 a certain length of the wires or stems of the plates employed, 

 could scarcely have given rise to new causes of current. 



At first, simple glass tubes, 12 millimetres in diameter and 1 

 decimetre long, were operated with, but afterwards some experi- 

 ments were repeated with two series of four new porous cells, 

 such as are used in Bunsen's battery ; before using the latter 

 they were boiled for a long time in pure water. 



As electrodes, wires, plates of 6 square centimetres, and lastly, 

 plates of from 30 to 40 square centimetres were used. 



In the course of the investigations, where it was necessary to 

 observe currents of very different intensities, various galvano- 

 meters were employed*. Their sensitiveness was made to vary 

 very much ; sometimes by means of a simple magnet, according 

 to Melloni's method, and sometimes by means of a small mag- 

 netic compass with which Ruhmkorff provides his galvanometers. 

 Occasionally the needles were rendered sufficiently astatic as to 

 require 120 seconds to make a complete oscillation. 



When the plates are withdrawn from one apparatus in order 

 to plunge them into the other, it is necessary to operate quickly, 

 and to avoid as much as possible all agitations which could modify 

 the phsenomena under consideration. With a little practice, and 

 by always employing very fine and well-annealed wires to con- 

 nect the electrodes with the galvanometer, this source of error 

 may to a great extent be avoided ; and the danger will be further 

 diminished, if, instead of the initial deviations, those which exist 

 two or three minutes after immersion be noted. 



In certain cases, in order to compare the results, it is neces- 

 sary to employ great regularity in experimenting, to observe 

 equal intervals of time, dating from each immersion. In the 

 present investigations a new experiment was generally made every 

 four minutes, and the deviations noted at the end of the twelfth, 

 thirteenth, and fourteenth. The time was indicated by a clock 

 beating seconds. 



Lastly, it is advisable to introduce the same liquids into each 

 apparatus on commencing each series of experiments, so as to 

 ensure like deviations under like circumstances. 



In order to obtain solutions exactly at the same point of satu- 

 ration, and at different states of oxidation, the liquid was first 

 boiled, then a portion enclosed in a vessel with a ground stopper, 

 and the rest exposed to the action of the air for one or two days. 



In the tables showing the results of my experiments, the letter 

 b indicates that the tubes of the apparatus contained boiled 

 liquid, the letter a that they contained aerated liquid, ba that 



* One of the most sensitive had 1800 coils of wire, the other 3000. 



