170 PHENOMENA ACCOMPANYING 



surmount those difficulties, and to arrive at results which I can with confidence 

 present to the society. 



My curlier researches, which had chiefly for their object the study of the 

 general phenomena, were directed only to hydrogen and nitrogen, two gases, 

 diflfering greatly as regards their physical and chemical properties, and ofiering, 

 moreover, the advantage of being at once simple, unalterable, and without action 

 on the metals serving as electrodes. Atmospheric air, on Avhich also I have 

 often operated, acts very much as nitrogen, whether because the proportion of 

 oxygen it contahis is small in comparison Avith that of the nitrogen, or because 

 this oxygen, at least in great part, quickly disappears by reason of the trans- 

 mitted eleotricity, which, converting it into ozone, facilitates its combination 

 with the metal of the electrodes. I have also, in some cases, mixed with the 

 gas submitted to experiment a little vapor of water or of alcohol. 



Electricity has, in my experiments, been produced by a Ruhmkorff induction 

 apparatus of mean force, set in action by one or two pairs of Grove's cups,* 

 and operating by means of the ordinary cut-off. The electricity thus produced 

 is transmitted by means of copper Avires covered with gutta-j)ercha through the 

 gaseous mediums, more or less rarefied, contained in glass vessels of different 

 forms, tubes, jars, spherical or ovoid globes, &c. These vessels are to be carefully 

 closed with good taps, and furnished with metallic electrodes of divers forms 

 and natures, which serve to introduce the electric currents, t In the circuit 

 which these currents are destined to traverse we place distilled water in a small 

 glass trough, some twenty centimetres in length by five in width and three in 

 depth. Two plates of platina fixed respectively at the extremities of the trough, 

 and whose surface is exactly equal to the transverse section of the stratum of 

 water, serve to establish this water in the circuit. The purpose of the interpo- 

 sition of the water is to determine the intensity of the' electric current by means 

 of an expedient which permits, with that view, the employment of a very deli- 

 cate galvanometer. Two Avires of platina, each inserted in a glass tube, are 

 attached vertically to solid supports, so as to be immersed in distilled water at 

 their lower extremities, Avhich extremities project from the glass only a milli- 



* The battery in question is but a particular form which I have given to Grove's apparatus 

 to render its management more convenient and prompt. It is constructed as follows : 



A glass jar with a large opening of about ten centimetres, closed with a glass stopper rubbed 

 with emery, contains about a litre of nitric acid. When the pair is to be used, Ave remove the 

 stopper and replace it by a porous cylinder of such diameter that it can enter freely into the 

 jar by the opening. This cylinder, long enough to be plunged nearly to the bottom of the 

 jar, has on its upper portion an annular protuberance, by means of which it rests on the edge 

 of the opening. It contains sulphuric acid diluted Avith water, and a tube or strip of zinc im- 

 mersed in tiio acid solution. It is, besides, sunounded externally with a thin plate of platina, 

 to which is soldered with gold a Avire, also of platina, which terminates outside, traversing 

 the annular projection of the porous cylinder. The zinc and the platina Avire each carry 

 nippers, by which the conductors are readily attached. There may be several similar 

 pairs, and nothing is easier than to arrange them in series, so as to obtain a battery more or 

 less powerful. But a single pair is suthcient, if well mounted, for nearly all electro-dynamic 

 experiments, and particularly lor the demonstration of the laAvs of Ampere, as Avell as for the 

 production of the phenomena attending the discharge of the Euhmkortf apparatus in rarefied 

 gases. 

 ^ It is not necessary otten to change the nitric acid, since the jar contains a large quantity. 

 The same acid may serve for several days and for many experiments. It is of advantage, 

 however, frequently to change the acidulated water which tills the porous tube— a very easy 

 and unexpensive operation. Finally, an important precaution to be taken is, that, Avhen we 

 cease to use the pair, the porous cylinder should be withdraAvn from the nitric acid, care being 

 taken nnmediately to replace it with the stopper rubbed with emery, and the cylinder should 

 be immersed ui a bottle tilled with pure water. Thus the emanations of the nitrous vapors, 

 and the penetration of the nitric acid through the porous cylinder, are avoided. We should 

 guard agamst immersing the amalgamated zincs in the same water in Avhich the porous 

 cylmdors have been plunged, for the smallest trace of nitric acid in water suffices to alter the 



ZUU-H. 



t For electrodes I have chiefly used balls of platina, one centimetre in diameter. 



