William Robert Grove

Coal mining has always been an activity of extreme importance for mankind. Because of the darkness of mine galleries it was necessary to have a light source for the miners to accomplish their day's work. Perhaps candles were first used, but the presence, sometimes, of a dangerous gas (methane) could result in explosions. If the presence of such a gas was suspected, a person swathed in wet wrappings would slowly proceed into the mine walkways with a candle attached to a long pole. A great advance was made by Humphry Davy, who developed a safety lamp that employed small inlet and exit tubes through which air would flow to the glass-covered candle or oil light source. Later, wire mesh was used in such lamps. Davy studied the requirements for an explosion and designed his lamp to avoid those conditions.

In order to achieve higher light levels, so-called voltaic arcs were used, but mine explosions were still a problem. Boussingault and Auguste De la Rive worked on the problem separately² and published articles⁸ but they did not arrive at satisfactory solutions. It was then that Grove entered the picture and proposed a design. William Robert Grove, M.A., F.R.S., was Professor of Experimental Philosophy in the London Institution.

It might be of some value to mention briefly the inconsistencies encountered in the literature with regard to early lamp development dates. The Grove lamp is often given a development date of 1840. However, the article mentioned here³ was published in 1845. In that article Grove gave, perhaps, the reason for the claim, by others, of the earlier date. In Grove's 1845 article he said:

"Four or five years ago, soon after publishing the nitric acid battery, I was naturally struck by the facility and constancy with which the voltaic arc could be obtained by that combination, as compared with any previous one, and made several attempts to reduce it to a practical form for the purposes of illumination, but my success was limited...Not being able satisfactorily to overcome these difficulties, I abandoned it for the time, and made some experiments on another method of voltaic illumination, which appeared to me more applicable to lighting mines; their publication was postponed, and I had nearly forgotten them, until reminded by the papers...mentioned."

Mine illumination was of paramount importance in 1845, otherwise the work area would be in total darkness. Arc lighting was the norm, where the arc existed between two charcoal sticks, operating from a battery source. The problem that existed involved the occasional escape of methane gas from the bedrock, which could result in an explosion. Boussingault and De la Rive2 both worked on solutions to that problem. W. R. Grove had worked on the problem earlier but laid the work aside until the papers of Boussingault and De la Rive rekindled his interest in the subject. The following quotes were taken from the article by Grove³ in The Philosophical Magazine of 1845:

"I substituted the voltaic ignition of a platina wire for the disruptive discharge. Any one who has seen the common lecture-table experiment of igniting a platina wire by the voltaic current nearly to the point of fusion, will have no doubt of the brilliancy of the light emitted; although inferior to that of the voltaic arc, yet it is too intense for the naked eye to support, and amply sufficient for the miner to work by. My plan was then to ignite a coil of platinum wire as near to the point of fusion as practicable, in a closed vessel of atmospheric air, or other gas, and the following was one of the apparatus which I used for this purpose, and by the light of which I have experimented and read for hours:—A coil of platinum wire is attached to two copper wires, the lower parts of which, or those most distant from the platinum, are well-varnished; these are fixed erect in a glass of distilled water, and another cylindrical glass closed at the upper end is inverted over them, so that its open mouth rests on the bottom of the former glass; the projecting ends of the copper wires are connected with a voltaic battery (two or three pairs of the nitric acid combination), and the ignited wire now gives a steady light, which continues without any alteration or inconvenience as long as the battery continues constant, the length of time being of course dependent upon the quantity of the electrolyte in the battery cells. Instead of making the wires pass through water, they may be fixed to metallic caps well-luted to the necks of a glass globe.

"The spirals of the helix should be as nearly approximated as possible, as each aids by its heat that of its neighbour, or rather diminishes the cooling effect of the gaseous atmosphere; the wire should not be too fine, as it would not then become fully ignited; nor too large, as it would not offer sufficient resistance, and would consume too rapidly the battery constituents; for the same reason, i. e. increased resistance, it should be as long as the battery is capable of igniting to a full incandescence.

"The helix form offers the advantages, that the cooling effect being lessened, a much longer wire can be ignited by the same battery; by this increased length of wire, the battery fuel is economised, while a greater light is afforded; by the increased heat, the resistance is still further increased, and the consumption still further diminished, so that, contrary to the usual result, the increment of consumption decreases with the exaltation of effect produced. The very necessity of inclosing the coil in a glass recipient also augments the heat, the light, and the resistance; if I remember rightly, Mr. Faraday first proposed inclosing wire in a tube for the purpose of being able to ignite a longer portion of it. Lastly, only two or three cells are required (one indeed might be sometimes sufficient), and the whole apparatus thus becomes portable and economical. The light is perfectly constant, subject to no fluctuation or interruption, and the heat is not so excessive as to destroy the apparatus.

Grove had an appreciation of the effect of different conductivity gases on the practical application of the lamp. He applied the constant voltage of the battery to his lamp when filled separately with the gases. He filled with hydrogen, carbonic acid (a weak colorless acid, H₂CO₃), oxygen, nitrogen and atmospheric air. The observed colorations of the platinum wire were: hydrogen, not visible even in the dark; carbonic acid, cherry-red by daylight; oxygen, incandescent by daylight; nitrogen and atmospheric air gave the same results as oxygen. The reader is reminded that unlike most metals, platinum can be heated in many gases, including air, without severe, or any, oxidation.

It should be mentioned that Grove's work predated the much later work of Irving Langmuir in 1912, when the gas-filled incandescent lamp was developed. That is, the present-day gas-filled lamp has a filament of tightly coiled (tungsten) wire and a filling of low conductivity gas (usually nitrogen and argon, and sometimes, krypton). In a sense, Grove's knowledge and observations could not be universally applied until a better metal filament was found. That occurred with the development of ductile tungsten.