As the intense light obtained from the
heating of a pellicle of small particles of non-combustible matter is destined
to act an important part in the future of economic and brilliant gas lighting,
some particulars of the phenomenon may call for notice.
It may oftentimes have been observed that in the dull embers of burning charcoal from logs of oak or ash some stationary sparks appear at times, giving out an intense white light, which illuminates all surrounding objects, and lasts for several seconds, much resembling in colour and brilliance the light of the electric glow lamp.
It is a property of very small particles to attract invisible heat and disperse it in the form of light. The effect depends principally on the minute size of the radiating atoms, their non-conduction for heat, and its consequent retention, and also their absolute infusibility. A very fine platinum wire held in the out-flame of a candle gives an intense light, and has a collective power for heat by which such a high temperature is induced, that the cobweb wire becomes actually fused.
In the year 1852 some tufts of confervae, or common ‘hair weed’ were sent to me for examination. These were taken from some rock pools called ‘Hell’s Kettles’ in consequence of continuous bubbles of carbonic-acid gas [carbon dioxide] rising to the surface of the water. The filaments of the weed were coated with a white deposit in which diatoms were expected to be seen under the microscope. I found that the coating was amorphous, being nothing else but a very fine deposit of carbonate of lime without structure. I held a few of the filaments in a gas-flame and was struck by the intense light given out. The vegetable substance of the filament was of course consumed but the lime coating, being infusible, retained its form. I then attached a fringe of these filaments from a ring of wire, and suspended it so as to encircle a small solid or Bunsen gas-flame, and got a fine white light arising entirely from incandescence of the lime. I took no further hint of this at the time as the least puff of air was sufficient to break up the fabric.
In the year 1880, having then in view improvements for increasing the intensity of ordinary gas light, I called to mind the foregoing experiment and reproduced it in a more substantial and stable form. I first constructed a cage of very fine platinum wire to inclose a Bunsen gas-flame; knowing that thin platinum in time became disintegrated and wasted by the continued action of gas-flame, I brushed on a protective coat consisting of a paste of very fine fluor-spar. The heat from the flame acted upon both the inner and outer surfaces of the cage. By this means I got a brilliant light from an otherwise invisible flame. The chief objection to this light was that it had a somewhat greenish tinge.
The fluor-spar is quite infusible and is decomposed into its elements by continued heating. The light, though very economical in gas consumption is far surpassed in this respect by the now well-known regenerative lamp, a form which I soon afterwards introduced into the market, but the ‘incandescent’ gas-light has the merit of great simplicity, and can be understood and managed by anyone, and consequently has recently been very popular, and improvements will probably be forthcoming that will greatly enhance its use and efficiency.
F.H.Wenham, The English Mechanic, 1894