SAFETY LAMP. On one occasion George Stephenson of locomotive fame observed that the flame of the candle did not pass through the small apertures of the latticed fender, and he gathered from this fact the rude idea of his safety lamp which he constructed and tried at Killingworth colliery, near Newcastle upon-Tyne, before anyone else had tested one under similar con ditions; and, in 1818, he was presented at Newcastle with a silver tankard containing one thousand guineas as the "discoverer of the safety lamp." In May 1818, however, Sir Humphry Davy gathered together and published his collected papers that he had written on the subject, from which it is evident that the ideas he had worked out were his own, so it would appear that Stephenson and Davy had been independent labourers in the same field, just as Daguerre and Talbot in the art of photography reached the same goal by somewhat different paths.
Sir H. Davy first turned his attention particularly to the subject of explosions of fire-damp in Aug. 1815, in consequence of a letter from the Rev. Dr. Gray. He arrived at the conclusion that a metallic tissue, however thin and fine, of which the apertures filled more space than the cooling surface, so as to be permeable to air and light, offered a perfect barrier to explosion. By sur rounding the light entirely by wire gauze he established the prin ciple which has governed the flame safety lamp since his day.
Dr. W. Reid Clanny (1776-185o) invented, a safety lamp about the same time as Stephenson and Davy, but whereas Stephenson covered the light with a glass cylinder surrounded by an outer casing and top of wire gauze, the feed air being admitted through small holes in a copper ring below the level of the wick; and whereas Davy entirely enclosed the light by a cylinder of gauze, Clanny on the other hand substituted a glass cylinder for the lower portion of the wire gauze, the air entering at the bottom of the gauze and passing down the inner side of the glass.
In Great Britain, in any mine comprised within the Coal Mines Act of 1911, no lamp or light other than a locked safety lamp is allowed to be used in any seam the air current in the return air way of which is found normally to contain more than one half per cent of inflammable gas; and there are specified certain other conditions relative to safety lamps. Wherever safety lamps are
required by the act, or regulations under that act, to be used the lamp must be of a type approved by the Secretary of State.
The safety lamps at present in use in the coal mines of Great Britain are divisible into two broad classes, viz., flame safety lamps and electric safety lamps. The official test of the lamps is in respect of general design, strength and general character of construction. Flame safety lamps must be provided with double gauzes or some other adequate arrangement serving the same pur pose, the nature of the material forming the gauze being specified. The gauze to be composed of wire with 28 meshes to the linear inch (784 to the square inch) and the lamp must be so con structed that it is not possible to put together the component parts without the gauze ; and it must be provided with an efficient locking device. Electric safety lamps must be so constructed that no liquid can escape from the battery when the lamp is turned upside down. The switch and other electrical contacts must be contained in flame-tight enclosures. For the United States, see COAL AND COAL MINING, United States.
The number and type of safety lamps in use in Great Britain during the years 1907 and 1926 were :— The flame safety lamp is put to another use besides that of illumination, namely, that of ascertaining the presence of inflam mable gas, for when the lamp is placed in an atmosphere con taining fire-damp, the flame elongates, and if the gas is present in considerable quantity the lamp is filled with blue flame. For testing the presence of gas the flame of the lamp is lowered until the yellow part is almost non-existent, when the gas will be dis cernible as a small blue cap to the flame ; as the size of cap and the percentage of gas present in the air have been correlated, it is possible by this means to detect the presence of as low as one per cent of fire-damp in the air current. (R. R.) SAFETY RAZOR: see RAZOR.