Safety lamp, Clowes, Gray type, use: gas testing, 1893, with spare hydrogen cylinder, and mahogany box (see 3 stroke numbers).

This is a form of the Ashworth Hepplewhite Gray lamp, provided with an attachment patented in 1892 by Mr. J. Ashworth and Prof. Frank Clowes, D.Sc., for estimating the combustible gases in mine air, petroleum tanks, etc.; it depends on the fact pointed out by Messrs. Mallard and Le Chatelier in 1881 that when such gases are present they cause a hydrogen flame to assume a bluish grey cap. A cylinder of compressed hydrogen is attached by a bayonet joint, and communication is made with a fine tube to act as a burner passing direct through the reservoir and terminating level with the wick. The hydrogen is turned on by a screw plug tap and lit from the oil flame, which is then turned down till extinguished. The height of the cap above the flame is read on a scale which gives a rough approximation to the percentage of combustible gas present. A screw lock is fitted.