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XXI. On Sir H. Davy's Safe-Lamp. By Dr. Ure, M.D. 



Professor of Chemistrij, &c. &fc. 



To Mr. Tilloch. 



Df.ar Sir, — Jlermit me to join my voice, to the decisive testi- 

 monies already publislied, in favour oF Sir H. Davy's safety-lamp. 

 I vvras lately present at several experiments, which place in a con- 

 spicuous view, its wonderful power of giving protection against 

 the explosion of fire-damp, so often fatal to the miner. During 

 a visit which I paid a few weeks ago to Dublin, my ingenious 

 friend Richard Griffith esq. mining-engineer to the Dublin So- 

 ciety, requested my assistance in preparing and exhibiting some 

 experimental illustrations of the lamp, for'^his deservedly popular 

 course of lectures on geology. Two lamps were tried. The 

 cage of one was formed of iron-wire, each mesh being l-20th 

 of an inch in width ; — the other cage was of copper-'vvire, its 

 meshes were each about l-30th of an inch wide. A table with 

 raised edges, painted so as to hold water, and a large glass re- 

 ceiver of the c if)acity of a cubic foot and a half were provided : 

 the water was about an inch and a half in depth. 



Things being in this state, a glass syphon was introduced un- 

 der the edge of the receiver, and the atmospherical air was sucked 

 out till the water rose wiiliin, to a certain mark, correspondincr 

 to a known ratio of the whole volume. A gasometer filled with 

 the compouufl combustible gas obtained from acetate of potash 

 by heat, was connected by a flexible pipe, with a brass tube which 

 was fixed tight in an aperture made through the table under the 

 receiver, and gas was slowly introduced into it, til! the water was 

 again displaced. 



Various jjvoportions of air and gas were used in different 

 experiments. When the lamp with its cage screwed on, was 

 introduced into the receiver containing eleven parts of atmo- 

 spherical air and one of carburetted hydrogen, the flame en- 

 larged, but continued moderate and of a blue lambent appear- 

 ance. When six parts of air and one of gas were used, the 

 flame was more vivid, filling the whole cage ; and when the com- 

 bustible gas constituted l-.5th of the vvhoie, the flame of the 

 wick was extinguished very soon after the lamp was introduced 

 but the gas continued to burn with great violence within the 

 cage, and its v/ire became distinctly red hot : yet the flame did 

 not communicate through the meshes, so as to kindle the large 

 volume of combustible gas by which the lamj) was enveloped. 

 At the end of the experiment the cage v/is found to be distorted, 

 from its free expansion being counteracted by the strong parallel 

 wires that constitute the exterior frame, and which serve to 

 connect the metal plate at top with the bodv <:f the lamp below 

 Vol. 48. No. 220. Ani^itst IS16. ' F Similar 



