SAFETY LAMP 



733 



This is formed by the changes which go on in the carbonaceous compounds of which 

 coal is constituted, and it is condensed in the coal. 



A few of the analyses which have been published by different chemists will show 

 the composition of the fire-damp of our coal-mines. 



1741 



1740 



Mr. Tennant, in his ' Researches on flame,' first noticed that burning gases would 

 not pass through tubes of a certain diameter. Dr. Paris says, Davy was not aware of 

 Tennant's researches. Be this as it may, he greatly extended the inquiry. 



The first full account of Davy's beautiful researches was published in the ' Philoso- 

 phical Transactions ' for 1816. his memoir being entitled ' An account of an invention 

 for giving light in explosive mixtures of fire-damp in coal-mines, by consuming the 

 fire-damp.' In January 1817, the principle was announced in a paper on 'Some new 

 experiments and observations on the combustion of gaseous mixtures, with an account 

 of a method of preserving a continued light in mixtures of inflammable gases and air 

 without flame.' 



The lamp of Davy, fig. 1740, con- 

 sists therefore of a common oil- 

 lamp, surmounted with a covered 

 cylinder of wire-gauze, for trans- 

 mitting light to the miner without 

 endangering the kindling of the 

 atmosphere of fire-damp which 

 may surround him. 



The gauze-cylinder should be 

 fastened to the lamp by a screw, 

 b,fig. 1741, of four or five turns, 

 and fitted to the screw by a tight 



ring. All joinings in the lamp should be made with hard 

 solder; as the security depends upon the circumstance, that 

 no aperture exists in the apparatus larger than iu the wire- 

 gauze. 



The parts of the lamp are, 



1. The brass cistern a, d, fig. 1741, which contains the oil. 

 It is pierced at one side of the centre with a vertical narrow 

 tube, nearly filled with a wire which is recurved above, at the 

 level of the burner, to trim the wick, by acting on the lower 

 end of the wire e with the fingers. It is called the safety- 

 trimmer. 



2. The rim b is the screw neck for fixing on the gauze- 

 cylinder, in which the wire-gauze cover is fixed, and which is 

 fastened to the cistern by a screw fitted to b. 



_ 3. An aperture c, for supplying oil. It is fitted with a screw 



or a cork, and communicates with the bottom of the cistern by 

 a tube at/, a central aperture for the wick. 



4. The wire-gauze cylinder, fig. 1 740, which should not have less than 625 apertures 

 to the square inch. 



5. The second top, -J of an inch above the first, surmounted by a brass or copper 

 plate, to which the ring of suspensiou may be fixed. It is covered with a wire cap iu 

 the figure. 



6. Four or six thick vertical wires, g' $' g' _</, joining the cistern below with the top 

 plate, and serving as protecting pillars round the cage, g (fig. 1741) is a screw-pin to 

 fix the cover, so that it shall not become loosened by accident or carelessness. The 

 oil-cistern, ;?#. 1741, is drawn upon a larger scale than fig. 1740, to show details of 

 the smaller parts. 



When the wire-gauze safety-lamp is lighted and introduced into an atmosphere 

 gradually mixed with fire-damp, the first effect of the fire-damp is to increase the 

 length and size of the flame. Whea the inflammable gas forms so much as ^th of 



