Patent GB-385354-A (GB)
Title: Improvements in and relating to miner's lamps
IPC: G01N27/16
Filed: 1931-08-27
Abstract: <PICT:0385354/III/1> The lamps serving for the general lighting of the mine are provided with means operated by catalytic or combustion heating when fire damp is present to cause the electric bulb to be directly surrounded by a coloured liquid.  The liquid may be of a distinctive colour such as violet to prevent confusion with signalling lamps.  The amount of discolouration of the light gives a measure of the percentage of gas present in the vicinity of the lamp, and different lamps may be differently coloured to give indications of the direction in which shelter places or exits can be reached. The tubular lamp bulb 4 is arranged in a glass tube 3 leaving a narrow annular space, the tube being closed at the bottom where it contains a coloured liquid 5.  An outer protecting bell 1 is filled with a cooling liquid 2 and protected by a cage 33.  Up to the normal level of the coloured liquid 5 the glass tube 3 is silvered so that the liquid cannot be seen.  An insulating baseplate 9 is screwed into the annular member 29 supporting the bell and cage and carries a combustion chamber 10 with perforated walls containing a heating coil 12 of platinum or p  palladium connected across the lamp terminals 13, 15 through a contact screw 14 and a bimetallic strip 11.  When the heating coil reaches a temperature of about 250 DEG  C. the bimetallic strip 11 moves away from the contact screw 14 and if no explosive gas is present the coil cools down, the bimetallic strip again makes contact at 14 and the heating is repeated.  If, however, explosive gas is present catalytic action increases the temperature above 250 DEG  C. and the bimetallic strip 11 makes contact with a screw 16 so that current flows through a heating coil 17 in the form of an arc arranged around a second bimetallic strip 19 one end of which is secured to the baseplate 9 while the other end is connected by a linkage 20 .. 23 to the movable lamp socket 39.  The lamp bulb 4 is thus moved downwardly, displacing the coloured liquid so that it rises between the bulb and the tube 3, colouring the light, the extent of rise giving a measure of the content of explosive gas in the mine atmosphere.  The lamp bulb may remain stationary and the glass tube 3 be moved.  The combustion chamber and heating coils are enclosed by a double perforated jacket 24, 25 filled with metal turnings, which may be treated with non-inflammable oils or fats to catch dust.  A protecting cover 47 and suspension device 48 are provided above the jacket.  In a modification the second bimetallic strip 19 may be dispensed with and the heating coil 17 enclosed in a chamber connected by a tube with the lower end of the glass tube 3 so that the expansion of the air when the coil is heated forces the coloured liquid upwardly.  In modifications particles of coloured material may be made to eddy upwards into the cooling liquid 2 to colour the light, a colouring matter may be injected into the cooling liquid and be deposited when the increased pressure in the air chamber ceases, or an alkali may be introduced by the increase of pressure into an acidified liquid containing phenolphthalein to produce a colouration which disappears after a time.  Instead of making the coil 12 of catalytic material the combustion of the gas entering the chamber 10 may be sufficient to bend the bimetallic strip 11.  To avoid dazzle the protecting bell 1 may have a matt surface or the cooling liquid 2 be made cloudy.