TRANSACTIONS OF SECTION G. 817 



brass cylinder attached to an outer case of brass or copper. The exciting liquid is 

 a mixture of bichromate of potash, nitric acid, and sulphuric acid. Luminosity 

 (with a reflector) sufficient to enable newspaper print to be read at a distance of 

 twelve feet, for ten hours' duration. "Weight, 7 lbs. Price, by the gross, 32s. 

 Cost of maintenance, Id. per day. 



The Portable Electric Syndicate's Lamp. — Secondary battery. Luminosit}' 

 (without reflector), IJ candle for ten hours' duration. Weight, 4j lbs. Price, 

 one guinea. The lamp is fitted with an automatic arrangement in connection with 

 the incandescent lamp, whereby if an outer casing of toughened glass be broken 

 the current is cut off to prevent explosion of fire-damp. 



The Vaughton Lamp. — Secondary battery. The electrodes are wedged 

 tightly in the cell, rendering the battery so compact that it may be subjected 

 without injury to much rough usage. The lamp weighs 5 lbs. It takes six hours 

 to charge. The working cost is estimated at Id. per day. The electrolyte used is 

 sulphuric acid diluted with eight times its volume of water, and is renewed twice 

 a week. One shilling's worth of acid suffices for 100 lamps for one week. The 

 price is from 25s. to 27s. Qd. 



The author concluded by referring to the questions of primary versus secondary 

 batteries, and considered the position of the light on the lamp case as not finally 

 settled. 



9. Oil an Automatic Fire-clamp Detector. i?(/ Joseph Wii.soN Swan, J/.^. 



At the last meeting of the Association, the author communicated to this Section 

 a description of a fire-damp detector and meter, designed, more especially, to be em- 

 ployed as an appendage to electric safety lamps and exhibited a working model of 

 the combination. 



The object of that apparatus was to provide means by which the manager or 

 one of the overseers of a colliery could, by making tests in various parts of a mine, 

 ascertain, with a considerable degree of exactness, whether or no fire-damp is pre- 

 .sent, and, if it be, in what proportion. That apparatus fulfilled its purpose very 

 well ; it was accui-ate and sensitive, so much so that if only the one-tenth of 1 per 

 cent, of fire-damp existed in the air it was clearly shown. 



But it was not sufficiently simple to allow of its being made an adjunct to 

 everi/ lamp, nor was it automatic in its action. It therefore appeared de- 

 sirable, if possible, that these deficiencies should be met or complemented by a 

 ■simple and automatic apparatus, suitable for attachment to everi/ electric safety 

 lamp, or at lea.st to all those used where gas is likely to be found. Such an 

 apparatus he has the honour to bring under the notice of the members. The 

 primar}' principle of its action is the same as in Liveing's well-known gas indicator, 

 in which diflference of temperature in two similar electrically heated platinum 

 wires (one exposed to the air to be tested, and the other enclosed in a glass tube) 

 is caused by the combustion of fire-damp in contact with the exposed wire. 



In Liveing's apparatus the quantity of gas present in the air is estimated by the 

 degree of difl'erence in the luminosity of the two wires. 



In my apparatus use is made of the difference of temperature arising in the 

 manner described, but so as to cause movement in a column of mercury, and 

 through that the interruption of the electric current which lights the lamp ; there- 

 fore the lamp provided with this apparatus goes out just as an ordinary safety lamp 

 does when placed in air contaminated to a certain extent with fire-damp. 



In another form of the apparatus, difference of temperature in the indicator 

 wires causes the free ends of a pair of thermoscopic metallic spirals to separate, 

 and by separating to interrupt the electric current which lights the lamp connected 

 with the indicator, and in that way to bring about the extinction of the light. 



The new gas detector is therefore distinct from what has hitherto been pro- 

 posed in its acting automatically upon the lamp, so as to extinguish its light. 



It takes the form of a small circular metallic box, fastened upon the outside of 

 the lamp case ; the box contains a differential thermometer. 



In the first-mentioned form of the apparatus it consists of two glass bulbs (con- 



1888. 3 G 



