260 HYDROGEN. 



tensely hot ; few combinations producing so high a temperature, 

 as the combustion of hydrogen. In the oxi-hydrogen blow- 

 pipe, oxygen and hydrogen gases are brought by tubes from 

 different gas-holders, and allowed to mix immediately before 

 they escape by the same orifice, at which they are inflamed. 

 This is most safely effected by fixing a jet for the oxygen within 

 the jet of hydrogen, so that the oxygen is introduced into the 

 middle of the flame of hydrogen, a construction first proposed 

 by Mr. Maugham, and adapted to the use of coal gas instead of 

 hydrogen by Mr. Daniell.* At this flame the most refrac- 

 tory substances, such as pipe-clay, silica and platinum, are 

 fused with facility, and the latter even dissipated in the state of 

 vapour. The flame itself, owing to the absence of solid matter, 

 is scarcely luminous, but any of the less fusible earths, upon 

 which it is thrown, a mass of quick-lime for instance, is heated 

 most intensely, and diffuses a light, which for whiteness and 

 brilliancy may be compared to that of the sun. With a requi- 

 site supply of the gases this light may be sustained for hours, 

 care being taken to move the mass of lime slowly before the 

 flame, so that the same surface may not be long acted upon ; 

 for the high irradiating power of the lime is soon impaired, it is 

 supposed from a slight agglutination of its particles occasioned 

 by the heat. This light placed in the focus of a parabolic re- 

 flector, was found to be visible, in the direction in which it was 

 thrown, at a distance of 69 miles, in one experiment made by 

 Mr. Drurnmond, when using it as a signal light. The heating 

 effects are even more intense when the gases are forced into a 

 common receptacle, and allowed to escape from under pressure, 

 but there is the greatest risk of the flame passing back through 

 the exit tube and exploding the mixed gases, an accident which 

 would expose the operator to the greatest danger. Mr. Hem- 

 ming's apparatus, however, may be used without the least 

 apprehension. A. common bladder is used to hold the mixture, 

 and the gas before reaching the jet, at which it is burned, is 

 made to pass through his safety tube. This consists of a brass 

 cylinder about six inches long and 3-4ths of an inch wide, filled 

 with fine brass wire of the same length, which is tightly wedged 

 by forcibly inserting a pointed rod of metal into the centre of 

 the bundle. The conducting power of the metallic channels 



* Phil. Mag. 3rd Series, vol. II, p. 57. 



