124 OPERATn'E TFXHNIQUE. 



benzol into gas as it issues from the reservoir, and to keep the benzol 

 in the reservoir itself nearly at boiling-point. It may be imagined, 

 however, that the pressure in the apparatus would become dangerous 

 and involve an explosion. Two safeguards are provided against this. 

 Firstly, the apparatus is very strong ; and secondly, an undue pressure 

 in it would force benzoline outwards in such quantit}' as to produce 

 large white flames, and thus give timely notice of danger. In practice 

 the author has found the apparatus remarkably steady and reliable. 

 The firing points and edges are easily heated to a bright cherry red, 

 and the apparatus works without any regulating for twenty minutes to 

 half an hour, when a turn of the milled head will enable cne to 

 continue for another quarter of an hour, a sufficient period to finish 

 any ordinary operation. 



As the whole apparatus would otherwise become unpleasantly 

 warm, the main body of the reservoir is covered with a tube of 

 insulating material, — " vulcanised fibre."' The fact that the expensive 

 platinum heads and points are entirely dispensed with permits of the 

 apparatus being sold at a very reasonable sum. 



For heating the ordinary iron a forge or small stove is usually 

 employed. Charcoal or coke is preferable to coal. Within recent 

 years, however, advantage has been taken of the numerous automatic 

 lamps, burning petroleum spirit or benzole, to produce a convenient 

 and easily transported stove. In these lamps the pressure produced 

 within the bod\' of the lamp b}' warming the fluid, causes a small 

 quantity to mount through a capillary tube into a chamber sur- 

 rounding the flame, which chamber is therefore always at a high 

 temperature. Arrived here the liquid is rapidl}- transformed into 

 gas, and escaping through a small hole, emerges in the form of a 

 powerful jet which sucks air through orifices surrounding it, and when 

 ignited burns with a very intense flame. B}- adapting to such a lamp 

 a suitable hood for receiving the heads of the firing irons an excellent 

 portable furnace is produced. 



A very good form of automatic petroleum furnace is that shown 

 in Fig. 151. The reservoir {a) contains ordinary paraffin oil, with 

 which it is filled through the plug [b). To set the apparatus in 

 action, the small air-pump (c) is worked for a minute or two, 

 until the air pressure in the reservoir is sufficient to force the 

 oil up to the burner (/). A little methylated spirit is then poured 

 into the ring at the base of the burner and ignited, thus heatmg 

 the burner. On then cautiously relaxing the screw (C), a fine 

 stream of petroleum flows into the burner, becomes vaporised, 

 and issues as a powerful jet from a small orifice at the base of 



