THE BUNS EN LAMP. 



379 



attained is practically limited only by the capacity of the furnace 

 itself to withstand it. 



In all or nearly all the applications of illuminating gas to heating 

 purposes, however, a practical difficulty has to be overcome. The gas 

 is made for illuminating purposes, and therefore burns with a bright 

 flame, which deposits a layer of lamp-black, or soot, on everything 

 brought into contact with it. Evidently this difficulty must be over- 

 come before any extensive use could be made of gas as fuel, particu- 

 larly for those domestic purposes to which it finds one of its chief 

 applications. For practical purposes one of two methods is adopted. 

 One of these is to cause the gas to burn from a number of small open- 

 ings in a metal pipe. Two effects are thus produced. The large mass 

 of metal in the tubes abstracts heat from the flame, and, as a result, 

 the latter burns mostly blue and produces little smoke or soot ; and, 

 secondly, the distribution of the gas into several small flames allows us 

 to place the article to be heated high enough over the flame to avoid 

 the soot, and yet near enough to get a good heating effect. A second 

 and more common method of preventing the deposition of soot is by 

 the use of some form of the Bunsen lamp. 



Nearly all the common gas-stoves and other arrangements for heat- 

 ing by gas are essentially Bunsen lamps, more or less modified to suit 

 particular purposes. One of the simplest and most common forms of 

 this lamp is represented in section in the annexed figure. The gas 

 enters through the metallic tube a, 

 passes through the block b, and 

 finds an outlet through one or more 

 small apertures at c. Surrounding 

 c is a larger metallic tube, d d, 

 having at its base two apertures 

 for the admission of air.. The 

 mixed gas and air rise through 

 the tube d d, and burn at the top 

 with a pale-blue, smokeless flame. 

 The lamp is supported by a heavy 

 cast-iron foot, e. 



Though this lamp is of simple 

 construction, the explanation of its 

 operation involves some very cu- 

 rious and interesting facts regard- 

 ing the theory of flame, as well as some very familiar ones, and in 

 order to comprehend it we shall need to begin with a study of flame 

 in general, and of luminous flames, like that of ordinary gas, in par- 

 ticular. 



When a solid combustible, like charcoal, burns in the air, it pro- 

 duces no flame, but simply glows. The blue flame that is often observed 

 playing over the surface of a coal-fire is that of the carbonic-oxide gas 



