nXYCKN AND ITS SALINE COMBINATIONS 



173 



Mixtures of hydrogen and of various other gases with oxygen 

 are taken advantage of for obtaining high temperatures. By the 

 aid of such high temperatures metals like platinum may be melted 

 on a large scale, which cannot be 

 done in furnaces heated with char- 

 coal and fed by a current of air. The 

 burner, shown in fig. 34, is constructed 

 for the application of detonating gas 

 to the purpose. It consists of two 

 brass tubes, one fixed inside the other, 

 as shown in the drawing. The internal 

 central tube C C conducts oxygen, and 

 the outside, enveloping, tube E' E' con- 

 ducts hydrogen. Previous to their 

 egress the gases do not mix together, 

 so that there can be no explosion inside 

 the apparatus. When this burner is 

 in use C is connected with a gasholder 

 containing oxygen, and E with a gas 

 holder containing hydrogen (or some- 

 times C0al-as). The flow of the FlG - 34 -~ Safety burner for detonating gas,. 



described in text. 



gases can be easily regulated by 



the stop-cocks O H. The flame is shortest and evolves the greatest 

 heat when the gases burning are in the proportion of 1 volume of 

 oxygen to 2 volumes of hydrogen. The degree of heat may be easily 

 judged from the fact that a thin platinum wire placed in the flame 

 easily melts. By placing the burner in the orifice of a hollow piece 

 of lime, a crucible A B is obtained in which platinum may be easily 

 melted, even in large quantities if the current of oxygen and 

 hydrogen be sufficiently great (Deville). The flame of detonating gas 

 may also be used for illuminating purposes. It is by itself very pale, 

 but owing to its high temperature it may serve for rendering infusible 

 objects incandescent, and at the very high temperature produced by the 

 detonating gas the incandescent substance gives a most intense light. 

 For this purpose lime, magnesia, or oxide of zirconium are used, as they 

 are not fusible at the very high temperature evolved by the detonating 

 gas. A small cylinder of lime placed in the flame of detonating gas, 

 if regulated to the required point, gives a very brilliant white 



formerly, and Otto's is now, the best known. The explosion is usually produced by coal- 

 g.is and air, but of late the vapours of combustible liquids (kerosene, benzene) are 

 also being employed in place of gas (Chap. IX.). In Lenoir's engine a mixture of coal- 

 KJIS and air is ignited by means of sparks from a RuhmkorfF s coil, but in the most recent 

 marl lines the gases are ignited by the direct action of a gas jet. 



