ARTIFICIAL LIGHTS. Ii 



hibition, and is especially well adapted for experiments 

 in fluorescence on account of the abundance of ultra 

 violet rays. A three-inch transparency can be magni- 

 fied up to thirty feet in diameter, and be well enough 

 lighted for a large audience to see plainly. 



THE OXYHYDROGEN, OR DRUMMOND LIGHT. 



A very intense light is produced by projecting a blow- 

 pipe flame of mixed hydrogen and oxygen gases upon a 

 stick of unslacked lime. The great heat raises the 

 lime to vivid incandescence. Sometimes magnesia is 

 employed instead of lime ; it is then called magnesia 

 light, and when zirconia is used it is called zirconia light. 

 The two latter are seldom used in the United States, 

 but the former is very common. The gases are stored 

 in portable tanks or india-rubber bags, which are con- 

 nected by flexible tubes to the jet, from which it is 

 driven by pressure upon the bags, and is lighted at the 

 outlet. There are many patterns of these jets, some 

 of them permitting the gases to mix before their .escape, 

 and others not until they are ignited. The mixed jet 

 is the most economical one, and is to be preferred for 

 most purposes. Such a piece of apparatus had better 

 be bought of a reliable dealer. 



Common illuminating gas can be used in place of 

 pure hydrogen, but the light is not quite so intense. 

 The demand for these gases has been so great during 

 the past three or four years that they are now manufac- 

 tured on a commercial scale in New York city, and are 

 compressed into copper tanks holding from ten to sixty 

 cubic feet. These tanks are exceedingly convenient. 

 They retail for twenty-two cents a foot for oxygen, and 

 eight cents a foot for the common gas. 



