HOMOGENEOUS YELLOW LIGHT. 109 



descends into a platina or metallic cup D. This 

 cup is strongly heated by a spirit-lamp L, in- 

 closed in a dark lantern, and when the diluted 

 alcohol in D is inflamed, it will burn with a fierce 

 and powerful yellow flame. If the flame should 

 not be perfectly yellow, owing to an excess of 

 alcohol, a proportion of salt thrown into the cup 

 will answer the same purpose as a further dilution 

 of the alcohol.* 



A monochromatic lamp for producing yellow 

 light may be constructed most effectually, by 

 employing a portable gas lamp, containing com- 

 pressed oil gas. If we allow the gas to escape 

 in a copious stream, and set it on fire, it will 

 form an explosive mixture with the atmospheric 

 air, and will no longer burn with a white flame, 

 but will emit a bluish and reddish light. The 

 force of the issuing gas, or any accidental current 

 of air, is capable of blowing out this flame, so 

 that it is necessary to have a contrivance for sus- 

 taining it. The method which I used for this 

 purpose is shown in Fig. 22. A small gas tube 

 a b c, arising from the main burner M N of the 

 gas lamp PQ-, terminates above the burner, and 

 has a short tube d e, moveable up and down 

 within it, so as to be gas-tight. This tube d e, 

 closed at e, communicates with the hollow ring 

 f g, in the inside of which four apertures are per- 

 forated in such a manner as to throw their jets of 

 gas to the apex of a cone, of which f g is the 

 base. When we cause the gas to flow from the 

 burner M, by opening the main cock A, it will 

 rush into the tube a b c d, and issue in small 

 flames at the four holes in the ring/y. The size 

 * See Edinburgh Transactions, vol. ix., p. 435. 



