The Microscope. 67 



landmarks so distinct and prominent that the recognition of a par- 

 ticular spectrum is made easy, even to the novice v?ho is not accus- 

 tomed to vpork with the spectroscope. 



Gases are examined by means of electric induction sparks. 

 Experience has taught us that diluted gases are good electric con- 

 ductors, vsrhilst in a state of density they are, vv^ithout exception, bad 

 conductors. It was Dr. Geisler of Bonn who constrvicted gas tubes, 

 from which he exhausted the air with an air pump, until about only 

 T5 ^o -jl-Q of the atmospheric pressure was left. These tubes were 

 then filled with the gas to be experimented with, and the tubes her- 

 metically closed. At both extremities of the tubes, electrodes of 

 platinum or of aluminum are soldered in, so that they can be thereby 

 connected to a Spark inductor. (All other metals would oxidize into 

 the intense heat created). In this state of attenviation the gas offers 

 but slight resistance to the passage of the spark, intense heat is 

 generated, and brilliant and beautiful light is emitted of various 

 colors, changing, of course, with the different gases employed. In 

 a darkened room the display of colors is charming, and this is 

 heightened by the skillful manner with which the glass-blower per- 

 forms his delicate task. Splendid effects may also be produced by 

 thin-bored thermometer tubes, with a bulb at each extremity, into 

 which the electrodes are fused. 



DIAGNOSIS OF GASES BY THEIR COLOR. 



Hydrogen, according to Thudicum (who used the thin cored 

 thermometer tubes with bulbous end), gives crimson in the narrow 

 part and reddish light in the wide part of the tube: 



Narrow Part. Wide Part. 



Nitrogen Violet red. Violet red. 



Chlorine Green. Reddish violet. 



Bromine Greenish blue. Violet. 



Iodine Green. Fawn color. 



Hydrocarbon, C. H. 2 Rose colored. Greenish. 



Garb. Acid Greenish while. Same. 



DIAGNSOSES OF GASES BY THEIR ' SPECTRA (tHUDICUm) : 



Oxygen, nine colored lines; the most brilliant; one red and one 

 violet, two in green, two blue, two greenish yellow ones and one 

 dark red line. 



Hydi'ogen, three light lines, at C, F, and G. 



Carbonic cxide, eight colored lines, a most interesting spectrum 

 that shows also dark lines. 



