62 Hutchins — Absorption of Gases in a High Vacuum. 



As the following experiments had for their object the pro- 

 duction of a permanent state of vacuum under the electric dis- 

 charge, they were limited to such gases as could be produced 

 readily in the tubes themselves, and whose use seemed to hold 

 out promise of success. 



A number of Pliicker tubes were made, as nearly alike as 

 possible, and each provided with a small communicating tube 

 containing some chemical that would yield the desired gas by 

 the application of heat. The chemicals were prepared as pure 

 as possible, and dried at a hundred degrees for twenty-four 

 hours. The dried-out tubes, containing the chemicals, were 

 then attached to the mercury pump and exhausted ; heated 

 very hot and pumped to remove all water vapor. The tube 

 containing the chemical was then heated, gas driven off into- 

 the tube and the exhaustion repeated. 



In nearly every case it was found impossible to entirely get 

 rid of water vapor, even by repeatedly washing out with the 

 gas. The tubes were sealed at such a degree of exhaustion as 

 would allow the subsequent rise in vacuum to be well marked, — 

 when the green fluorescence of the glass appeared at the 

 cathode, and the sparking distance across the terminals of the 

 coil and in parallel with the tube was 2 mm . After the tube was 

 sealed, it was placed before a spectroscope, and the current 

 from the coil passed until the spectroscope showed the entire 

 absorption of the gas, or until the vacuum became too high 

 for the current to pass readily. A fairly good idea of the rela- 

 tive rates of absorption of the various gases may be obtained 

 from the time required for the absorption to take place. 



Tube containing zinc cyanide. — This substance yields 

 cyanogen when heated. The tube was washed out with 

 the gas as above described and sealed. The vacuuui began 

 to rise at once as soon as the current was turned on. In 

 five minutes the whole tube became fluorescent, and in 

 seven minutes the cyanogen was entirely absorbed, the spec- 

 trum being now that of the trace of water vapor from which 

 the zinc cyanide could not be freed. It is difficult to see why a 

 gas which if decomposed by the discharge would remain as the 

 chemically inert nitrogen, should disappear at such an extra- 

 ordinary rate. To test the matter further another tube was 

 made in such form that when the vacuum became higher than 

 a certain value, a portion of the current was shunted through 

 a platinum wire surrounded by zinc cyanide, and so the vacuum 

 was automatically maintained nearly constant. This tube was 

 worked for four hours, and the yield and absorption of the gas 

 went on for the whole time at a nearly constant rate. 



Tube containing lead ferrocyanide, yielding nitrogen when 

 heated, also gave considerable water vapor. Sealed at 

 a slightly lower vacuum than the first, yet the nitrogen all 



