224 Trowbridge — Spectra of Hydrogen and the 



Moreover the thin glass of the "bulb did not appreciably absorb 

 the ultra-violet rays until the wave length 1800 was reached, 

 and this absorption did not affect my conclusions since my 

 work was confined to the portions of the spectrum studied by 

 astrophysicists. The diameter of the narrowest portion of the 

 tubes was about l cm . I employed still another form of 

 tube, shown also in fig. 1. At one side of this tube there was 

 an adjunct consisting of a palladium tube P on the outside of 

 the spectrum tube joined hermetically to a platinum wire 

 inserted in the walls of the tube. A glass vessel filled with 

 dilute sulphuric acid slipped over the palladium tube. At 

 one end of this glass vessel was inserted a platinum wire. The 

 palladium wire was made the cathode and the platinum wire 

 the anode of a battery. In this way hydrogen is liberated on 

 the surface of the palladium tube, is then occluded and can be 

 made to pass into the spectrum tube.* 



The tubes which were not provided with palladium tubes 

 were filled with hydrogen or nitrogen, through a series of 

 tubes filled with caustic potash, and through a number of 

 tubes filled with phosphoric pentoxide provided with partitions 

 of glass wool. After many attempts I adopted the following 

 arrangement of these tubes, which proved satisfactory. In the 

 first place I fuund it necessary to discard all gums or other 

 adhesive material and to use ground-glass joints and mercury 

 seals for these joints, having satisfied myself that all other 

 forms of connections consume time and are worthless. 

 The tubes were mounted on a board and after the joints had 

 been adjusted the final adjustment with the gas holder could 

 be readily and safely accomplished by means of a rack and 

 pinion which raised or lowered b} T slow degrees the gas holder 

 fig. 2. This drying arrangement could be exhausted to a high 

 degree and would hold the rarified gas as long as desired. The 

 method of filling the tubes was as follows : the spectrum tube 

 was exhausted to about 'l mm , having been repeatedly filled with 

 hydrogen. This operation was continued until the hydrogen 

 spectrum appeared. Finally the tube was exhausted to the 

 X-ray stage by long heating and by employing a strong con- 

 denser discharge. Then the dried gas was admitted until a 

 pressure of about 'l mm remained in the tube. The vessels with 

 palladium tubes were carefully exhausted to the X-ray stage 

 (and beyond, a spark preferring to jump six inches in air to 

 passing through the tube). When these tubes with the palla- 

 dium adjunct were connected to the terminals of the battery a 

 slight heating was sufficient to start a discharge and to cause 

 the occluded hydrogen to appear in the spectrum tube. 



* A device due to Dr. William Kollins, Boston. 



