T/n' Stratification* of ffi/droyi'ii. 401 



At l*mm. pressure very little hydrogen could lie detected by the 

 spectroscope, the stratifications had almost disappeared, and mercury 

 was strong throughout the tube. 



Elimination of Mercwry 



The mercury apparently diffused into the tube from the pump and 

 many devices were adopted to keep it out. Long glass tubes filled 

 with purified sulphur broken into coarse pieces were partially successful, 

 but something (probably sulphur) was communicated to the hydrogen 

 which interfered with the purity of the colours. Also the sulphur did 

 not prevent a little mercury diffusing in if the tubes were left on the 

 pump all night. 



Experience showed that mercury was very difficult to eliminate 

 from a tube once it had gained access. It adheres to the walls of the 

 tube, and defies detection in the cold, but becomes visible in the 

 spectroscope as soon as the tube is heated by a lamp. Therefore a 

 new hydrogen tube was made, and connected with tubes containing 

 sulphur, bright copper turnings, and phosphoric anhydride ; the copper 

 intervening to keep out the sulphur. Here, again, mercury was 

 detected after some days, but only in minute traces. In each of these 



twenty-one double strata intensely blue, but with a carmine line between the com- 

 ponents." ' Phil. Trans.,' vol. 169, pp. 175, 190. 



Frequently a change from all of one colour to all of the other colour is recorded. 

 Thus : " The tube was filled to within 1 inch of the negative with strata ; nil 

 these were blue, but they turned pink when 200,000 ohms resistance was intro- 

 duced. When 7,590,000 ohms resistance was introduced, a very close and somewhat 

 agitated pink stratification was produced." " Thirty-four steady blue strata were 

 produced ; on introducing 200,000 ohms resistance, the strata turned pink." 

 "With 3600 cells the strata were blue and sixty-one in number. With 700,000 

 ohms resistance the strata were reduced to eighteen and turned pink." " A change 

 of current frequently produces an entire change in the colour of the strata. For 

 example, in >i hydrogen tube, from a cobalt-blue to a pink." 'Phil. Trans.,' 

 vol. 169, pp. 183, 190, 231. 



Very few spectrum observations were made by the authors, and they are not 

 very definite in character. One tube, which gave ten luminosities, was examined 

 with the spectroscope. " The C and F lines were brilliantly seen in the glow 

 around the negative terminal, but were not visible in the spectrum of the nebu- 

 losities, notwithstanding that they were brighter than the negative glow ; there 

 were blue, green, and red visible, but not the characteristic green and red lines of 

 hydrogen." In another tube, " The characteristic hydrogen lines were very brilliant 

 when the spectroscope was directed to the glow around the negative terminal, but 

 quite a different spectrum was seen on a bright stratum, with mercury lines in the 

 orange." " The hydrogen lines could not be seen either in the strata or the glow 

 on the negative ring, but instead of them mercury lines came out strongly. There 

 is reason to think that at this stage there was little gas except mercury vapour in 

 the tube." " A change of current frequently . . . changes the spectrum of the 

 strata ; moreover, the spectra of the illuminated terminals and the strata differ."- 

 Phil. Trans.,' vol. 169, pp. 180, 216, 232. 



