Page:Proceedings of the Royal Society of London Vol 69.djvu/419

Rh 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.

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.