472 



Sir W. Ramsay and Prof. J. N. Collie. [May 18, 



-on to the burette; the burette was washed out twice with oxygen, 

 and by lowering the reservoir several times the upper end was made a 

 torricellian vacuum ; it was left thus for some time, so as to insure the 

 Temoval of adhering nitrogen from the walls of the tube. 



The electrolytic gas was then introduced, and exploded. As the 

 explosion-burette was graduated, the total volume of the gas, as well as 

 that of the residual hydrogen, was read. There were 16 - 43 c.c. of 

 gas; the residual hydrogen measured TOl c.c. at normal temperature 

 •and pressure, and thus amounted to 6T8 per cent, of the total. The 

 volume of this gas was increased by lowering the pressure so that it was 

 in contact with the fused potash. It was left for more than an hour ; 

 the potash, of course, was wet with the water formed by the explosion. 



The capillary tubes above the stop-cock of the gas-burette, which had 

 been twice washed out with oxygen, were pumped as empty as possible, 

 until the vacuum-tube showed only the yellow and green lines of the 

 mercury spectrum, and the faintest trace of a hydrogen spectrum. A 

 strong current was passed between the electrodes so as to heat them 

 and expel occluded oxygen. After this process had been repeated as 

 long as was thought safe, until, as remarked, the hydrogen spectrum 

 was extremely faint, the tap to the pump was closed. The hydrogen 

 containing the emanation was then admitted from the explosion- 

 burette ; it was dried by passage through the narrow tube B filled 

 with phosphoric anhydride, and it entered the bulb C, and the vacuum- 

 tube D. This vacuum-tube was made of lead glass, with electrodes of 

 aluminium. It was 2*5 cm. long, with a capillary of about 1 cm. in 

 length. The aluminium electrodes were closely surrounded with glass, 

 fused round them, so as to limit the capacity of the tube as much as 

 possible ; it was probably under one-twentieth of a cubic centimetre. 



Liquid air was next poured into the jacket surrounding the bulb C, 

 and the reservoir was raised and lowered half a dozen times, so as to 

 convey all the gas into contact with the cooled bulb. The mercury 

 was then raised to the level a, and the tap to the pump opened ; and 

 while the jacket was kept replenished with liquid air the hydrogen was 

 pumped off, until its spectrum had almost entirely disappeared, the red 

 line being hardly visible. The tap to the pump was then closed, the 

 level of the mercury was raised to b, and the liquid air allowed to 

 evaporate. The bulb was so bright that it was easy to read the time 

 on a watch. The mercury was then raised to the level c, and the 

 current passed. The spectrum was very brilliant, consisting of very 

 bright lines, the spaces between them being perfectly dark ; it had a 

 striking resemblance in general character to the spectra of the gases of 

 the argon group. 



A direct-vision spectroscope, made to special design by Heele, with 

 an illuminated scale for reading, had immediately before been 

 standardised by noting the position of the leading lines of helium and 



