9 



" Argon." They proceeded, not with the object of solving 

 Cavendish's doubts, but for the purpose of ascertaining the exact 

 weight of nitrogen gas, and it was found that the nitrogen 

 obtained by one method — namely by passing atmospheric air 

 through liquid ammonia and then through a red hot tube and so 

 converting the oxygen into water — differed ia weight from the 

 nitrogen produced by absorbing the oxygen by red hot copper, 

 the nitrogen produced by the latter method being 1 000th part 

 heavier than that obtained by the former process. That this was 

 due to something iu the atmospheric nitrogen was proved by 

 weighing pure nitrogen obtained from ammonia, pure oxygen 

 being used in the first of the processes I have mentioned in place 

 of atmospheric air. The difference in weight between the gases 

 so obtained was about half per cent. 



The method employed by Lord Rayleigh for isolating the 

 argon was the same as that used by Cavendish, with the advantage 

 of greater electric power than he had at his command. 



A U tube is filled with mercury and inverted. A mixture 

 of air and oxygen in equal proportions is passed up the tube which 

 takes its place at the junction and so separates the two mercurial 

 columns. When a current of electricity is sent from one column 

 to the other the nitrogen combines with the oxygen and a 

 residue is left amounting to about -rairth part of the nitrogen. 

 This residue is argon, and is found to be free from nitrogen except 

 to about 1 1 per cent. 



Whether argon is an element is still undecided, but that it is 

 so is I understand considered highly probable. 



During his experiments on nitrogen the attention of Professor 

 Ramsay was called to a means of producing it from ui'aninite 

 acted on by sulphuric acid. The Professor tried this, but the 

 conditions under which he worked being somewhat different it 

 was found by the spectroscope that the gas produced was not 

 nitrogen (although there was a slight quantity), but that the gas 

 produced a yellow spectrum answering to the yellow band 

 in the solar spectrum which had been named helium as repre- 

 senting a metal in the sun, but unknown to us. It was then 

 found that helium existed in the spectra of nebula and stars, and 

 in a degree varying with their temperature. 



While on these subjects I should like to devote a few moments 

 to air in its liquid state. 



Pictet, in Geneva, and Cailletet, in France, solved the pro- 

 blem of the liquefaction of the permanent gases — as they were 

 called, but it was reserved for Dewar to bring this feat into 

 practical use and to obtain liquid air, liquid oxygen, and liquid 



