THE DISCOVERY OF ARGON AXD HELIUM. 17 



metallic magnesium ; thus, all the various impurities in the gas 

 are absorbed, and finally only argon is left. 



The next diagram represents apparatus for conducting opera- 

 tions on a larger scale. It is an automatic arrangement for making 

 the gas circulate round and round, and is a very effective appara- 

 tus for the manufacture of argon on a large scale. 



After argon had been obtained in this way, the difficulty was to 

 find out how it differed from other substances, and unless chemists 

 had been able to make use of the electric discharge through a gas 

 they never would have been able to find out that this argon was 

 different from ordinary nitrogen or any other element. A great 

 many substances are able to give out light when they are sub- 

 jected to the electric discharge, and I will now show you three 

 extremely beautiful experiments, by means of apparatus lent me 

 by Mr. Jackson, of King's College. The first will show you how 

 a solid emits light when submitted to an electric discharge, the 

 second a liquid, and the third a gas, and in each case you will find 

 that we get a very beautiful light given out. In this vessel I have 

 some ordinary lime, made by igniting bits of calc spar. I will 

 connect it with a battery producing sparks, and when I turn on the 

 current we shall find this solid produces a most beautiful light. 



The next experiment deals with a liquid, a solution of sulphate 

 of quinine, which you will see gives out a beautiful blue light. 



Finally, I will take a gas and show you how we can, by passing 

 an electric discharge through it, get it to light up just in the same 

 way as the soHd and the liquid. It is a long tube filled with air ; 

 in its normal condition it gives no light, but it is connected with 

 an air-pump, and as I gradually exhaust the air you will see how 

 the light begins to appear, and increases as the vacuum becomes 

 more perfect. When I turn the stopcock and allow air to enter it 

 diminishes, and finally disappears. If it had not been for the 

 power of lighting up gases in that way by electricity, it would have 

 been extremely difficult to detect argon in small quantities. 



All gases can be lit up by means of the electric currer^t, if 

 they are exhausted to a sufficient degree of rarity. I have several 

 tubes here containing different gases, which I should like to show 

 you. Some contain air, one contains hydrogen, and one carbonic 

 acid, and each gas gives a different kind of light. 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. VII. c 



