20 THE DISCOVERY OF ARGON AND HELIUM. 



This element, helium, has a most magnificent, brilliant yellow 

 spectrum ; in fact, the spectrum of helium, and the colour it gives 

 out when subjected to the electric discharge are by far the most 

 beautiful of any gas that I know; far more briUiant than hydrogen; 

 far more brilliant than any ordinary gas ; and if we examine it by 

 means of the spectroscope it almost seems as if the whole of the 

 most striking spectra had got mixed up together and put into one 

 tube. There is a beautiful red line, which is as brilliant as the 

 best red line in the hydrogen ; there is a magnificent, intensely 

 bright yellow line; and, moreover, there are green, blue, and 

 purple ones. All these lines exist in the helium in the most won- 

 derful manner. If you look at it through a spectroscope you see 

 a most magnificent spectrum. 



There is but little more time to tell you about these gases — 

 that is, about their general properties, and I have also not told 

 you about the preparation of argon by Cavendish, but that will 

 not take very long. What he did was this :— He actually absorbed 

 all the nitrogen by means of sparking, and I have here a diagram 

 of the apparatus he used. It is perfectly marvellous that he was 

 able to carry out the experiment with a couple of wine-glasses, a 

 bent tube, and some potash lees, and an ordinary electric machine, 

 and that was all Cavendish had when he produced argon. He 

 took the nitrogen and put it into the bent tube above mercury ; 

 he then introduced, by means of a pipette, certain quantities of 

 oxygen, and sparked them with a wire introduced here from an 

 ordinary electrical machine. In that way he was able to get the 

 very feeble electric spark which could be obtained from the elec- 

 trical machine of those days to pass from the level in one tube of 

 gas down to the liquor in the other tube. Then he added more 

 oxygen and more nitrogen, and went on thus keeping the machine 

 going for about two months, probably for twelve hours a day, and 

 was able to get the gas absorbed slowly ; and, lastly, by a little 

 liver of sulphur in this tube he absorbed the last traces of oxygen, 

 and there was a minute bubble of gas left, and so accurate had he 

 been with his measurements that he said : " After I had done this 

 there was left a small bubble, but whether that was due to another 

 constituent of the atmospheric air or not I was not able to say. 

 At any rate," he said, " if this is a new constituent of the atmo- 



