18 THE DISCOVERY OF ARGON AND HELIUM. 



Now I will show you a tube of the gas argon. Argon can be 

 made to give out two different kinds of light when excited by- 

 means of the electric current — one a purple and the other a beau- 

 tiful blue. I will first show you the purple. That tube is the 

 historic argon tube. It was lent me by Professor Ramsay, and is 

 the one which was used for the measurement of the argon lines 

 by Mr. Crookes, and is the one which has been shown at all the. 

 different exhibitions of argon. It owes its beautiful colour to its 

 long life. There are very few argon tubes which give anything 

 like the brilliancy of this ; in fact, I believe there are none, because 

 there are none so pure. By this incessant violent knocking of the 

 atoms of the gas against the sides of the tube and against each 

 other, it becomes purer and purer, as the other gases get absorbed 

 by the electrodes, which are made of magnesium, so that this is a 

 perfectly pure sample of argon inside the tube. Now, I want you 

 to see the wonderful change that takes place in the argon light the 

 moment I put a Leyden jar with a spark-gap into the circuit. It 

 now becomes a beautiful blue colour. 



This light was examined by the spectrum and found to give 

 out various lines, which showed that it was different to any other 

 gas. It was also found on weighing the gas that it was heavier 

 than ordinary nitrogen, being twenty times heavier than hydrogen, 

 whilst ordinary nitrogen is only fourteen and a half times heavier, 

 and therefore the discovery was put on a firm basis at once. 



Now, we come to the other new gas, helium, which was the 

 direct outcome of this piece of work on argon. The gas which is 

 given off when certain minerals are dissolved in acids is usually 

 carbonic acid, and there was a curious mineral which Professor 

 Ramsay's attention was called to, which is found in America and 

 also in Sweden, called cleveite. An American chemist named 

 Hildebrand had worked at it and got a large quantity of gas from 

 it, and on examining it carefully he came to the conclusion that it 

 was nitrogen. Professor Ramsay's attention was called to it in 

 order that possibly he might be able to prove that it was argon, 

 for it was a very curious thing for a mineral to give off nitrogen. 

 Professor Ramsay, immediately he heard of it, obtained some of 

 the mineral, dissolved it in acid, heated it, and got the gas off. 

 It was on a Friday afternoon that a tube was filled and looked at 



