1895.] on Argon. 531 



in a large gasholder, and are fed in automatically as required. Tbe 

 argon gradually accumulates ; and when it is desired to stop opera- 

 tions the supply of nitrogen is cut off, and only pure oxygen allowed 

 admittance. In this way the remaining nitrogen is consumed, so 

 that, finally, the working vessel is charged with a mixture of argon 

 and oxygen only, from which the oxygen is removed by ordinary well- 

 known chemical methods. I may mention that at the close of the 

 operation, when the nitrogen is all gone, the arc changes its appearance, 

 and becomes of a brilliant blue colour. 



I have said enough about this method, and I must now pass on 

 to the alternative method which has been very successful in Professor 

 Ramsay's hands — that of absorbing nitrogen by means of red-hot 

 magnesium. By the kindness of Professor Ramsay and Mr. 

 Matthews, his assistant, we have here the full scale apparatus before 

 us almost exactly as they use it. On the left there is a reservoir of 

 nitrogen derived from air by the simple removal of oxygen. The 

 gas is then dried. Here it is bubbled through sulphuric acid. It 

 then passes through a long tube made of hard glass and charged 

 with magnesium in the form of thin turnings. During the passage of 

 the gas over the magnesium at *a bright red heat, the nitrogen is 

 absorbed in a great degree, and the gas which finally passes through is 

 immensely richer in argon than that which first enters the hot tube. 

 At the present time you see a tolerably rapid bubbling on the left, 

 indicative of the flow of atmospheric nitrogen into the combustion 

 furnace ; whereas, on the right, the outflow is very much slower. 

 Care must be taken to prevent the heat rising to such a point as to 

 soften the glass. The concentrated argon is collected in a second 

 gasholder, and afterwards submitted to further treatment. The 

 apparatus employed by Professor Ramsay in the subsequent treat- 

 ment is exhibited in the diagram, and is very effective for its 

 purpose ; but I am afraid that the details of it would not readily be 

 followed from any explanation that I could give in the time at my 

 disposal. The principle consists in the circulation of the mixture of 

 nitrogen and argon over hot magnesium, the gas being made to pass 

 round and round until the nitrogen is effectively removed from it. 

 At the end that operation, as in the case of the oxygen method, 

 proceeds somewhat slowly. When the greater part of the nitrogen is 

 gone, the remainder seems to be unwilling to follow, and it requires 

 somewhat protracted treatment in order to be sure that the nitrogen 

 has wholly disapj^eared. When I say "wholly disappeared," that, 

 perhaps, would be too much to say in any case. What we can say 

 is that the spectrum test is adequate to show the presence, or at any 

 rate to show the addition, of about one-and-a-half per cent, of 

 nitrogen to argon as pure as we can get it ; so that it is fair to ar^ue 

 that any nitrogen at that stage remaining in the argon is only a small 

 fraction of one-and-a-half per cent. 



I should have liked at this point to be able to give advice as to 

 which of the two methods — the oxygen method or the magnesium 



