The Preparation and some of the Properties of Pure Argon. 187 



each end by a reducing socket with an iron tube, 0*25 inch in diameter. 

 The tube contained 250 grams of magnesium, cut into coarse shavings 

 in a shaping machine ; the magnesium was not pressed very tightly into 

 the tube. Since after each operation it was necessary to remove the 

 sockets in order to clear the tube, the joints were luted with red lead, 

 and the tube was made of sufficient length to project about 3 inches at 

 each end of the furnace. 



The greater part of the nitride was generally removed by using an 

 iron rod, and the remainder by means of water, which converted it into 

 the hydroxide. The tube was raised to a bright red heat before con- 

 necting it with the (J -tube 0, in order to allow the greater part of the 

 hydrogen occluded by the magnesium to escape. The absorption of 

 the nitrogen, which was indicated by the rate of flow of the gas 

 through the U -tubes N and 0, was maintained briskly until practically 

 the whole of the magnesium was converted into nitride ; the volume 

 of the gas absorbed was equivalent to half the capacity of the large 

 gasholder. 



The gas, after leaving the U'tube O, passed through a second iron tube 

 H, containing copper oxide ; next, through the vessel P, in which water 

 condensed; and it finally collected in the gasometer B. That which 

 passed during the first stages of the process consisted of nitrogen con- 

 taining much argon ; but towards the end of the operation the argon 

 became much diluted, until finally the gas which passed through the 

 U-tube consisted almost entirely of atmospheric nitrogen. The 

 tube G was then replaced by another containing a fresh supply of 

 magnesium. 



The tap c was then closed, and the taps d and e turned, so that the 

 gas in the gasometer B could be made to flow through the magnesium and 

 copper oxide tubes into the gasometer C. In this process its volume 

 was very much reduced, and the gas which collected in C probably 

 contained as much as 25 per cent, of argon. When the whole of the 

 gas had been expelled from B, the taps d and e were again turned, and 

 atmospheric nitrogen was allowed to flow through the magnesium tube, 

 -as in the first stage of this operation. 



When the gasometer C had become full of the mixture of nitrogen 

 and argon, as it did at the end of every third or fourth operation, 

 it became necessary to reduce its volume by further absorption 

 of nitrogen. The method employed, which was first described by 

 Maquenne,* consisted in passing the gas through a hard glass tube 

 containing a mixture of magnesium powder and lime, heated to 

 a dull red heat in a combustion furnace. The lime was obtained 

 by thoroughly calcining precipitated chalk in a muffle. The nitrogen 

 continued to be completely absorbed as long as calcium remained 

 unattacked, so that the product of this operation consisted of pure 

 * ' Compt. Eend.,' 1895, vol. 121, p. 1147. 



