INERT CONSTITUENTS OF THE ATMOSPHERE. 587 



of a balloon of six liters capacity, in the interior of which an electric 

 flame is kept alight by means of a transformer, while a jet of caustic 

 alkali forms a fountain in the interior, gives good results. By its help, 

 seven or eight liters of mixed gases can be made to combine per hour. 



Such experiments show the inactive nature of the argon group of 

 gases towards an electro-negative element, oxygen. The gases are 

 absolutely incombustible. No other elements can withstand such 

 treatment, save platinum and its congeners, and gold. But even these 

 metals combine with fluorine or clilorine, when heated in a current of 

 one or other gas. Argon, however, is wholly unaffected when electric 

 sparks are passed through its mixture with chlorine or fluorine, the 

 two other most electro-negative elements. To them, too, it shows 

 itself completely indifferent. 



A more convenient method of separating the nitrogen from its 

 admixture with argon in atmospheric air is by means of red-hot 

 magnesium. The metal magne- 



sium, which is now made on a 

 considerable scale for photo- 

 graphic and signaling purposes, is 

 a white, silvery metal, which can 

 be planed or turned into shav- 

 ings. In the early experiments, a 

 measured quantity of atmospheric -; 

 nitrogen, dried by passing over 

 suitable drying agents, was ^^^- ^^ 



brought into contact with magnesium turnings, heated to red- 

 ness in a tube of hard glass. It has been found, however, by 

 M. Maquenne, that the metal calcium, which, for this purpose 

 is most easily produced by heating together a mixture of mag- 

 nesium filings and pure dry lime, is a more efficient absorbing agent 

 for nitrogen, for it does not require such a high temperature, and 

 can be effected without danger of melting the glass tube. Indeed, the 

 operation is a very easy one, and can be carried out with the very 

 simple apparatus shown in Figure 3. M. Guntz has also found that 

 lithium, an element belonging to the same colimin in the periodic 

 table as sodium and potassium, is an exceedingly good absorbent for 

 nitrogen, for it tarnishes in nitrogen even at atmospheric temperature, 

 owing to the formation of a nitride. 



On a large scale, the magnesium turnings are contained in iron 

 tubes, and the gas-holders are made of copper or of galvanized iron. 

 By this means, fifteen liters of argon were separated from about two 

 cubic yards of air. 



The inactivity of argon in contact with such highly electro-positive 

 ■elements as lithium, magnesium and calcium again demonstrates its 



