16 



ARGON, A NKW CONSTITUENT OF THE ATMOSPHERE. 



tiihe (t liaviiii,' tlieii ceased to absorb, was quickly reinovetl and replaced by a 

 fif.sli tube. Tliis tube was, of course, full of air, and before the tube G was 

 heated, the air was carried back from B towards A by passiug a little uitrotjen 

 from right to left. The oxygen in the air was removed by the metallic copper 

 and the nitrogen passed into the gasholder A, to be returned in the opposite 

 direction to B. 



Ill till' course of about ten days, most of the nitrogen Ii.nl been absorbed. 

 The niagnesiuni was not always completely exhausted ; usually the nitride pre- 

 sented the appearance of a blackish-yellow mass, easil)' shaken out of the tube. 

 It is needless to say that the tube was always somewhat attacked, becoming black 

 with a coating of magnesium siiicide. The nitride of magnesium, whether black- 

 ish or oiange, if left for a few hours exposed to moist aii-, was completely con- 

 verted into white, dusty hydroxide, and during exposure it gave off a stroncr odor 

 of ammonia. If kept in a stoppered bottle, however, it was quite stable. 



It was then necessarj^ in ordei- to continue the absorption to carry on opera- 

 tions on a smaller scale, with [necautions to exclude atmospheric air as completely 

 as pos.sib]e. There was at this stage a re.sidue of 1500 cubic centimetres. 



The apparatus was therefore altered to that shown in Fig. 3 so as to make it 

 possible to withdraw all the gas out of the gas-holder A. The left-hand exit led 





KiG. 3. 



to the Spicngel's puiiip; the compartment (a) of the drying tube B was filled with 

 soda-lime, and (/») with phosphoric anhydride. C is a tube into which the gas 

 could be dr.iwn from the ga.s-holder A. The stopcock, as shown, allows gas to 

 pass through the hoi-izontal tubes and does not communicate with C ; l)Ut a vertical 

 groove allows it to ])e jdaced in communication either with the gas-holiler, or with 

 the apparatus to tli.- li'Jil. The compartment (/>) of the second drying tube D 



