ARGON, A NEW CONSTITUENT OF THE ATMOSPHERE. 11 



tube, until all the metal has united with nitrogen. Tlie heat developed by the 

 couiI)ination is considerable, and the; glass softens; but by careful attention and 

 regulation of the I'ate of the current, the tube lasts out an operation. A piece of 

 combustion tubing of the usual length for organic analysis, packed tightly witli 

 magnesium turnings, and containing about 30 gi'amnies, absorbs between seven and 

 eight litres of nitrogen. It is essential that oxygen be excluded from the tube, 

 otherwise a fusible substance is produced, possibly nitrate, which blocks the 

 tube. AVith the precaution of excluding oxygen, the nitride is loose and porous, 

 and can easily' be removed from the tube with a rod ; but it is not possible to use 

 a tube twice, for the glass is generally softened and deformed. 



(g) Nitride of aluminum has been investigated by Mallet.' He obtained it iu 

 crystals by heating the metal to whiteness in a carbon crucible. IJut ahuninum 

 shows no tendency to unite with nitrogen at a red heat, and cannot l)e used as an 

 absorbent for the gas. 



(h) Garresheim^ states that he has induced combination between nitrogen and 

 mercury ; but the affinity between these elements is of the slightest, for the com- 

 pound is explosive. 



(i) The union of hydrogen with nitrogen to form anunonia in jireseuce of an 

 acid seems to pi'oceed at a fair I'ate under the influence of electric spai'ks fi-oni a 

 battery and coil ; but an atteiupt to increase the rate by use of the alternating 

 cuirent from a dynamo has not so far succeeded. 



The process of removing nitrogen by a coml>ination with oxygen is treated in 

 § 2, 4, an<l 8. 



4. Early Experiments on Sparking Nitrogen with Ox;ygen in Presence 



OF Alkali. 



In our earliest attempts to isolate the suspected gas by the method of 

 Cavendish, we used a Ruhndcorff coil of medium size actuated by a battery of five 

 Grove cells. The gases were contained in a test tube standing over a large 

 quantity of weak alkali, and the current was conveyed in wires insulated by 

 inverted U-shaped glass tubes passing thi'ough the liquid round the mouth of the 

 test tube. The inner platinum ends of the wii'e were sealed into the glass insu- 

 lating tubes, but reliance was not placed upon the sealings. In oi'der to secure 

 tightness in spite of cracks, mercury was placed in the bends. This disposition of 

 the electrodes complicates the apparatus somewhat and entails the use of a large 



' Transactions of the Chemical Society, 1876, II, 349. 

 " Annalen dcr Chemie iiiid Phannacie, 195, 373. 



