272 Lord Rayleigb and Prof. Rarnsay. [Jan. 31, 



Besides these, a mixture of barium carbonate and carbon at a high 

 temperature is known to be effective. Of those tried, magnesium in 

 the form of turnings was found to be the best. When nitrogen 

 is passed over magnesium, heated in a tube of hard glass to bright 

 redness, combustion with incandescence begins at the end of the tube 

 through which the gas is introduced, and proceeds regularly until 

 all the metal has been converted into nitride. Between 7 and 8 litres 

 of nitrogen can be absorbed in a single tube; the nitride formed is a 

 porous, dirty orange- coloured substance. 



IY. Early Experiments on Sparking Nitrogen with Oxygen in 

 presence of Alkali. 



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

 of Cavendish, we used a Ruhmkorff 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 \J -shaped glass tubes passing 

 through the liquid round the mouth of the test-tube. With the given 

 battery and coil a somewhat short spark or arc of about 5 mm. was 

 found to be more favourable than a longer one. When the mixed 

 gases were in the right proportion the rate of absorption was about 

 30 c.c. per hour, or thirty times as fast as Cavendish could work with 

 the electrical machine of his day. 



To take an example, one experiment of this kind started with 

 50 c.c. of air. To this oxygen was gradually added until, oxygen 

 being in excess, there was no perceptible contraction during an hour's 

 sparking. The remaining gas was then transferred at the pneumatic 

 trough to a small measuring vessel, sealed by mercury, in which the 

 volume was found to be 1*0 c.c. On treatment with alkaline pyro- 

 gallate, the gas shrank to 0*32 c.c. That this small residue could 

 not be nitrogen was argued from the fact that it had withstood the 

 prolonged action of the spark, although mixed with oxygen in nearly 

 the most favourable proportion. 



The residue was then transferred to the test-tube with an addition 

 of another 50 c.c. of air, and the whole worked up with oxygen as 

 before. The residue was now 2*2 c.c., and, after removal of oxygen, 

 0-76 c.c. 



Although it seemed almost impossible that these residues could be 

 either nitrogen or hydrogen, some anxiety was not unnatural, seeing 

 that the final sparking took place under somewhat abnormal condi- 

 tions. The space was very restricted, and the temperature (and with 

 it the proportion of aqueous vapour) was unduly high. But any 

 doubts that were felt upon this score were removed by comparison 

 experiments in which the whole quantity of air operated on was very 



