500 Scientific Intelligence. 



means of the spark on the walls of the tube; since on heating, the 

 helium is again liberated and the colors successively appear in the 

 inverse order. The best defined line, obtained when the green 

 glow is most intense, has the wave length 501 5-6. And if now the 

 still remaining gas is removed, and the tube is gently heated, the 

 absorbed gas is set free and the greenish glow reappears. It 

 would appear therefore that the glow is not due to the last 

 absorbed portion of helium, but comes solely from the lowering 

 of the pressure arising from the absorption. Moreover, the author 

 finds that while hydrogen, nitrogen and gaseous carbon com- 

 pounds, like helium, are more or less readily absorbed when 

 sparked in presence of platinum electrodes, argon is taken up only 

 in very small amount. And he has taken advantage of this fact 

 to separate helium from argon ; the process succeeding when 

 only 2 per cent of helium is present. By means of a Sprengel 

 pump, a mixture of these gases is kept in circulation at 3 ram pres- 

 sure, through a Plticker tube kept cool by a water jacket, for six 

 hours. And now, on removing the residual gas, and heating the 

 tube, the helium which is obtained contains only a trace of 

 argon. — Proc. Roy. Soc, lx, 449-453, 1897. g. f. b. 



3. On Calcium, nitride. —The recent noteworthy address of Sir 

 Wm. Crookes as President of the British Association has given 

 increased interest to every proposed process for rendering the 

 nitrogen of the atmosphere available in agriculture. A purely 

 chemical process of this sort has now been proposed by Moissan 

 in connection with his production of metallic calcium.* In con- 

 tact with nitrogen at the ordinary temperature, calcium under- 

 goes no change. But as the temperature is raised, the metal 

 changes from white to yellow, until, at a low red heat, it takes 

 fire and burns in the nitrogen, absorbing it with great rapidity, 

 and giving a bronze-colored nitride. The best result is obtained 

 by placing the calcium in a boat of nickel, placed within a tube 

 of the same metal, through which is sent a current of pure and 

 dry nitrogen. Under the microscope, calcium nitride appears in 

 the form of small transparent crystals yellowish-brown in color, 

 having a density of 2*63 at 17°, and fusing at 1200° approxi- 

 mately. Heated in hydrogen to redness, ammonia is evolved 

 with production of hydride. Chlorine decomposes it with incan- 

 descence giving the chloride. It burns in the air, and in oxygen, 

 even below a red heat. Mixed with carbon and heated to 800° 

 calcium nitride suffers no change. But in the electric furnace it 

 is converted into calcium carbide. If the mixture be heated to 

 1200°, a small quantity of cyanide is produced. Heated to bright 

 redness in a current of nitrogen dioxide, it is converted with 

 incandescence into calcium oxide and nitrogen. In the absence of 

 water, acids have no action on the nitride. Anhydrous alcohol 

 gives calcium ethylate and ammonia. Thrown into water, it 

 decomposes it with effervescence, producing ammonia and calcium 



* This Journal, IV", vi, 428, November, 1898. 



