Mixter — Experiments with Endothermic Gases. 325 



of an indifferent gas checks the explosion of acetylene, as the 

 following show : A dry mixture of 1 volume of acetylene and 

 2 volumes of hydrogen at a pressure of 5 atmospheres was not 

 exploded by sparking ; carbon separated slowly but there was 

 no cloud of soot. The result was the same with equal volumes 

 of the two gases at 6 atmospheres, while with a mixture of 2 of 

 acetylene and 1 volume of hydrogen at 5 atmospheres, the ex- 

 plosion promptly followed the electric discharge. The spark 

 used was 2 cm in air and was passed between electrodes 3 mm 

 apart in the gas. 



a 



The following experiment illustrates beautifully and simply 

 the endothermic character of acetylene and also shows that a 

 dull red heat is sufficient to decompose it. A slow current of 

 the gas is passed through the tube a, fig. 4, into the larger tube, 

 which is heated as shown by a Bunsen burner. When the 

 part of the outer tube about the end of a is heated to a faint 

 glow there is a slight puff and then the gas issuing from the 

 end of a glows or rather the carbon, separating beyond the 

 end of the little tube, glows. It is a jet of gas filled with a 

 cloud of lampblack glowing with the heat resulting from the 

 dissociation of the acetylene. In order to obtain the result the 

 flow of the gas must be carefully regulated. If too fast, the 

 gas does not attain the temperature of decomposition, and if 

 too slow it does not glow. 



Cyanogen. 



Experiment 1. — The U-tube, fig. 1, was charged with cya- 

 nogen made from dry mercuric cyanide. The gas was nearly 

 free from air or other permanent gases, as it was found that 

 100 cc left only a small volume of gas when liquefied by pres- 

 sure. When induction sparks were passed through the vapor 

 of cyanogen at a pressure of about five atmospheres, at which 

 a portion of the compound was liquid, carbon separated at 

 once and connected the electrodes. There was no explosion 

 and no decomposition except in the path of the spark. A 

 primary current from two large storage cells was next passed, 

 the carbon filament connecting the platinum wires in the tube 



