248 CHEMICAL DISCOVERY AND INVENTION 



which yields hydrogen at the cathode, oxygen and potassium 

 bicarbonate appearing at the anode. A solution of potassium 

 hydroxide at a temperature of 60 to 70 is also employed ; in 

 this case gaseous hydrogen and oxygen are the only products 

 liberated. 



The hydrogen obtained by any electrolytic process is apt to be 

 accompanied by small quantities of oxygen, while the oxygen 

 simultaneously set free is liable to contain a little hydrogen 

 which in certain cases would be objectionable or even dangerous. 



5. Miscellaneous methods. Some of these are designed to 

 furnish the means of generating hydrogen in moderate quantities 

 in the field by requiring only simple and portable apparatus. 

 One substance proposed for this purpose is impure calcium 

 hydride, CaH 2 , a white powder to which the name hydrolith has 

 been given. It is produced under a French patent. When mixed 

 with water about one cubic metre of hydrogen is evolved from 

 one kilo of the material, and this costs five francs. 



Hydrogenite is the name given to another material in which 

 ferrosilicon is mixed with a relatively large quantity of caustic 

 soda and some lime. When heated this mixture evolves hydrogen 

 and leaves a mass of silicates of sodium and calcium. Ferro- 

 silicon in fine powder also dissolves in solution of caustic 

 soda. 



Acetylene is producible by igniting carbon in hydrogen at the 

 temperature of the electric arc, and the process is endothermic, 

 that is, a large amount of heat is absorbed and the energy is 

 stored up in the gas. In common with other endothermic com- 

 pounds it is therefore somewhat unstable and it can be de- 

 composed by heat alone, being resolved into hydrogen gas and 

 finely divided carbon. As acetylene is produced pretty cheaply 

 from calcium carbide this principle has been made the subject 

 of a patent by the German Carbonium Company. The gas con- 

 tained in steel cylinders is decomposed by electric sparks, and 

 the very fine carbon deposited is valued for making printer's 

 ink. The process has been used at the Zeppelin factory at 

 Friedrichshafen, but it appears not to be entirely free from 

 danger, as it is said that explosions have occurred. 



Another process of Dutch origin yields a gas, which though 

 reported to be very light is certainly far from pure hydrogen. 

 The process consists in heating coke to bright incandescence by 



