HYDKOGEN 247 



water by iron has been patented by a German chemical engineer 

 named Bergius, and it is stated that hydrogen, containing a 

 very minute percentage of impurity, can be produced at a cost 

 of about Jd. per cubic metre (about 35 cubic feet). Water is 

 heated to between 300 and 340 C. in a strong steel cylinder 

 containing iron turnings in contact with copper, and a little 

 common salt. The cylinder has a long neck fitted with a screw 

 cock by which the hydrogen is allowed to escape under the 

 pressure generated, which may amount to 300 atmospheres. The 

 gas can therefore be stored under pressure in gas cylinders and 

 is thus rendered portable. The oxide of iron produced is left 

 in the form of a fine powder which is easily reduced to the 

 metallic state by carbonic oxide. 



3. Decomposition of water by carbon. The hydrogen contained 

 in water gas to the extent of about half its volume may be 

 secured by the comparatively simple process of freezing out the 

 attendant impurities. These consist of a nearly equal volume 

 of carbonic oxide, together with 2-5 per cent of carbon dioxide, 

 and about the same bulk of nitrogen and traces of hydrocarbons, 

 also sulphuretted hydrogen. The boiling-point of hydrogen 

 being about -253 C., it boils at some sixty degrees below the 

 boiling-point of nitrogen (-195-196), oxygen (-183), or 

 carbonic oxide (-190), and consequently when cooled by liquid 

 air under a moderate pressure these impurities are liquefied and 

 removed, while the hydrogen retains the gaseous state. 



4. Electrolysis. Hydrogen is liberated in several operations 

 as a by-product which till recently has had but little value. In 

 the Castner-Kellner process for obtaining caustic soda by 

 electrolysis of brine, the sodium ions in contact with mercury 

 dissolve, but the amalgam formed is in the presence of water, 

 and consequently hydrogen is set free, while sodium hydroxide is 

 produced. In the manufacturing method for production of 

 metallic sodium, by electrolysis of fused caustic soda, hydrogen 

 equivalent in quantity to the sodium is liberated. But these two 

 methods are necessarily associated with the caustic soda and 

 sodium which are of greater value, and to collect the gas a com- 

 pressing plant would be required. 



With cheap electric energy available, as in Germany, hydrogen 

 can be produced, it is said, at a cost of about three farthings per 

 cubic metre. The electrolyte is a solution of potassium carbonate 



