246 CHEMICAL DISCOVERY AND INVENTION 



3. The action of carbon on steam at a red heat. 



4. Electrolytic processes. 



5. Miscellaneous methods. 



1. Metals and acids. The traditional laboratory process for 

 making hydrogen by the action of diluted sulphuric acid on zinc 

 cannot be considered, as the cost of the zinc would be far too 

 great. The only metal by which it could be replaced is iron, 

 but inasmuch as 28 parts by weight of iron are required to pro- 

 duce 1 part by weight of hydrogen, the mere mass of material 

 would be an objection. One ton of iron would require 3920 

 pounds or If tons of sulphuric acid, and would produce only 

 13,917 cubic feet of gas, a quantity which would be about one- 

 twentieth of the capacity of a small balloon. The action of 

 metals on acids may therefore be at once ruled out of the prac- 

 ticable processes for generating hydrogen for industrial purposes. 



2. Decomposition of water by metals. The action of red-hot 

 iron on steam results in the production of hydrogen gas and a 

 residue of magnetic oxide of iron. 



3Fe+4H 2 0=Fe 3 4 +4H 2 . 



In this case iron theoretically yields one-third more hydrogen 

 than when it is made to act on sulphuric acid. By associating 

 with this process another for the restoration of the oxide of iron 

 to the metallic state, and working the two alternately, a plan 

 for the production of hydrogen on a practical scale results. The 

 reduction is most advantageously effected by means of water 

 gas, the product of the action of steam on red-hot coke : 



O ' -L 



C+H 2 0=CO+H 2 . 



The equation indicates that theoretically the interaction should 

 result in the production of equal measures of carbonic oxide and 

 hydrogen gases. This, however, involves the assumption that 

 coke is pure carbon, and that the steam employed is free from 

 air, while in practice neither of these conditions is fulfilled. 

 Consequently the amount of carbonic oxide is somewhat below 

 the theoretical amount, a small quantity of carbon dioxide being 

 formed by the intrusion of a little air, the oxygen of which is 

 of course accompanied by four times its bulk of nitrogen. These 

 operations have been the subject of numerous patents. 



Another very remarkable process for the decomposition of 



