200 CHEMICAL DISCOVERY AND INVENTION 



source of loss to the manufacturer, and of annoyance to the 

 district. 



Small mountains of this material are to be seen in the " Black 

 Country " of Staffordshire and in parts of Lancashire. Attempts 

 to deal with it proved unsuccessful till about the year 1887 

 when Messrs. Chance, alkali makers, of Oldbury, succeeded in 

 overcoming the difficulties which had previously stood in the 

 way of success. Their process consists essentially in decomposing 

 the wet tank waste or impure calcium sulphide with carbon 

 dioxide, obtained from limekiln gases, in such a way as to obtain 

 a gas very rich in sulphuretted hydrogen, the residue being 

 almost inodorous and harmless. The problem then is to get the 

 sulphur out of this gas in a convenient form, so as at once to get 

 rid of the offensive smell and obtain a marketable product. 

 This is done by the use of the catalytic action of ferric oxide, 

 which in the presence of a mixture of sulphuretted hydrogen and 

 a limited quantity of air, slightly warmed, causes the hydrogen 

 to unite with the oxygen while sulphur is set free. The Claus 

 kiln is a cylindrical brick chamber having a perforated bottom 

 on which is laid first a quantity of broken fire brick, upon which a 

 layer of peroxide of iron in the form of some suitably porous ore 

 is laid. The mixture of about 4 volumes of air with 5 volumes 

 of sulphuretted gas (containing 38 per cent of H 2 S, the rest 

 being chiefly nitrogen) is passed through this bed of oxide, and 

 the water vapour and sulphur vapour pass into adjoining 

 chambers, where some of the sulphur is collected in the fluid 

 state and some in the form of crystalline powder or flowers of 

 sulphur. 



The action of the oxide of iron seems to consist in local re- 

 duction to a lower oxide and reoxidation by the passing air. A 

 somewhat similar action occurs in the oxide of iron purifier 

 employed in the gas works for the removal of the last portions 

 of sulphuretted hydrogen from coal-gas. 



The combination of nitrogen with hydrogen so as to produce 

 ammonia has long been a desideratum. The passage of electric 

 sparks through such a mixture gives rise to the formation of a 

 minute amount of the compound, but inasmuch as ammonia is 

 decomposed by heat the process soon reaches a stage at which 

 equilibrium is established, the ammonia being destroyed as fast 

 as it is formed. Pressure has been found to promote the com- 

 bination of the two elementary gases in accordance with the rule 



