THE DRY PURIFICATION OF COAL GAS 575
is found, and anything approaching this proportion impairs the value of the material for purification. Apparently American bauxites are prejudiced by the presence of considerable quantities of silica. As regards other sources, Scott speaks of a high quality oxide heing procured as a by-product in the reduction of aniline, and mentions the faet that waste water from the West Pennsylvanian coal-mines yieldeda very efficient natural oxide. Called upon to abate the nuisance caused by ninning it into the rivers, the owners collected it in large settling basins for treatment; and the sediment thus obtained had been found to be an excellent purification material. Metallic paint oxide showed results fairly comparable with. good mamifactured oxide, and would come into more general use. Finely ground pyritic cinder had met with favour as yielding good working, although somewhat crystalline and vitreous in structure. Many of these newer forms of oxide would be mueh improved for the purpose by experience, as manufacturers and gasworks chemists were feeling their way towards a material that would take up several times its own weight of sulphur, and not be liable to cake and cau.se back-pressure in the purifieis.
Tn absorption tests conducted on a number of oxides under similar circumstances (four foulings to each test), the percentage of sulphur taken up was as follows :—
Residae from aniline reduction
Sediment from mine water
Pennsylvania bog-ore Ground pyritic cinder . Hematite ore
Hydrated iron ore
Residue from American bauxite
„ ,, French ,,
„ „ English ,,
Cuban bog-ore Metallie paint
Becquevort and Deguide1 have introchiced a process for the recovery of a gas-purifying material as a by-product from the manufacture of Glauber s salts. The process consists in treating scrap iron with a solution of sodium bisulphate at a temperature of ab out 90° C. The following reaction results :—
2 NaHSO4 + Fe = Na2SO4 + FeSO4 + H2.
An excess of powdered lime is then added, so that sulphate of lime and insoluble ferrous hydrate are produced, together with neutral sodium sulphate
Na2S04 + FeSO4 + H2O + CaO = Na2SO4 + CaSO4 + FeH2O2.
The mass is then aerated and shaken until the ferrous hydrate is transformed to ferric hydrate—
2 FeH2O2 + H2O + O = Fe2O3,3 H2O.
After filtration the mass left in the filter-piess is a mixture of sulphate of lime
1 Eng. Pat. 9747/16.
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