The process, however, is
declared by Herr Hasenclever to be too costly for ordinary working,
although he does not deny its value under special circumstances.
The removal of anhydrous sulphuric acid from the gases from
roasting-furnaces has hitherto, as at the Waldmeister works, near
Stolberg, been effected by means of water trickling down in a tower
filled with coke, the gases entering below and moving upward. Herr
Hasenclever tested the Freytag method, in which the water is replaced
by sulphuric acid, and obtained favorable results, as shown by the
following analyses of the gases before and after treatment. The figures
given are grammes per 1,000 liters:
BEFORE. AFTER.
SO_2. SO_3. SO_2. SO_3.
8.24 0.63 5.74 0.00
8.29 0.37 6.74 0.07
9.36 0.69 6.96 0.00
9.46 0.63 7.38 0.05
10.03 1.08 7.69 0.09
16.52 2.97 14.39 0.23
17.90 1.97 13.32 0.11
17.80 2.46 16.18 0.69
The average absorption for the first set of four analyses when three
roasting-furnaces were discharging into the tower was 95 per cent. of
the sulphuric acid, and that of the second set of four or five furnaces
was 90 per cent. The amount of sulphuric acid charged per twenty-four
hours was about 5,000 kilogrammes of 50 degrees Baume, which flowed off
with a density of from 56 to 58 degrees Baume.
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