742 GEOLOGY OF OHIO. 
it will be found on removing the cover from the foul box, that the free 
ammonia (especially if the lime used has been made very wet), will 
almost stifle the workmen, and yet the sulphuretted hydrogen and 
carbonic acid had been freely and profusely passing through that box. 
Their affinity for ammonia is apparently not great, and their union easily | 
divorced. With lime as the purifying agent, the sulphuretted hydrogen 
is arrested and sulphide of calcium is formed; the carbonic acid is 
arrested, and carbonate of lime is formed. Bi-sulphide of carbon is 
supposed to be arrested by the sulphide of calcium. However, 
the almost intolerable stench of spent lime when used to arrest sul- 
phur, and the first cost of lime, and the extra cost of labor in manipulat- 
ing, have caused a general substitution of some of the forms of oxide of 
iron for removing sulphuretted hydrogen, which is really the most objec- 
tionable impurity that the gas manufacturer has to contend with. In 
most works lime is still used in a limited way to arrest carbonic acid, 
and in some the boxes are arranged so as to cause the gas first to pass 
through lime, then through oxide of iron. The chemical changes are 
supposed to be about as follows: The sulphuretted hydrogen is arrested 
in the Jime boxes and soon fouls all three, if that is the number used. 
The first box arrests the carbonic acid, forming carbonate of lime, and the 
affinity of the lime being greater for carbonic acid than for sulphuretted 
hydrogen the latter is driven out of the first box into the second, after 
the saturation of the first box with earbonic acid, then that impurity 
attacks the second and drives the sulphur on the third, and from that 
on to the oxide of iron boxes. ‘The advantage claimed for this system 
over passing gas through the iron first, is, that the lime fouled with 
sulphuretted hydrogen breaks up the bi-sulphide of carbon, which is 
not arrested when the process is reversed. In the oxide boxes there are 
no important chemical changes other than the decomposition of sulphu- 
retted hydrogen and the formation of sulphide of iron. When the second 
box of a plant of four boxes of oxide begins to show traces of sulphu- 
retted hydrogen passing, the foulest box is thrown out of the system and 
a clean one brought into use. On removing the cover of the oxide box 
the material is found to be quite black, and to heat rapidly on exposure 
to the atmosphere, and in some instances, when improperly treated, it 
has been known to ignite. | 
The heat is produced by the decomposition of the sulphide, the 
deposition of the sulphur, and the reoxidation of the iron. The color 
vs 
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