744 GEOLOGY OF OHIO. 
found in the retort, that there was necessarily imperfect combustion in 
the furnace. The largest per cent. of the gas drawn in must be nitrogen, 
and if combustion in the furnace Is perfect, the carbonic acid drawn into 
the retort and intermingling with the red hot coke would be mostly 
broken up into carbonic oxide. It is more probable that the carbonic 
oxide results from the reduction, or partial reduction of the metallic 
oxides of the ash, the highly heated condition of the coke at the end 
of the charge favoring such reduction. 
The iron pyrites of the coal would be oxydized during the earlier 
stages of the decomposition by the water of the coal and by oxygen from 
other sources of the coal, sulphur escaping as sulphuretted hydrogen, 
and the iron becoming an anhydrous sesquioxide. During the last stages 
of the decomposition, the oxide of iron is reduced, possibly to the 
metallic state, but probably only to a protoxide, the oxygen forming 
first carbonic acid, which by contact with the highly heated coke is 
broken up into two volumes of carbonic oxide. 
The carbonic acid of the lime in the ash is given off very slowly 
and mostly near the end of the charge, and it also is converted into car- 
bonic oxide. The conditions near the end of the charge are favorable 
for the reduction of all the oxides of the ash. The various metals of the 
ash are not found reduced in the coke, from the simple fact that they 
are reoxydized when they are exposed to the atmosphere in being drawn 
from the retort. ‘The principal oxides of the ash are silica and alumina. 
Whether the heat attained in a gas retort is sufficiently high to reduce 
these oxides with carbon is a little doubtful, though in the case of 
silica, not wholly improbable. 
By the use of coal for manufacturing gas, valuable residuals are 
obtained. It would probably be nearer the truth to say that residuals 
are obtained, from which valuable compounds may be distilled or ex- 
tracted. The most valuable of residuals is coke. Next in value comes 
coal tar, and lastly ammoniacal liquor. 
The character and quantity of coke to be derived from coal, as 
before stated, enters largely into the: question of its value to gas 
manufacturers. 
There was probably not less than 125,000, and possibly 165,000 
tons gas coke manufactured in the State of Ohio last year. Of this 
large quantity about one-half was used in the works, the remaining 
half being sold for use in cupolas, malt and green-houses, bakeries, 
