WATER GAS
711
the usual external steel stell. In normal cases the quantity of tar used for carburet-ting is about 1| gallons per 1,000 cubic feet of water gas made.
It may be mentioned here that within the past few years a number of experi-ments have been made with the object of eliminating the outer steel sliell of water-gas generators. On the whole, it would not seem advisable to build up the generator from brickwork, for trouble is likely to result from the numerous joints which. such a method introduces. On the other hånd, reinforced concrete, if built monolithically
and lined with firebrick, appears to be more or less satisfactory. Concrete has been successfully applied in this way in America.
Products of the “ Blow ”
When air is admitted to the base of a deep fuel-bed, CO2 is formed in large proportion in the first place ; but on travelling through the remainder of the fuel it is partially reduced to carbon monoxide so that a semi-producer gas results. The percentage of the CO present in the products varies inversely with the speed of the biast, and directly with the depth and temperature of the fuel-bed. At first sight the presence of CO might appear to be a distinct disadvantage, for it is produced