16 
BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
batteries of 50 or more, side by side, there is but little chance to 
modify the method of heating. All of the ovens in this country, with 
the exception of the Semet-Solvay oven, heat the coking chamber by 
gas burned in vertical flues at the side of the chamber. The Semet- 
Solvay oven heats the coking chamber by gas burned in horizontal 
flues. 
WATER-GAS TAR. 
Water-gas tar is produced in the manufacture of carbureted water 
gas. This gas is produced in a machine known as a " water-gas set." 
It consists of three principal parts — a generator in which the true 
water gas is produced; a carburetor consisting principally of checker 
Fig. 8.— Cross-sectional view of Koppers coke ovens. 
brick on which petroleum oil is sprayed in order to render the water 
gas of value for illuminating purposes; and a superheater, also of 
checker brick, in which the gases formed in the carburetor are fixed 
and made permanent. In operation the generator is filled to a 
suitable level with coke or anthracite coal. This is rendered incan- 
descent by blowing through it air under pressure, the products of 
combustion passing through the carburetor, where they meet a 
secondary air supply and are completely burned in the carburetor 
and superheater. The gases passing from the superheater are allowed 
to escape in the stack and are lost, as they contain no material of 
heating value, and are used to obtain the proper temperature in the 
set. When the superheater and the rest of the water-gas set are of 
the proper temperature, the blowing is interrupted momentarily 
until the valves leading to the gas holder can be opened and the 
