82 ILLINOIS- ACADEMY OF SCIENCE 



meters and with pyrometers to show temperatures in the 

 fixing chambers, and tlie gas maker times the operation 

 with a clock equipped vAtli a second hand. The steaming 

 and blowing periods are different in different plants. 

 While an iufinitesimally short blow, followed by an infin- 

 itesimail}^ short run would probably be the ideal arrange- 

 meut or C3^cle, the time required to operate valves makes 

 extremely short periods impracticable. In practice we 

 find blow periods from 2 to -t minutes and run periods 

 from 3 to 6 minutes or possiblj^ even longer in some cases. 

 During the blast period the air always passes upward 

 through the fire, but in modern practice a ]3ortion of the 

 steam runs are made down through the fuel, the gas pass- 

 ing to the carburetor through the refractory lined pipe, P. 

 This reversal not only protects the hot valve, H, from be- 

 coming overheated, but also puts the fire in better condi- 

 tion for gas making. The lid on the top of the generator 

 is opened at intervals of perhaps five or six runs to intro- 

 duce a fresh charge of fuel. At intervals of perhaps 8 to 

 10 hours, depending upon the fuel, operation has to be dis- 

 continued and the accumulated ashes and clinkers re- 

 moved through the lower doors. This procedure, which 

 may require anywhere from a few minutes to four or five 

 hours, of course shortens the actual operating time and 

 may cause the rejection of a particular fuel, which other- 

 wise might be considered suitable, and frequently much ex- 

 perimenting is done to find a set of operating conditions 

 which will make practical the use of a particular fuel 

 which, though otherwise good, gives an obstinate clinker. 

 It is remarkable what can sometimes be accomplished by 

 slightly modifying the amount or duration of the blowing 

 or steaming, or by changing the percentage of up and down 

 steam runs. 



Coke or anthracite coal, since they contain very little 

 volatile matter, could, except for the complications some- 

 times introduced by the nature of the ash formed, be con- 

 sidered as pure carbon. With bituminous coals, however, 

 tlie gas maker is confronted by new problems. The coals 

 of the central district usually contain from 35 to 45 per 

 cent of volatile matter, and exhibit the property of caking 

 when heated. The volatile matter of the coal consists not 

 only of water vapor and permanent gases, but also of 

 heavy condensible vapors which upon cooling form tar. 



