172 GEOLOGY OF OHIO. 



1st. The method of generating the heat is sure to produce 

 inequality of temperature. It is impossible to always get the proportion 

 of outside air mixed with the right proportion of gases from the fire to 

 keep mixture at any given temperature. 



2d. It requires a fireproof structure to make its use safe. 



3d. The smoke, unless it can be prevented by use of gas fuel, 

 or coke, is a serious draw back to the cleanliness of the place. 



In favor of the plan, it may be said that the total heat generated is 

 used, except a very small amount for the radiation of the furnace, and 

 the cost of fuel can be thus kept very low; and also that the plan has 

 the advantage of using the fans or positive blowers without the expense 

 of installation attaching to the usual methods of heating the air supply. 



"C. " By the radiation of steam pipes placed under the floor of the 

 dryer at its hot end, and extending part way back toward the cold end. 

 This is the plan adopted by the Ironclad Dryer Co. of Chicago who have 

 one of the best and most popular dryers in the market. The pipes are 

 filled with live steam which is kept in the heating coils at boiler pressure. 

 The water of condensation is trapped out and returned to the boiler 

 for use again, so that really all the expense in generating the heat, is the 

 cost of the fuel used in vaporizing the water. 



The advantage of the use of steam as a means of generatng the 

 heat required are: 1st. That there is no possibility of getting the dryer 

 very much hotter than is intended; indeed the general mode of operation 

 is to use all the heat that can be obtained. 2nd. The cheapness of con- 

 struction which is thus possible, using wood and sawdust partitions and 

 no brickwork, or iron work except the running parts of the dryer cars. 

 3d: The comparatively even efficiency of the heating apparatus even 

 under careless management. If there is any steam in a boiler the tem- 

 perature of the dryer pipes is over 212°. If the steam pressure is 60 lbs. 

 the temperature of the dryer pipes is 307°. Thus the steam may vary in 

 pressure considerably without materially injuring the work of the dryer. 

 But if a fireman is careless or negligent in tending the fires of direct com- 

 bustion dryer, it cannot fail to produce bad results by excess or defiency 

 at once. 



"D." By the use of a compact coil of steam piping arranged to se- 

 cure the largest possible heating surface in the smallest convenient bulk. 

 B}' blowing or exhausting air through such a heater by a fan and con- 

 veying the heated air in underground brick flues to the dryer, the amount 

 of heating surface may be greatly reduced over the plan of direct radia- 

 tion on the dryer. 



This is the plan adopted in the Benedict dryer, the Sturtevant dryer 

 and various others. The heaters are all so arranged that exhaust steam 

 can be used during the day, while it is being made, and then be replaced 

 by live steam at night. Also in the Buffalo Forge Company's heater the 



