CLAY WORKING INDUSTRIES. 171 



The use of fans to produce the air current in brick dryers is increas- 

 ing rapidly. The advantage lies in the fact that the fan's action is a 

 positive force; that so many revolutions per minute mean so many 

 thousand cubic feet of air per minute; and that the action of the dryer 

 is not made to depend on the natural conditions of the atmosphere, 

 which greatly influence the draft of a stack, especially where the available 

 head is so small. 



The stack has the advantage of operating without power or the 

 expenditure of fuel for the purpose, while the fan has the advantage of a 

 positive supply against a variable one. 



The means employed to heat the air supply in these dryers are 

 four: 



"A." By the Radiation of Hot Floors and Brick work, which is heat- 

 ed by the direct combustion of fuel. The products of combustion pass off 

 in the stack at the rear, without having been in direct contact with the 

 ware in the tunnel. This is the principle adopted by the Sherer Dryer of 

 Philadelphia. A number of dryers of similar design, but each con- 

 structed on its own plans, are in operation. One at Middleport, Ohio, is 

 using producer gas as a means of getting the initial heat. The following 

 points can be raised against this class of dryers. 



1st. They consume fuel expressly for drying brick while more 

 heat than is needed to do the work is thrown away from the plant unused 

 each day. 



2d. They consume more fuel than ought to be necessary, be- 

 cause all the heat they impart to the atmosphere is by the radiation of 

 the heated brickwork. 



3d. They involve an extra heavy expense for original outlay, as 

 the structure of the dryer and the brick cars have to be fireproof. 



4th. The losses in drying brick are almost universally greater 

 where direct combustion is used, than where steam heat is the supply, as 

 the range of temperature is greater, and the radiating surfaces go clear 

 to the rear end of the tunnel. The brick when newly put into the dryer 

 are therefore subjected to heat underneath them at once, which is not the 

 case where steam heat is applied. 



"B" By the combustion of fuel and the direct use of the heated 

 gases, diluted with air as the means of drying. This plan was in opera- 

 tion at one point. A large flat hearth furnace with grate bars was 

 used to burn the fuel and the heat, smoke and gases were drawn 

 away by a fan, and, mingled with the proper quantity of outside 

 air to cool them down to the proper point, were blown into the tun- 

 nel. 



The operation at the point where it was used was very crude, though 

 successful and cheap. But the plan is capable of modification to give 

 good results. It has some inherent faults, however : 



