By-Products of the Apple Industry 353 



The older types used steam pipes, a system which permits 

 exact regulation of the temperature and permits also of 

 " boosting " the temperature of the air as it passes through 

 the tunnel. Those who have used both steam and direct 

 heat, however, prefer the latter because it is claimed to be 

 more economical of fuel. Some heating systems are very 

 similar to those used in the kiln, stack and tunnel types, 

 consisting of a sheet metal furnace attached to radiating 

 pipes, the air being heated by being drawn over the heated 

 metal surfaces. In another form of heater, the air is 

 forced through large pipes held in a fire-box much after 

 the fashion of boiler flues. The most interesting develop- 

 ment, however, is the use of the gases of combustion 

 directly in drying, thus doing away with all stack loss of 

 heat. Many machines, of different designs, have recently 

 come to the attention of the public. At present, stove dis- 

 tillate, a more expensive fuel than crude oil, must be used 

 in this style of heating device to avoid bad odors, soot, and 

 the like. Whether the saving in fuel, therefore, counter- 

 balances the difference in price of distillate and of crude 

 oil is an open question. If it does not more than equal 

 this difference, the saving in fuel cost is more apparent 

 than real. 



Stack type of air blast drier. Some commercially built 

 evaporators consist of several stacks or tiers of trays placed 

 one above the other and hot air is forced upward through 

 and over the trays. Whether it is a more logical type than 

 the horizontal blast remains to be seen. 



Continuous evaporators have been developed success- 

 fully for vegetable drying, soap chip drying, kelp drying, 

 and the like, but have not worked out well for fruits, be- 

 cause of the bruising of the fruit and its sticking to the 



