Hot-air Apparatus. 205 



the fan-chamber, and outside the building, should 

 be constructed a large furnace, in the upper part 

 of which are fixed a number of heavy iron tubes, 

 opening at one end to the outer air, and at the 

 other into a flue or chimney which communicates 

 with and terminates in the upper apartment, which 

 is appropriated for the hot-air process (and which 

 of course must be close and air-tight, all except the 

 floor). As soon as these tubes become heated by 

 the fire, the air rushes into them from the outside, 

 and passes up into this chamber at a considerable 

 temperature, while the fans at the other end of the 

 building, being meanwhile kept rapidly in motion, 

 draw this heated air through the floor, and the wet 

 parchment coffee which has been previously spread 

 on it for this purpose is soon dried. The great 

 difficulty with this process is that only a compara- 

 tively small quantity can be dried at a time, owing 

 to the limited surface available within a building. 

 This can, however, be remedied to some extent by 

 using hand trays, similar to those seen on drying 

 grounds in the open air, which can be piled one on 

 the other six or eight deep if necessary. As soon 

 as the parchment has become tolerably dry, it may 

 be passed on to the cool-air chamber previously 

 described, and can there be heaped up and left to 

 the good offices of the fans, which should be kept 

 going night and day. 



