THE ARTIFICIAL SEASONING OF TIMBER 



391 



modern. The " Smoke Kiln " appears to have been the first attempt 

 to treat timber with heat restrained by moisture. These were used in 

 France seventy to a hundred years ago, and a few have been put up 

 in this country. 



A smoke kiln consists of an upper chamber, in the floor of which are 

 holes communicating with the space below. Chimneys or outlets are 

 also provided for the escape of the used air and smoke. In the lower part 

 is a furnace, above which a water tank is generally placed. The heat of 

 the furnace causes the water in the tank to evaporate, and the vapour, 

 together with the hot air and fume from the fire, passes through the 

 perforated floor, circulates round the timber which is stacked in the upper 

 chamber, and finally es- 



/\ 



h WET AIR OUTLET 



I ^STACKED TIMBER; | 



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'mmmjm'' 



capes through the chimney 

 outlets. It was considered 

 advantageous to burn 

 green branchwood from 

 the same species of timber 

 as that which was being 

 dried ; it was claimed that 

 the smoke from this 

 toughened the timber 

 under process. The im- 

 pregnation of timber with 



solids, liquids, or gases, y. j^ 



comes under the heading ^rm^'^^mmmm^mfiz'^ 

 of timber preservatives, the 

 merits of which are not 

 discussed here. This 

 smoke-kiln process, while 

 it contains the elements 

 required for drying timber, that is, ventilation, heat, and moisture, 

 cannot be strictly regulated to follow a predetermined course, and 

 although on a small scale good results have been obtained, this type of 

 dryer has not proved of real commercial value. Also, in a large kiln 

 it would be impossible to guard sufficiently against the danger of fire. 



The first development of timber dryers on a large scale was by 

 B. F. Sturtevant in America, who invented the progressive kiln, in order 

 to deal with enormous quantities of soft woods, of one or two thicknesses. 

 He erected large dryers, and developed accessories, such as kiln trucks 

 and transfer systems, which are standard to the present day. 



The illustration from B. F. Sturtevant's catalogue of 1890 shows a 

 two-decker kiln which was put up, and which had an output of 125,000 

 board feet per day (p. 392). 



Diagram of Smoke Kiln 



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Heat from Fipe 



Moisture frow WtT Ftjel Jf Evapobation fpoMTAWK 



