13 



various forms of kilns in which wood was formerly charred are 

 of historic interest, especially in connection with the modern improved 

 retorts ; but as the yield of alcohol and acetate is very low even in the 

 best kilns, these old forms are now employed only in localities pro- 

 ducing charcoal iron, where char- 

 coal is practically the only product 

 recovered. Figures 1, 2, and 3 il- 

 lustrate these early forms of kilns. 

 The yield of condensed products in 

 a kiln, such as is shown in fig. 3, is 

 about one-half that from a modern 

 retort. 



When attempts were made to 

 recover and condense the volatile 

 products an air-tight iron retort 

 (fig. 4), known as the " Swedish 

 thermo-kettle," set in brickwork 

 and connected with a condenser, 



was devised and is still quite extensively employed abroad, where it has 

 been in use since 1857. The round retort (fig. 5), which is a modified 

 and later form of the above, is made of three-eighths inch steel, is 9 

 feet long and 50 inches in diameter, and is provided with a large, 

 tightly fitting door at one end and an outlet pipe, about 15 inches in 



FIG. 3. Early kiln for recovery of alcohol and 

 acid. 



FIG. 4. Swedish thermo-kettle: A, retort; a, furnace; b, spiral flue; .c, tar pipe; d, neck conducting 

 the gases; B, drums where tar vapors condense and collect; C, condenser; e, steam pipe; /, pipe 

 conducting acid vapors to condenser. 



diameter, connected with the condenser at the other end. The retorts 

 are preferably set horizontally in pairs in brickwork, and batteries of 

 from 6 to 16 pairs are common. The chief objection to this form of 

 retort is that, as usually built, it must be filled and emptied by hand, 



[Cir. 36] 



