IRON MANUFACTURE. 507 
one to three tuyers; in most of the smaller furnaces using cold-blast, a 
single tuyer is all that is used ; this is the case in Hamden, Hecla and 
Jefferson furnaces. 
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Where the blast is heated, as is the case in many of the charcoal fur- 
naces, the heating apparatus consists of a pipe-stove, having either 
horizontal or vertical pipes, as shown respectively in either the Wasser- 
halfingen or Player patterns; these stoves are placed on the bank of the 
furnace, and generally heated by the gases which have previously passed 
under the boilers, an arrangement shown in Figure II. 
The blast temperature in charcoal furnaces is usually not high. 
The furnaces are distinguished by cold-blast, warm-blast and hot-blast ; 
the warm-blast being an indefinite quantity, extending to a temperature 
that will melt zinc or higher; the exact temperature of blast used, 
though registered by so-called pyrometers, is rather a matter of con- 
jecture than knowledge; the faulty construction of the instrument pre- 
venting any very great reliance being placed on their indications. The 
furnace men usually report the temperature of the blast from seven to 
eight hundred degrees Fahrenheit. 
As to the details of construction of these furnaces, the stone stack 
has already been alluded to; these stacks are built of the carboniferous 
sandstone, and are most of them quite old, as will be seen by the dates 
attached to the table of the works on pp. 456-58. The expense of such 
stacks, compared with the more modern and lighter iron mantle, would 
preclude their being built at the present time. The only charcoal fur- 
nace built with an iron mantle in the Hanging Rock region is the 
