Jamie

I think that your only chance of finding any quantitative data is from the
Brazilian furnaces. I cannot remember whether they were hot blast.  Most
charcoal furnaces were long gone before it was possible to measure high
temperatures except by eye. Even the mercury thermometer was not
atsndardised until 1731 and was then probably too expensive for general
use. This leaves a wide range from about 350 deg. to around 900 deg Celsius
where there was absolutely no way of measuring the temperature except by
comparitive tests. (melting lead or charring of wood in a measured time or
softening of clay mixtures). The measurement of the temperature profile of
the descending stock with a thermocouple was a new development in the UK in
the last 30 years or so. It probably was a little earlier in America. The
routine measurement of molten metal temperatures probably dates from the
1940s

Percy (1864) reports some investigations of the temperature in the stack.
The temperatures are like "wrought iron rod 0.79" diameter melted in less
than half a minute" "copper and gold were melted and the rod was white hot
but not distorted" Percy was probably the most knowledgeable metallurgist
of that time.

Here is another bit from Turner:-
(Scannned and spell checked. Read through but absolute accuacy not
guaranteed. What the internet will do to the table I don't know)

"Temperatures of the Blast Furnace.--The maximum temperature in the blast
furnace is in the hearth immediately in front of the twyers; the position
of this point of maximum varies, however, according to the temperature of
the air used, it being further removed from the twyers with cold blast. The
temperature of the zone of fusion, just above the hearth, is determined
largely by the fusibility of the slag, and that of the upper part of a
furnace of given capacity, chiefly by the temperature of the blast, the
proportion of moisture in the air, and the nature of the fuel. In coke
furnaces the use of hot blast cools the upper part of the furnace, and
increased capacity acts in a similar manner, though this cooling can only
be carried to a certain extent owing to the liberation of heat, due to the
action of carbon monoxide on ferric oxide, which leads to the production of
a certain minimum temperature in the upper part of the furnace, so long as
the ore and fuel are the same, whatever is the height of the furnace or
temperature of the blast. With charcoal fhrnaces, where the zone of
reduction is lower, the materials in the upper parr of the furnace are
cooler, so that while tile temperature of the escaping gases from a coke
furnace is usually over 200° C., that of the gases from a charcoal furnace,
despite its smaller capacity, is according to the determination of Ebelmen,
about 100° C., and sometimes even so low as 50°. Ebelmen determined
temperatures below the mouth of a charcoal furnace by lowering into the
furnace an iron rod, at the end of which was a small crucible containing
pieces of various metals, and showed that at 26 feet 4½ inches down the
furnace, or 2 feet above the boshes, though silver melted, it was not
sufficiently hot to melt copper; at the twyer, wrought iron melted almost
instantaneously. In a coke furnace the same observer found the temperature
at the mouth about 300° with a heavy charge, and 400° with a lighter
charge, while at the top of the boshes copper meltedp and white pig iron
softcried. By a somewhat similar method Tunner also determined the
temperature of a charcoal furnace at Eisenerz, Stytin, with the following
results :-

Depth in feet,     0      7     11    15    17     21    24   25½    29    
34
Temperature,   320° 340° 550° 640° 680° 840° 910° 950° 1150° 1450° 

These temperatures would doubtless require modification in view of modern
determination of the melting point of copper, which does not exceed 1,080°
O. Relatively to each other, however, the values determined by Tunner are
probably trustworthy.

It will be seen from these figures that the temperature increased very
uniformly from the mouth to the twyers. The temperature of the issuing
gases was higher than observed by Ebelmen, but in this case calcined ore
was employed, and with raw ore the temperature at the mouth is lower.

 According to Sir L. Bell,t the reduction of ferric oxide by carbon
monoxide may be considered to commence at about 200° O., while the
reduction of ferric oxide by solid carbon commences at about 400° C. It is
evident, therefore, that in ordinary working in large furnaces, as the
materials are gradually heated as they pass down the furnace, the ore will
be almost completely reduced by carbon monoxide before it reaches the
temperature at which solid carbon can begin to act. The action of carbon
dioxide on metallic iron, which would lead to oxidation of the iron sponge,
does not commence till the temperature reaches about 425° C, and when this
temperature is reached the charge is in an atmosphere which contains
relatively little carbon dioxide. The action of carbon dioxide on hard
coke, leading to the production of carbon monoxide, commences at about 815°
C., or at a full red heat. It must, however, be remembered that some ores
are more easily reduced than others, and that charcoal and other soft fuels
are more readily attacked by carbon dioxide than coke.

The impregnation of the reduced ore with carbon by the reduction/of carbon
monoxide commences almost immediately after the reduction of the oxide of
iron, and the temperature mos~ favourable for carbon deposition is about
400° or 450° C. There does not, however, appear necessarily to be any
connection between the rate of carbon deposition and that of reduction.
According to It. Le Chatelier, the highest temperature attained in front of
the twyers of a blast furnace is about 1,930°0., while the first part of
the tappings from a blush furnace making grey Bessemer iron had a
temperature of 1,400°, and the last and hottest portion of the same
tappings had a temperature of 1,570° O. According to the same authority,
Swedish white cast iron melts at 1,135° C., and grey cast iron at 1,220° O.
The temperature of the waste gases from a modern coke blast furnace under
normal conditions varies from about 150° to 270oC. (300' to 700' F.), being
lower after the introduction of fresh ore. The greatest variations are
caused by irregularity in filling, due to stoppages at meal times, or for
other purposes, and subsequent rapid charging to make good the deficiency.
Regularity of charging leads to better working, and to diminished fuel
consumption."

There are references but not to the table. The OCR couldn't read them.

Similarly the charge was usually measured volumetrically, especially the
charcoal, using a basket which was probably only standard for the one
ironworks.

If you are looking for a description of the operation of a charcoal furnace
there is one for about 1740 quoted in"The history of the British Iron and
Steel Industry" by H.R. Schubert (London,1957). There is some operational
data too, but no temperatures. This is a standard text in this country.

Peter Hutchison


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