Andy Dingley wrote:
On 27 Oct, 22:15, Rod wrote:

the coal consumed was two hundredweight".

"Coal" in that period was commonly used to refer to any of the black,
lumpy fuels. You have to check carefully as to which was used. Even
charcoal is sometimes described as "coals" in the 16th century. "Pit
coal" or "sea coal" is the sort that we commonly know as coal.


Rubbish

Much of Trevithick's work took place in the Welsh valleys at Pen-y-
darren, but although this was a coal-mining area it was also an
ironmaking town and he had ready access to the coke that was being
used in the furnaces.

Coke was initially developed to cast iron making - cf Abraham Darby and
the BLAST furnace. Note that its COKE that needs the blast furnace, not
coal.

Coke is used in iron smelting because it is relatively pure carbon And
general silcates that form ash): As such, it is much harder to burn than
coal, which contains lots of other more easily burnable hydrocarbons.

Coke was made from coal in a similar way to charcoal from wood. In fact
since coal is essentially fossilised wood, the same principles ought to
apply. heated coal in the absence of oxygen gives off hydrogen and
carbon monoxide and leaves mainly pure carbon. That's the coking process.