guy_bourgogne
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Peculiar iron assay in Agricola
I found an interesting method of iron assay in Agricola's De Re Metallica:
“Lastly, we assay iron ore in the forge of a blacksmith. Such ore is burned, crushed, washed, and dried; a magnet is laid over the concentrates, and
the particles of iron are attracted to it; these are wiped off with a brush, and are caught in a crucible, the magnet being continually passed over
the concentrates and the particles wiped off, so long as there remain any particles which the magnet can attract to it. These particles are heated in
the crucible with saltpetre until they melt, and an iron button is melted out of them. If the magnet easily and quickly attract the particles to it,
we infer that the ores is rich in iron; if slowly, that it is poor; if it appears actually to repel the ore, then it contains little or no iron.”
What is going on in this description? Is it actually a smelt, or is there something else involved? I don't see how saltpeter can be used as a reducing
agent.
Guy
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Mr. Wizard
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It doesn't exactly say that the iron ore is reduced in the 'forge of the blacksmith', but maybe it is assumed. If you heat crushed iron ore to a red
heat in a charcoal fire, the iron may be reduced to the elemental form without actually melting. The nitrate may act as a flux. If the iron is going
to melt it is going to completely decompose the saltpetre.
BTW the translator of this book into English was Herbert Hoover, the President of the US when the "Great Depression" started. Can you picture any
recent politician undertaking this sort of task, or even being qualified to do so?
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12AX7
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Hoover wasn't so much a president (he was somewhat pushed into that position, and the Depression only added to his ignominy) as he was the chief
supreme court justice, which he later served after his presidency. In fact, he swore in the next couple presidents.
Coincidental that translation happened to be one of his interests and reached such interesting books as De Re Metallica 
For sure, the saltpet(re/er) decomposes at higher heat (and it takes how much heat to melt iron?  ), so it would just amount to potash. Salt or potash could be used just as well, I imagine, but maybe the nitrate has
certain other characteristics, like the extremely basic melt dissolving silicates faster, or something.
It could be that the burning itself reduces the iron to metal, but it would be at least partially oxidized by the saltpeter, so it would have to come
from the fire I guess.
Tim
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Mr. Wizard
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"Hoover wasn't so much a president (he was somewhat pushed into that position, and the Depression only added to his ignominy) as he was the chief
supreme court justice, which he later served after his presidency. In fact, he swore in the next couple presidents."
I read his bio on:
http://hoover.archives.gov/education/hooverbio.html
Very interesting guy. I'd vote for him today.
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Mr. Wizard
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Here's another link on Hoover, and the translation.
http://www.uh.edu/engines/epi139.htm
http://www.uh.edu/engines/epi136.htm
The whole series , "The Engines of our Ingenuity" is quite interesting, and can located in the Index at the bottom of the link.
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JohnWW
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I thought Herbert Hoover was also a mining engineer. This would explain his interest in the smelting of iron and other metals.
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