Wartime Nickels

Reverse side of a 1942-P Jefferson nickel

While reading and thinking about wartime coinage, I remembered that nickel was also in such short supply during WW II that the mint replaced it with silver. Link  Nickel was needed to harden steel for armor plating. Special nickels were marked with huge mint marks P, D, and S over Monticello on the reverse to facilitate re-collection and melting.  But Gresham's Law kicked in after the war and the silver nickels were hoarded when the price of nickel fell. I still have a few, found in change, darkened with age due to their manganese content.

Lastly, copper was in such short supply during WW II that the Treasury loaned out 14,700 tons of coinage silver for use in making electrical coils for uranium isotope separation at Oak Ridge National Labs. Link

Manganese Is Neither Transgendered Nor Racist

The words manganese and magnesium are related. Their entwined roots stem back to a place called Magnesia in ancient Greece where they were both found in abundance. Some speculate that Spartan swords were exceptionally hard because of manganese content in their iron. Manganese's word history is parsed here and van der Krogt has his take here.

Manganese has been used since antiquity both to color and to decolorize glass. The Venetians perfected "glassmaker's soap," making high art with it.  Glass always contains iron in trace amounts and this imparts a greenish "coke bottle" tinge. The addition of manganese to the molten glass produces a reddish-brown tinge which equalizes the absorption across the visible spectrum and gives so-called colorless glass. More reading on colored glass can be found here.

Manganese also demarcates an important trend in the Periodic Table. Moving from left to right across the first transition metal series, i.e., Sc -> Ti -> V -> Cr -> Mn, each element adds one more positive charge to its core (and one surrounding electron). Yet those electrons can be stripped by oxygen. A tipping point is reached between manganese and iron. Manganese is the last metal in that series to exhaustively lose all of its valence electrons to oxygen. Thus the manganese atom in permanganate MnO₄^-, is fully oxidized back to having an argon core. But moving just one element further to the right (to iron) is just enough change in electronegativity that iron retains two valence electrons: there is a ferrate but no perferrate.

Ironically, despite its reputation for rusting, iron retains an inner core of two valence electrons, even when completely surrounded by rapacious oxygen. Iron is one step closer to the noble metals.

Pigments of My Imagination

I got sidetracked by vacation and few other things and lost my way regarding the chemical elements. The following inorganic pigments are mostly familiar.

Red is for red and white lead in striped lighthouses and also miniature manuscripts. The red color comes from lead tetroxide and the stark white comes from lead carbonate. Both pigments are impervious to the elements which is precisely why Michael Faraday chose them to coat Britain's lighthouses.
Red is also for Barn Red. Farmers in Europe started this tradition by adding ground up rust to the linseed oil they used to protect their barns and sheds (the iron inhibits mold).

Orange is for terracotta roof tiles: The color comes mainly from iron oxides.

Yellow is for yellow school buses.  Originally the pigment came from lead chromate (the color comes from the chromate, not the lead). It too was impervious to the elements. Lead chromate is no longer used to paint buses, but the traditional color stuck with us.

Green is for emeralds. Beryl and emerald are essentially the same material, viz., Be₃Al₂Si₆O₁₈. The only difference is that emerald also contains about 2% chromium, the source of its green color. Chromium also makes rubies red, and sapphires blue.  How does the same element do that?

Blue is for the Prussian Blue. I wrote about this back here. Gun bluing, a form of metal passivation, is another iron coating in disguise. Blue is also for cobalt blue.  As the saying goes: if it's blue, it's cobalt (II).

Indigo is for itself. Its color is challenged by some as a separate distinct color: link The most vivid indigo colors I ever saw were solvated electrons trapped as either sodium electride or as sodium benzophenone. What do electrons really look like? link

Violet is for purple permanganate, KMnO₄ which is actually pinkish purple but I couldn't think of a better example. Can you?