Saltpeter Is Not Rock Salt



Rock Salt (Halite)


If word histories made any sense, saltpeter should be rock salt. But instead rock salt is halite.

LL made a nice comment back here:

I thought that you would take this thread in the direction of Potassium Nitrate (saltpetre), accused falsely of causing impotence in men and at the same time allowing gunpowder to go boom.

Saltpeter

The Lewis structure of potassium nitrate invokes all that separated charge, which in a way depicts internal potential energy. Nitrates give explosions not just an oxidant (oxygen) but also nitrogen atoms badly wanting to make nitrogen gas. Whence the added oomph first discovered by the Chinese. The same principle is behind nitroglycerin (dynamite), trinitrotoluene (TNT), and nitromethane racing fuel: enhanced combustion.

I find nitrogen oxides intrinsically interesting and I even wrote a bit about them back here already; I mentioned impotence, but it's at the very end of the post. It's an odd coincidence that NO gets one hard while NO₃^- stands accused of the opposite.

It's Amino World

The sky overhead is an ocean of nitrogen. Around 4,000 trillion tons of nitrogen (N₂) float trapped up there because it's too light to sink back to earth and yet too heavy to float away into space (it's gravity shackled-unlike helium-the next lightest gaseous element). That enormous enveloping ocean has storms too. Nitrogen, and to a lesser extent oxygen, once set into motion, are essentially wind.

I once naively thought that azote, the French term for nitrogen, was etymologically related to the azure of a blue sky. Wrong! The aptly named azote literally means "no life" and that name was acquired shortly after oxygen and nitrogen were distinguished as the essential components of air: one gas supported life and one did not. The Germans call nitrogen Stickstoff, which literally means "suffocating-stuff". We call nitrogen "nitrogen" because it engenders "nitro" (nitro being an older word for saltpeter) which is an essential ingredient of gunpowder and plant fertilizer.

Despite the name azote, nitrogen compounds are quite lively and have a long and interesting history of blowing things up: gunpowder, dynamite, nitromethane racing fuel, TNT, and even airbags. In a very real sense, nitrogen's instability (chemical reactivity) under those circumstances is ultimately related to the stability of N₂ and the element's propensity to get back to that elemental state, serenely floating above the fray.

Nitrogen is essential for all living organisms, which have tamed its volatility.  Organic nitrogen is of course a constituent element of amino acids and thus of proteins, and also presents in nucleic acids (DNA and RNA). I wrote earlier about boron being fundamentally electron-poor with respect to carbon. Nitrogen, which sits on the right hand side of queen carbon, is the converse-electron rich with respect to the queen. That's really why nitrogen is an organic base.

Relatively little usable nitrogen is found in the earth. The amount in the air is about one million times larger than the total nitrogen contained in living organisms. Nitrogen availability is often the limiting factor in plant growth.  Plants make organic nitrogen from air and we get usable nitrogen from plants (actually bacteria within the roots of some plants "fix" nitrogen to usable forms). 

We no longer depend exclusively upon plants to make ammonia from the sky.  During the First World War, Imperial Germany was cutoff from its sources of fixed nitrogen (mainly Chilean saltpeter and bat guano). Fritz Haber, the father of chemical warfare, developed the direct conversion nitrogen (N₂) to ammonia (NH₃) using hydrogen gas.  Haber won the 1918 Nobel Prize in Chemistry for this feat, despite Germany losing the war and despite his wartime culpabilty in making things like chlorine and phosgene gases for trench warfare. The commercial Haber-Bosch process literally allowed the subsequent population bloom known as the Green Revolution. The process is still used today, highly refined, but essentially unchanged.