calcinations (calcinations) wrote,

Making Nitric Acid

A couple of weeks ago, (before I went away for a week) I made Nitric acid. It is very easy to make. Just take Alum (Potassium Aluminium Sulphate) and Potassium Nitrate, and distill together, I suggest at a temperature around 5 to 600C. I got a nice bit of liquid, which tested with a pH of 1 with some pH paper. This means that it is about as acidic as you can get.
The whole operation took less than two hours, with the distillation taking around 20 minutes. Now I just need to work out what to do with it.

Of course, the details are also important. I did not measure the yield. I set up my distillation apparatus the same as I have done before, with some linen on the Alembic to help hold water on it to cool it, and some Aluminium foil acting as another long cooling zone before the collection jar. Biringuccio recommends one part saltpeter to three parts Alum, which is what I used. Some other recipes use Vitriol (Copper Sulphate) instead of the Alum. Essentially it works by decomposition of the Potassium Nitrate, with water coming over first from the salts (Salts like these almost always have water bound up with them, they will absorb it from the atmosphere), then nitric fumes, which collect in the water and form the acid.

One thing that is recommended by Biringuccio is the placing of half a pennyweight of pure silver in every pound of acid produced, so as to take up the Hydrochloric acid, which would have been formed by impurities in the materials used. In using modern industrially produced ingredients, I have no such problems. The Silver I dipped into it did not react. He also says to add the Silver granulated or beaten with a hammer, thus demonstrating at least an empirical knowledge of the importance of surface area to reaction rate. The greater the surface area, the faster a powder will go into solution because it can react quicker.

The first mention of Nitric Acid manufacture is apparently in works accredited to Geber. The name is a Westernisation of the Arabic for Jabir, who was an alchemist of some note in the Arabic world in the mid medieval period. However, the record we have of this recipe comes from Arabic sources in the 13th century. With the addition of Sal Ammoniac or Hydrochloric acid to the Nitric acid, Chlorine is set free which means the liquid is able to dissolve Gold, a material which at that time was thought to be almost incorruptible.
The acid is prepared on a Lab scale by distilling Sulphuric acid and potassium nitrate:
H2SO4 + KNO3 = KHSO4 + HNO3
After reading that I suspect that my yield is quite poor, and it also explains why you need more Alum than Nitrate for its production. Once I make Sulphuric acid I shall try this better method.

My Nitric acid seems to react slowly with lime, and I suspect it is not as strong as I would like. I shall have to make some more soon.
Meanwhile, I have this material:

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To do something with. Lumps of Aluminium Potassium Sulphate with extra potassium. I wonder what I could do with it?
Tags: distillation

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