Tuesday, April 30, 2013

More saltpeter math - I am enlightened


Nitrates are enormously useful compounds, and this blog is about simple chemistry, so investigating simple methods of producing them are extremely relevant.


FIRST: Despite far too many bad internet references about making gunpowder out of urine, I have finally figured out why nobody gives instructions on how to do it. It is, for the most part, impractical.

SECOND: If what you're looking for is soluble nitrates, it's far easier to use "normal" composting materials like grass clippings and animal products than to try to leverage the urea in urine directly.

The investigation

After doing the math on the saltpeter yield and after a lot more research on the composting process, I have decided to take another whack at figuring out what it would take.

Target values

Ideal hot, nitrifying composting seems to occur near a C:N ratio of 25 and a moisture content of 40-60%. If there were nothing in the mass that wasn't nitrogen, carbon, or water, the ratios might look like: 40% water, 57.7% carbon, 2.3% nitrogen.

Raw Materials

To produce 1 kg of soluble nitrates, we need 140g of nitrogen. Targeting a C:N of 25, we need 3.5kg (25 x 140g) of carbon. Since straw and sawdust are still 20% moisture, we would need 4.375kg of that material to provide the right amount of carbon to balance out the nitrogen. To get 140g of nitrogen from urea, we need  32L of urine, which is essentially 100% water.

MaterialUrineStraw or

That would leave a moisture content of 90%. (32875g water vs 36515g total mass)


The light has come on. Given the urea content of 32L of urine, we only need 3.5kg of carbon to get the ratio right, but the water content is beyond all reason. That's probably why no one documents urine as anything other than a "de minimus additive".

Forcing the issue

Presuming the 32L could be reduced (boiled down?) to 1.625L (20-to-1 reduction) without loss of nitrogen, the numbers would add up more like
MaterialUrineStraw or

Which gives a moisture content of 40%. (2500g water vs 6140g total mass) Close enough.

So if the presumption is valid and you had to do it this way, you'd do something like:

  1. Reduce volume of urine to 5% original
  2. Add 2.3-3 times (by weight) straw or sawdust
  3. Mix and compost it

Nota Bene

Most of the "municipal water purification" references on the web (which also deal with nitrifying bacteria) have an end goal of anaerobic denitrification so the organic nitrogen is ultimately expelled as inert nitrogen gas. In this case, the high water content is no problem.

More practically

Follow the instructions from numerous sources which use fruit, vegetable, and fresh green plant matter. It produces the same nitrates, but doesn't require boiling urine.


Saturday, April 27, 2013

Acetone 1 (honey + chalk = acetone)

My longest chain to date:
  • Honey + Water + Yeast = Mead
  • Mead + Acetobacter = Vinegar
  • Vinegar + Chalk = Calcium Acetate
  • Dry distilling Calcium Acetate = Acetone
Acetone could be used to thin or strip paints, but I think the most likely use is as a recoverable solvent to extract oils from seeds. That would indeed be a labor boon.

  1. My original vinegar was made from mead, and thus contained a variety of compounds beyond simple acetic acid. I distilled it, and got a very clear product.
  2. It takes a surprisingly large amount of chalk to slake a relatively small amount of vinegar.
  3. The drying step is by far the longest part. I used a glass pie pan in a 200ºF oven. It took hours.
  1. Add chalk to vinegar until fizzing stops
  2. Add 10% more chalk than you have already added
  3. Add 100% more water by volume
  4. Filter the mixture to remove undissolved chalk, leaving a calcium acetate solution
  5. Place solution in a shallow bowl and apply gentle heat. (Over 160ºC would break down the acetate)
  6. Collect the calcium acetate
  7. Dry distill the calcium acetate producing acetone.

  • The calcium acetate came out a little dusky rather than totally white.
  • The distilled acetone came out light brown, but smell and application to styrofoam confirm acetone was present
  • Much of the solid remained unchanged

Acetone is a List II Substance

Tuesday, April 23, 2013

Saltpeter math

Nitrogen: The math

From Wikipedia
  • Grams of urea in a liter of urine: 9.3
  • Molar mass of urea: 60g
  • Molar mass of potassium nitrate: 101g
Break out the Unit Factor Analysis manual...

So to get 1kg of Potassium Nitrate, you would need about 32L of feedstock.

Wednesday, April 17, 2013

Glycerine 2, Soap 1

New attempt:
  • 380g tallow
  • 5 oz water
  • 86g store bought lye (WAY too much due to miscalculation)
  1. added the lye to the water and let it cool.
  2. melted the fat completely and let it cool for a minute or two
  3. combined the two and mixed lightly
  4. poured into a glass container and set aside to cool overnight.
Result: still an unseparated emulsion in the morning.

tallow on a scale - 380g
Tallow on the scale
cloudy solution of lye and water in a beakerPartially melted tallow in a potUnseparated
Lye and Water MixtureMelting before adding lyeUnseparated result
After 24 hours it was still pretty much a homogeneous gel, so I "remade" it:
  1. melted it over a stove
  2. added a cup of water (to aid in melting)
  3. added a cup of vegetable oil (to balance the excess lye)
  4. left to cool in the metal pot I did the melting in
Result: Really granular/void-filled soap, but definitely soap.

I also collected about a cup of water and a couple ml of cloudy glycerin

The soap was still really granular, and when I squeezed it I got a lot more glycerin. So I divided it into three balls and wrapped them in cheesecloth, then pressed them. This produced dryer soap and more glycerin, but not much more water.

Next note: Decanting two separated liquids is hard without the right equipment. I think that if I were doing this at scale I'd probably find it useful to make some specialized equipment

Day 6: The balls of soap are still in their cloth and still very slick. I think they're still exuding a bit of glycerin. But they do work as soap.

Day 20: The soap is now hard enough to be considered ready

Lye is hard to find these days. Went to 2 hardware stores, a supermarket and 2 drugstores. No dice. Ordered it from Amazon instead. Easy.