Print PDF
Favorite
Email
Granny's gone and so is her box of ashes for making lye. Here's a modern technique to make high quality lye (Sodium Hydroxide) at home for any number of reasons, including soap making.
We'll be using an electrochemical process called electrolysis in a two chamber apparatus. In one chamber we will put a saturated saltwater solution and a positive electrode. In the other we will put pure water and the negative electrode. The two chambers are separated by a salt bridge composed of gelatin and table salt. While Jello brand gelatin can be used, we will be using Knox unflavored gelatin. The salt bridge allows sodium ions to pass between the two chambers.
NOTE: This is dangerous. Chlorine gas is extremely toxic and hydrogen gas is highly flammable. This should only be done outdoors in a well ventilated area. Avoid breathing the fumes which escape from the chamber.
When current is applied the sodium and chlorine ions are attracted to the negative and positive poles respectively. In the positive chamber the free chlorine combines into chlorine gas which escapes while the sodium ions travel across the salt bridge to the negative electrode. Meanshile in the negative chamber the pure water separates into hydrogen gas and an a hydroxide molecule. The hydrogen gas escapes and the sodium ions from the salt bridge combine with the hydroxide molecules to form Sodium Hydroxide in solution.
This process can be used to produce NaOH solutions of up to 40% or so concentration. This can be further reduced or dried to produce higher concentrations. I believe the "raw" syrup will be sufficient for soap making.
Traditionally the lye syrup made from ashes was boiled down until sufficiently concentration. This was tested using the egg test. If an egg was placed in the solution it should sink up to an area about the size of quarter (between 1/2 and 3/4 of the egg below the surface).
If you want to get all green about it use a solar oven to heat the water for making the saturation solution and use a small solar panel or solar battery charger for the electrolysis.
We'll be using an electrochemical process called electrolysis in a two chamber apparatus. In one chamber we will put a saturated saltwater solution and a positive electrode. In the other we will put pure water and the negative electrode. The two chambers are separated by a salt bridge composed of gelatin and table salt. While Jello brand gelatin can be used, we will be using Knox unflavored gelatin. The salt bridge allows sodium ions to pass between the two chambers.
NOTE: This is dangerous. Chlorine gas is extremely toxic and hydrogen gas is highly flammable. This should only be done outdoors in a well ventilated area. Avoid breathing the fumes which escape from the chamber.
When current is applied the sodium and chlorine ions are attracted to the negative and positive poles respectively. In the positive chamber the free chlorine combines into chlorine gas which escapes while the sodium ions travel across the salt bridge to the negative electrode. Meanshile in the negative chamber the pure water separates into hydrogen gas and an a hydroxide molecule. The hydrogen gas escapes and the sodium ions from the salt bridge combine with the hydroxide molecules to form Sodium Hydroxide in solution.
This process can be used to produce NaOH solutions of up to 40% or so concentration. This can be further reduced or dried to produce higher concentrations. I believe the "raw" syrup will be sufficient for soap making.
Traditionally the lye syrup made from ashes was boiled down until sufficiently concentration. This was tested using the egg test. If an egg was placed in the solution it should sink up to an area about the size of quarter (between 1/2 and 3/4 of the egg below the surface).
If you want to get all green about it use a solar oven to heat the water for making the saturation solution and use a small solar panel or solar battery charger for the electrolysis.
Remove these ads by
Signing UpStep 1Bill of Materials
Many of these items may seem familiar if you've tried "Make a Microbial Fuel Cell - Part II" as it is the same assembly.
2 1x1x1 PVC Schedule 40 Tee
3 1" PVC Schedule 40 Connector
2 1" PVC Schedule 40 Plug
2 1x1/2 Slip vs FPT threaded adapter
1 /21" PVC Schedule 40 Threaded Cap (Optional)
Clear plastic wrap
Rubber bands
Distilled Water
Plain salt ( not iodized )
4.5-12V Power Supply with leads
Salt Bridge Medium (Pick one)
Very nice stainless steel electrodes can be constructed using the reinforcing rods from automotive windshield washers
Alternatively pieces of carbon fiber rod, such as those available from model airplane and hobby shops can be
2 1x1x1 PVC Schedule 40 Tee
3 1" PVC Schedule 40 Connector
2 1" PVC Schedule 40 Plug
2 1x1/2 Slip vs FPT threaded adapter
1 /21" PVC Schedule 40 Threaded Cap (Optional)
Clear plastic wrap
Rubber bands
Distilled Water
Plain salt ( not iodized )
4.5-12V Power Supply with leads
Salt Bridge Medium (Pick one)
- Knox Unflavored Gelatin/Jello brand instant gelatin
- Hide Glue (powdered not liquid)
- Agar
Very nice stainless steel electrodes can be constructed using the reinforcing rods from automotive windshield washers
Alternatively pieces of carbon fiber rod, such as those available from model airplane and hobby shops can be
| « Previous Step | Download PDFView All Steps | Next Step » |
Let me know if anyone tries it. I'm too lazy to experiment.
http://www.instructables.com/id/Get-Lithium-Metal-from-an-Energizer-Battery-1/
I suspect that the white plastic seperator from the battery is an ion exchange membrane. perhaps this would be a good membrane for a chlorate / lye cell. i'm too lazy to try it. lemme know if anyone does and what the results are.
The process that uses a physical barrier lets brine be on both sides, and the hydroxide side eventually gets to a point where it is about half&half salt and hydroxide (which you then have to separate.) The membrane version starts with brine only on the chlorine side, but with some hydroxide in the hydroxide side; the hydroxide gets more concentrated and is extracted/re-diluted or something.
(I also can't tell how much of the process descriptions in the above link are specific to commercial scale production. Presumably the details have been optimized for continuous large-scale operation, and wouldn't necessarily apply to home-scale production. For some applications, it may not be necessary to remove the salt, for instance.)
(Sorry for seemnig to pick on your instructable. It's an interesting topic!)
It is pretty amazing stuff. Ever wanted to eat your coffee with a spoon? It works instantly with hot and cold liquids, even beer (nasty, by the way).
I connected up some electrodes to a DC power supply set at 30V, and dunked them in some tap water. According to the meters, current flow was imperceptible, but there was some slight bubbling at the electrode.
Adding some salt (about a teaspoon in 500ml; far from saturated) sent the current up to nearly an amp and resulted in vigorous bubbling.
So I'll stand by my statement that distilled water isn't very conductive, but I guess it would rapidly acquire enough salt from the "membrane" to become adequately conductive. Once NaOH starts forming, it would rapidly become more conductive, I guess. If neither water nor lye melts the gelatin.
http://www.flickr.com/photos/58843278@N00/4826112408/in/set-72157624451118581/