Make Lye From Salt and Gelatin

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.
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Also, if you use a cell in which the halves are not separate, but the electrodes are as close as possible to each other, the NaOH and Cl produced react with each other to form NaOCl, Sodium Hypochlorite, otherwise known as bleach.
I love this idea for a salt bridge. Does it noticeably dissolve during the electrolysis? I am currently trying to design some minimum maintenance electrolysis cells for easy personal production of some useful reagents.
Do you know if this would work with baking soda instead of salt?
It depends on what your electrodes are made of. Generally baking soda solutions will dissolve the positive electrode to for it's corresponding carbonate and maybe hydroxide. I have done a baking soda electrolysis with copper electrodes once to get CuO. The positive electrode forms a precipitate of copper carbonate and copper hydroxide. The negative forms CuO. I just filter it all, and heat in a beaker until completely dry, then further heat it for a while to decompose the carbonate and hydroxide into CuO. Worked very well.
I have no theory at all on what alternatives there might be. Be extremely careful in experimenting as dangerous and potentially deadly gases or other undesired by products can occur.
this is quite an interesting method, but this is an area of expertise i dont fare very well in, id much rather buy my lye, but thats just me, I buy mine from, i figured some of you might like to know. im aware that lye is almost impossible to find locally anymore unless its found online or its made (as you guys are talking about) anyways, i figured id share that tid-bit of info, have a great day.
egbertfitzwilly (author)  Bill_the_Baker2 years ago
I buy mine also. This is part of a larger project intended to explore the use of al-air batteries in parts of the world where scrap aluminum is readily available but a renewable source of NaOH is needed. Everywhere that humans can be found salt is readily available....
Mike sr2 years ago
How about using the white plastic ion exchange membrane that is roled up in a lithium battery. put it pulled over the pvc tube end & slide the coupling over to secure it. might have to sand the pvc end slightly if the fit is too tight with the membrane in the joint to prevent tearing it. might have to seal up the joint with silicone glue to prevent seeping.

Let me know if anyone tries it. I'm too lazy to experiment.
egbertfitzwilly (author)  Mike sr2 years ago
You have my undivided attention. Please tell me more about the plastic ion exchange membrane rolled up in a lithium battery.
Check out this to see the parts in a lithium battery.

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.
westfw3 years ago
So how well does this work? The best info I could find ( ) indicates that there are two main processes used to separate the chlorine and hydroxide sides of the cell. One uses a rather fancy ion exchange membrane that only passes positive ions (Na+), and the other (the asbestos-based version you mention) primarily provides a physical barrier. I can't figure out whether the salt bridge acts as a cation membrane or just a physical barrier.

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!)

egbertfitzwilly (author)  westfw3 years ago
This is a conventional ion exchange membrane cell. It works well enough to max out the pH test and power an Al-Air cell. Its not that the membrane passes only Na+ ions, its that it doesn't transport the hydroxide and chlorine ions which results in bleach production rather than sodium hydroxide. You are correct that salt water can be used in both chambers. I used distilled water to demonstrate that the NaOH is produced from the brine. Suitable for use in a science fair project. In production devices a porous membrane is normally used to allow fluid flow to a continuous drain. The flow rate is such that it maximizes the production of NaOH by controlling time in the hydrolysis tanks. In this design the abestos fibers also serve to trap the chlorine until the molecules combine and outgassed. The fluid flow serves a number of functions, it provides ion transport for the Na+ ( in solution ) and it prevents the backflow of hydroxide ions. This eliminates the need for an ion bridge. I have no well defined plan for how one might adapt this to home brew production in sufficient quantities for hominy or soap making.
aeray3 years ago
Excellent. The home-made hominy production can now commence. As to hide glue- you do know that it is water-soluble?
egbertfitzwilly (author)  aeray3 years ago
Yeah, so is agar. I think the hide glue ( unrefined gelatin ) may last longer than either of the other two. I really want to come up with a new salt bridge (or other low cost ion transfer) solution. I like this one for its novelty but as you point out its a temporary fix that needs to be replaced periodically. I hadn't even thought of hominy.....but you are correct.
In the US food-grade agar is pretty easily available in Asian (and other) groceries. I have a few sticks in my cupboard right now. Try asking for "kanten" or "dai-choy-go".
egbertfitzwilly (author)  aeray3 years ago
I love you man. This is one of the single most useful pieces of information that has ever been submitted. I knew that this existed and was readily available but no one seemed to know that they had it. What section is it in?
In the "asian" or "ethnic" section. At actual Asian groceries, look around for the dessert section.
westfw aeray3 years ago
Also used in "molecular gastronomy": How does current start flowing at the start? The distilled water in the "destination" chamber ought to be a pretty good insulator...
egbertfitzwilly (author)  westfw3 years ago
I don't believe that listening to the radio in a bathtub full of distilled water is safe. Electrolysis of distrilled water is easy to validate, take a glass of distilled water, a couple/three batteries, some duck tape and a couple pieces of wire. Use the duct tape to wire the batteries in series by placing them end to end and securing the joint with tape. Attach one wire to the positive pole of the series, one wire to the negative pole ( each of the batteries ). Put the wires into the distilled water and watch for bubbles to appear. Please post your results with pictures if possible.
Oh, very well. Hmm. All out of distilled water, and image uploads are unavailable during maintenance...  Sigh.

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.
egbertfitzwilly (author)  westfw3 years ago
Nice picture. The server issues are a pain in the ..... The rate of electrolysis is a function of amperage, the rate of bubbles should increase proportionally to the input amps. The introduction of electrolytes also changes the electro-chemical nature of the reaction. A 10% salt solution should produce a reasonable chlorine bleach ( about 3% if I recall correctly ). You are correct the salt bridge can break down quite rapidly. I'm not particularly fond of this design, particularly with gelatin. I've ordered some hide glue off the net, it will be interesting to see how that fares mechanically in this and the MFC designs. The salt bridge can also be mechanically reinforced, for instance by making it on a base of silkscreen material, to increase longevity.
egbertfitzwilly (author)  aeray3 years ago
It would be most useful if you were to make an instructable that showed how to prepare agar plates and so on using these products. I would link to them in any instructable of mine that uses a culture medium or salt bridge.
Ha! I use it for cooking! (to thicken sauces, and because it breaks down at a higher heat than gelatin, so you can make things like savory jello cubes to put in soups, etc)
This might also be a gel option:
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).
egbertfitzwilly (author)  aeray3 years ago
I can see where edible beer is a concept whose moment has not quite arrived... Do you know if its conductive?
I'm not sure, but I would think so, if the liquid it was added to was.
rimar20003 years ago
Very interesting.
egbertfitzwilly (author)  rimar20003 years ago
Thanks. There's about 2M web pages that talk about how to do this but this is the only design I found that seemed to actually work. Now if I could just figure out a bathtub way to vapor deposit abestos fibers as the membrane this would be a production grade design...:-)
Egbert, have mercy on me. Your last paragraph is too difficult to understand for an Italian descent living in Argentina, that does not speak a word of English.
egbertfitzwilly (author)  rimar20003 years ago
Sorry, what I said was if I could figure how to make the same kind of electrode they use in a factory that makes NaOH this design would be perfect. In a real factory the stainless steel electrode is coated with tiny particles of absestos using a highly technical process that I will be unlikely to copy...
Oh, now I understand. I am a "hard dude". Hard of brain.

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