Making Soap from Washing Soda?

Today, soap is generally made from sodium hydroxide or potassium hydroxide. But I've been doing a little research, and found that potassium hydroxide was not the "potash" used to make soap in the old times, but it was, rather, potassium carbonate.

Since potassium and sodium hydroxide both can make soap, and potassium carbonate can make soap, I was wondering if sodium carbonate (washing soda) can make soap. Anyone know?

I always read that the liquid trickled through the ashes of hardwood (or palm fronds, or kelp...) was high in potassium hydroxide. I thought that's what potash was. Where would potassium carbonate come from?

I also recently read how you could make washing soda (sodium carbonate) from baking soda (sodium bicarbonate) by baking it. I've not tried it, but it looked reasonable. If one could make soap from washing soda that was derived from baking soda, that would be pretty wild.

After tons of research, and even confirming on wikipedia (see their articles on lye and potash), I'm almost certain that potash back then was potassium carbonate. This is what leached from wood ashes when watered was poured on and the "lye" that was used. Potassium hydroxide is and was known as "caustic" potash.

Caustic potash (used today) was created, to my knowledge, by treating the regular potash with lime.

On that note, I've also confirmed that you can create lye by mixing potassium carbonate (potash from wood ashes) or sodium carbonate (washing soda) with lime (find it at the hardware store) in water. The results will be lye water and chalk. The chalk (calcium carbonate) precipitates out of the water during the reaction as it is insoluble. It can then be removed, the water boiled down, and voila, KOH or NaOh! From what I've read of others' experiments, at least.

I have hydrated lime in my kitchen, it's used in in the nixtamalization of corn: http://en.wikipedia.org/wiki/Nixtamalization

It would be cool to try and make soap with that and washing soda, if I knew where to start.

Well, there is this, but can't recommend it.:???:

http://www.homesteadingtoday.com/co...ing/459629-alternative-method-making-lye.html

Well now, welly well well. This would be fun to test. Thanks!

According to this post, you add 2 oz of hydrated lime (Calcium hydroxide) to 4 oz of water, and 2 oz of washing soda (sodium carbonate) to 4 oz of water. Mix these two, let sit for up to 24 hours, let the chalk precipitate and settle, then carefully filter all this out for approximately 4 oz of lye at 50% solution. It looks like this lye would be sodium hydroxide, leaving behind the calcium carbonate (chalk).

Makes sense. Be fun to try it out.

Let us know how it turns out. I really can't remember if the OP figured out how to measure the lye strength. I didn't read all of the posts in the thread, but remembered the experiment.

Seawolfe said:

Well now, welly well well. This would be fun to test. Thanks!

According to this post, you add 2 oz of hydrated lime (Calcium hydroxide) to 4 oz of water, and 2 oz of washing soda (sodium carbonate) to 4 oz of water. Mix these two, let sit for up to 24 hours, let the chalk precipitate and settle, then carefully filter all this out for approximately 4 oz of lye at 50% solution. It looks like this lye would be sodium hydroxide, leaving behind the calcium carbonate (chalk).

Makes sense. Be fun to try it out.

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Yeah, it would be sodium hydroxide that you get. After removing the precipitate, you can boil off the water and you should be left with pure lye. Also, if you take the precipitated chalk (calcium carbonate), and heat it up to around 900 degrees F, it will turn into Calcium Oxide (CaO or quicklime). CaO can then be mixed with water to get hydrated lime! If your oven has a self-cleaning cycle, that gets up to 900 degrees. If you try any of this, just be sure to remember that CaO is extremely caustic.

I believe the chemical reaction between washing soda and hydrated lime would be as follows:

Na2CO3 + Ca(OH)2 > 2NaOH + CaCO3

This means that if you wanted everything to completely react, with no leftovers, you would need to ensure that you have equal amounts of each molecule of the reactants. To do this, you'd simply have to take into consideration molar masses. Washing soda is 105.9885 g per mol, and hydrated lime is 74.093 g per mol. This means if you had 105.9885 g of washing soda, you'd need 74.093 g of hydrated lime to completely react with it.

http://www.countryfarm-lifestyles.com/soap-recipes.html Scroll down to "SOAP MAKING RECIPES for HOMEMADE SOAP WITHOUT LYE or CAUSTIC SODA".

http://www.countryfarm-lifestyles.com/make-lye.html

I LOVE you science geeks!!!

My husband caught me gathering up the supplies for my grand lye experiment and blocked me!! Some blather about doing it under a fume hood...
Maybe Ill book time in the fume hood at work this week, or do it outside at work where there's less of these "rules"

Seawolfe said:

My husband caught me gathering up the supplies for my grand lye experiment and blocked me!! Some blather about doing it under a fume hood...
Maybe Ill book time in the fume hood at work this week, or do it outside at work where there's less of these "rules"

Click to expand...

LMAO! He sounds like my husband - it's only because they love us . I would have happily joined you on your experiment! I wait till hubby is traveling or at work and then do all my unsafe things like getting on 20 ft ladders, etc. etc. (basically things that make his blood run cold). I have built myself a reputation in the neighborhood :-D

AnnaMarie said:

LMAO! He sounds like my husband - it's only because they love us . I would have happily joined you on your experiment! I wait till hubby is traveling or at work and then do all my unsafe things like getting on 20 ft ladders, etc. etc. (basically things that make his blood run cold). I have built myself a reputation in the neighborhood :-D

Click to expand...

I'm not allowed on a step-stool without him there lol.

Seawolfe said:

Some blather about doing it under a fume hood...

Click to expand...

Pish tosh .. men who stick their fingers near fast moving machinery blades all the time seem to worry about women getting hurt changing a light bulb.

I love my hubby .. he knows that after 20 years of working in forestry, *I* operate the chainsaw better than him!

ETA: I needed to buy hydrated lime for my Tadelakt plaster anyway .. and wanted washing soda to make laundry soap .. so this is the next experiment I'll have to try, as soon as I'm out of this walking boot/cast-y thing.

Ok, so I was cleaning out some of my cupboards recently, and found a can of powdered calcium hydroxide with calcium carbonate, and minor amounts of various oils like olive and almond -- not enough to wet the powder, so they must be miniscule.

Anyhow, I remembered this thread, about using calcium hydroxide and sodium carbonate to make lye, with the precipitate being more calcium carbonate, which can then be baked to make calcium oxide, and water added to make, once again, calcium hydroxide.

So I'm thinking --
A) If I attempted to use this to create lye, would the oils interfere? make curds of soap that I'd need to strain out?
B) Will having existing calcium carbonate in the mix interfere? Or just add to what's going to precipitate out?
C) Once all this calcium carbonate has been strained out and baked, how many cycles of this hydrating, creating lye, straining the carbonate out, baking, hydrating, etc, do you think it would take to use it all up? I mean, it can't be a perpetual lye machine, right?
D) Can soap be made simply using Calcium hydroxide instead of potassium or sodium hydroxide? If so, what would its properties be like?


Should I even attempt it? Or just toss it? Other uses for it, besides its intended use as a depilatory?

I don't know what the chemical formula or even the chemical name but potash is mined from the ground. The province where I live (in Canada) is a big exporter of potash. It is a component of chemical fertilizer.

DeeAnnaaaaa... Oh great and wonderful chemistry guru! I have a (few) question(s)

I love you science geeks, also!!!

"...A) If I attempted to use this to create lye, would the oils interfere? make curds of soap that I'd need to strain out?
B) Will having existing calcium carbonate in the mix interfere? Or just add to what's going to precipitate out?
C) Once all this calcium carbonate has been strained out and baked, how many cycles of this hydrating, creating lye, straining the carbonate out, baking, hydrating, etc, do you think it would take to use it all up? I mean, it can't be a perpetual lye machine, right?
D) Can soap be made simply using Calcium hydroxide instead of potassium or sodium hydroxide? If so, what would its properties be like? ..."

Ugh. You guys. Just got back from a camping trip and I have to bring my mind out of the forest and back to chemistry. :roll:

From what I understand -- I have not done this personally, mind you --

A. and B. You ~could~ make soap from a mixture of calcium carbonate, water, and sodium hydroxide. You would have to make a "grained" soap using a "boiled" soapmaking process, not a modern CP or HP method. The solids will end up being mixed with the soap curds and liquid phase, and will be tough to separate out without a lot of care.

I think some of the very oldest soap makers I've read about did make their soap this way because it was easy and relatively simple, but most did not due to the difficulty of producing a pure high-quality soap. These makers made their ley (old name for lye solution) separately by mixing calcium hydroxide (lime) and sodium carbonate (soda ash) with water in a special mixing tank. They let the solids settle out, and decanted the liquid ley (sodium hydroxide and water) from the settled solids and used that as a clear solution to make the soap.

Several solutions of ley were made from one charge of soda ash, with the first ley being the strongest and the final (third or fourth) ley being the weakest. They kept the different leys in separate tanks and added these solutions to the fats at specific times while boiling the soap. Usually the weakest ley was used first and the strongest at the last. They used the different leys in part to manage the density of the fat/soap vs the ley solution. Too much difference in density between the two immisicible layers reduced the ability of the ley and fats to mix and thus slowed the rate of saponification. Remember ... there were no stick blenders back then!

C. The old makers used the soda ash and lime mixture several times as I've described. They would sometimes add fresh soda ash to the tank if needed. I don't think they removed the settled solids and reconstitute the lime for reuse, although I can't say I'm absolutely certain about that. One issue of this plan is that any metallic and other impurities in the soda ash and lime will gradually build up in the recycled lime and potentially cause problem. Another is the cost of reconstituting the lime vs. the cost of buying fresh lime. Lime is pretty cheap.

D. Yes you definitely can use Ca(OH)2 to make soap, just like the ammonium, sodium, and potassium hydroxides. A calcium soap is water insoluble and can be used as a grease-like lubricant. It is also a component of soap scum (aka that grey hard-water ring around the bathtub).

Cool! I won't throw the stuff out then, I will tuck it away for a day I feel like experimenting. Thanks DeeAnna! Did you have a good camping trip?