# Lime ( Ca(OH)2 ) Soap



## bodhi (Aug 18, 2013)

I just found a couple recipes for Lime soap.  One recipe states that it makes an excellent soap, but I have also read that it does not and its more suited to industrial use because it is 'greasy'.  

Seems interesting though.  Has anyone tried it?


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## bodhi (Aug 18, 2013)

I forgot to post the recipe.  Here it is: 

3 lb lime (calcium hydroxide)
7 lb fat
1 lb resin
3 gallons water
6 lb washing soda
3 tablespoons borax

Place the lime, washing soda and water in a large suitable pot for soap making and boil for 1 hour. Remove from the stove and leave overnight.

The following day, drain off the clear liquid that has risen to the top and place in a separate container.
Add the fat, resin and borax to the clear liquid that you have just drained off. Boil for 3 hours, stirring all the time.
You must stir the mixture, and this is a very important part of the process which will make excellent soap.

And here is the link: http://www.countryfarm-lifestyles.com/soap-recipes.html

It looks like she is taking regular lime, mixing it to make calcium hydroxide (slaked lime?) And then using that to saponify the fats?  Interesting..


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## Obsidian (Aug 18, 2013)

She has some interesting recipes. Do you know what she means by resin?


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## DeeAnna (Aug 18, 2013)

The old references I have that talk about using lime explained the lime was used to make a calcium soap, then the insoluble lime soap was decomposed with a strong acid into fatty acids. The fatty acids were then used for soap making. In her recipe, the borax would be a source of sodium, so I imagine the reaction would be something roughly like this:

fat + lime = calcium soap + sodium = sodium soap

Resin might be rosin, the the solid sticky stuff that's left after removing the turpentine from the pitch from pine trees. It can be saponified and was used a century ago as an inexpensive filler in laundry soaps and cheap toilet soaps. It adds hardness, a yellow color, and some cleansing ability to a soap.

She also has a recipe for an ammonia soap, which would dissolve in water even more easily than KOH soap --

SOAP MAKING RECIPES: LAUNDRY SOAP
6 pounds rendered down mutton fat
2 gallons water
0.5 pound resin
2 ounce powdered borax
1 pound caustic soda
1 bottle cloudy ammonia ....


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## bodhi (Aug 18, 2013)

Sounds about right to me DeeAnna.  In the little i could find, I did see mention about the Ca soaps being not very soluble in hard water in addition to being greasy, but nothing about acidifying and re-soaping.    Do any of those references describe the soap itself or how it lathers or washes or smells, etc?  Im quite curious, but have no desire to try such large batches or how to go about shrinking them to a manageable trial size.  

That ammonia one looked interesting too but, mutton fat and ammonia?  :sick:  blech, no thanks.


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## Robert (Aug 18, 2013)

DeeAnna said:


> The old references I have that talk about using lime explained the lime was used to make a calcium soap, then the insoluble lime soap was decomposed with a strong acid into fatty acids. The fatty acids were then used for soap making. In her recipe, the borax would be a source of sodium, so I imagine the reaction would be something roughly like this:
> 
> fat + lime = calcium soap + sodium = sodium soap


I very strongly doubt that's what was going on there.  Rather, this looks like a process that's used both industrially and in children's chemistry sets to make lye solution:

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

The calcium carbonate precipitates as a chalk, and then the NaOH is there to make soap.  The borax doesn't participate in the reactions.


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## bodhi (Aug 18, 2013)

Robert said:


> I very strongly doubt that's what was going on there.  Rather, this looks like a process that's used both industrially and in children's chemistry sets to make lye solution:
> 
> Ca(OH)2 + Na2CO3 --> 2 NaOH + CaCO3(s)
> 
> The calcium carbonate precipitates as a chalk, and then the NaOH is there to make soap.  The borax doesn't participate in the reactions.



Really?  I was assuming she was starting with CaO and making Ca(OH)2 with a little Na and precipitate left over and saponifying with the calcium hydroxide.  Its been way too long since i was in a chem class to actually run out the reactions.  So in this case the borax is probably a buffer and possibly hardening agent and this is indeed not a soap without lye?   What would the formula look like if you started with CaO instead of calcium hydroxide?

DeeAnna, If youre interested, are there any recipes in those books of yours so we can see if what they are all referring to as calcium soaps are this type of scenario?  The other recipe in the link i referenced just referred to it as lime not calcium hydroxide, so maybe its two different soaps?

Edit, I just looked at this again.  Im now thinking there is a problem with the recipe?  Or at least I am wondering if she starting with CaO or Ca(OH)2..  

Robert, assuming she started with Ca(OH)2, for the sake of your reaction above, the water is left out so the formula should be Ca(OH)2 + Na2CO3 + H20 ---> ??    No?  
Or maybe she did start with CaO  which would make it CaO + H2O + Na2CO3 ---> 2 NaOH + CaCO3(s)


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## DeeAnna (Aug 18, 2013)

Calcium soaps are pretty much insoluble in water and would not be useful as a "soap", in the sense that you and I think of soap. There has to be a secondary reaction going on in this recipe to make a useful sodium soap, but I'll let you and Robert debate that issue. 

The old makers didn't do lime saponification this way -- they did a multi-step process as I described earlier to make a lime soap, decompose the lime soap with a strong acid, and use the resulting fatty acids to make a sodium soap. Here is an excerpt from one soap making manual of the day:

"While by the term saponification as used in soap making it is inferred that this is the combination of caustic alkalis with the fatty acids to form soap, this term is by no means limited to this method of saponification, as there are various other methods of saponifying a fat. The chemical definition of saponification is the conversion of an ester, of which glycerides are merely a certain type, into an alcohol and an acid or a salt of this acid.

"Thus, if we use caustic alkali as our saponifying agent for a fat or oil, we obtain the sodium or potassium salt of the higher fatty acids or soap and the alcohol, glycerine. On the other hand, if we use a mineral acid as the saponifying agent, we obtain the fatty acids themselves in addition to glycerine....

[The author goes on to explain that soap making industry sometimes made its profit on the sale of the recovered glycerin, so making soap without recovering the glycerin was not a profitable venture. Lime saponification and other forms of saponification were developed to convert fats into fatty acids and glycerin. This was done, not so much because these processes made better soap, but because the glycerine could be more easily recovered and purified from the fatty acids than from the soap.]

"LIME SAPONIFICATION. The saponification in an autoclave is usually carried out by introducing the fats into the autoclave with a percentage of lime ... together with water. If the fats contain any great amount of impurities, it is first necessary to purify them either by a treatment with weak sulfuric acid ... or by boiling them up with brine and settling out the impurities from the hot fat.

"To charge the autoclave ... the required quantity of unslaked lime, 2 to 4 per cent. of the weight of the fat, is run in with the molten fat, together with 30 per cent. to 50 per cent. of water. While 8.7 per cent. lime is theoretically required, practice has shown that 2 per cent. to 4 per cent. is sufficient. The digestor, having been charged and adjusted, steam is turned on and a pressure of 8 to 10 atmospheres maintained thereon for a period of six to ten hours. 

"When the saponification is completed the contents of the autoclave are removed... The mass discharged from the digestor separates into two layers, the upper consisting of a mixture of lime soap or "rock" and fatty acids, and the lower layer contains the glycerine or "sweet" water.

"The calculated amount of sulfuric acid to decompose the lime "rock" is then added, and the mass agitated until the fatty acids contained therein are entirely set free. Another small wash is then given...

"Due to the difficulties of working the autoclave saponification with lime, decomposing the large amount of lime soap obtained and dealing with much gypsum formed thereby which collects as a sediment and necessitates cleaning the tanks, other substances are used to replace lime. Magnesia, about 2 per cent. of the weight of the fat, is used and gives better results than lime. One-half to 1 per cent. of zinc oxide of the weight of the fat is even better adapted..."

Source: E. G. Thomssen. Soap-Making Manual: A practical handbook on the raw materials, their manipulation, analysis and control in the modern soap plant. 1922. From Project Gutenberg, www.gutenberg.net.


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## DeeAnna (Aug 18, 2013)

PS For some reason, I totally blanked out the washing soda in this recipe. Duh, of course you're right the washing soda would be the source of the sodium, not the borax. It's been a tough weekend, and I'm just not thinking too straight.  :-?


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## bodhi (Aug 18, 2013)

DeAnna, thats fabulous.  Thank you!  It seems the little bits of info i found were not entirely off, but merely scratching the surface.  Now im wondering if i can do this without it being at pressure.  I think i need to see what one of these rocks is like and how much glycerine actually remains.  

No worries about leaving out the Soda.  Ive just realized that in trying to remember how to write out a reaction, i somehow decided that Ca hydroxide could not be formed by a mere combination of CaO with water.  Time for bed.  Thanks for sourcing that too,  Its going to be a good read.


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## Robert (Aug 19, 2013)

bodhi said:


> What would the formula look like if you started with CaO instead of calcium hydroxide?


No difference, because there's an excess of water in there.  Calcium hydroxide is just hydrated calcium oxide.

The instructions have the water-soluble ingredients stand overnight, which is plenty of time to react and leave a NaOH solution.  I won't figure the stoichiometry, but just assume the amounts given are enough sodium carbonate to react with all the calcium, because if making soluble soap is the object, that's the way they'd work it out.  You wouldn't want any calcium left in solution once the oils are introduced.  If there's an excess of sodium carbonate, that won't hurt, and the borax is further alkali.

If you can find a chemistry set with soapmaking instructions, that's the way they do it, except they don't require overnight for the NaOH to form.  Standing in the barrel overnight is for time for the CaCO3 to settle out so just the liquid can be used and the soap won't be chalky.


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## bodhi (Aug 20, 2013)

Thank you Robert.  My brain was not working.  See my response to DeeAnna.  At the time of my writing that, CaO and H2O did not compute.  :crazy:    Would having any extra chalk in there affect the saponification?


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## Robert (Aug 20, 2013)

bodhi said:


> Would having any extra chalk in there affect the saponification?


No, although it could leave the product chalky.  The instructions called for letting it settle and using the supernatant clear solution.


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