# A safety caution about heating KOH and glycerin



## DeeAnna

One method for making the lye solution for liquid soap is to heat KOH in glycerin until the KOH dissolves. This method was developed by pharmacists some time ago as an alternative to dissolving the KOH in water to make soap for medical purposes.

The advantage of using glycerin rather than water is the KOH-glycerin mixture saponifies fats very quickly. The obvious downside to the "pharmacist's method" of dissolving the KOH in glycerin is the mixture must be heated carefully to get the KOH to dissolve. The mixture foams furiously while it is heated, so the liquid must be stirred constantly and the heat controlled to keep the mixture from boiling over. 

A cautionary comment on a YouTube video about the pharmacist's method was brought to my attention this past weekend. The author advised against using the pharmacist's method and suggested soapers instead use the alternative method of dissolving KOH in water at room temperature. Glycerin can later be added to the KOH-water mixture to gain most of the benefits of the pharmacist's method with fewer of the risks. 

The obvious risk of the pharmacist's method is the danger of heating a strong alkali (KOH). If the hot caustic mixture spills onto the skin, severe chemical and thermal burns will result in seconds. Prompted by information given in the YouTube comment, I looked deeper into the chemistry involved with hot KOH-and-glycerin mixtures and found other serious risks to this method that I want to share with you.

The heated mixture bubbles and foams so furiously because the KOH and glycerin are reacting with each other to form bubbles of water vapor and hydrogen gas. The amount of combustible hydrogen gas is large enough that this reaction has been studied as a way to recover useful energy from waste glycerin formed by commercial biodiesel and soap production. Needless to say, it is not safe to mix combustible hydrogen gas with an open flame or hot burner! Hydrogen is a light, buoyant gas, so it will most likely rise safely away from the stove burner, but I'm not sure I want to trust the idea that hydrogen gas will always rise out of harm's way rather than burn or explode.

When glycerin decomposes, it can also form toxic and irritating byproducts such as acrolein, acetic acid, formaldehyde, and formic acid as well as carbon dioxide, water, and combustible gases. Although pure glycerin decomposes only when heated to temperatures that would be unusually hot for a kitchen stove, when mixed with other chemicals, glycerin decomposes at much lower temperatures.

Acrolein is one of the most hazardous chemicals formed by this decomposition. It is a colorless to yellow liquid with an acrid, disagreeable odor and is a severe respiratory irritant. It is flammable and unstable and can form explosive compounds. The US Occupational Safety and Health Administration (OSHA) limits acrolein exposure to a maximum of 0.3 ppm in one short term exposure and an average of 0.1 ppm per 8 hour exposure. http://www.cdc.gov/niosh/docs/81-123/pdfs/0011-rev.pdf

In summary, the pharmacist's method carries the risk of severe chemical and thermal burns from a spill, the risk of combustible hydrogen gas near open flame or hot burner, and the risk of toxic, irritating compounds being released into the air. 

I do not think most of us soapers, even the ones who use the pharmacist's method with good results, are fully aware of these potentially serious risks. It was certainly an eye opener for me. I am sharing this information not to stir controversy, but so people have the knowledge to make an informed choice whether to use the pharmacist's method or to dissolve KOH in water at room temperature.

Thanks -- I appreciate your taking the time to read this!


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## IrishLass

Wow! Thanks DeeAnna! I've been using the pharmacist method since I first started making GLS (it was the only method offered to me at that time). I personally haven't had any problems with it-  I'm always extremely careful and take all the necessary precautions, part of which is to mix the KOH/Glycerin both together cold before heating- but after reading your post, methinks I shall cease from using the pharmacist method from here on out. I also think I shall go back and post a disclaimer on my tutorials, with a link to this thread. 


IrishLass


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## Susie

Thank you for posting that!  I had no idea!


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## snappyllama

Excellent post, Deanna! Thank you for sharing this. I think it should be a sticky on this forum since it is a valuable safety message that shouldn't get lost.


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## cmzaha

Thankyou DeeAnna, thinking I shall go back to my original way of making LS or at least dissolve the KOH in distilled and add in additional glycerin


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## Seawolfe

I  SAID IT WAS LAVA!!
This is why I did it in a deep pot and poured the oils in on it. Maybe next time Ill dissolve the KOH in water first...


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## shunt2011

Very inciteful information. Thank you for this!


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## The Efficacious Gentleman

Would be interesting to see something like a 50% KOH in water solution being mixed with enough glycerine to bring it up to the usual weight, how that would work.  I don't need to make any LS for a while (my Nag Champa "Hippy" soap is lasting much longer than I would hope) but I wonder if someone who is making a batch soon and who usually uses the Apothe"scary" method could try the mixed option.


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## IrishLass

Gent- I shall be making a batch today so I can update my Creamy Cocoa Shea GLS tutorial (I just added a disclaimer to it). 


IrishLass


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## DeeAnna

"...Would be interesting to see something like a 50% KOH in water solution being mixed with enough glycerine to bring it up to the usual weight..."

If I am following you correctly, Gent, that's how I make my KOH solution. Dissolve a given weight of KOH in an equal weight of water. After the KOH is dissolved, add additional liquid (water or glycerin or both) equal to 2 times the KOH weight. I have done Irish Lass' olive, castor, and coconut soap with three different mixtures -- (1 part water + 2 parts glycerin) and (2 parts water and 1 part glycerin) and all water. It all works good. The more glycerin there is, the stiffer the paste tends to be, at least for me, but it saponifies well and dilutes nicely. http://www.soapmakingforum.com/showthread.php?t=51237

***

I want to thank the SMF member who let me know about this issue!


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## lenarenee

The Efficacious Gentleman said:


> Would be interesting to see something like a 50% KOH in water solution being mixed with enough glycerine to bring it up to the usual weight, how that would work. I don't need to make any LS for a while (my Nag Champa "Hippy" soap is lasting much longer than I would hope) but I wonder if someone who is making a batch soon and who usually uses the Apothe"scary" method could try the mixed option.


 
Apothe"scary"!  I would pay money to have a sense of humor like yours!


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## ngian

Thank you DeeAnna for the additional info upon the specific matter, and I am glad I had followed your way of KOH's dilution in my one and only so far liquid soap.


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## KristaY

Wow, DeeAnna. As usual, you've provided us with very important, detailed info. I've never been one to blindly accept "just do it this way" or "it's always been done that way". I like to know why. Drove my parents crazy when I was a kid, lol. So I really appreciate you not only saying there's a safety caution, but giving us the specifics as to why. If you've helped just one person avoid a serious injury, it's definitely time well spent in the research and typing it all out. So today I'm really grateful for DeeAnna's generosity!


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## topofmurrayhill

This is rather alarmist. I don't see people making informed decisions based on it. I see them getting scared and "blinded by science."

I've been concerned about this technique also, but entirely due to the risk of chemical and thermal burns. It has always struck to as contrary to the usual high degree of safety consciousness among crafters.

The other concerns are not realistic. To get any significant degree of degradation products, you would need much more caustic and much more time (hours) and preferably much more heat. The minutes it takes to dissolve a smallish amount of KOH in a largish amount of glycerin should do no harm. You get more acrolein and other degradation products from cooking. So definitely don't fry anything, try not to sautee, and avoid eating food if possible.

Your KOH is 10% water. The glycerin can be heated above the boiling point of water, which creates a lot of bubbling when the water is driven off. That's all. It's not hydrogen.


Seawolfe said:


> I  SAID IT WAS LAVA!!
> This is why I did it in a deep pot and poured the oils in on it. Maybe next time Ill dissolve the KOH in water first...



Yep, THAT is the point. It's really hot and caustic and it boils.


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## lenarenee

Alarmist?

We just received information that would increase our safety during the process of making gls. Using water to dissolve koh instead of heating the glycerin and dissolving the koh doesn't change the product outcome. It does reduce the potential risks.

I soap in the kitchen of a house I don't own. We have pets and kids running around....not to mention me....standing over a pot of lye. I'm intelligent and cautious, but far from being a 100% expert soap chemist. DeAnna just gave me the knowledge to make even safer choices that will protect me, the ones I love and our home.

I can't soap in a lab with equipment that can measure gasses my method does or doesn't  release.  Nor is there anything that can guarantee my environment is utterly conducive to preventing complications from the hot glycerin method.

I've been on the forums for 2 years and never found DeeAnna's info to be half baked or superfluous.
She's given us researched info, and left us to choose for ourselves. I'm taking it.


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## topofmurrayhill

lenarenee said:


> Alarmist?
> 
> We just received information that would increase our safety during the process of making gls. Using water to dissolve koh instead of heating the glycerin and dissolving the koh doesn't change the product outcome. It does reduce the potential risks.
> 
> I soap in the kitchen of a house I don't own. We have pets and kids running around....not to mention me....standing over a pot of lye. I'm intelligent and cautious, but far from being a 100% expert soap chemist. DeAnna just gave me the knowledge to make even safer choices that will protect me, the ones I love and our home.
> 
> I can't soap in a lab with equipment that can measure gasses my method does or doesn't  release.  Nor is there anything that can guarantee my environment is utterly conducive to preventing complications from the hot glycerin method.
> 
> I've been on the forums for 2 years and never found DeeAnna's info to be half baked or superfluous.
> She's given us researched info, and left us to choose for ourselves. I'm taking it.



Alarmist is an apt description.

I'm not interested in forum politics. I don't care who posted the information. I don't comment for people who are interested in personalities rather than facts. I have no problem with your believing what you want, but you can do so without criticizing me when you don't know better.

The method is risky because it involves a very hot caustic mixture plus water boiling off. For that reason I agree with dissolving the KOH in water before adding glycerol. Simple as that.

People like IL are smart and well aware of the true risks of dissolving KOH in glycerin, and they choose to do it. If they stop on the basis of this post, it is because the information is misleading and, for practical purposes, inaccurate.


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## Arimara

I, for one, am thankful DeeAnna made this post. I had forgotten about this method as I only use H2O in my liquid soaps. I prefer to know the risks of a said method than not to. I like perspectives.


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## lenarenee

topofmurrayhill said:


> Alarmist is an apt description.
> 
> I'm not interested in forum politics. I don't care who posted the information. I don't comment for people who are interested in personalities rather than facts. I have no problem with your believing what you want, but you can do so without criticizing me when you don't know better.
> 
> The method is risky because it involves a very hot caustic mixture plus water boiling off. For that reason I agree with dissolving the KOH in water before adding glycerol. Simple as that.
> 
> People like IL are smart and well aware of the true risks of dissolving KOH in glycerin, and they choose to do it. If they stop on the basis of this post, it is because the information is misleading and, for practical purposes, inaccurate.


 
There is absolutely no criticism in my post. Nor politics. Please notice that I didn't quote your post, or use your name. I gave my opinion, (explained why I didn't find the info alarmist) as did you and others, and shared my observation regarding DeeAnna's posting habits.


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## The Efficacious Gentleman

The most important part of the post that stuck out for me was about the super-heated lye/gly mix, which seems to be the part we all agree is a danger to soapers even if they are careful. The results of a spill would be terrible. 

That is enough for me to classify the post as 'not alarmist'. Parts of it, however, might be on the outside edges of practicable in common methods (there might be people who cook for longer than is needed, leading to some degradation and breakdown), but that means that the post is not alarmist, rather that parts of it maybe.


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## topofmurrayhill

lenarenee said:


> Please notice that I didn't quote your post.



Don't BS me. The very first word of your post was quoting me and it was obviously a response.

Hydrogen is obtained from glycerin oxidation when you drip small amounts slowly into molten caustic. Sodium and potassium hydroxide melt at over 600 degrees. The best you can do is a eutectic mixture of the two with a lower melting point, but the lowest temperature referenced for this reaction is 500 F and it takes many hours to complete at that temperature.

There is nothing of consequence happening between KOH and glycerin on anyone's stove top aside from making a hot a caustic liquid that threatens to boil over from the water content. Everyone should be scared about that, but they already know about it if they've been doing this -- and the risk is evident from every description or demonstration of the technique.

Nobody should get scared by the other stuff mentioned. Making french fries is way more dangerous in terms of being hotter, more flammable, and producing quite measurable quantities of toxic decomposition products that you breathe and eat with the food. If you barbecue hamburgers, you can enjoy some tasty acrolein.

I don't know what kind of forum it is that downright swoons over incorrect or misleading information and goes passive-aggressive when it's pointed out.


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## The Efficacious Gentleman

Going outright aggressive is not allowed. Do bear that in mind with your responses. 

The correction in itself is never an issue - or if it is, that is for each person to deal with on their own. The manner in which it is done, when the information in question is from someone who is not known for purposefully misleading (in fact, contributes a lot to the forum in general and is quite to admit mistakes), is the problem for me. 

"Actually, the hydrogen is unlikely to be an issue because of x y and z, so that's not going to affect most of us. But the hot glycerin warning is very important, as anyone who uses it will know" might well have been a better way to word it.


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## Misschief

I, for one, did not find DeeAnna's original post to be alarmist in any way. She titled the thread "A safety caution...." It is an appropriate title and an appropriate thread. As pointed out, there are dangers when it comes to cooking almost anything. Safety precautions SHOULD be taken and even more so when you're working with hot AND caustic materials. If there is a safer way of mixing hot glycerin and KOH, then it is advisable to do it in the safest way possible. 

I've used the method for making glycerin liquid soap as per IrishLass' method and have had no issues. From now on, I will mix the KOH with water first, then add the glycerin. Safety first.


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## topofmurrayhill

The Efficacious Gentleman said:


> The most important part of the post that stuck out for me was about the super-heated lye/gly mix, which seems to be the part we all agree is a danger to soapers even if they are careful. The results of a spill would be terrible.
> 
> That is enough for me to classify the post as 'not alarmist'. Parts of it, however, might be on the outside edges of practicable in common methods (there might be people who cook for longer than is needed, leading to some degradation and breakdown), but that means that the post is not alarmist, rather that parts of it maybe.



You're entitled to critique the tone of my post, but it wasn't really so terrible.

What struck me badly was to hear IL swear off the method and Susie saying "Thank you...I had no idea." These are experienced and knowledgeable soapers -- IL is actually our local expert on this method and Susie is perfectly familiar with it and liquid soaping in general. They are among the leaders who guide everyone here in making LS and were already making informed choices. They were not reacting to the actual risk, which they were already perfectly aware of, but rather to being misinformed because the post was overboard. I have to stand by my adjective.

Do I think it was on purpose? Of course not, but more caution might be due in posting technical information and folks should not forget to maintain a critical eye when reading.


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## DeeAnna

Thank you to all those who have tried to keep this discussion on track as a healthy, respectful debate -- I appreciate that.

I spent a lot of time researching this matter before I started this thread, and I am prepared to answer questions and discuss concerns. If anyone would like to continue the conversation, please contact me by PM and I will be glad to talk about this more.


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## Steve85569

So if I follow this correctly....

If I decide to use this method to make LS I should be prepared for steam, caustic bubbles and possible release of gases so good ventilation would be in order. I'm thinking exhuast fan. Further IF since I am inexperienced I over heat/ over cook the combination I may in fact create a chemical reaction ( breakdown) that produces a rather nasty gaseous material. Again good ventilation and avoid breathing any fumes would be a word to follow. A non contact thermometer seem like a very helpful tool here.
I should also be very careful to not spill the caustic mix as with any soap making.

I myself do not see any need for a great deal of alarm. I do see that I should proceed with informed caution and use the proper PPE's and monitor the temperature of the mixture. Normal safe practices have just been improved by having more information.

Thanks to DeeAnna for providing us with the information.


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## IrishLass

I must admit, if anyone was being alarmist, it was most likely me more than anyone else. I had a bit of a knee-jerk reaction because of my posted GLS tutorial in which I give instructions for the method being discussed in this thread. Granted, in my tutorial instructions I do stress the utmost importance of taking the proper safety precautions before proceeding, and I also give instructions on what to do if things look like they're boiling over, but since that's _my_ tutorial, I was beginning to feel the weight of responsibility pressing on me, if you know what I mean. 

After having read all the posts and varying viewpoints in this thread from everyone this morning (btw, thank you all- this has been a very good discussion, which I sincerely hope will continue so we all can learn), I have decided that instead of removing the method from my tutorial as I was intending to yesterday, that I shall leave it up, but with a provided link to this here thread so people can make their own choice. 

But in order for people to have a real choice, there must be another option from which to choose......so I will also be editing my tutorial to post the "dissolve KOH in water, then add glycerin" method......which I am actually working on right now. I made my Creamy Cocoa Shea paste with the method yesterday (went great, btw), and I am now in the fun (not) process of figuring out my new dilution rate for it. lol


IrishLass


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## jules92207

This has been a very interesting topic as I am interested in making liquid soap eventually and I appreciate ALL views and precautions to make an educated decision on which method to use. I appreciate all the helpful information and safety suggestions provided.


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## snappyllama

jules92207 said:


> This has been a very interesting topic as I am interested in making liquid soap eventually and I appreciate ALL views and precautions to make an educated decision on which method to use. I appreciate all the helpful information and safety suggestions provided.




I'm in the same boat. I haven't made LS yet, but I plan to in the future. I'm a safety-first type of person (girl scout lessons last forever). Having clear information for precautions to take and methods that may make myself safer makes me more confident when I do attempt it. 

I sincerely thank all of the contributors on this forum for taking their time to inform us!


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## LisaAnne

I've yet to make LS, it's definitely on my growing to do list. As stated above this has been an informative discussion on both sides. When I do attempt it I will use the pharmaceutical method, but I definitely appreciate the heads up.


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## galaxyMLP

I really appreciate this thread! 

I (personally) would not do the pharmaceutical method only because the idea of dissolving KOH in very hot glycerin without a fume hood genuinely worried me. And it had nothing to do with hydrogen production; it was all about thermal burns and caustic fumes for me.

I decided to look it up to see if the hydrogen production was of significant concern (I was genuinely interested). From what I could find, an article published in 1928 states that hydrogen can be produced in the presence of an excess of KOH to glycerin (they used 5g glycerin/ 8g KOH). We are using an excess of glycerin to KOH in order to dissolve the KOH in glycerin. The article also states that the reactions were run at 250 (~480 F) degrees. It does not specify Fahrenheit or Celsius but, I will assume Celsius as it is a scientific journal. In that case, we are working below that temperature when dissolving the KOH in glycerin. 

Despite the fact that we are working in conditions that may not be ideal for the reaction to purposely form hydrogen, we may be generating some. I don't know for certain of course, but, it's possible given the conditions during their experiment. If we are generating any hydrogen at all, it will likely be enough to ignite if there is a spark or flame in a closed environment. Hydrogen will ignite at concentrations of 4%-96% in the air. That is a huge range. Yes, in a well ventilated area you don't have a problem but its still something to consider. 

As far as the acrolein goes, I do agree thats not something I would worry too much about unless you actually smell it. It smells "burnt" and is apparently very identifiable. As it was pointed out though, it is found in minute quantities in fried foods. "The WHO suggests a "tolerable oral acrolein intake" of 7.5 μg/day per kilogram of body weight." Thats about 3.75 mg a day for an average person. I don't think we'd be exposing ourselves to near that amount during the KOH/glycering mixing. I did not do enough research on the other decomposition products to comment on them. 

I do think this was important to bring up. I think that someone can safely dissolve KOH in glycerin in an open, well ventilated environment. I do not believe this post was alarmist. I think the post was written to provide information as found to allow anyone reading it to come to their own, informed decision on how they want to proceed. I think the pharmacists method has its advantages and can be continued to be used safely with the proper knowledge and engineered controls in place. 

Where I found my information:
http://pubs.acs.org/doi/abs/10.1021/ja01391a023

http://thirdworld.nl/the-liberation...ol-and-glycerol-with-fused-caustic-alkalies-1

https://en.wikipedia.org/wiki/Acrolein

http://www.aciscience.org/docs/chemical_properties_and_derivatives_of_glycerol.pdf


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## topofmurrayhill

galaxyMLP said:


> I decided to look it up to see if the hydrogen production was of significant concern (I was genuinely interested). From what I could find, an article published in 1928 states that hydrogen can be produced in the presence of an excess of KOH to glycerin (they used 5g glycerin/ 8g KOH).



Your post is reasoned and realistic. I wanted to mention that, and most of this isn't specifically a response to you.

BTW, the scientist who conducted those experiments was a bit of a pioneer as far as women making long term careers in chemistry. She later spent many years as a chemist with Proctor and Gamble (she has of course passed away, but was interviewed in the 1980s). The 5g/8g was actually a reference to prior work. Her own research involved dripping glycerin into a mixture of molten sodium and potassium hydroxide (they melt at a lower temperature together than separately). That was at 480 degrees.

Glycerin is stable and non-toxic. It's heated and vaporized in e-cigarettes. The temperature you usually hear for the start of thermal decomposition is 280 C, well over 500F. For that, one could cite "Kinetic study of thermal processing of glycerol by thermogravimetry" by Margarida L. Castello, Jo Dweck, Donato A. G. Aranda, 2011.

It's safe to say that there is no appreciable decomposition of glycerin until it's in the vicinity of 500 F and up, temperatures associated with severely overheated cooking oil. Anyone who has gotten oil smoking knows what acrolein smells like (acrid!). If your glycerin smells like that, it's burning. That's not good, so don't overheat your glycerin. Burning stuff is smelly and bad and potentially dangerous. Your glycerin lye doesn't need to go anywhere near that temperature or even near the temperatures you routinely use for cooking oil.

IrishLass recommends starting with cold glycerin rather then preheating it. That is a great suggestion, since if you add KOH to very hot glycerin its water content can boil off violently. If you only add a very small amount, you find that the bubbling only lasts a few moments until the water is gone. It's simply not hydrogen.

Risks should be described accurately and put into proper, realistic perspective to avoid needless fear. Failing to do that, intentionally or not, is alarmist. I saw IL's reaction and she was initially scared enough by the post to swear off the method, even being the most experienced person with it. I don't want to beat a dead horse, but each respondent is weighing in on my use of a word. For the record, I'm good with knowing what words mean.


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## dingi

DeeAnna said:


> In summary, the pharmacist's method carries the risk of severe chemical and thermal burns from a spill, the risk of combustible hydrogen gas near open flame or hot burner, and the risk of toxic, irritating compounds being released into the air.
> 
> I do not think most of us soapers, even the ones who use the pharmacist's method with good results, are fully aware of these potentially serious risks. It was certainly an eye opener for me. I am sharing this information not to stir controversy, but so people have the knowledge to make an informed choice whether to use the pharmacist's method or to dissolve KOH in water at room temperature.
> 
> Thanks -- I appreciate your taking the time to read this!



Thanks DeeAnna for extensive write-up on the potential risk of Glycerin boiling for KOH solution. I just logged in today only to ask about the same topic, surprisingly DeeAnna had already posted this with good info.
I think this is not coincidence and just few days before only, I thought of asking someone here about the same topic I read it on the internet elsewhere about toxic chemical, When glycerin is heated to 280 degree C, it decomposes into acrolein and other potential risks.

Edited to add: topofmurrayhill mentions that it not that alarming and the solution is not heated or need to heat to 280 C or 500 F to dissolve KOH. 

Now a new query arises in my mind that if KOH is dissolved in water and then glycerin is added to it, how much heat is produced when mixing this solution with oils? Any chance that acrolein or any other toxic chemicals come out in vapor even though it not heated manually? if this is a silly question please bear with me and I am asking this out of safety instinct just to be sure how safely we must do the LS  and I just waiting for some stainless steel pot to arrive to start practically to do LS for the first time


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## topofmurrayhill

dingi said:


> Now a new query arises in my mind that if KOH is dissolved in water and then glycerin is added to it, how much heat is produced when mixing this solution with oils? Any chance that acrolein or any other toxic chemicals come out in vapor even though it not heated manually? if this is a silly question please bear with me and I am asking this out of safety instinct just to be sure how safely we must do the LS  and I just waiting for some stainless steel pot to arrive to start practically to do LS for the first time



When you dissolve KOH in water, the issue is the same as making bar soap with NaOH. For a minute or so, the heat and fizzing causes a mist of caustic solution to be launched into the air and you should be careful not to breathe it. However, none of the temperatures in the process are extreme if you follow IL's tutorial, and there are no toxic products from making the soap. Not much to worry about except protecting yourself from the lye.


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## DeeAnna

Thanks to all who have answered with factual information and thoughtful responses. I appreciate the time and effort you have contributed to fleshing out this matter.


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## dingi

Thanks topofmurrayhill


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## Marc Gaspard

DeeAnna said:


> One method for making the lye solution for liquid soap is to heat KOH in glycerin until the KOH dissolves. This method was developed by pharmacists some time ago as an alternative to dissolving the KOH in water to make soap for medical purposes.
> 
> The advantage of using glycerin rather than water is the KOH-glycerin mixture saponifies fats very quickly. The obvious downside to the "pharmacist's method" of dissolving the KOH in glycerin is the mixture must be heated carefully to get the KOH to dissolve. The mixture foams furiously while it is heated, so the liquid must be stirred constantly and the heat controlled to keep the mixture from boiling over.
> 
> A cautionary comment on a YouTube video about the pharmacist's method was brought to my attention this past weekend. The author advised against using the pharmacist's method and suggested soapers instead use the alternative method of dissolving KOH in water at room temperature. Glycerin can later be added to the KOH-water mixture to gain most of the benefits of the pharmacist's method with fewer of the risks.
> 
> The obvious risk of the pharmacist's method is the danger of heating a strong alkali (KOH). If the hot caustic mixture spills onto the skin, severe chemical and thermal burns will result in seconds. Prompted by information given in the YouTube comment, I looked deeper into the chemistry involved with hot KOH-and-glycerin mixtures and found other serious risks to this method that I want to share with you.
> 
> The heated mixture bubbles and foams so furiously because the KOH and glycerin are reacting with each other to form bubbles of water vapor and hydrogen gas. The amount of combustible hydrogen gas is large enough that this reaction has been studied as a way to recover useful energy from waste glycerin formed by commercial biodiesel and soap production. Needless to say, it is not safe to mix combustible hydrogen gas with an open flame or hot burner! Hydrogen is a light, buoyant gas, so it will most likely rise safely away from the stove burner, but I'm not sure I want to trust the idea that hydrogen gas will always rise out of harm's way rather than burn or explode.
> 
> When glycerin decomposes, it can also form toxic and irritating byproducts such as acrolein, acetic acid, formaldehyde, and formic acid as well as carbon dioxide, water, and combustible gases. Although pure glycerin decomposes only when heated to temperatures that would be unusually hot for a kitchen stove, when mixed with other chemicals, glycerin decomposes at much lower temperatures.
> 
> Acrolein is one of the most hazardous chemicals formed by this decomposition. It is a colorless to yellow liquid with an acrid, disagreeable odor and is a severe respiratory irritant. It is flammable and unstable and can form explosive compounds. The US Occupational Safety and Health Administration (OSHA) limits acrolein exposure to a maximum of 0.3 ppm in one short term exposure and an average of 0.1 ppm per 8 hour exposure. http://www.cdc.gov/niosh/docs/81-123/pdfs/0011-rev.pdf
> 
> In summary, the pharmacist's method carries the risk of severe chemical and thermal burns from a spill, the risk of combustible hydrogen gas near open flame or hot burner, and the risk of toxic, irritating compounds being released into the air.
> 
> I do not think most of us soapers, even the ones who use the pharmacist's method with good results, are fully aware of these potentially serious risks. It was certainly an eye opener for me. I am sharing this information not to stir controversy, but so people have the knowledge to make an informed choice whether to use the pharmacist's method or to dissolve KOH in water at room temperature.
> 
> Thanks -- I appreciate your taking the time to read this!




Hi DeeAnna a very informative thread. Really appreciate your efforts in educating people about the dangers one might come across. One quick question, if I add KOH to glycérine and leave it over night will it dissolve on its own? (Without heating)


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## DeeAnna

Marc Gaspard said:


> ...if I add KOH to glycérine and leave it over night will it dissolve on its own? (Without heating)



No, it won't.


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## Marc Gaspard

DeeAnna said:


> No, it won't.


Thank you DeeAnna


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## lsg

OK, everyone stop and count to one hundred.  Lets keep our comments amiable and non-confrontational.  We strive to keep this forum friendly, so that opinions and information can be received without flaming.


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## DeeAnna

@lsg -- This thread got started almost 5 years ago. It did get a little heated back then, but that was many moons ago.

In the years since I started this thread, I haven't seen a good reason to change my opinion that dissolving KOH in hot glycerin is unnecessarily dangerous. Too many people leap into the process without first fully understanding the method and the risks involved. There have been several soap makers in the years since this thread was started who have overheated the glycerin-KOH mixture until it has turned brown and acrid. This change in color and odor are scary signs the glycerin has decomposed and created noxious fumes.


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## lsg

Thanks DeAnna.  There was a report on the thread, today.  I should have checked the date of the last reply.   I will just close the thread, then.


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