# Why is soap alkaline?



## engblom (Jan 29, 2014)

Even if you superfat a soap, it will be to some degree alkaline. Why is this? Lye + excess of acids should not end up being alkaline.

Is it because the NaOH solution gets too weak for breaking the fatty acids away from the oils and the whole process halts? 

Could this explain why even fully gelled soaps get milder by age? Is it because of a natural breaking down into fatty acids take place, which is neutralizing the soap when it gets older?

Could this be an additional reason why washed and salted out soap is very mild on the skin? In a washed and salted out soap, any lye residues are washed away.


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## neeners (Jan 29, 2014)

sounds like you need a chemist to answer this.....  let me take a stab with the knowledge that i have...

i think with your statement that base + acid = neutral doesn't apply to soap making.  oils are not acid, nor are they basic.  they're a fat.  so adding lye to oils/fats won't give you the same reaction as mixing baking soda with vinegar.  here's wiki's explanation of saponification: http://en.wikipedia.org/wiki/Saponification

a gelled soap is soap that went through saponification quicker than non gelled soap.  non gelled soap takes a few more days for the whole process to complete.  

when a soap is cured, the water evaporates out of the soap.  i would also think that any leftover minute amount of lye is still working eating away at any un-saponified oils left in the bar.  so over time, the soap gets hard and mild.  all soaps, HP, CP, M&P, would get milder over time.  (think almost like fine wine - takes a long time to get really really good)

i'm not sure what washed soap is, but with salt bars, i've never personally used them, but from reading the forum, some people love it some don't, works on some skin and not on others.  also, salt bars take a LONG time to cure.  the long curing time could account for the fact that it becomes so mild.

i hope that helps some, and that someone else can chime in with some more details.....


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## Obsidian (Jan 29, 2014)

Salt bars don't really take that long of a cure, 8 weeks is good for most people including me who has a sensitivity to coconut oil soaps.

Also, I didn't find washed and salted soap to mild, in fact it dried my skin so bad that I had to toss it out and I'll never salt out soap again. To answer your question though, yes, any excess lye will get washed out.


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## neeners (Jan 29, 2014)

huh...i thought i read somewhere salt bars take a while to cure?  guess i read wrong or am remembering wrong (i vote remembering wrong....).  thanks for the clarification


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## DeeAnna (Jan 29, 2014)

edit: Um, Neeners, I regret to differ with you. The quick chemistry answer is this: The fats break down into fatty acids and glycerin. The fatty acids react with the lye (a base) to form soap molecules. But read on for the long answer........

Yes, soap will always be alkaline, even with superfat. The natural alkalinity of soap is determined by the reaction kinetics of the fatty acids and the base (the lye). It's hard to explain it fully without getting into a chemistry course, but here's the best brief explanation I can offer: 

Fatty acids are acidic, yes, but they are ~weak~ acids. If you put, say, stearic acid on your skin, it is a weak enough acid that it can't damage your skin. A strong acid is something like hydrochloric acid. If you put hydrochloric acid on your skin, it is a strong enough acid that it will definitely cause a chemical burn. The difference is how "willing" each acid is to break apart and release its hydrogen ion(s) (H+) when mixed in water. A strong acid ionizes almost completely. A weak acid does not ionize as easily -- it will only "give up" some of its hydrogen ions when made into a water solution. The natural pH of a solution of water and a strong acid will be lower (closer to 1) than a weak acid solution for this reason.

There are strong bases and weak bases as well. A weak base is bicarbonate of soda (baking soda). If you put it on your skin, baking soda won't damage your skin. A strong base is the lyes we use to make soap -- sodium hydroxide and potassium hydroxide. If you put either of these on your skin, it will certainly cause a chemical burn. The idea is the same as weak and strong acids, except bases release hydroxide ions (OH-) rather than hydrogen ions. The pH of a solution of water and a strong base will be higher (closer to 14, the max pH possible) than the pH of a water solution of a weak base.

So, if you mix acids and bases together -- what happens?

If you mix chemically equal parts of a strong acid and strong base, the resulting pH may indeed be close to a neutral (7) pH. What a neutral (7) pH means is there are exactly the same number of OH- ions in the water solution as there are H+ ions -- they cancel each other out, in effect. But that's not necessarily true when you mix, say, a strong base with a weak acid. 

The pH of such a mixture, even if you carefully measure out equal parts of each chemical so they should precisely cancel each other out, will still not be neutral. The reason for that, as I've explained, is that the weak acid does not easily give up the H+ ions needed to cancel out the OH- ions from the strong base. The weak acid gives up ~some~ H+ ions and thus lowers the pH of the water solution, but it won't give them ALL up. Vice versa is true in a water solution of a weak base and strong acid.

When we make soap, we're combining a weak acid with a strong base just as I've described. The resulting bar of soap is not a boringly static, unchanging block of stuff. Soap is a "colloid", meaning it's a complex structure of solid soap crystals surrounded by a film of water-based liquid. The chemistry going on in this colloid is constantly changing -- it's like a huge party where all kinds of microscopically tiny people are circulating around. Some people "hook up" with each other and some just cruise. Some may hook up, but later unhook, cruise for awhile, and hook up with someone different.

In chemistry terms, all this partying and circulating is called a "dynamic equilibrium". Obviously, many soap particles are created when the fatty acids and the sodium ions "hook up" more or less permanently to form the chemically neutral molecules we call soap. But there are also the chemical loners who circulate in the watery liquid inside the soap structure -- these include some sodium ions (Na+), some fatty acid ions (Ste- and others), and the H+ and OH- ions released by the lye and the fatty acids. 

In soap, the pH of this dynamic equilibrium is naturally alkaline, meaning there are more OH- ions from the lye wandering around than there are H+ ions liberated from the fatty acids. This will be true EVEN IF there are exactly as many fatty acid ions in the soap as there are molecules of lye -- or even if there are more fatty acids and fats than lye molecules. It's just the nature of the beast when you're dealing with the dynamic equilibrium between a strong base and a weak acid.

Whew! That's enough for now -- I'm going to let others chime in on your other questions ... gotta get back to work!


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## Lindy (Jan 29, 2014)

When you salt out a soap you are removing the glycerin, which is the liquid you see released.  Depending on how much salting & washing down you do will determine how much glycerin you are going to lose.  It is similar to the process used by commercial soap companies to harvest the glycerin.

 Most people are not going to find a salted out soap to be mild.  There are always exceptions but that is the general rule.


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## Obsidian (Jan 29, 2014)

neeners said:


> huh...i thought i read somewhere salt bars take a while to cure?  guess i read wrong or am remembering wrong (i vote remembering wrong....).  thanks for the clarification



I don't think you are wrong at all. If I remember right, there is one member on here who has to cure salt bars for 4-6 months but thats not the norm.

Another wonderful post by Deeanna, thank you.


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## neeners (Jan 29, 2014)

DeeAnna to the rescue.  always learn lots from you!


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## The Efficacious Gentleman (Jan 29, 2014)

When DeeAnna posts like that, it makes me see why the Starfleet ship yards are based in Iowa!

DeeAnna, can you put that on your blog?  If you don't blog, can you start and put that on your blog?  I want to reblog it so more people can read it!  It's superb


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## songwind (Jan 29, 2014)

I had been wondering this exact question the other day. Great timing.

Thanks for the great explanation, DeeAnna!


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## Saponista (Jan 29, 2014)

Eel done dee, great easy to understand explanation, thanks


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## DeeAnna (Jan 29, 2014)

You're welcome, everyone. Glad I could help. 

I don't have a blog ... what I write here at SMF is pretty much the only outlet for my ramblings. I do find myself thinking I should save some of my posts on my local hard drive so I can just cut 'n paste.


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## engblom (Jan 30, 2014)

I'm very thankful for all the time DeeAnna has taken to write this answer and answers to other things I have been wondering about.  This forum is very privileged to have her here.


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## yadonm (Jan 30, 2014)

DeeAnna comes to the rescue of us mere mortals once again.  Speaking as a person who dropped out of college chemistry you make things so easy to understand.


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## DeeAnna (Jan 30, 2014)

Well, it helps to have taught science and math for 10 years at the local community college. I had lots of math- and science-phobic students, so I tried my best to translate these subjects to "mere mortal" level. Teaching like that was more fun for me too.

One time I had to teach the rules of correct mathematical rounding to a bunch of guys who had more cocky attitude than common sense. Their collective attitude was "H*ll, just round UP. Who cares about this crap!?!?" complete with bored yawns and rolling eyes.

Then I explained why they might care a LOT by using an example of a guy getting stopped on a Saturday night after having a beer or three and having to blow in the "machine" to measure his blood alcohol. 

If the officer always rounded the machine's results UP, I showed how the driver was going to end up in jail. If the officer rounded the results properly, the driver would be okay. 

Interesting how these yahoos ended up thinking maybe it might be good to have a clue about rounding properly. 

That was fun!


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## MadMadamMim (Feb 4, 2014)

Ah! Your explanation makes perfect sense, DeeAnna. Thanks for filtering it for us mere mortals 

So, in your opinion, is there any possible way to bring soap's pH down or is it inherent in the nature of soap? I am thinking of this shampoo bar recipe from Soap Queen. Is adding the dissolved citric acid at a thin trace simply reacting/neutralizing the lye (resulting in additional superfatting rather than simply lowering the overall pH)?

Thanks for any insight you'd be willing to share~


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## DeeAnna (Feb 4, 2014)

"...So, in your opinion, is there any possible way to bring soap's pH down..."

It's a black and white answer, not an opinion. The chemistry of lye soap says absolutely no. You can lower the pH to the 8 or 9 range by choosing appropriate fatty acids. 

But a lye soap being neutral (7) or even acidic? Not a chance. If that's the direction a person is determined to go, he/she needs to look at non-soap detergents or a blend of soap and non-soap detergents.

"...Is adding the dissolved citric acid at a thin trace simply reacting/neutralizing the lye..."

Yep that's basically what happens. If you add enough citric (or other) acid, you'll end up with a soft mush of fatty acids, unreacted fat, and sodium citrate. And the pH will remain alkaline until you really go overboard with the citric acid.


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## MadMadamMim (Feb 5, 2014)

Many thanks, DeeAnna. It was what I suspected but I am an utter novice, so thank you for letting me pick your brain


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## engblom (Feb 10, 2014)

DeeAnna said:


> "
> Yep that's basically what happens. If you add enough citric (or other) acid, you'll end up with a soft mush of fatty acids, unreacted fat, and sodium
> citrate.


And what happens if you have ready reacted liquid soap wanting to make it neutral? The same, as the ions from the salt are separated when it is disolved in water?


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## MadMadamMim (Feb 10, 2014)

I wondered that same thing, engblom, regarding already saponified soap.  I thought one day I would try experimenting to see what happens...


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## FlybyStardancer (Feb 10, 2014)

engblom said:


> And what happens if you have ready reacted liquid soap wanting to make it neutral? The same, as the ions from the salt are separated when it is disolved in water?



That's my understanding. It's why liquid soap books and other resources warn to be careful not to add too much citric or boric acid while neutralizing the soap--if you add too much it starts breaking the salts apart, clouding the soap.


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## DeeAnna (Feb 10, 2014)

Don't confuse a SALT, in the chemistry sense of the word, with an acid or a base. When you use citric ACID or boric ACID to adjust the pH -- that is neutralization. When you add table SALT (sodium chloride, NaCl), there is no "neutralizing" going on. What you're doing when you "salt out" a fully saponified soap is you are using salt to reduce the solubility of the soap in a water-based solution until it precipitates out of solution.

A lot of water + a little bit of soap = a true solution in the chemist's sense of the term, meaning a mixture of individual molecules of soap dissolved in water
Begin to add salt -> the soap molecules begin to coalesce into larger droplets to form a colloid of soap-in-water. When a soap-water mixture becomes colloidal, the mixture becomes thicker and may become cloudy.
Add enough salt -> the soap precipitates into a more or less solid soap curd. The curd is a colloid of water-in-soap. The liquid solution left after the soap curd is removed is a solution of water, salt, glycerin, any excess lye, and soap.


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## judymoody (Feb 10, 2014)

I "heart" Dee Anna.  Cruising molecules at the saponification party, I love it!  I'll never think of my soap in the same way again.


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## boyago (Feb 10, 2014)

judymoody said:


> I "heart" Dee Anna.  Cruising molecules at the saponification party, I love it!  I'll never think of my soap in the same way again.



If we click the "Follow" button on DeeAnna's profile do we have to wear robes or have to show up at dinner handing out pamphlets? Do we get cool names or a "compound"? Trip to central America?


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## DeeAnna (Feb 11, 2014)

Hmmm, well, Boyago, my "followers" actually get a pair of dorky polyester high-water pants, a white plastic pocket protector with a mechanical pencil and separate eraser included, and really geeky glasses.  

Unless you qualify for my super-duper package, and then I'll throw in a full-size vintage slide rule complete with leatherette holster and belt loop -- but you have to actually know how to use it to qualify!

http://www.starpulse.com/news/Dee_Doyle/2009/06/02/everything_geeky_the_meaning_of_geek_aam


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## boyago (Feb 11, 2014)

I sound so much less sexy when you describe me.

What's a slide ruler? Is that something used to measure cassette tapes?  Must be one of those ancient inventions like fire or Sky lab.  Actually I was talking to a friend the other day who's brother was an engineer and growing up he actually had the leather belt case for his slide ruler and rocked it all the time.

Anyway back to soap.  I was reading a blog that was basically saying that there would never be a decent shampoo bar because the PH of bar soap was inherently too high and the difference between human hair and bar soap was just too great and damaged the hair.  Sounded like BS to my gut but is there any validity to this? By this logic it would seem that no one had clean or healthy hair before detergents??


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## MadMadamMim (Feb 11, 2014)

So, to reiterate for those who are not cool enough to don pocket protectors and flood pants (ie. me!), after saponification has occured, the pH could be raised to a certain degree (pH 7?) but after that point, the addition of the acid would break apart the bonds formed during saponification so we'd have a soupy mess? (technical term)


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## DeeAnna (Feb 11, 2014)

I just got done reading a thread on DDS (dreaded drag marks) and snorted a noseful of cookie when I tried to chew and laugh at the same time. Nearly did it again on this thread. What a lunch hour!

Anyways, to show what a dinosaur I am, I took one of the last slide rule classes taught at Iowa State. I had to buy a huge Versalog slide rule for the class. (To save the tiny shred of self respect I still have, I won't mention the precise year.) Yes, I was a huge geek in those days -- I confess I put my slide rule holster on my belt because I didn't dare lose or damage it -- no money for any stupidity or frivolity in my undergrad days. And when I did scrape together enough $$ to buy an engineering calculator, it was, of course, a Hewlett Packard, the best I could afford. No self-respecting engineering student bought anything less. It was a major loss of geek points to own a TI (Texas Instruments). And, yes, the calculator case hung on my belt because I didn't dare lose or damage that either. 

And, yes, anyways back to soap. Shampoo bars to be specific. I can't speak about the chemistry, but I can speak about my hair. 

I make a shampoo/face bar that has zero cleansing and it does a nice job of getting my hair clean without drying my scalp. (For the record, my regular bath soaps have 8 to 12 for a cleansing score, so there's not a huge difference between a face/shampoo bar and a regular bath bar in my house.) Even using a zero cleansing recipe, however, the soap was making my shoulder length, fine hair gradually more harsh feeling and tangly, especially the drier ends. After several months of using shampoo bars, I was about ready to get my hair cut really short to get rid of the dry ends and switch to store-bought shampoo. But I thought, before I did that, I would try the acid rinse thing. It couldn't make matters any worse and (edit) would avoid major fireworks with my dear husband who would prefer my hair to be longer rather than shorter. (end edit)

It really does work. My hair went from rough and dry to much smoother and softer feeling after just a few treatments. I now use my shampoo bars happily, followed by a dollop of hair conditioner (home made of course) that I've dusted with a tiny pinch of dry citric acid powder (canning acidifier, Vitamin C). I let the conditioner/acid do its magic for about a minute and give my hair a thorough rinse. 

Vinegar (acetic acid) or lemon juice (citric acid) work as well as dry citric acid powder. I'm just not fond of messing with bottles of vinegar or squeezing lemons. I tried ascorbic acid (Fruit Fresh) but it is not nearly as effective as the others, so I can't recommend it. Regardless of the acid, a little bit is all you need -- too much is just wasteful and the excess acid can irritate the scalp.

I question the idea of ~permanent~ hair damage from shampooing with lye soap. The acid rinse obviously reversed the trend for me without a major haircut needed. Also, my husband with much shorter hair doesn't bother to do an acid rinse. His hair feels fine without it. I'd guess hair that is fine, permed, colored, or not cut often may benefit more than hair that is coarser or is trimmed frequently. But that's just a guess. 

You are right, Boyago -- lye soap was the only shampoo in my mother's and grandmother's day, but I also know that gals back then also used vinegar or lemon juice rinses to help their hair stay shiny and soft. So I think there's something to this idea.


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## DeeAnna (Feb 11, 2014)

"...saponification has occured, the pH could be raised to a certain degree (pH 7?) but after that point, the addition of the acid would break apart the bonds formed during saponification so we'd have a soupy mess? (technical term) ..."

Yes, Madam, you are basically correct, with the caveat that pH is lowered by adding acid, not raised. The pH at which the soap will begin to break down into a soupy mess (definitely a technical term!) will be something above 8, depending on the fatty acids in the recipe. No lye soap will ever have a pH of 7 and still be lye soap.


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## Lin (Feb 11, 2014)

DeeAnna said:


> http://www.starpulse.com/news/Dee_Doyle/2009/06/02/everything_geeky_the_meaning_of_geek_aam


Interesting, so I'm a geek, nerd, and dork!


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## DeeAnna (Feb 11, 2014)

Welcome to the club, Lin!


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## engblom (Feb 12, 2014)

DeeAnna said:


> And when I did scrape together enough $$ to buy an engineering calculator, it was, of course, a Hewlett Packard, the best I could afford. No self-respecting engineering student bought anything less. It was a major loss of geek points to own a TI (Texas Instruments).



I have experience of HP, Casio and TI graphical calculators. I fully agree with you about TI. 

I had a TI89, but I noticed the only thing it was good at was to play Tetris, which would be a waste of time. All the real stuff required way too many key presses comparing to other calculators. It had the features there, but way too far away for to easily reach.

The TI I quickly sold because of the disapointment. Both HP and Casio do make excellent calculators, but I found Casio to be the better of those two. It probably have slightly less features than HP, but they are very easy to reach.


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## Lin (Feb 12, 2014)

I had a casio graphing calculator. I believe everyone else had TI, at least I was the only one with casio. So the direct instructions on key presses from the teacher never applied to my calculator... Was a pain.


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## engblom (Feb 12, 2014)

Lin said:


> I had a casio graphing calculator. I believe everyone else had TI, at least I was the only one with casio. So the direct instructions on key presses from the teacher never applied to my calculator... Was a pain.



I was in the same situation. However I think it was really good.  I had to read the manual and I ended up knowing exactly everything about my calculator.  I was really efficient with it. The other pupils barely knew what the teacher had shown them. Useful knowledge comes by studying on your own.  The whole experience surely helped you later in your life when you had to solve something on you own regardless if it had to do with math or not.  Many are not capable of reading manuals anymore. 

I'm working with computers and I often end up reading manuals.


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## DeeAnna (Feb 13, 2014)

Hmmm, well, in the days I'm talking about, TI and HP were an engineering student's ONLY choices. I believe I first had an HP 25C if I remember right. I could barely afford it because it cost in the $300 range in its day -- that was a LOT of $$ for a starving college student. I eventually upgraded to an HP 15C, and I still have and like that one. It's basically an engineering version of the financial 12C that is still being sold. I also have a much newer complicated HP graphing calculator that can take memory sticks pre-programmed for different disciplines (can't remember the model number). I used that one in my very short career as a land surveyor, but I never got comfortable with it. 

But isn't this one just the ultimate geek accessory? From 1977, comes the amazing HP 01 calculator watch:  http://www.hpmuseum.org/01ssteel.jpg

When I was teaching math and science in the local community college, I remember dealing with the TI vs Casio thing. It was as awkward for the teacher as it was for the students. Ugh.


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## Susie (Feb 13, 2014)

Awesome explanation DeeAnna, as always.  I actually understood all of that! Finally!:clap:

DeeAnna, I will second The EG's suggestion to do something with these super helpful explanations!  I actually think you should collect them together into an e-book.  Something like, "Soapmaking Science for Regular People".  And please, please, please make it available for Kindle!


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## songwind (Feb 13, 2014)

I have read in a few places that the alkaline nature of soap is part of why shaving soap works as well as it does to soften the beard as well as lubricate the shave. So there may be something to the idea of alkaline shampoo possibly damaging the cuticle of the hair. However, like DeeAnn pointed out, it can be reversed, and seems to be less of a concern the closer one is to the source of the oils.


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## DeeAnna (Feb 13, 2014)

Very interesting, Songwind. I wasn't aware of the idea that the alkalinity can enhance the function of a shaving soap. I'm really glad you pointed that out! Hmmmmm.....

As far as collecting my stuff and putting it in a blog or book or something ... okay, I'm working on it.


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## The Efficacious Gentleman (Feb 13, 2014)

Soap-Empress.com?


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## Lin (Feb 13, 2014)

I also recommend saving your explanations, at least so you don't have to re-type them all yourself lol. I've got a folder full of dog/cat/horse related stuff so I didn't have to retype everytime. I'd just copy and paste, then read through it making relevant changes for the forum or email I was doing. 

I bought my calculator in high school, I can't remember if I'd needed it for pre-calc or not until AP calc. I do remember having to pay for it myself which sucked, and I ended up going with the cheapest I could find lol. Then I wasn't an engineering student, pre-med, but Purdue threw me in the engineering calc courses. OMG. Glad I wasn't an engineering student... haha. It super sucked because when I was at the west Laf campus taking calc, it was quite a few years since high school and classes at Purdue NC. So I'd forgotten how to do a lot of simple math, much less calculus. Plus in my first semester I was ALSO thrown in biology with bio major students.


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## MadMadamMim (Feb 18, 2014)

DeeAnna said:


> "...saponification has occured, the pH could be raised to a certain degree (pH 7?) but after that point, the addition of the acid would break apart the bonds formed during saponification so we'd have a soupy mess? (technical term) ..."
> 
> Yes, Madam, you are basically correct, with the caveat that pH is lowered by adding acid, not raised. The pH at which the soap will begin to break down into a soupy mess (definitely a technical term!) will be something above 8, depending on the fatty acids in the recipe. No lye soap will ever have a pH of 7 and still be lye soap.


 

Many thanks DeeAnna! You just saved me a big soupy mess because I was going to try it. What a waste that would have been :cry:


I understand that the high pH raises the cuticles on the hair and to that extent does damage hair. But even just water does that, though perhaps to a lesser degree? I don't know but from my own experience, my hair has never felt and looked better since I started using purchased shampoo bars (soap, not solid shampoo) about a year ago. I do always follow with an apple cider vinegar rinse. So I guess, "if it ain't broke, don't fix it."


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