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What is the pH of lime?

paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14987
Location: missoula, montana (zone 4)
    ∞
I'm pretty sure it is 8.0.  But I'm having trouble finding definitive proof.  Anybody know of a link?


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Al Loria


Joined: Apr 21, 2010
Posts: 395
Location: New York
paul wheaton wrote:
I'm pretty sure it is 8.0.  But I'm having trouble finding definitive proof.  Anybody know of a link?




Paul,

I tried to find it and can't either.  Hydrated lime for industrial use is 12.4, but the lime used in agricultural practices (ag lime) is basically limestone, and has its neutralizing effect on acidic soils by ion exchange.  Hydrogen ions, I believe I read.

So, I don't think there is a standard PH of agricultural lime.

Here is one link that might help, if only slightly.

http://pubs.cas.psu.edu/FreePubs/pdfs/uc038.pdf
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14987
Location: missoula, montana (zone 4)
    ∞
Over my head:

http://en.wikipedia.org/wiki/Calcium_carbonate

Al Loria


Joined: Apr 21, 2010
Posts: 395
Location: New York
Over mine too. 
Emerson White


Joined: May 02, 2010
Posts: 1206
Location: Alaska
That's because you are asking the wrong question (like what color is a bed made of sleep?) pH is a measure of the concentration of H[sup]+[/sup] (well technically we know now that it's mostly H[sub]3[/sub]O[sup]+[/sup]) ions in solution. Since lime is a powder it technically doesn't have a pH, though it will when it gets dissolved into solution (read water).

Here is a slightly simplified run down I wrote for Gardenweb back in August.
Muriatic acid is another name for Hydrocloric acid (HCl), which is much stronger than Acetic acid (CH3COOH).
20% acetic acid (MW 60.05) is 200 Grams per liter or a 3.33 M solution. At room temp the pKa is 4.76 so the Ka is 1.737X10^-5 Ka=[A-][H+]/[HA]=[Conjugate base][Acidity]/(Associated Acid]=[x]^2/[3.33-x] Solve for x and you get 7.599X10^-2=[H] -Log10 of that gives you pH=2.119.

For 12.5% pH=2.22
For 10% pH=2.26
For 7% pH=2.34
For 5% pH=2.42

The problem comes when you add some bases and you tie up the acids and your final solution is less acidic, the 20% can handle a lot more than the 5% as you approach the pH's that botulism grows in.


Since no one ever replied I guess it's not that interesting.

Anyways Calcium Carbonate is a little more complicated because you have a solubility product to deal with, and you then have to deal with carbonate tuning into carbonic acid (which makes the OH[sup]-[/sup] and CO[sub]2[/sub] and the partial pressure of the CO[sub]2[/sub] and there is a whole chin of back and forthing.

If you would like to know what the pH of lime dissolved in distilled water is you can tell me your elevation and the water temperature and I can figure it out for you, but if not you can assume Lime in water to be around 12-13, and save me 15 minutes of figuring it out exactly.

If you are working with anything living (which I assume that you are) you don't really need to know about the pH of lime in solution, when you apply it there will be a complex acid base balance struck that is unique to the composition of your soil. There are rules of thumb (like if your pH is X start by applying Y ounces of lime every 100 Sq ft. but really putting it on the ground and testing (or just watching your plants grow) is the best option.

Keep in mind that lime washes away.
Al Loria


Joined: Apr 21, 2010
Posts: 395
Location: New York
Emerson,

So I can assume from what I read, hydrated lime being 12.4 pH is about right.

Complicated stuff, but somehow I knew you would come up with the detailed explanation.  Still, to much for me to wrap my head around.  I just need to know that it works...


Al
Joel Hollingsworth
volunteer

Joined: Jul 01, 2009
Posts: 2103
Location: Oakland, CA
I'd like to second the opinion that it is usually not worth the effort of running the numbers, with this sort of question. If you're buying enough lime that it becomes an important financial concern, then by all means learn the quantitative chemistry you need to, or hire someone who already knows it. I think permaculture typically works with refined minerals/industrial chemicals on much smaller scales than that, and an empirical approach like trying a little bit on a small patch of earth, informed by the qualitative chemistry of what reactions are likely to take place, is likely to be much more appropriate.


"the qualities of these bacteria, like the heat of the sun, electricity, or the qualities of metals, are part of the storehouse of knowledge of all men.  They are manifestations of the laws of nature, free to all men and reserved exclusively to none." SCOTUS, Funk Bros. Seed Co. v. Kale Inoculant Co.
rose macaskie


Joined: May 09, 2009
Posts: 2134
      I have been reading about chemistry which stresses me. If you become a billionaire Paul Wheaton, through having your forum, remember my stress now trying to understand chemistry and send me a lot of money for trying to write things out simply for the forum.
      Surely the most basic of this lime question is that some soils need lime and why on a simple level.
      Lime breaks up clay soils a bit which means it helps drainage in them and that is one erason it is put on soils. Another one is  that  it is needed as a nutrient by plants and by the animals that eat plants so there is calcu¡ium in cows milk and bones in calves so if there is not in the soil maybe they will need it and you will need to add it.

      It looks to me as if the comments of Deeston Lee on rocks being full of phosphorus might apply to calcium or lime, too. Rocks have calcium in them some more than other but all of them a bit, as far as I could make out from a quick look  into the subject, it seems for example that granite has calcium in it and lava’s do too. If you have fungi whose hypha secrete acids and enzymes that dissolve rocks you won’t need lime. Paul Stamets says that fungi dissolve rocks. I am writing on the supposition that as this is internet someone will correct me if I am wrong, i have not researched this bit about fungi getting the calcium out of rocks exhaustively.

    In a deep bog, all full of peat, the rocks would be way under the peat so only airborne sand could bring anything like rock with calcium in it into peat.
 
      Unless it is peat which is all vegetable matter that you want to remediate, growing lots of plants and having fungi and bacteria should take the place of putting on expensive lime, expensive at least when you buy it for a lot of acres, because the life in the soil dissolves the rock, takes the chalk out of rock and puts it at the disposition of other plants.

    If you want lime because you want to break up your clay, well roots are an alternative way of breaking up soilmecanical rather than chemcical way., Roots will open up clay soils so they have air in them and water does get through them and soil being full of rotting leaves and flowers and old roots and such breaks up clays too and this method remediates clays more efficient that putting on lime does.
  This might be a good place to remember that Darrel Doherty says that if you put a lot of manure on soils the roots of plants don’t grow to any depth they are not forced to find  nutrients so they stay on the surface, so if you want to break up deep clay soils don’t feed the plants too much.

    If your soil is very bad you may need to give it fertilizer and chalk to get it to grow anything, to jump start it, just untill the cycle of life and death is feeding the soil itself. The cycle of life and death started, the dead plants will give nitrogen to the soil, and  the enzymes and acids of roots by dissolving the calcium and phosphorus in the soil will release these.
    This still leaves us with why in detail you put lime on soil and how much. what the base does to the acid in clays .
      I shall get my chemistry tip top and explain it. Agri rose macaskie.
Joel Hollingsworth
volunteer

Joined: Jul 01, 2009
Posts: 2103
Location: Oakland, CA
Rose, it sounds like your chemistry is basically sound, as far as I can see.

It's tough to say anything truly general about rocks, though...there are so very, very many kinds.

rose macaskie wrote:I have been reading about chemistry which stresses me...This still leaves us with why in detail you put lime on soil and how much. what the base does to the acid in clays .
      I shall get my chemistry tip top and explain it.


I worked in a national lab years ago, and the chemist who supervised my research there had a side project involving bentonite clay. We talked about that a little bit, and I got the general sense that the chemistry was too complex and poorly-understood to be completely predictable on the basis of theory alone; technology based on it involves a lot of trial and error. My over-educated guess is that you could be the world's expert on the ionic chemistry of one particular variety of very pure clay, and even that variety would still hold a lifetime of mystery (and headaches and frustrations) for you. Soil tends to include a mix of different sorts of clay, of course... 

My simplistic understanding, though, is that wet clay particles each have a strong electric charge, that gently repels all of its neighbors. I imagine the effect of an air hockey table, only the air is being puffed out of the puck itself rather than the table...then I imagine an unfathomlably-large pile of those pucks, sliding around one another (perhaps responding to a colossal hand, forming them on a galaxy-sized potter's wheel...). Lime, as I understand it, cancels the electric charge at the particle surface: with our air hockey metaphor, it's as if the little holes became clogged with lint and couldn't puff out as much air. The pucks begin to lock together, and as they collapse together, some larger spaces open up between them.
rose macaskie


Joined: May 09, 2009
Posts: 2134
i have been reading about chemistry for this thread and i  have decided i should have known more because what i  have picked up should be general knowledge so i am going to have a bash at explaining a bit of a start on the chemistry you need to understand why lime breaks up clay a bit and makes it less impermeable in the way Joel hollingsworth explains.
    first you need to know that  atoms and molecules get electrons stolen off them or get landed with someone else's electron or electron pair and this makes the atom or molecule either positively charge or negatively charged so they are like little magnets and are attracted to other atoms and molecules. The positively charged to negatively charged atoms and molecules and the negatively charged to positively charged atoms and molecules forming new molecules.
 
 
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