Whats difference between pulverized and dehydrated lime?

Are they both the same thing but one is processed differently? I see gardeners at the community garden use lime. They said it keeps the insects and animals eating there plants. Is there any truth behind this?
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Joseph A. Zupko said:

Pulverized lime is limestone (calcium carbonate) that has been crushed finely enough to pass through a 'number 20' sieve. Hydrated lime (calcium hydroxide) is lime that has been reacted with heat and water.
Hydrated lime is caustic and I wouldn't recommend puffing it around a garden.
Pulverized lime is sometime spread in barns to control flies (by making the animal waste too alkaline for flies to breed in).
Pulverized (sometimes called 'agricultural') lime is occasionally used as part of a fungicidal dust and occasionally recommended against slugs, but I've not heard of it being used as an insecticide or insect repellent. (The Organic Method Primer has no index entry for lime used as an insect control.)
Diatomaceous earth is regularly used as a dust against insects.
I've also heard about ground kaolin clay being sprayed on plants to use as an insect barrier or repellent.
http://www.garden.org/articles/scripts/articles.taf?id 98
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Pat in Plymouth MI ('someplace.net' is comcast)

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snipped-for-privacy@someplace.net.net (Pat Kiewicz) wrote in message

Pardon my ignorance, but I think it is hydrated (the caustic one) that is used to control flies in stables, or at least I saw it used - unless it costs more per unit of pH than pulverized, which is what most people use in gardens. However, I also see it sold in small (maybe 3lb) boxes in garden centers as a soil amendment for veggies (Franks has it for example). I suppose what really matters is the dose...
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I don't know nothing about nothing... just reading along and doing some research myself.
So correct me if the links I'm placing are wrong: http://www.organiclandcare.org/standard/products_pest.htm
Indicates that there is hydrated calcium hydroxide as well as calcium hydroxide. Plain calcium hydroxide is sometimes called "hot lime". Hot lime should NOT be used for anything according to that link. Hydrated calcium hydroxide is designated to be used in a restricted manner as a fungicide only.
Perhaps that's where the confusion is coming into play. I don't know nothing about it, so if this information looks correct, please provide an afirmative statement. If it is incorrect, please say so.
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Not quite. "Hot" lime or quicklime is calcium oxide. If you add water you get calcium hydroxide (slaked lime) and heat. That's why its called hot lime. There is only one form of calcium hydroxide (chemically speaking) although it might be of various levels of purity and ground up to finer or coarser levels.
That web site seems quite confused on this matter.
David
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Thanks, David. Yes, after further investigation it seems that link is a little confusing. I'm sending them an email describing the problem.
I don't know much about nothing... just trying to understand what's going on here.
CaO seems to be "lime or unslaked lime" like you've stated... http://dictionary.reference.com/search?q lcium%20oxide Calcium oxide: 1 and 2) A white, caustic, lumpy powder used in analytical and manufacturing procedures, in glassmaking, in waste treatment, in insecticides, and as an industrial alkali. Also called lime. 3) A white crystalline oxide used in the production of calcium hydroxide.
Calcium hydroxide is defined as: http://dictionary.reference.com/search?q lcium%20hydroxide 1) Ca(OH)2 = "slaked lime, lime" 2) a caustic substance (Ca(OH)2) produced by heating limestone [syn: lime, slaked lime, hydrated lime, calcium hydrate, caustic lime, lime hydrate]
Compare to: CaO = "lime, unslaked lime, quicklime"
Lime is defined as: 1. See calcium oxide. 2. Any of various mineral and industrial forms of calcium oxide differing chiefly in water content and percentage of constituents such as silica, alumina, and iron. Also called quicklime.
I think what were seeing is that there may not be a standard for the words hotlime. Maybe in certain industries it's used in one mannerism and maybe in other industries it is used in another manner. I don't know. But the lack of a formal definition could easily result in different people using it to mean different things.
The words hotlime, hot-lime and "hot lime" were not found in the dictionary at dictionary.com. The word "burnt lime" is used to refer to lime/limestone (CaO), which is used to make "calcium hydroxide" as you have indicated.
And one other confusing issue is there is no formal definition for hydrated calcium hydroxide. Because I don't see a formal definition for that, and there is reference to hydrated lime which would be hydrated calcium oxide. After all, hydrated Ca(OH)2 means hydrated (combined with water) ? Maybe that is a misnomer ? I see it at various other websites but it's definitely confusing, because prefixing it with hydrated means you are hydrating slaked lime, which in turn was hydrated calcium oxide.
Those are the two very confusing issues I'm reading.
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Jim
What it being called pulverized lime her is normally called ground limestone. It is naturally occurring limestone (rock) that is ground into a dust in a mill. Many times it is pelletized (A water soluble binder is added added to the ground limestone and it is molded into pellet form) This makes it more convenient to use in mecahanical spreaders and is the form most often seen at lawn and garden centers, All calcium carbonate reacts with acid to form CO2 and a calcium salt. Remember the marble chips in your high school chemistry.?
Next if you heat limestone to a high temp. the Carbon dioxide releases and leaves Calcium Oxide. Usually called quick lime but hot lime is appropriate. This is the stuff that was used in some cultures to dispose of bodies, When I was a kid it was used to make white wash.
Now if you add water to calcium oxide (If you try this add the calcium oxide to the water) it reacts rapidly forming Calcium hydroxide (Ca(OH)2 Usually sold as hydrated or water slaked lime. This a weak base but because no futher chemical reaction is need will raise pH rapidly.
There are organisms like powdery mildew which do not thrive in a basic environment, so hydrated lime may help in those situations. As an insecticide it has no major effectiveness. Might descourage some soft bodied insects but there are better solutions like safers soap.
dill
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simy1 said:

The old saying is "the dose makes the poison." But some people are pretty firm that it's not a good idea to use hydrated lime in the animal barn, even though vendors are likely to offer it. For example:
http://fiascofarm.com/goats/flies.html
I tend to be moderately over-cautious. 8^)
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