Burning lime

 I've just watched them burning and spreading lime, in 'The Victorian
Farm'. But I don't quite understand why they had to burn it for
spreading on the fields (as opposed to making lime mortar with it).
Surely, they might just as well have spread the limestone. It would
have taken a bit longer to neutralise the soil, but they weren't in a
great hurry, and the lime would have reverted to calcium carbonate
anyway in a few weeks. Why not just crush the limestone to a powder in
the first place? In Cornwall, shelly beach sand was used to neutralise
acid soils, with no burning AFAIK.

--
 
Chris

Gardening in West Cornwall overlooking the sea.
Mild, but very exposed to salt gales

E-mail: christopher[dot]hogg[at]virgin[dot]net

 says...

  Not easy to do with hand labour; and the finer the product is the
easier it is to spread?


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

   Janet

 On 10/11/2010 21:25, Chris Hogg wrote:

Burning the lime is probably the easiest way to make it into a fine
enough powder to use for the application. It is a bit hazardous after
being fired - quicklime is very nasty stuff indeed. Once you add water
the heat released shatters the limestone and gives you slaked lime.

Regards,
Martin Brown

 On 10/11/2010 21:25, Chris Hogg wrote:

The neutralising capacity of quicklime (Calcium Oxide) exceeds that of
slaked lime (Calcium Hydroxide) and limestone/chalk (Calcium Carbonate).
  Here beginneth the chemistry lesson (sorry!)...

Let's use the neutralisation of hydrochloric acid as an example.

Quicklime:
CaO + 2HCl -> CaCl2 +H20
The molecular weight of CaO is 36, and that of HCl is 36.5. So 36 grams
of CaO can neutralize 73 grams of HCl.

Slaked lime
Ca(OH)2 + 2HCl -> CaCl2 + 2H2O
The molecular weight of Ca(OH)2 is 54, so it takes 54 grams of Ca(OH)2
to neutralise 73 grams of HCl.

Limestone:
CaCO3 + 2HCl -> CaCl2 + CO2 + H2O
The molecular weight of CaCO3 is 80, so it takes 80 grams of CaCO3 to
neutralise 73 grams of HCl.

On this basis, quicklime is more than twice as effective for
neutralising acidity as limestone/chalk.

I can only assume that in terms of economics and speed quicklime wins
out over limestone/chalk for improving soil fertility.

--

Jeff

 On Thu, 11 Nov 2010 09:48:58 +0000, Jeff Layman


Ah, that must be the explanation: burnt lime is twice as
effective/efficient, weight for weight, as chalk or crushed limestone,
as well as being quicker acting. It must have been something like
that, because lime kilns were ubiquitous, and obviously burning lime
was not a trivial or cheap thing to do, so there must have been
significant advantage over just using crushed limestone. It wouldn't
have been because the limestone was difficult to crush. Small portable
crushers driven either by horsepower or later by traction engines must
have been fairly widely available.

Of course, these days the 'lime' you get in most garden centres is
actually ground limestone, such are the banes of H&S.

Thanks, and I enjoyed the chemistry!

--
 
Chris

Gardening in West Cornwall overlooking the sea.
Mild, but very exposed to salt gales

E-mail: christopher[dot]hogg[at]virgin[dot]net