The WiZard is In
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Simple chemical prep of elemental potassium
Home production of elemental potassium.
Supplement to Mellor’s Comprehensive Treatise on Inorganic and Theoretical Chemistry
Prepared under the direction of an Editorial Board
Volume II
Supplement III
The Alkali Metals Part 2
Longmans 1963
P. 1478
In a comprehensive survey of laboratory scale methods for the preparation of the
alkali metals either by thermal decomposition of alkali salts, or thermal
reduction of alkali compounds with metallic or non-metallic reducing agents,
Hackspill states that the simplest and most convent method of preparing
potassium is by the reduction of potassium chloride with metallic calcium under
reduced pressure. [18]
2KCl + Ca = CaCl2 + 2K @ Appx. 400o - 0.01 mm. of mercury.
“The reaction maybe conveniently be carried out in glassware ….” [Details]
A number of modifications of the Haskspill method have been proposed [8, 19].
Thus, for the preparation of batches of potassium in the order of 100-200 g. it is
desirable to use an all metal apparatus, and one constructed of iron has been
described in detail. [8]
Skips forward past 4 pages of other methods to page 1482.
Potassium may be prepared conveniently by reducing potassium compounds
with zirconium powder at high temperatures under reduced pressure…. Details.
Potassium permanganate and zirconium powder in the proportions 1:4 react
explosively at 300o C. but a mixture in the proportion 1:10 the reaction proceeds
quietly at the same temperature….
Zirconium & Potassium -
molybdate
tungstate
sulphate
dichromate
The reduction of potassium halides with zirconium is not satisfactory. The
zirconium halides formed as by-products of the reaction distill off with the
potassium, and in the cooler portions of the apparatus the condensed mixture
reacts to give metallic zirconium and potassium halide. [21]
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Panache
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Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
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nice one, however what does, 400o-0.01mm. of mercury, mean?
At its simplest i imagine the implication you're driving at is say potassium permanganate and tungsten powder, ratio's 1:10, heated to 300C under what
pressure though?
Does the excerpt give any details to sample prep, ie is ground in a ball mill etc.
i always like your posts btw sort of like doing a cryptic crossword however with something valuable at the end )other than the personal satisfaction
of having completed said crossword, something that i never got anyway)
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JohnWW
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Such preparations are possible only because of the low melting and boiling points of K metal, which enable it to be distilled off under reduced
pressure, shifting the high-temperature equilibrium in favor of K metal plus the compound of the less-volatile metal. But I do not think that they are
any more satisfactory than electrolytic preparation by electrolysis of a fused salt such as KCl, with the cathode enclosed under argon, and with the
byproduct of Cl2 which can be collected at the anode.
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woelen
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400 degrees Centigrade at a pressure of 0.01 mm of mercury (normal atmospheric pressure is appr. 760 mm of mercury, so this is a very low pressure).
Not something achievable for most of us, even obtaining a pressure as low as 1 mm of mercury is hard enough for most of us.
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watson.fawkes
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Quote: Originally posted by woelen  | | [...] at a pressure of 0.01 mm of mercury [...]. Not something achievable for most of us, even obtaining a pressure as low as 1 mm of mercury is hard
enough for most of us. |
This pressure, often quoted as 10 micron, is achievable by a single mechanical pump,
but not by an inexpensive one. It's beyond the capacity of ordinary refrigeration service pumps, but within the range of one designed for scientific
or commercial vacuum chamber use. I checked the pumping rate vs. pressure table in Strong's Procedures in Experimental Physics, specifically
because it's from 1938 and so provides a benchmark for maturity. In that table the ultimate pressure from the mechanical pumps listed was from 1
μm down to about 0.1 μm, so it's a perfectly reasonable thing to try to hunt down a good pump if you want to try this. By contrast, the
ultimate pressure for the best Harbor Freight refrigeration service pump is 25 μm.
The other way to approach this is with a diffusion pump. Diffusion pumps go down three more orders of magnitude (four with a LN2 trap), so you don't
need a very effective diffusion pump to get the one factor of 10 required to be able to use a refrigeration service pump for the roughing pump. There
are some pretty simple designs in the book sited that should be adequate and easy enough to construct. The one I'm thinking of uses a single downward
jet. It's shown built of glass, but I see no reason it couldn't be soldered up out of copper and brass.
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Eclectic
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But at 443 degrees C the vapor pressure of Potassium is 10 Torr...all you need to do is raise the temp a little to be in the 1 Torr range..
341 C for 1 torr vapor pressure....
[Edited on 7-5-2010 by Eclectic]
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The WiZard is In
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---------
No. You are going to have tooooo consult the original ref.
[18] Hackspill. L.. Helv. Chim. Acta, 1928, 11, 1003-26
"A number of modifications to the Hackspill method have
been proposed. [8, 19]
[8] Plank, H. J., Theses présentées á la Faculté des Sciences
de l' Université de Strasborug, 2-5-1928.
[19] Buou, M. Bull. Soc. Chim. 1923, 33, 994-5.
Just take these refs to your intralibrary loan librarian and tell
them that "There will never be a cure for cancer if you don't
get these refs." Works every time for me.
--
By da if the original post was somewhat cryptic is was on account
of Mellor's description being 23-pages. I am not prepared to
scan/OCR it.
I am a Closet Calvinist - and operate under the theory that
you don't help people by making things easy for them - you
help them by making things possible.
As the famous Chinese philosopher (the one who stood in front
of the tank in Tiananmen Square — Sum Dum F....) once
said If you give a woman a fish — you feed her for a one meal.
If you teach her how to give good ---- you will both be happy
for life.
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