Calcium is a rather hard element that is purified by electrolysis from calcium fluoride[?] that burns with a yellow-red flame and forms a white nitride[?] coating when exposed to air. It reacts with water displacing hydrogen and forming calcium hydroxide.
Calcium is an important component of a healthy diet[?]. Its minor deficit can affect bone and teeth formation. Its excess can lead to kidney stones. Vitamin D is needed to absorb calcium. Dairy products are an excellent source of calcium.
Other uses include:
Reducing agent in the extraction of other metals such as uranium, zirconium, and thorium.
Deoxidizer, desulfurizer, or decarburizer for various ferrous and nonferrous alloys.
Alloying agent used in the production of aluminum, beryllium, copper, lead, and magnesium alloys.
(Latin calx, lime) Lime was prepared and used by the Romans as early as the 1st century, but
calcium was not discovered until 1808. After learning that Berzelius and Pontin[?] prepared calcium amalgam by electrolyzing lime in mercury, Sir Humphry Davy was able to isolate the impure metal.
Calcium is the fifth most abundant element in the earth's crust (forming more than 3%) and is an essential part of leaves, bones, teeth, and shells. Due to its chemical reactivity with air and water, calcium is never found in nature unbound to other elements. This metallic element is found in quantity in limestone, gypsum, and fluorite. Apatite is the fluorophosphate or chlorophosphate of calcium. Electrolysis of molten calcium chloride[?] (CaCl2) can be used to isolate pure calcium. Isolation (* follow): cathode: Ca2+* + 2e- --> Ca anode: Cl-* --> ˝Cl2 (gas) + e-
Quicklime (CaO) is used in many chemical refinery processes and is made by heating and carefully adding water to limestone. When CaO is mixed with sand it hardens into a mortar and is turned into plaster[?] by carbon dioxide uptake. Mixed with other compounds, CaO forms an important part of Portland cement.
Calcium has six stable isotopes, two of which occur in nature: stable Ca-40 and radioactive Ca-41 with a half-life = 103,000 years. 97% of the element is in the form of Ca-40. Ca-40 is one of the daughter products of K-40 decay, along with Ar-40. While K-Ar dating[?] has been used extensively in the geological sciences, the prevalence of Ca-40 in nature has impeded its use in dating. Techniques using mass spectrometry[?] and a double spike isotope dilution have been used for K-Ca age dating. Unlike cosmogenic isotopes that are produced in the atmosphere, Ca-41 is produced by neutron activation of Ca-40. Most of its production is in the upper meter or so of the soil column where the cosmogenic neutron flux is still sufficiently strong. Ca-41 has received much attention in stellar studies because Ca-41 decays to K-41, a critical indicator of solar-system anomalies.
feet, with angry looks at being interrupted in their feast,
vainly trying to shut out the dreadful uproar.
`If THAT doesn't "drum them out of town,"' she thought to
CHAPTER VIII
`It's my own Invention'
was dead silence, and Alice lifted up her head in some alarm.
must have been dreaming.html">dreaming about the Lion and the Unicorn and those
cake, `So I wasn't dreaming, after all,' she said to herself,
hope it's MY dream, and not the re/re.html">re/red.html">Red King's! I don't like
complaining tone: `I've a great mind to go and wake him, and see
of `Ahoy! Ahoy! Check!' and a Knight dressed in crimson armour
he reached her, the horse stopped suddenly: `You're my
herself at the moment, and watched him with some anxiety as he
began once more `You're my--' but here another voice broke in
for the new enemy.
This time it was a White Knight. He drew up at Alice's side,
he got on again, and the two Knights sat and looked at each other
other in some bewilderment.
`She's MY prisoner, you know!' the Red Knight said at last.
`Yes, but then _I_ came and rescued her!' the White Knight
took up his helmet.html">helmet (which hung from the saddle, and was something
Knight remarked, putting on his helmet too.
`I always do,' said the Red Knight, and they began banging away
out of the way of the blows.
`I wonder, now, what the Rules of Battle are,' she said to
hiding-place: `one Rule seems to be, that if one Knight hits the
off himself--and another Rule seems to be that they hold their
noise they make when they tumble! Just like a whole set of fire-
.
On
wordlookup.net
All is still licensed under the GNU FDL.
It uses material from the wikipedia.
