X-Ftn-To: Mio Elden 

Mio Elden  wrote:
>Evo tebi jedan, sjedi. (I svi se grohotom nasmijase. ;-))
>Ovo su ti cesto govorili na satovima kemije?

Bez drugih komentara osim citiranog...

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paraffin wax, colourless or white, somewhat translucent, hard wax
consisting of a mixture of solid straight-chain hydrocarbons ranging
in melting point from about 48° to 66° C (120° to 150° F). Paraffin
wax is obtained from petroleum by dewaxing light lubricating oil
stocks. It is used in candles, wax paper, polishes, cosmetics, and
electrical insulators. It assists in extracting perfumes from flowers,
forms a base for medical ointments, and supplies a waterproof coating
for wood. In wood and paper matches, it helps to ignite the matchstick
by supplying an easily vaporized hydrocarbon fuel. 
Paraffin wax was first produced commercially in 1867, less than 10
years after the first petroleum well was drilled. Paraffin wax
precipitates readily from petroleum on chilling. Technical progress
has served only to make the separations and filtration more efficient
and economical. Purification methods consist of chemical treatment,
decolorization by adsorbents, and fractionation of the separated waxes
into grades by distillation, recrystallization, or both. Crude oils
differ widely in wax content. 

Synthetic paraffin wax was introduced commercially after World War II
as one of the products obtained in the Fischer-Tropsch reaction, which
converts coal gas to hydrocarbons. Snow-white and harder than
petroleum paraffin wax, the synthetic product has a unique character
and high purity that make it a suitable replacement for certain
vegetable waxes and as a modifier for petroleum waxes and for some
plastics, such as polyethylene. Synthetic paraffin waxes may be
oxidized to yield pale-yellow, hard waxes of high molecular weight
that can be saponified with aqueous solutions of organic or inorganic
alkalies, such as borax, sodium hydroxide, triethanolamine, and
morpholine. These wax dispersions serve as heavy-duty floor wax, as
waterproofing for textiles and paper, as tanning agents for leather,
as metal-drawing lubricants, as rust preventives, and for masonry and
concrete treatment. 

Copyright 1994-1999 Encyclopaedia Britannica

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wax, any of a class of pliable substances of animal, plant, mineral,
or synthetic origin that differ from fats in being less greasy,
harder, and more brittle and in containing principally compounds of
high molecular weight (e.g., fatty acids, alcohols, and saturated
hydrocarbons). Waxes share certain characteristic physical properties.
Many of them melt at moderate temperatures (i.e., between about 35°
and 100° C, or 95° and 212° F) and form hard films that can be
polished to a high gloss, making them ideal for use in a wide array of
polishes. They do share some of the same properties as fats. Waxes and
fats, for example, are soluble in the same solvents and both leave
grease spots on paper. 
Notwithstanding such physical similarities, animal and plant waxes
differ chemically from petroleum, or hydrocarbon, waxes and synthetic
waxes. They are esters that result from a reaction between fatty acids
and certain alcohols other than glycerol, either of a group called
sterols (e.g., cholesterol) or an alcohol containing 12 or a larger
even number of carbon atoms in a straight chain (e.g., cetyl alcohol).
The fatty acids found in animal and vegetable waxes are almost always
saturated. They vary from lauric to octatriacontanoic acid
(C37H75COOH). Saturated alcohols from C12 to C36 have been identified
in various waxes. Several dihydric (two hydroxyl groups) alcohols have
been separated, but they do not form a large proportion of any wax.
Also, several unidentified branched-chain fatty acids and alcohols
have been found in minor quantities. Several cyclic sterols (e.g.,
cholesterol and analogues) make up major portions of wool wax. 

Only a few vegetable waxes are produced in commercial quantities.
Carnauba wax, which is very hard and is used in some high-gloss
polishes, is probably the most important of these. It is obtained from
the surface of the fronds of a species of palm tree native to Brazil.
A similar wax, candelilla wax, is obtained commercially from the
surface of the candelilla plant, which grows wild in Texas and Mexico.
Sugarcane wax, which occurs on the surface of sugarcane leaves and
stalks, is obtainable from the sludges of cane-juice processing. Its
properties and uses are similar to those of carnauba wax, but it is
normally dark in colour and contains more impurities. Other cuticle
waxes occur in trace quantities in such vegetable oils as linseed,
soybean, corn (maize), and sesame. They are undesirable because they
may precipitate when the oil stands at room temperature, but they can
be removed by cooling and filtering. Cuticle wax accounts for the
beautiful gloss of polished apples. 

Beeswax, the most widely distributed and important animal wax, is
softer than the waxes mentioned and finds little use in gloss
polishes. It is used, however, for its gliding and lubricating
properties as well as in waterproofing formulations. Wool wax, the
main constituent of the fat that covers the wool of sheep, is obtained
as a by-product in scouring raw wool. Its purified form, called
lanolin, is used as a pharmaceutical or cosmetic base because it is
easily assimilated by the human skin. Sperm oil and spermaceti, both
obtained from sperm whales, are liquid at ordinary temperatures and
are used mainly as lubricants. 

About 90 percent of the wax used for commercial purposes is recovered
from petroleum by dewaxing lubricating-oil stocks. Petroleum wax is
generally classified into three principal types: paraffin (see
paraffin wax), microcrystalline, and petrolatum. Paraffin is widely
used in candles, crayons, and industrial polishes. It is also employed
for insulating components of electrical equipment and for
waterproofing wood and certain other materials. Microcrystalline wax
is used chiefly for coating paper for packaging, and petrolatum is
employed in the manufacture of medicinal ointments and cosmetics.
Synthetic wax is derived from ethylene glycol, an organic compound
commercially produced from ethylene gas. It is commonly blended with
petroleum waxes to manufacture a variety of products. 


Copyright 1994-1999 Encyclopaedia Britannica
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