From Alchemical Recipes to Modern Chemistry
 (2003-10-08)
Black Powder / Blackpowder / Gunpowder
What is the composition of black powder ?
The French call it either poudre à canon (gunpowder)
or poudre noire (blackpowder).
The loose powder was called serpentine.
The name black powder is of relatively recent origin,
as it appeared only after other explosives were devised which lacked the
black luster of free carbon.
Obviously, the stuff wasn't called gunpowder
before the gun was invented, around 1313.
The invention of the gun is often credited to brother
Berthold Schwarz (Schwartz),
a Franciscan friar from Freiburg
with a bogus last name ("Black" in German) indicating
his interest in alchemy, the black art;
the real name of "Black Bert" was most probably Constantine Anelzin.
He "invented" gunpowder only in the sense that he found a new use for old serpentine
and thus made the new name meaningful.
Black powder was the first explosive ever devised,
and it remained the only one for centuries.
It is composed of the following three solid ingredients:
- Saltpeter:
KNO3 niter
(or, more rarely, NaNO3 Chilean nitrate).
- Sulphur: S.
["sulfur" and "sulphur" are equally acceptable spellings]
- Carbon: C.
Often in the impure form of charcoal from wood (willow).
However, simply mixing the ingredients produces only inferior meal powder...
To obtain what's now considered proper black powder,
the ingedients must be "incorporated" in a damp state.
This allows the application of great pressure to form a dense cake,
ultimately broken down into dry grains.
This process is called corning,
and it was first introduced in France in 1429.
Early forms of blackpowder may have existed in China around
AD 700, using crude recipes calling for equal weights of the three components...
Such mixtures would only burn violently without exploding...
Also, explosion cannot occur if raw saltpeter is used,
and the refining of saltpeter is not mentioned before 1240 in a book on
military
technology by the Syrian scholar Hassan Al-Rammah, entitled
al-furusiyya wa al-manasib al-harbiyya.
The first Chinese author to describe an explosive formula was apparently
Huo Lung Ching, in 1412.
In a six-page tract entitled Liber Ignium ("Book of Fires"),
Marcus Graecus [an otherwise unknown author, possibly a fictitious one]
describes 35 incendiary recipes,
including a formula which was once standard for English blackpowder:
[...] 1 lb of native sulfur,
2 lb of linden or willow charcoal, 6 lb of saltpeter,
which three things are very finely powdered on a marble slab.
The latin version of this pamphlet did not appear before 1280 or 1300 and may
have originated around that time, although the claim has been made that
it was an expanded translation by Spaniards of a more ancient Arabic text
(dated AD 848)
and/or a Greek version that did not include the last four formulas...
Roger Bacon (c.1214-1292) investigated black powder before 1249,
when he devised the recipe he communicated in 1268:
40% more saltpeter than
either sulphur or carbon (7:5:5 formula by weight).
However, the first unmistakable blackpowder explosive composition
is the "German formula" (4:1:1) proposed by Albertus Magnus (c.1200-1280).
The English standard formula around 1350 called for less sulphur and more charcoal
(6:1:2).
The most commonly quoted modern gunpowder composition seems to date
from around 1800 and calls for 75% saltpeter (niter) oxidizer, with
10% sulfur (S) and 15% charcoal (C) fuel:
Some Historical Formulae for Black Powder (by weight)
| Date | Who / What / Where |
KNO3 | Sulphur | Charcoal |
|---|
| c. 700 | Chinese alchemists (?) | 1 | 1 | 1 |
| 1249 | Roger Bacon | 7 | 5 | 5 |
| 1275 | Albertus Magnus ("German") | 4 | 1 | 1 |
| c.1300 | "English" (Marcus Graecus?) | 6 | 1 | 2 |
| | Swiss "Bernese Powder" | 76 | 10 | 14 |
| 1781 | Britain | 75 | 10 | 15 |
| 1794 | France | 76 | 9 | 15 |
| 1800 | Prussia | 75 | 11.5 | 13.5 |
| Stoichiometry (see below) | 74.8 | 11.9 | 13.3 |
The stoichiometry of the following
oversimplified
reaction would correspond to about
74.8% niter, 11.9% sulphur and 13.3% carbon (roughly 101:16:18):
2 KNO3
+ 3 C
+ S
®
K2S
+ 3 CO2
+ N2
+ 572 kJ
(505.8 cal/g)
The potassium sulphide
solid residue forms a thick white smoke,
capable of obscuring entire battlefields.
Newer propellants leave little or no such residue when properly exploded.
They are thus collectively known as smokeless powders.
The simplest idea
for a smokeless dark powder is called ammonpulver (AP) and involves
ammonium nitrate (AN) with 10% to 20% charcoal,
although the stoichiometry of the following reactions translates into only
7% to 13% carbon, by weight:
2 NH4NO3
+ C
®
CO2
+ 4 H2O
+ 2 N2
+ 629.6 kJ
(874.4 cal/g)
NH4NO3
+ C
®
CO
+ 2 H2O
+ N2
+ 228.6 kJ
(593.5 cal/g)
Other smokeless powders of historical interest
include the following propellants:
- Guncotton,
or nitrocellulose (also known as pyropowder, pyrocellulose,
trinitrocellulose and cellulose nitrate) invented in 1845
by the Swiss chemist Christian Schönbein (1799-1869).
- Poudre B
(flakes of nitrocellulose gelatinized with ether and alcohol)
invented in 1884 by Paul Vieille (1854-1934)
for the 1886 Lebel rifle.
- Ballistite
(nitrocellulose and nitroglycerin, with diphenylamine stabilizer)
invented by the Swedish industrialist Alfred Nobel (1833-1896) in 1887.
- Cordite N
(nitroguanidine,
nitrocellulose, and nitroglycerin)
invented by Frederick Augustus Abel and James Dewar in 1889.
Sulfurless powder (12.93% carbon) would yield 772.6 cal/g, with 60% smoke:
4 KNO3
+ 5 C
®
2 K2CO3
+ 3 CO2
+ 2 N2
+ 1501.4 kJ
It takes 92.9 g of this mix to release a mole of gas,
whereas only 67.6 g of black powder would suffice
(as sulfur prevents the wasteful production of carbonate).
(2003-11-14)
Simple Predictions of Chemical Outcomes
How do we tell what a given initial composition will produce?
This may be tough, since the result of a chemical reaction is
always an equilibrium containing everything that could be produced
(possibly only in minute quantities).
However, for reactions involving chemical explosives, a decent
rule
of thumb is to use the following hierarchy of
fictitious reactions and consider that
each occurs only when the previous ones have been completed
to the fullest possible extent:
| Metal + Oxygen |
® |
Oxide |
| C + O | ® | CO |
| 2H + O | ® | H2O |
| CO +
O | ® | CO2 |
| Oxide + CO2 | ® | Carbonate |
| N, O, or H | ® |
½N2, ½O2, or ½H2 |
| C | ® | C (black smoke) |
This is only a rough approximation of chemical reality
(useful, but not foolproof).
(2008-03-22)
Thermite
Thermite brings about thermal destruction chemically.
Thermite is a mix of rust
and powdered aluminum
which can be ignited with a strip of magnesium to produce
alumina and
iron.
This popular reaction is able
to deliver molten iron at a very high temperature
(about 2200°C).
Fe2O3 + 2 Al
®
Al2O3 + 2 Fe + 851.5 kJ
The precise stoichiometry calls for 2.9 g of ferric oxide for 1 g
of aluminum. An excess of aluminum helps prevent
the formation of hercynite (FeAl2O4 ).
The usual recipe calls for 8 grams of iron oxide for
3 grams of aluminum.
(2003-10-09)
Enthalpy of Formation
How do we compute the energy balance of a chemical reaction?
The enthalpy
of formation (DH) of a chemical compound is
roughly
the energy required to make it from its constituents
[in their standard forms, as gases, liquids, or crystals].
Once tabulated,
this data can be used to work out the energy balance
in a reaction involving such compounds.
The so-called bond energy is a misguided poor rule-of-thumb
which is unfortunatly still taught ar the introductory level.
In the few cases where it would be applicable (diatomic molecules) it's almost always
incompatible with the standard enthalpy of formation, which refers to formation
from realistic molecules rather than fictitious isolated atoms.
DH f < 0
for stable compounds (exothermic formation).
| Substance |
DH f
(kJ/mol) |
|---|
| alumina (s) | Al2O3 |
-1675.70 |
| potassium carbonate (s) | K2CO3 |
-1150.18 |
| calcium dihydroxide (aq.) | Ca++, 2 OH - |
-1003 |
| calcium dihydroxide | Ca(OH)2 |
-986.09 |
| calcium dihydroxide gas | Ca(OH)2 |
-610.76 |
| calcium ion | Ca++ |
-543.00 |
| potassium nitrate (nitre) | KNO3 |
-494.60 |
| sodium nitrate | NaNO3 |
-467.90 |
| carbon dioxide | CO2 |
-393.51 |
| potassium sulphide | K2S |
-380.70 |
| nitroglycerin |
C3H5(NO3)3 |
-371.10 |
| ammonium nitrate (AN) | NH4NO3 |
-365.60 |
| water | H2O |
-241.826 |
| hydroxide ion | OH - |
-230.015 |
| carbon monoxide | CO |
-110.53 |
| myricin (beeswax) |
C15H31CO2C30H61 |
|
| nitroguanidine | H2NC(NH)NHNO2 |
-91.63 |
| calcium carbide | CaC2 |
-59.80 |
| trinitrotoluene (TNT) | C7H5N3O6 |
-54.39 |
| black phosphorus | P |
-39.30 |
| red phosphorus | P |
-17.60 |
| white phosphorus (toxic) | P |
0.00 |
| phosphorus gas | P4 |
+58.90 |
| phosphorus gas | P2 |
+144.00 |
| acetylene | C2H2 |
+226.73 |
| phosphorus gas | P |
+316.50 |
For example, the energy released in the combustion of CO is
the difference between the enthalpies of
formation tabulated above for CO and CO2 :
CO + ½ O2
® CO2
+ 282.98 kJ
A positive enthalpy of formation indicates an unstable compound, like acetylene,
which would release energy by reverting back to its elemental components.
However, a negative enthalpy of formation is no practical guarantee of stability.
Like liquid
nitroglycerin,
some chemicals do detonate into more stable ones:
4 C3H5(NO3)3
®
12 CO2 + 6 N2 + 10 H2O + O2 + 5656 kJ
(1488 cal/g)
(2007-11-21)
Gibbs Function (G): Free Enthalpy (or "free energy").
The
sign of DG
indicates thermodynamic stability.
A thermodynamically stable compound is indicated by a
negative free energy
of formation DGf
The change in entropy DS
can be large enough to make an endothermic reaction spontaneous.
This is called an entropy driven reaction.
One example is the melting of ice. It's an endothermic reaction
(+6.95 kJ/mol) accompanied by a great increase in
the entropy (disorder) which actually makes
DG negative, so the reaction is indeed
a spontaneous one.
DH and
DG are normally given in kilojoules (kJ)
per mole, whereas DS is usually given in units
of J/K so the product by the absolute temperature (T)
comes out in joules (J).
With such conventions, a conversion factor of 1000 has to be applied
in actual computations.
Baking soda on the countertop and in the oven...
(2007-11-21)
"Labile" and "unstable" are not quite synonymous.
Kinetics
can make a compound not
labile in spite of unstability.
Benzene is one compound which is unstable according to its
free energy balance.
Yet, the kinetics involved make the spontaneous decomposition of
benzene into hydrogen and graphite so slow that it's
never observed in practice.
An unstable compound which can decompose fast enough is said to be
labile.
As the example of benzene illustrates, not all unstable compunds are labile.
 (2003-10-10)
Ink Formulas
What is the composition of traditional inks ?
Natural Ink
Sepia is the most lasting of natural inks, but it's not lightfast.
It is a dark brown liquid
consisting of concentrated melanin,
secreted by Mediterranean cuttlefish and other cephalopods
(it's stored in ink sacs and ejected to confuse attackers).
India Ink (Chinese Ink)
As early as 2500 BC, writing inks were carbon inks
consisting of fine grains of carbon black [from soot] suspended in a liquid.
The Latin name for this was
atramentum librarium and it's now called
India ink or Chinese ink.
On the famous Dead Sea Scrolls of Qumran
(from the third century BC to AD 68),
a red version of this ink is found which uses
cinnabar (HgS) instead of carbon.
The idea is simple:
When the liquid dries out, the solid pigment (C or HgS) remains which
leaves a permanent trace.
Such inks are best used on semi-absorbent stuff, like paper or papyrus (not parchment).
The problem was to keep the grains in suspension long enough to apply the ink.
In plain water, fine grains of carbon black would aggregate under the action of
Van der Waals forces and form flakes
large enough to fall quickly to the bottom of the container.
This flocculation process can be prevented with an hydrophilic additive
which minimizes Van der Waals interactions between the grains
by coating them (as was properly explained only in the 1980s).
Early ink recipes may thus have called for various plant juices
instead of plain water.
It turns out that gum arabic acts this way to stabilize
India ink into a colloidal suspension for days or weeks...
This wonderful invention is at least 4500 years old.
Traditional Chinese ink is not bottled.
Instead, ink is produced as needed
by grinding an inkstick on an inkstone after adding a little
water (the inkstone also acts as an inkwell).
Chinese ink-sticks consist of a pigment (usually soot from pine,
oil or lacquer) and a soluble resin which holds the dry stick together
and plays a critical part in the colloidal ink suspension produced by wet grinding.
Iron-Gall Ink, Indelible Ink, Encaustum
In the first century AD, Pliny the Elder described a basic chemical demonstration
of the principle behind what would become the primary ink of the Middle Ages:
Papyrus soaked in tannin turns black upon contact with a solution of iron salt.
This was not used for actual ink at the time of Pliny,
but "gallarum gummeosque commixtio" is already mentioned as
an established writing ink around AD 420,
in the
encyclopedia of the 7 liberal arts by Martianus Capella.
However, the latest analyses have disproved dubious reports that this type of ink might
have already been used on the famous Dead Sea Scrolls of Qumran (before AD 68).
Because of the secondary reaction discussed below, which makes it indelible,
iron ink was once known as encaustum
(Latin for "burned in", from the Greek enkauston, meaning
painted in encaustic and fixed with heat).
This is the origin of the English word "ink" itself,
and of its counterparts in a number of other languages:
encre (French),
inchiostro (Italian),
inkt (Dutch),
inkoust (Czech)...
Indelible iron-gall ink is considered the most important ink in the development
of Western civilization, up until the 20th century.
The best iron-gall inks were far superior to most modern inks,
but the corrosiveness of some compositions (discussed below)
regretfully led to the abandonment of all iron-gall inks in favor of
more sophisticated recipes with lesser chemical aggressivity.
Iron-gall ink normally includes what is effectively a
"Chinese ink" component, which provides both body (from gum arabic)
and some initial coloring upon application of the ink.
Otherwise, the main pigmentation of iron-gall ink comes paradoxically from
water-soluble ferrous chemicals with little color of their own:
When the ink dries in air, an oxidation occurs which turns these
ferrous salts into insoluble ferric dark pigments.
In addition, iron-gall ink may react with parchment collagen or paper
cellulose, in a totally indelible way.
Some poorly balanced iron-gall inks have even been observed to
burn holes through paper.
It has been shown
that an excess of ferrous salt in iron-gall ink
leaves permanent traces of active soluble salts
(not properly oxidized into inert pigments) which will catalyze
the slow decomposition of cellulose, especially when acidity is present.
This corrosion is reduced with a proper balance in the composition of the ink.
To prevent deterioration of historical iron-gall ink documents,
the Netherlands Institute of Cultural Heritage (ICN) has introduced an interesting
treatment,
which was first used on a large scale by the conservators of the
Nationaal Archief of the Netherlands:
First, a saturated solution is applied which contains a calcium salt and its acid, namely:
The salt is soluble up to twice the molar concentration of the acid.
This is an oxidation inhibitor which binds the metal ions.
Then, acidity is neutralized with calcium bicarbonate,
which creates an alkaline buffer and also leaves a phytate precipitate in the fibers,
for continued oxidation protection.
Iron-nutgall ink, tannin Ink, gallotannate ink, vitriolic ink.
Modern Inks
Key Ink Ingredients:
- Gum Arabic:
True gum Arabic is exuded by the
acacia
senegal tree, which has several other names:
Rudraksha, Gum Acacia, Gum Arabic Tree, Gum Senegal Tree.
Currently, 70% of the World's supply of gum arabic comes from
Sudan.
The related products of other trees of the
Acacia genus are usually considered
inferior substitues for true Gum Arabic.
This includes, most notably, what's known as Indian gum Arabic
which is produced by trees variously called
acacia nilotica,
acacia arabica, babul, Egyptian thorntree
or prickly acacia.
Gum Arabic is a very common thickener and colloidal stabilizer.
Some candies are made from up to 45% gum arabic (E414).
Also called acacia.
[info]
CAS 9000-01-5: Gum acacia;
Arabic gum or
acacia gum
(Indian gum Arabic identifies a lower grade of product).
The natural product is a mixture of the following ingredients:
- arabinogalactan oligosaccharides and polysaccharides.
- glycoproteins, (proteins with sugars attached).
- Ferrous sulfate:
Also known as kankatum, green vitriol or copperas.
(FeSO4, 7 H2O) iron sulphate
in hydrated crystal form (278.01 g/mol).
- Tannin: Tannic
(or gallotannic) acid,
extracted by water-saturated ether from crushed gallnuts
( galls, nutgalls, or gall apples ).
It is an anhydrid of gallic acid (see next):
COOH.C6H2(OH)2O.COC6H2(OH)3
- Gallic acid:
Produced (with glucose)
by the hydrolysis of tannin in acid.
Used in calotype
photography.
C6(COOH)H(OH)3H (170.12 g/mol)
Pigments:
- Carbon Black :
Lampblack, from soot. C (12.01 g/mol)
- Manganese Black :
Manganese dioxide. MnO2 (86.937 g/mol)
- Cinnabar :
Called vermillion, or Chinese red. HgS (232.66 g/mol)
- Red Ochre :
Hematite. Ferric oxide. Fe2O3 (159.69 g/mol)
- Sepia :
Natural sepiomelanin from sepia officinalis.
[ 1
| 2
]
- Viridian :
Chromium oxide dihydrate.
Cr2O3 . 2 H2O (Guignet, 1859)
- Green Malachite :
Basic cupric carbonate.
CuCO3-Cu(OH)2
- Egyptian blue :
Synthetic cuprorivaite.
CaCuSi4O10
3100 BC
- Indigo :
"Indian Blue".
CAS 482-89-3
C16H10N2O2
1580 BC
- Maya Blue :
Palygorskite clay and indigo complex.
[ 1 |
2 |
3 |
4 ]
- Lapis Lazuli :
Lazurite (sodium aluminum silicate)
not "lazulite".
[supplier]
(Na,Ca) 8 (AlSiO4 )6
(S, SO4 , Cl 2 )
especially:
Na 8 (AlSiO4 )6 S.
- Prussian Blue :
Ferric ferrocyanide.
Ferric hexacyanoferrate.
Fe4 [Fe (CN)6 ] 3
A chelating agent insoluble in water (Diesbach, 1704).
Iron Gall Ink
|
How to Make Iron Gall Ink
|
Ink Corrosion
|
Old Ink
|
Period Inks
Forty Centuries of Ink
|
Ink Recipes
|
Gallotannin
|
Pigment Chemistry
|
Rare Oil Colors
(2010-10-16)
Esters & Waxes. The complexity of natural beeswax.
Waxes are long-chained esters, like myricin :
C15H31COOC30H61
Crude
beeswax (raw beeswax)
is secreted by young female worker bees (6 to 18 days old)
from eight wax glands located on the inner sides of their
sternites,
beneath abominal segments 6, 7, 8 and 9.
Wax is produced in scales weighing about 0.9 mg
(about 3 mm across and 0.13 mm in thickness).
Bees produce wax when the temperature in the hive is between
33°C and 39°C.
For each pound of wax they produce, the bees must consume about 8 pounds of honey.
Beekeepers
will typically harvest 1 pound of beeswax for 10 pounds of honey.
Refined natural beeswax has a deep gold color. It's available as
yellow beeswax
(Cera Flava, CAS 8012-89-3 or CAS 8033-51-0).
A different product known as
white beeswax
(Cera Alba, CAS 8006-40-4) is actually beeswax
bleached chemically using
nitric or chromic acid
(traditional bleaching involved exposing for weeks thin slices of beeswax
to moist air and sunlight, next to the hives, possibly
remelting several times).
White beeswax is cream-colored.
 
The wax made by bees is a complex mixture
(of hundreds of compounds) whose composition
varies substantially from one batch to the next.
In 1848,
Sir Benjamin Collins Brodie,
Jr. (1817-1880) separated beeswax by means of alcohol into three main
constituents, found in varying proportions, which he called Myricin,
Cerin and Cerolein.
Those constituents are mixtures, rather than pure chemical compounds.
However, Myricin and Cerin
are routinely identified with their dominant compounds
(melissyl palmitate and cerotic acid respectively).
Thus, here's how natural beeswax may be
approximately described:
-
About 70% of Myricin (insoluble in boiling alcohol)
which is chiefly a long-chain ester melting at 72°C (see below):
C15H31COOC30H61
-
About 25% of Cerin, similar to cerotic acid
(dissolved by boiling alcohol) which melts at 79°C.
It was totally absent from one of the samples
(originating from Ceylon) analyzed by Brodie.
H(CH2)25COOH
-
About 5% of Cerolein (dissolved by cold
alcohol or ether) which melts at 23°C.
It is
cerolein which gives beeswax most of its odor and color.
Pure myricin is identified with
Triacontanyl palmitate or Melissyl palmitate
which is the long-chain fatty ester
formed by palmitic acid and the
long-chain saturated alcohol variously called
triacontanol, melissyl alcohol or melissin.
H(CH2)15COOH
+
H(CH2)30OH
®
C15H31COOC30H61
+ H2O
palmitic acid + melissin
®
myricin + water
Some other derivatives of beeswax :
-
Melene (1-Triacontene;
CAS 18435-53-5)
is also called melissene or melissylene.
It is an alkene
(or olefin) of the
ethylene series: C30H60
-
Cerene (1-Heptacosene;
CAS 15306-27-1)
is another alkene: C27H54
-
Chinese wax (ceryl cerotate) is a wax-ester:
C25H51COOC26H53
Geoffray's
Process with Cerolein in
The Silver Sunbeam (Joseph H. Ladd, NY: 1864)
Chemical and Technical Assessment
of Beeswax by Paul M. Kuznesof et al.
The composition of beeswax
alkyl esters by P. J. Holloway (1969)
Beeswax:
An ancient marvel (2009-06-19) at Green Crafts Products
Diego Rivera's
use of a wax medium in the 1920s by Lucy Pearce (1994)
Henriette's
Herbal Homepage
by Henriette Kress
|
Herbdata,
New-Zealand by Ivor Hughes
Beeswax Co. LLC
|
Waxes at Sci-Toys.com
|
Beeswax (Wikipedia)
Refined Beeswax:
Yellow ($12.50 / lb) or White ($13 / lb).
(2010-10-18)
Pine Tar Pitch (brewer's pitch) vs. Cedar Pitch
Pine tar pitch can be obtained by
dry distillation
of resinous wood.
It's a mixture of
resin acids,
similar to the so-called pyroabietic acid, obtained by heating
abietic acid
between 250°C and 350°C
(abietic acid is the main contituent of
rosin;
it's also known as abietinic acid or sylvic acid).
Such products are also found in
tall oil.
The principal constituents so obtained are:
- Dehydroabietic acid, or DHA
(CAS 1740-19-8)
C20H28O2
- Abietic acid
C20H30O2
- Dihydroabietic acid C20H32O2
- Tetrahydroabietic acid
C20H34O2
Also involved is
pimaric acid, a close relative
of abietic acid itself.
Cedar Tar Pitch :
The chemistry of Cedar pitch is not the same as that of pine pitch...
It involves a totally different type of resin acid:
plicatic acid
C20H22O10.
The Composition of So-Called Pyroabietic
Acid by E.E. Fleck & S. Palkin (1939)
Resin Acids from Pine Tar
by J.P. Bain (1942)
Resin Acid Soaps in GR-S
Polymerization by Julian Lo Azorlosa (1949)
Cutler's Resin (Wikipedia):
of pine pitch, beeswax and sawdust.
Brewer's
Pitch BP-293 (natural pine tar pitch) $12 / lb
Genuine
Pine Tar ($27.50 / L)
(2010-10-11)
Gum Arabic: A great ancient commodity.
The magic bullet of ancient chemistry is not just for candy or
ink.
Jerome A. Samounce is a minister in North Carolina who tries to
bring scripture to life by reproducing Biblical artefacts using ancient technology.
On 2010-01-06, he approached me with a few technical questions
about his latest project:
Reproducing an authentic 3-cubit Judean javelin from the
Davidic Dynasty...
The shaft of such a javelin was made of
ash wood
(finished with linseed
oil) 1" thick in
the middle (and ½" at either end).
At one end, it was split and carved to accomodate a bronze tip.
The two halves were then glued back together.
That was the main problem:
What could this weapon-grade Biblical glue be?
It had been merely described as "a glue based on cedar
pitch".
Jerome had also found that archeological reports consistently mention
two other ingredients besides cedar or pine pitch: Beeswax and ground ash powder.
(the presence of some inert powder should come as no surprise
to whoever has ever tried to optimize the mechanical properties of
thick layers of modern epoxy glue).
By themselves, those three ingredients don't mix and yield disappointing results.
On a hunch, I suggested that ancient craftsmen would almost certainly have tried
Gum Arabic as a key additive
(I even suggested that experimentation might start
with 1%, 2% and 4% of Gum Arabic ). Bingo!
The immediate result was an excellent Biblical glue.
Here is the recipe (by weight) obtained in the subsequent
backyard experiments
performed by Jerome Samounce et al
(see full
report).
- 50 parts of pine tar pitch (cedar pitch would be more authentic).
- 15 to 20 parts of beeswax (the more beeswax, the more flexibility).
- 10 parts of inert powder (finely ground sawdust, or ash).
- 3 parts of Gum Arabic.
At first, I had thought that gum Arabic would merely help the
mix form a water-free colloid which would freeze solid upon cooling
(compare that to frozen mayonnaise if you must).
However, the experiments of Samounce seem to indicate that
gum Arabic induces a decomposition of hot beeswax
(with emission of an unidentified gas which might be carbon dioxide).
This yields a compound that appears to act as a hardener of natural resin
(just like the hardener coompound in modern two-part epoxy glue).
We're still pondering what the actual chemical reactions might be... Stay tuned.
Gum Arabic $55 / lb
(2003-10-11)
Redox Reactions
An oxidizer gains the electrons which a reductant loses.
(The reductant is oxidized, the oxidizer is reduced.)
Oxidation is loss (of electrons)
reduction is gain.
[ OIL RIG ]
Redox reactions
are best described as transfers of electrons between chemical species:
An oxidizer (oxidant, or oxidizing agent) is "reduced" by gaining electrons;
a reducer (reductant, or reducing agent) is "oxidized" by losing them.
Some Redox Half-Reactions | Potential
(25°C, 1 atm) |
| Fluorine | ½ F2
+ e- |
® |
F- |
(+2.866 V) |
| Gold (aurous) | Au+
+ e- |
® |
Au |
(+1.692 V) |
| Permanganate | MnO4-
+ 4 H +
+ 3 e- |
® |
MnO2 + 2 H2O |
(+1.679 V) |
| Permanganate | MnO4-
+ 8 H +
+ 5 e- |
® |
Mn++ + 4 H2O |
(+1.507 V) |
| Gold (auric) | Au+++
+ 3 e- |
® |
Au |
(+1.498 V) |
| Nitrate | NO3-
+ 2 H +
+ e- |
® |
NO2
+ H2O |
|
| Chlorine | ½ Cl2
+ e- |
® |
Cl- |
(+1.35827 V) |
| Copper (cupric) |
Cu++
+ 2 e- |
® |
Cu |
(+0.3419 V) |
| Acid |
H +
+ e- |
® |
½ H2 |
( 0 V ) |
Methanoate
(or formate) |
CO2
+ H +
+ 2 e- |
® |
COOH - |
|
Ethanedioate
(or oxalate) |
2 CO2
+ 2 e- |
® |
C2O4- - |
|
| Zinc |
Zn++
+ 2 e- |
® |
Zn |
(-0.7618 V) |
| Lithium |
Li+
+ e- |
® |
Li |
(-3.0401 V) |
Each of the above half-reactions is written as the reduction
of an oxidizer, but the reverse direction (the oxidation of the reducer on the
right-hand side) is more common for the reactions with a low
redox potential (listed in volts V):
In a complete redox reaction,
a reduction occurs as written above
only if a balancing oxidation
with a lower redox potential occurs in the reverse direction.
For example, the nitrate ion has a higher potential than the cupric ion and
nitric acid may thus oxidize copper metal.
(The opposite relation holds between hydrogen and cupric ions,
so an ordinary acid can't oxidize copper.)
2 NO3-
+ 4 H +
+ Cu
®
2 NO2
+ 2 H2O
+ Cu++
In a balanced redox reaction, the difference DE
between the potentials of both half-reactions is simply
the change in free enthalpy DG
(G = H-TS) per unit of electric charge transferred.
If n moles of electrons are involved, this translates into
n moles of electronvolts in DG
for each volt in DE. Therefore:
DG
= -n F DE
= -n DE
(96485 J/V)
= -n DE (23.06 kcal/V)
A joule per volt (J/V) is a coulomb (C) and the above
bracketed constant is the Faraday constant
( F, the charge of a mole of electrons)
in two different units.
Only the DE (or DG)
of an actual redox reaction has a physical meaning,
while all the half-reactions are convenient fictions
whose redox potentials are defined within an additive constant,
which is conventionally set to 0 V for hydrogen.
[Another convention is used for the related "Oxydo-Reduction Potential" (ORP)
measured directly for aqueous solutions, which lets 1 V be the ORP of chlorine.]
The standard redox potential
(DEo )
tabulated for a normal pressure of 1 atm (101325 Pa)
at 25°C (77°F) is understood for unit
(1M) concentrations of
both reactants and products, otherwise the so-called
Nernst equation
is used:
| DG =
DGo +
|
RT |
ln ( |
[products] |
) |
 |
| [reactants] |
| |
| DE =
DEo -
|
RT |
ln ( |
[products] |
) |
|
|
| nF |
[reactants] |
Therefore, even if the comparison of standard redox potentials seems to
imply that a reaction does not occur, what actually evolves is an equilibrium
where the concentration of "products" is small, or even utterly negligible...
 (2003-11-01)
Gold Chemistry
Aqua regia, the "Royal Water" which dissolves gold and platinum.
Like silver, gold is impervious to ordinary acids like hydrochloric acid
( HCl, formerly called muriatic acid,
"marine acid" or "spirit of salt").
Unlike silver, gold cannot be oxidized by nitric acid
(aqua fortis)...
However, early alchemists did discover that a mixture of nitric and
hydrochloric acids was able to dissolve gold, the so-called royal metal.
They dubbed the potent mixture "Royal Water", aqua regis or
aqua regia.
Aqua regia is already mentioned in the world's
first
encyclopedia,
published in AD 77 by Pliny the Elder
(Gaius Plinius Secundus, AD 23-79).
Aqua regia is a mixture of at least 3 moles of
hydrochloric acid per mole of nitric acid
(it's better to have too much hydrochloric acid than too little).
It's used concentrated and hot for best efficiency.
Aqua regia is also called chloroazotic, chloronitric,
nitromuriatic, or nitrohydrochloric acid
("eau régale" in French).
Nitrosyl chloride
and chlorine fumes are evolved upon mixing:
HNO3 + 3 HCl
®
NOCl + Cl2 + 2 H2O
The chemical equilibrium for the oxidation of gold by the nitrate ions in nitric
acid would only result in a minute concentration of auric cations
[Au+++], but in aqua regia
the concentration of auric ions is constantly depleted because
auric cations combine quickly with chlorine anions to form complex
chloroaurate ions:
Au+++ + 4 Cl -
®
AuCl4-
The speed of the overall reaction is limited by the [Au+++ ]
concentration from the redox equilibria.
As this improves with temperature, aqua regia may be used
at 100°C or more (in a bath of boiling salty water).
Gold may form compounds in two oxidation states +1 (aurous)
and +3 (auric):
- Byproducts or reactants in the electrolytic refining of gold:
- CAS 10294-29-8:
Aurous chloride / Gold monochloride (AuCl).
- CAS 13453-07-1:
Auric chloride / Gold trichloride (AuCl3).
- CAS 16903-35-8:
Chloroauric acid (HAuCl4).
- CAS 16961-25-4:
--- trihydrated crystals
(HAuCl4, 3 H2O).
Note: The term "gold chloride"
is unfortunately used for any of the above!
- Gold-plating baths: (potassium aurocyanide, potassium gold cyanide).
- CAS 13967-50-5:
Potassium dicyanoaurate K[Au(CN)2].
- Rheumatoid arthritis medicine:
- CAS 15189-51-2:
Sodium aurichloride (NaAuCl4, 2 H2O).
The combination of gold trichloride with the chloride of
another metal is called an aurochloride, aurichloride,
chloraurate or [preferably] chloroaurate.
 Fulminating Gold, the First High Explosive:
Since gold is so difficult to combine with other elements,
all gold compounds are fairly unstable.
Some much more so than others, though:
In 1659, Thomas Willis and Robert Hooke demonstrated
that a powder of gold hydrazide explodes on a mere concussion,
without the need for air or sparks (which were once thought to be required
for any kind of ignition).
Gold hydrazide (also known as aurodiamine) is a water-soluble substance
obtained by letting an ammoniacal solution react with an auric hydroxide precipitate
(itself obtained from a gold solution prepared with aqua regia).
Gold hydrazide has a dirty olive-green color (AuHNNH2 ).
Gold hydrazide is apparently only one of several explosive compounds which have been called
fulminating gold (aurum fulminans).
Around 1603, another kind of fulminating gold ("Goldkalck" or "Gold Calx")
was described as the precipitate of gold by potassium carbonate.
These kinds of "fulminating gold" are distinct from "gold fulminate",
the gold salt of fulminic acid (CNOH), another expensive explosive...
In spite of its price, fulminating gold is said to have been used militarily in 1628.
The discovery of fulminating gold has been attributed to the
alchemist Basil Valentine (Basilius Valentinus)
a legendary benedictine monk who is regarded by some
as the "father of modern chemistry" [see next article].
We're told Basil Valentine was born in 1394,
although his main work (The Twelve Keys of Basil Valentine)
was first published only in 1599.
(2003-12-03)
Forefathers of Modern Chemistry
What alchemist or early chemist is the father of modern chemistry ?
Chemistry is a science with many "fathers".
Here are some popular contenders for the title...
- Pliny the Elder, Gaius Plinius Secundus (AD 23-79).
- Geber, Abu Musa
Jabir Ibn Hayyan
(c.740-803).
 - St.
Albert the Great, Albertus Magnus (1205-1280)
- Roger Bacon (c.1214-1294)
- Basil Valentine (1394-14??)
  - Paracelsus
(1494-1541)
- Sir Francis Bacon (1561-1626)
- Robert Boyle (1627-1691)
  - Antoine
Lavoisier (1743-1794)
- John Dalton (1766-1844)
- Amedeo Avogadro (1776-1856)
 
- Humphry Davy (1778-1829)
- Jöns Jakob Berzelius (1779-1848)
Arguably, chemistry became a science when
Antoine Lavoisier established that
mass is conserved in any chemical reaction,
about which he stated:
Rien ne se perd, rien ne se crée, tout se transforme.
It's only with the advent of Relativity Theory
that this fundamental conservation law would be proved to be only a first
approximation, albeit an excellent one:
Unlike what happens in nuclear reactions,
the relative variation of mass involved in chemical reactions is so minute
that it can't be measured directly.
The
Fathers of...
|
Geber
|
Chemists
that Shaped the Science
(2010-01-20)
Birth of Organic Chemistry (1824 or 1828)
The synthesis of urea by Friedrich Wöhler, in 1828.
Friedrich Wöhler |
|
Organic compounds are so named because they were
first exclusively observed as products or constituents of living
organisms.
Early chemists could not synthesize any of them
from inorganic compounds using chemical procedures.
That feat was first achieved by
Friedrich Wöhler
(1800-1882) when he
accidentally
synthesized
urea
CO (NH2)2 in 1828.
|
Arguably, Wöhler himself had founded organic chemistry 4 years earlier,
when he synthesized
oxalic acid
(COOH)2 from inorganic precursors, in 1824.
The work of Wöhler marked the beginning of the end for the doctrine
of vitalism
which argued that a mysterious
vital force in living things would distinguish its
constituents qualitatively from inorganic chemical compounds.
Today, organic chemistry is essentially synonymous with
carbon chemistry.
The tetravalence of carbon leads to the tremendous diversity
of carbon-based compounds which makes life possible.
Biochemistry is just a part of chemistry...
The
Building Blocks of Organic Compounds by Ken Costello
(Chemistryland)
(2010-01-20)
Saturated hydrocarbons: Alkanes and cycloalkanes.
Compounds of carbon and hydrogen atoms featuring only single bonds.
The structure of a saturated hydrocarbon is described by
a connected simple graph
where each node
(representing a carbon atom) is connected
[ by an edge representing a single
bond ]
to at most 4 other nodes.
It's understood that every carbon atom is bonded to 4 atoms
(of either carbon or hydrogen).
A molecule whose atoms do not form any cycles is called aliphatic.
Their carbon skeletons are acyclic graphs
(technically called trees).
All the other saturated hydrocarbons are called cycloalkanes
(although that term is often understood to denote s saturated hydrocarbon
where the carbon atoms form a single cycle).
Methane
(1 carbon atom) is represented by a graph of one node
and no edges.
Ethane (2 carbon atoms)
corresponds to a graph of two nodes connected by one edge.
Propane (3 carbons)
is three nodes connected by two edges.
There are two kinds of
butane (4 carbons)
corresponding either to a chain of 4 nodes or to a central node
connected to the other three. The latter is called
isobutane (or methylpropane, according to the IUPAC nomenclature).
There are 3 kinds of pentane
(5 carbons) including isopentane
(methylbutane) and neopentane (dimethylpropane).
Structurally, there are 5 hexanes,
9 heptanes,
18 octanes,
etc.
-
Chiral molecules are optically active :
Starting with heptane, the possibility exists that a single skeleton
corresponds to several spatial configurations.
In particular, this happens whenever the molecule includes just
one so-called chiral carbon,
namely a carbon atom bonded to 4 different
ligands.
In that case, we are faced with a
chiral compound
with two different possible configurations which are mirror images of each other
(they are called enantiomers).
As it is traversed by a ray of polarized light,
a pure enantiomer in fluid form (or in a solution) will rotate
the angle of polarization by a angle proportional to the molar density and the distance
travelled.
Such an optical activity
is observed for the following two types of heptane.
Each of these has two enantiomers because each has a single chiral atom :
The fact that either of those yields a pair of enantiomers is the reason why there are
11 stereoisomers of heptane for only 9 structural isomers.
It's often
the case that a molecule with k chiral carbons
has 2k stereoisomers.
The simplest exception among alkanes is the following octane,
featuring two chiral carbons but only
3 (not 4) stereoisomers; a pair of
optically active enantiomers and one inactive
meso compound.
(HINT: As the two halves may rotate around the axis of
the two chiral carbons, the meso isomer is center-symmetric.)
3,4-Dimethylhexane =
( C* H CH3 C2H5 ) 2
A star ( C* )
is often used to stress that a given carbon is chiral.
On the limited usefulness of the "chiral carbon" concept :
Spiranes are cycloalkanes which contain two cycles that share a
single carbon atom. At that central atom, the two pairs
of bonds that define the planes of the two cycles are perpendicular.
The simplest example of a spirane is spiroheptane,
which consists of 2 carbon quadrilaterals sharing one vertex.
Spiranes can illustrate some of the difficulties associated with
chiral carbons in the analysis of delicate cases.
For example, consider the following pair of enantiomers
for dimethylspiroheptane
C9H16
This is clearly a
chiral compound because those two mirror images cannot be superposed.
Such molecules are sometimes wrongly heralded as having
no chiral carbons.
A close examination reveals that this is not the case; the above chiral
molecule does feature 3 chiral carbons (the central carbon and the two
carbons attached to methyl groups).
Indeed, a carbon is chiral whenever it's attached to
4 different ligands. Two chiral ligands that are enantiomers of each
other are different!
When two ligands are interconnected by a structurally symmetrical chain,
the case may not be obvious to settle.
In the case of a carbon attached to a methyl group in the aforementioned molecule of
dimethylspiroheptane, the chain that goes from
one bond to the other and the chain that goes back have different chiralities
(otherwise the whole molecule would not be chiral). Both of those carbons
are therefore chiral.
The case of the central atom is even trickier.
It belongs to two oriented 4-cycles which are symmetrical but chiral
(we may decide to observe from the side of the methyl group and describe unambiguously
a direction as either clockwise or counterclockwise).
Some thinking is needed to realize that two
identical chiral loops meeting perpendicularly at one point form a chiral
configuration (the two chirality do not cancel, so to speak).
The central carbon is thus chiral as well.
Removing an hydrogen atom from an alkane yields an active
chemical entity called an alkyl group
(it's eager to combine with some other "free" group,
as the two unpaired electrons from both groups tend to form a
covalent bond).
As already illustrated above, such groups are commonly
named after the
simple alkane they are derived from (by removing an hydrogen from
a carbon atom at the end of a chain):
Methyl, ethyl, propyl, butyl, etc.
-CH3
-C2H5
-C3H7
-C4H9 ...
In the standard nomenclature used to describe "branched" alkanes,
the longest carbon chain
is used along with the names and numeric positions of the akyl grouos borne
by carbons on that chain. Symmetries are usually taken advantage of,
in order to make the numeric positions as small as possible.
For example, a descriptive name for isobutane is
methylpropane: A methyl group attached to the middle atom
(position 2) in the 3-chain of propane...
The position is not explicited in this case because there's
only one possibility which does not yield a compound with a
simpler name (namely, straight butane ).
Several akyl groups may be attached to the same carbon atom.
For example, dimethylpropane properly describes a pentane
(also called neopentane)
consisting of a central carbon atom attached
to 4 identical methyl groups.
Wikipedia :
Alkanes
|
Cubane
|
Dodecahedrane
|
Cahn–Ingold–Prelog convention
(2010-02-05)
Unsaturated Hydrocarbons
They feature at least one pair of carbon atoms tied by multiple bonds.
(2010-01-23)
Functional Groups
Groups of atoms that determine a class of molecular reactions.
In organic chemistry, some common chemical reactions
involve only certain well-known groups of atoms within molecules.
Those are called functional groups.
The nature of the aforementioned reactions is determined by the functional groups,
but the rest of the molecule (abbreviated R in the following tables)
may influence reactivity. Here are a few frequently encountered groups:
-
- Esterification :
Alcohol + Acid
®
Ester + Water
- Alcohol Dehydration :
Alcohol + Alcohol
®
Ether + Water
Epoxides (with the structure depicted at left)
are commonly obtained industrially
by the catalytic oxidation of alkenes, especially
ethylene
(ethylene oxide is known as oxirane)
and propylene
(propylene epoxide).
Wikipedia :
Functional group
|
Organic chemistry
|
Dehydration reactions
|
Cumene process
|
