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Final Answers
© 2000-2014   Gérard P. Michon, Ph.D.

Basic Chemistry

 Lavoisier (1743-1794)  Humphry Davy (1778-1829)  A.W. von Hofmann (1818-1892)  Kekule (1829-1896)  Marie Curie (1867-1934) Chemistry is physics without thought.
Mathematics is physics without purpose.

Anonymous
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Articles previously on this page:

Related articles on this site:

Some noted mineralogists, chemists and physical chemists :

  • Axel Fredrik Cronstedt  (1722-1765).  Nickel  (1751).
  • Franz-Joseph Müller von Reichenstein  (1742-1825).  Tellurium  (1783).
  • Sir Humphry Davy  (1778-1829).  Alkali Metals  (1807).
  • Justus von Liebig  (1803-1873).  Organic Chemistry  (1840).
  • Carl Leverkus  (1804-1889).  Industrial Ultramarine  (1834).
  • August Wilhelm von Hofmann  (1818-1892).  Organic Chemistry  (1845).
  • August Kékulé  (1829-1896).  Benzene  (1865).
  • Dimitri Mendeleev  (1834-1907).  Periodic Table  (1869).
  • Sir James Dewar  (1842-1923).  Dewar Flask  (1892).
  • Marie Curie  (1867-1934).  Polonium & radium  (1898).
  • Ernest Rutherford  (1871-1937).  Atomic nucleus  (1909).
  • Hans von Euler-Chelpin  (1873-1964).  Enzymes  (1904).
  • Margaret Thatcher  (1925-2013).  British prime minister  (1979-1990).

Related Links (Outside this Site)

NIST Chemistry WebBook  |  CAS Registry Numbers (CAS RN)
The Alchemy Web Site  |  Caveman Chemistry  |  Chemical How Tos
History of Black Powder  |  Cannons & Gunpowder  |  Blackpowder 101
Les piles ("Batteries" in French)  |  Baghdad Battery
Pigments through the Ages  |  Sciencemadness.org  by  Matthew Ernst
General Chemistry Starting Points  (for students)   by  Steve Lower.

Videos :

MIT OpenCourseWare Basic Chemistry  by  Sylvia Ceyer  &  Catherine Drennan.
Edward Kent's Chemical Demonstrations  |  Alkali Metals in Water  by  Dnn87
Top 10 Amazing Chemistry Videos  by  Aaron Rowe  at  Wired Science.
Chemical Curiosities  by  Chris Bishop  (Royal Institution of Great Britain, 2012-02-16).
 
The Periodic Table of Videos :   118 video clips produced by  Brady Haran,
featuring Martyn Poliakoff, Pete Licence, Stephen Liddle, Debbie Kays and Neil Barnes.
 
Inside the Mind of an Alchemist  by  Prof.  Larry Principe  (Johns Hopkins).
 
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 International Year 
 of Chemistry - 2011

From Alchemical Recipes to Modern Chemistry
 Geber      Madame Curie


(2011-08-07)   Basic chemical accounting:  Moles  of stuff.
A modern convention that helps put chemical history in perspective.

In chemical equations, a symbol or a formula for a substance is always understood to denote a definite quantity of it  (measured by weight)  technically called a  mole  of that substance  (symbol:  mol ).  Thus, when a non-chemical quantity  (most commonly, energy)  appears in a chemical equation,  it's understood to pertain to the implied number of  moles.

The name stands for the deprecated term  molecule-gram  which was coined when it became known that a chemical species is normally made of identical units  (molecules, ions, etc.).  A  mole  is merely a particular number of those things  (as many of them as there are atoms in  12 g  of carbon, when only the dominant isotope is present).  The  number of things per mole of stuff  is a huge constant, called  Avogadro's number :

Na   =   6.02214...  10 23 / mol

Nevertheless, the convention of using  moles  uniformly for all chemical substances doesn't strictly depend on the underlying concept of atoms and molecules.  It was already made legitimate by the prior  law of definite proportions  (Proust's Law)  formulated by the Frenchman Joseph Proust (1754-1826)  based on the combustion experiments he conducted between 1798 and 1804.  Proust observed that iron (Fe) and "almost every known combustible" may unite with only two constant proportions of oxygen  (by weight).  In modern terms, one example would be  CO  and  CO2

The study of the simple fixed ratio in which moles of various chemicals  combine to form pure chemical compounds is known as  stoichiometry.

Mixtures  are different from pure chemical compounds.  Although this is rarely done, if ever, they could be expressed as linear combinations of the pure chemicals they consist of.  For example, a mole of dry  air  at sea-level is approximately:

0.7808 N2  +  0.2095 O2  +  0.0094 Ar  +  0.0003 CO2

Incidentally, this gives the often-quoted  molar weight of air  (29 g/mol):

28.965 g/mol   =   0.7808 (28.0134 g/mol)  +  0.2095 (31.9988 g/mol)
+  0.0094 (39.9481 g/mol)  +  0.0003 (44.0095 g/mol)

For gases, such molar compositions are often said to be  by volume  because of the great nineteenth-century discovery  (Avogadro's law)  that the same volume of two different gases contains approximately the same number of moles  (the lower the pressure, the better the approximation).

For anything but gases, we must use the known  molar weights  of the constituents to obtain the molar composition of a mixture from its weight composition  (or vice-versa).

 Dmitri Mendeleev  
 (1834-1907) Molar weights were the key to the final classification of the chemical elements presented by  Dmitri Mendeleev in 1869  (before the more fundamental notion of  atomic number  was made clear, in part as a result of this classification).  The molar weight of a molecule is the sum of the molar weights of the individual atoms that compose it.

When the utmost in precision is called for  (it almost never is)  a relativistic adjustment should be made by subtracting from that sum a tiny "mass defect" equal to the binding energy divided by  c2.

 Robert Boyle 
 (1627-1691) The modern notion of a chemical element was first proposed, on empirical grounds, by Robert Boyle in 1661.  A chemical element is a species that cannot be obtained by combining other chemicals.

 Jacob Berzelius  
 (1779-1848) The system of  chemical symbols  we currently use to represent every element was devised by Jacob Berzelius around 1810.  Every symbol consists of one or two latin letters, only the first one is capitalized:  H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar...

 Ernest Rutherford 
 (1871-1937) Every element is now known to correspond to one type of atomic  nucleus.  The structure of every neutral atom as a positive nucleus "orbited" by negative electrons was first proposed by Ernest Rutherford in 1911  (to explain the results of the notorious  Gold Foil Experiment  of 1909).  More precisely, each element is identified by a unique integer called its  atomic number  which is usually denoted by the capitalized letter  Z  (initial of the German word  Zahl  for  number ).  The number  Z  corresponds to the number of elementary positive charges  (one such charge per proton)  cointained in every atomic nucleus of that element.

The atomic nuclei corresponding to a given element  (i.e., a given atomic number  Z)  exist in slightly different masses because they may contain different numbers of  neutrons  (a neutron has a mass nearly equal to that of a proton but no electric charge at all).  The total number of  nucleons  (i.e., protons and neutrons)  in a nucleus is called its  mass number  and is usually denoted by the letter  A.  Nuclei that have the same value of  Z  but different values of  A  are said to be different  isotopes  of the same element.

The existence of isotopes explains a fact that puzzled early chemists, namely that the molar weight of a substance is usually close to an integer multiple of that of elemental hydrogen  (weighing half as much as hydrogen gas)  but is occasionally far from that.  In particular, the molar weight of elemental chlorine  (Cl)  is  35.45 g/mol  because natural chlorine is essentially a mixture of two isotopes:  75.8% of Chlorine-35 (34.9688527 g/mol)  and 24.2% of Chlorine-37 (36.9659026 g/mol)
 
The discovery of isotopes is usually credited to J.J. Thomson (1856-1940; Nobel 1906)  because his invention of mass spectrometry, in 1913, established the existence of two stable isotopes of Neon  (Neon-20 and Neon-22).  However, the existence of radioactive isotopes was also established in 1913 by Frederick Soddy (1877-1956; Nobel 1921)  who coined the word  isotopes  in 1914, from a suggestion made by a distant relative of his, Dr. Margaret Todd (1859-1918).

Isotopes have virtually identical chemical properties, except possibly for the lightest elements  (e.g., the different masses of protium and deuterium, the two stable isotopes of hydrogen, yield measurably different ionization potentials).  Most elements below Uranium  (Z = 92)  have several stable or very long-lived isotopes.  Some have only one, some have none.

The lightest element without a naturally occuring stable isotope is  Technetium  (Z = 43)  whose many isotopes include Technetium-99, which is the most significant long-lived fission product from commercial nuclear reactors, featuring a half-life of 211100 years and a  specific radioactivity  of  0.62 GBq/g.

The element  carbon  (C)  corresponds to  Z = 6.  "Old" natural carbon found in mineral deposits  (including carbonates, coal and crude oil)  is not radioactive at all because it consists only of the two stable carbon isotopes:  Nearly 99% of Carbon-12  (6 protons and 6 neutrons, which serves for the above modern definition of the  mole)  and 1% of Carbon-13  (6 protons, 7 neutrons).  On the other hand, "new" carbon in living organisms is radioactive because of trace amounts of Carbon-14, a radioactive isotope  dubbed  radiocarbon  (6 protons, 8 neutrons)  which is obtained from the carbon dioxide in the air  (either directly by photosynthesis or indirectly by consuming carbon compounds from other living organisms).  Radiocarbon  is constantly formed cosmogenically by transmutation of nitrogen in the upper atmosphere.  As  radiocarbon  decays with a half-life of about  5700 years, the radioactivity of a sample of carbon depends directly on its  age,  defined as the time elapsed since the creature that originally fixed the carbon stopped breathing  (this is the basis for the technique known as  carbon dating ).  Mineral carbon is not radioactive at all because  either  it lacks any biological origin  or  because its biological origin is so ancient that all traces of  radiocarbon  have long disappeared.

This modern view of chemical elements has replaced the antiquated doctrine of the four  classical elements  (fire, water, air and earth)  which was first proposed by  Empedocles  around 450 BC.  Backed by the great authority of  Aristotle (384-322 BC)  that misguided doctrine hindered the development of both alchemy and chemistry for  two millenia.


   Still of Democritus
Still "of Democritus"
 
(2011-07-18)   Alembics and Stills  (3rd century AD)
Purification by evaporation and condensation.

According to Egyptian mythology,  Alchemy  was founded by the goddess Isis.  As  Alchemy  seemed similar to cooking, it was once considered to be a  feminine  art, or women's work  (opus mulierum).

This goes a long way toward explaining that one of the earliest alchemist on record is a woman...  She lived in Alexandria in the third century AD.  Her real name was probably  Miriam.  In English, she's known as  Mary the Jewess.

According to the custom of her day, she concealed her identity by using a legendary name as a pseudonym, signing  Miriam the Prophetess, sister of Moses  (amusingly, this caused a lot of confusion among people who took this literally).  Miriam  is also known by many other names, including  Maria Prophetissa, Maria Prophetissima, Mariya al-Qibtyya, Maria the Copt, Maria the Sage "daughter of the King of Saba", the Matron Maria Sicula, etc.

Aristotle (384-322 BC)  already knew that fresh water could be obtained by condensation from evaporated seawater  (that's the way Nature produces rain).  Pliny the Elder (AD 23-79)  describes how distillation was done in his days, using fibers to absorb condensed vapor in the lid of a covered vessel.

Miriam  devised the first true distillation apparatus by letting the vapor escape in pipes through a modified lid which is now called a  still-head  (the learned term is  alembic  which is the Arabic name denoting either that specific part or the whole apparatus).  The still-head and/or the rest of the pipes are cooled by air or water  (wet sponges)  to make vapor  condense.  Finally, the condensed liquid is collected in receiving vessels.

 Alexandrian Stills (3rd century)  
  1. Fire, heater, oven.
  2. Boiler, cucurbit, still.
  3. Still-head, alembic.
  4. Condenser.
  5. Receiver.

Miriam's original contraption, the  tribikos,  called for 3 pipes and 3 receivers.  It is pictured at right, with another simpler design attributed to her most famous student Zosimos of Panapolis.  The illustration is from a famous Alexandrian manuscript written by Zosimos  (third or fourth century AD)  which seems to be the oldest extant alchemical text.

If the condenser operates normally, the apparatus works at constant volume (no vapor escapes).  Arguably, this key innovation marks the beginning of the slow transition from ancient  alchemy  to modern  chemistry.

 Retort
(2011-07-19)   Retort  (8th century AD)
More than a simplified  alembic.

Around 750 AD, Geber invented a simplified distillation apparatus called a  retort  (French:  cornue)  as a single piece of glassware adequate for crude distillations into any receiver vessel.  The shape remains one of the most recognizable symbols for  alchemy  or  chemistry.

Although non longer as popular as it once was, this device remains a great choice for crude high-temperature distillation or as a reaction vessel for chemical reactions where a gas is evolved.


(2011-07-18)   Production and Distillation of Alcohol
Alcoholic beverages in Prehistory.  Hard liquor since the Middle Ages.

For thousands of years, alcohol  (C2H5OH)  was of primary importance to human survival, because it provided safe beverages under unsanitary conditions.  The ancestors of beer and wine had enough ethanol in them to kill common bacteria and viruses before they infected the drinker.  (In the Orient, the tradition of boiling water to make tea had similar benefits.)

Even sour wine  (vinegar)  is fairly safe, because of the sterilizing effects of the acetic acid that results from the oxidation of alcohol, mediated by  AAB  using oxygen from the air  (properly sealed wine won't turn into vinegar):

C2H5OH  +  O2   ®   CH3COOH  +  H2O

At first, the inebriating properties of alcohol were just a side-effect that may or may not have been welcome...  However, with only weak alcoholic beverages available, those who sought that inebriation could not achieve it without consuming relatively large quantities of liquid fairly rapidly...

At a concentration of about  14%  (by volume)  alcohol inhibits the very enzymes  (Zymase)  that catalyze its production by anaerobic fermentation:

sucrose  water  glucose  ethanol  gas
C12H22O11   +   H2O ® 2 C6H12O6 ® 4 C2H5OH   +   4 CO2
 (invertase)  (zymase) 
 

Fermentation is thus unable to directly produce strong alcoholic spirits.  Those were first obtained in the Middle Ages by large-scale  distillation.

  • Whiskey and Scotch whisky from malted barley.
  • Kentucky bourbon from corn.
  • Brandy, Cognac, Armagnac from wine.
  • Fruit brandy, Schnapps, Kirsch, eau-de-vie from fruit.
  • Calvados from apples.
  • Gin from juniper berries.
  • Cointreau, Triple-sec from oranges.
  • Vodka from grain.
  • Tafia and rum, from sugarcane (in warm regions).
  • Spirit recipes: Grand-Marnier, Chartreuse, Pastis, etc.

Under normal atmospheric pressure, ethanol  (C2H5OH)  cannot be separated from water by distillation alone, because a mixture of 95.629% alcohol and 4.371% water  (by weight)  actually forms what's called an  azeotrope  (a mixture whose vapor retains the same composition as the liquid).  As the boiling point of that  ethanol-water azeotrope  (78.1°C)   Everclear is less than the boiling point of either ethanol  (78.5°C)  or water  (100°C)  it tends to evaporate first.  Therefore, the vapor will never contain more than  95.629%  of alcohol by weight  (unless the liquid itself was stronger than that to begin with).

The 190-proof grain alcohol Everclear  made the Guinness Book of World Records  in 1979 as the  World's most alcoholic beverage.  Other brands of neutral grain spirits now include  Golden GrainGem Clear  and  Spirytus  (rectified spirit from the former Polish state monopoly  Polmos).

Some of those brands  (including Everclear)  are also sold in lesser grades, because full-strength rectified spirits cannot legally be sold in several countries or states, including California.  Typically, they are downgraded to 151-proof spirits that mimick the alcohol content, but not the flavor, of  overproof rum  (which has itself been banned in some places).

In the US,  "N-proof"  denotes a proportion of ethanol   x = N/200  (by volume)  corresponding to the following percentage by weight:

y   =   79% / (200/N - 0.21)       [ that's 100% for N = 200 ]

Conversely,   N   =   200 / (0.21 + 0.79/y)   =   200 x

For the aforementioned azeotrope  (y = 0.95629)  we obtain  N = 193.03.  Thus, repeated distillation  (rectification)  at normal atmospheric pressure cannot yield anything stronger than 193 proof  (96.5% by volume).  The  Spirytus Luksusowy  Polish vodka is labeled  192 proof  (96% by volume).

As no ethanol-water azeotrope exists below a pressure of  70 mmHg,  it would be possible to obtain nearly pure alcohol by vacuum distillations  (there are several more economical ways to do so for chemical purposes).

Wikipedia :   Retort   |   Alembic   |   Azeotropes (data)   |   Ethanol (data)   |   Ethanol purification
Video :   Distillation of Ethanol   |   Dangers of Distillation   |   Radioactive Alcohol
Hillbilly Stills (Copper moonshine stills for sale)


Albertus
Magnus (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 as  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 the 6 pages of  Liber Ignium  (Book of Fires),  Marcus Graecus  [an otherwise unknown, possibly fictitious, author]  describes 35 incendiary recipes, including the one for what became known as  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 the pamphlet didn't appear until 1280 or 1300 and it may well have been created at that time, although it was claimed to be 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)
DateWho / What / Where   KNO3  SulphurCharcoal
c. 700Chinese alchemists (?)111
1249Roger Bacon755
1275Albertus Magnus ("German")411
c.1300"English" (Marcus Graecus?)612
 Swiss "Bernese Powder"761014
1781Britain751015
1794France76915
1800Prussia7511.513.5
Stoichiometry (see below)74.811.913.3

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)  Black powder, 
 white smoke !

The potassium sulphide solid residue forms a thick white smoke, capable of obscuring entire battlefields.

Without sulfur (12.93% carbon) there would be 60% smoke as  potassium carbonate  (and 772.6 cal/g):

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  (sulfur prevents wasteful carbonate production).

Newer propellants leave little or no solid 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)

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 & nitroglycerin, with diphenylamine stabilizer) invented by Alfred Nobel (1833-1896) in 1887.   Sir James Dewar 
 (1842-1923)
  • Cordite N (nitroguanidine, nitrocellulose, and nitroglycerin) invented by Frederick Augustus Abel and James Dewar  (1889).

The Science of Fireworks!   by  Professor Chris Bishop   (Cambridge Department of Chemistry, 2011-11-05).


(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 rough approximation of chemical reality is useful, but not foolproof.

Explosive Science!   by  Professor Christopher M. Bishop   (Cambridge, published November 1, 2012).


(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   (= 3985 J/g)

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 (FeAl2O).

The usual recipe calls for 8 grams of iron oxide for 3 grams of aluminum.

This is the most popular special case of what's known as a  Goldschmidt reaction (1893)  whereby the oxide of a metal  (like iron)  is reduced by a more reactive metal  (aluminium is the usual choice).  The reaction is initiated either by permanganate and glycol or by a burning ribbon of magnesium.  When the difference in the reactivities of the two metals is large, a  dangerous  explosion may occur.  For example :

3 CuO  +  2 Al   ®   Al2O3  +  3 Cu  +  1203.8 kJ   (= 4114 J/g)

The stoichiometry of that reaction yields the recipe for  copper thermite :  Mix  31 g  of  cupric oxide  with about  7 g  of powdered aluminium

  Iron  Fe Alumina  Al2O3 Copper  Cu
Mass55.846 g/mol101.9618 g/mol63.546 g/mol
Heat Capacity25.10 J/K/mol195624.440 J/K/mol
Melting Point1811 K2345 K1357.77 K
Heat of Fusion13.81 kJ/mol 13.26 kJ/mol
Boiling Point3134 K3250 K2835 K
Heat of Vaporization340 kJ/mol 300.4 kJ/mol

Videos :   Thermite reactions | Copper thermite explosion | Don't play with copper thermite!


(2003-10-09)   Enthalpy of Formation.  Hess's Law  (1840).
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.
 
The standard allotrope of an element  (zero enthalpy of formation)  can be a matter of convention, based on historical considerations.  The table below highlights the case of phosphorus, which was first isolated as a waxy solid, in 1669, in the toxic form of  white phosphorus.  A more sensible substance of reference would have been  black phosphorus, the only thermodynamically stable form below 550°C.
Enthalpies of Formation  ( DH f < 0   for exothermic formation )
Substance   (normalized to 298.15 K,  1 atm)
s = solid,   l = liquid,   g = gas,   d = dissolved
DH f
(kJ/mol)
aluminasAl2O3 -1675.70  
potassium carbonatesK2CO3 -1150.18  
sodium carbonatesNa2CO3 -1130.77  
calcium dihydroxidedCa++  +  2 OH - -1003
calcium dihydroxidesCa(OH)2 -986.09  
rustsFe2O3 -824.20  
calcium dihydroxide gasgCa(OH)2 -610.76  
calcium iondCa++ -543.00  
potassium nitrate (nitre)sKNO3 -494.60  
sodium nitratesNaNO3 -467.90  
carbon dioxidegCO2 -393.51  
potassium sulphidesK2S -380.70  
nitroglycerinl C3H5(NO3)3 -371.10  
ammonium nitrate (AN)sNH4NO3 -365.60  
waterlH2O -241.826
hydroxide iondOH - -230.015
hydronium iondH3O+ -196.32  
cupric oxidesCuO -157.30  
carbon monoxidegCO -110.53  
myricin (beeswax)s C15H31COOC30H61  
sodium acetate trihydrates  (NaCH3COO, 3H2O)   
nitroguanidines H2NC(NH)NHNO2 -91.63  
calcium carbidesCaC2 -59.80  
trinitrotoluene (TNT)sC7H5N3O6 -54.39  
black phosphorussP -39.30  
red phosphorussP -17.60  
 white phosphorus (toxic) s P4  [ CAS 7723-14-0 ] 0.00  
phosphorus gasgP4 +58.90  
phosphorus gasgP2 +144.00  
acetyleneg C2H2 +226.73  
phosphorus gasgP +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 a fairly unstable compound which, like acetylene, can release energy by reverting back to its elemental components.  On the other hand, a negative enthalpy of formation is no guarantee of stability.  Some such chemicals may even  detonate  violently into more stable ones, as does liquid nitroglycerin in the following reaction:

4 C3H5(NO3)3  ®  12 CO2 + 6 N2 + 10 H2O + O2 + 5656 kJ   (1488 cal/g)

Nitroglycerin was invented in 1847 by the Italian chemist Ascanio Sobrero (1812-1888)  who had been working under the Frenchman Théophile-Jules Pelouze (1807-1867)  after the discovery of guncotton (1845).  Sobrero was so frightened by his own discovery that he kept it secret for more than a year,  describing it as "impossible to handle".
 
The problem would be solved in 1867 by another student of Pelouze's Alfred Nobel (1833-1896) with the invention of  dynamite,  a mixture of nitroglycerin with minerals that prevent spontaneous detonation.  That discovery became the source of Nobel's large wealth, which ultimately allowed the creation of the  Nobel Prize...

Of particular theoretical and historical interest is the so-called  heat of neutralization  evolved in the aqueous neutralization of a strong acid and a strong base  (e.g., HCl and NaOH).  Remarkably, it doesn't depend on the nature of the acid or the base, since it boils down to the following reaction:

H3O+  +  OH -   ®   2 H2O  +  57.32 kJ  (13.7 kcal)   at 25°C

Like all "complete" chemical reactions, this one actually results in a lopsided equilibrium where the reactants have nonzero concentrations (in mol/L) verifying the notorious relation:

[ H3O+ ]  [ OH - ]   =   10 -14

As Arrhenius first noted in 1884, the very notion of aqueous acidity is based on that critical equilibrium and the disturbances caused to it by other reactions that involve either of the two relevant ions.

Wikipedia :   Hess's law (1840)   |   Germain Hess (1802-1850)   |   Standard enthalpy of formation   |   Data Table


(2011-06-21)   Hot Ice   (the constituent of  reusable  heating pads)
The crystallization of  sodium acetate trihydrate  is exothermic.

Here's the crystallization reaction for the hot ice found in the reusable PCM  heating pads  that have been widely available since 1978  (136.0796 g/mol).

Na+  +  CH3COO-  +  3 H2O   ®   (NaCH3COO, 3H2O)  +  38 kJ

The data from the above table is equivalent to a  latent heat  of  280 J/g.

This solidification occurs  (below  58°C)  only when nucleation can be initiated by various impurities or, more reliably, by a little bit of already crystallized  sodium acetate trihydrate.

Interestingly, the reaction can also be triggered mechanically by a special  clicker  (consisting of a slotted metallic disk)  invented in 1978.  That device made possible a fascinating consumer product known as a  reusable heating pad  (also called  heat pack  or  hand warmer  by campers).

The thing consists of a permanently sealed soft transparent pouch containing a clicker and some hot ice  (possibly with a very slight excess of water).  The pack is stored or carried in its liquid form.  When needed, a mere click turns it into a very warm solid object  (which can later be returned to it metastable liquid form by heating the pouch in boiling water until all traces of the crystals have disappeared).


(2007-11-21)   Gibbs Function (G): Free Enthalpy (or "free energy").
The sign of  DG  indicates thermodynamic stability.

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...

 Come back later, we're
 still working on this one...

Josiah Willard Gibbs (1839-1903)   |   Chemical affinity


 Claude Berthollet 
 (1748-1822) (2011-08-07)   Berthollet's Law of Mass Action
[ Products ] / [ Reactants ]   =   Equilibrium Constant

Before Berthollet debunked the notion  (between 1800 and 1803)  chemists believed in the concept of  elective affinities  (Wahlverwandtschaften).  According to that alchemical doctrine, chemical compounds would form or dissociate in  substitution reactions  in strict accordance to the so-called  affinities  of pairs of chemical species for each other.  This was thought to occur essentially to the fullest possible extent, regardless of the repective concentrations of the reactants involved.

 Come back later, we're
 still working on this one...

Wikipedia :   Law of mass action
 
From Elective Affinities to Chemical Equilibria: Berthollet's Law of Mass Action
by  Frederic L. Holmes.   Chymia, vol. 8, pp. 105-145  (1962)


(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.

 Come back later, we're
 still working on this one...

Ink blot. (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.

Nowadays, Chinese ink produced in this traditional way is known by its Japanese name  (Sumi ink)  whereas bottled Chinese ink is called India ink.  However, bottled Sumi ink is also available with features that some artists swear by  (see video review by web comics artist Bryan Christopher Moss).

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.

 Come back later, we're
 still working on this one...

Iron-nutgall ink, tannin Ink, gallotannate ink, vitriolic ink.

Modern Inks

 Come back later, we're
 still working on this one...

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 niloticaacacia arabicababulEgyptian 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 (next):  COOH.C6H2(OH)2O.COC6H2(OH)3  Gallic Acid
  • Gallic acid:  Produced (with glucose) by the hydrolysis of tannin in acid. Used in calotype photographyC6(COOH)H(OH)3H   (170.12 g/mol)

Iron Gall Ink  |  How to Make Iron Gall Ink  |  Ink Corrosion  |  Old Ink
Period Inks  |  Forty Centuries of Ink  |  Ink Recipes  |  Gallotannin


(2003-10-10)   Traditional Pigments
Chemicals traditionally used as coloring agents in paints, dyes or inks.

Most of these substances are fairly harmless but some of them are too toxic for regular use, by modern standards at least...

 Brazilin At left is  brazilin,  (the expensive dye behind the  lake pigment  used for  red velvet)  from brazilwood,  the tree after which the country of  Brazil  was named.

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)
  •   Brazilin :  Natural Red 24 [video].  C16H14O5 (286.2794 g/mol).
    CAS 474-07-7  (ChemSpider #66104
  •   Turkey Red :  Alizarin C14H8O4 (240.2109 g/mol).  CAS 72-48-0  with a mordant of  (Al2(SO4)3 , H2O).  Used for the British Army's  red coats.
  •   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).

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 one 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.

 Benjamin Collins Brodie, Jr. 
 1817-1880 The wax made by bees is a complex mixture  (of at least 284 distinct 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  MyricinCerin  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).  It's formally called  myricyl palmitate  or  melissyl palmitate  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 as Triacontanyl palmitate  or  Melissyl palmitate  which is the long-chain fatty ester formed by palmitic acid and the long-chain saturated alcohol  variously called  triacontanolmyricyl alcoholmelissyl 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)
The chemistry of Bees  (University of Bristol, School of Chemistry)
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 constituent of  rosin; it's also known as  abietinic acid  or  sylvic acid).  Such products are also found in  tall oil.  The principal compounds so obtained are:

  • Dehydroabietic acid, or DHA  (CAS 1740-19-8)   C20H28O2
  • Abietic acid   C20H30O2   (rosin)
  • Dihydroabietic acid   C20H32O2
  • Tetrahydroabietic acid   C20H34O2

 Dehydroabietic acid  Abietic acid
 Dihydroabietic acid  Tetrahydroabietic acid

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.

 Plicatic acid

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.

 Come back later, we're
 still working on this one...

The Rediscovery and Making of LOST Biblical Cedar Pitch Glue!  (2012-02-14)
Gum Arabic   $55 / lb
How Modern Javelins are Made. 1.2" in diameter. 7.2' shaft / 1.3 lb (Woman's).  8.5' shaft / 1.8 lb (Man's).


(2011-08-02)   Ancient Acids
From vinegar to vitriolic and muriatic acid.

Acetic Acid, Ethanoic Acid, CH3COOH :

This is what gives  vinegar  its acidity.  It results from the oxidation of alcohol in the air, induced by bacteria.

Sulfuric Acid, Vitrolic Acid, Oil of Vitriol, H2SO4 :

Pure  sulfuric acid  (H2SO4 )  is an oily substance formerly known as  oil of vitriol.  The purified form  (which is colorless)  was probably obtained shortly after the introduction of the copper still for alchemical research by  Mary the Jewess  (third century AD).  Vitriolic acid doesn't attack copper.

Sulfuric acid is a dangerous substance with a high boiling point  (337°C)  which makes its distillation very hazardous.  Above a concentration of 80% or so, the vapor contains a substantial amount of acid and is highly toxic.

Without distillation, vitriolic acid can be concentrated by boiling it partially  (which is itself dangerous enough, as previously noted).  As this ancient method also concentrates impurities, it makes the stronger grades of vitriolic acid appear darker and the Sumerians were trading different grades according to their colors...

Spirit of Salt, Muriatic Acid, Hydrochloric Acid, HCl :

Many modern accounts advocate a fairly recent discovery of  muriatic acid  (hydrochloric acid, HCl)  which is plain silly.  Dropping a pinch of ordinary table salt  (NaCl)  into sulfuric acid will evolve a gas with the unmistakable corrosive smell of  HCl  (I just did that with some drain opener labeled CAS 7664-93-9,  just to check how obvious this really is).

H2SO4  +  NaCl2   ®   NaHSO4  +  HCl

Unavoidably, some of the  HCl  remains in the solution, giving it a smell that wasn't there before.  It's impossible that an experimenter of the caliber of  Mary the Jewess  could have missed that with the means at her disposal.

Ferdinand Hoefer (1811-1878)  rightly attributes to her the discovery of  muriatic acid.  This is legitimate in spite of the  usual  fact that the original discoverer could have been some earlier anonymous soul  (with access to vitriolic acid)  who did the same experiment before  Miriam  but didn't follow-up the way she  (undoubtedly)  did.

Acetic acid   |   Vitriolic acid   |   Muriatic acid


 Aurum Solis 
 Gold (Au) (2003-11-01)   Gold Chemistry
Aqua regia, the "Royal Water" which dissolves gold and platinum.

 Acidum Salis 
 Symbol (HCl) Like silver, gold is impervious to strong acids like hydrochloric acid  ( HCl,  formerly called muriatic acid, "marine acid" or "spirit of salt").

 Aqua Fortis 
 Symbol (HNO3)

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 regiaAqua regia is already mentioned in the world's first encyclopedia,  Aqua Regia 
 Symbol  Aqua Regis
 Symbol 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 in the relevant  redox equilibrium.  As this improves with temperature, aqua regia may be used at 100°C or more  (in a bath of boiling salty water).

Gold forms 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 [best] chloroaurate.
 Aurum
 Fulminans

   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 (AuHNNH).

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"  (and at least one "mother").
Here are some popular contenders for the title...

  • Pliny the Elder, Gaius Plinius Secundus  (AD 23-79).
  • Mary the Jewess  (third century AD).
  • Geber, Abu Musa Jabir Ibn Hayyan (c.740-803). Roger BaconSt. Albert the  Great
  • St. Albert the Great, Albertus Magnus  (1205-1280)
  • Roger Bacon (c.1214-1294)
  • Basil Valentine (1394-14??) Robert BoyleParacelsus
  • Paracelsus (1493-1541)
  • Sir Francis Bacon (1561-1626)
  • Robert Boyle (1627-1691) AvogadroLavoisier
  • Antoine Lavoisier (1743-1794)
  • John Dalton (1766-1844)
  • Amedeo Avogadro (1776-1856) BerzeliusHumphry Davy
  • 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

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