(2011-08-07) A modern convention that helps put chemical history in perspective.
In chemical equations, a symbol or a formula for a substance is always understoodto denote a definite quantity of it (measured by weight) technically called a mole of that substance (symbol: mol ). Thus, whena 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 speciesis normally made of identical units (molecules, ions, etc.). A mole is merely a particularnumber of those things (as many of them as there areatoms in 12 g of carbon, when only thedominant isotope is present). The number of things per mole of stuff is a huge constant,called Avogadro's number, known to 7 decimal places:
Na = 6.022141 10 23/ mol
Nevertheless, the convention of using moles uniformly forall chemical substances doesn't strictly depend on the underlying conceptof atoms and molecules. It was already made legitimate by the prior law of definiteproportions (Proust's Law) formulated by theFrenchmanJoseph 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 twoconstant 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 aslinear combinations of the pure chemicals theyconsist of. For example, a mole of dry air at sea-level isapproximately 0.78 N2 + 0.21 O2 + 0.01 Ar or, more precisely:
0.7808 N2 + 0.2094 O2 + 0.0094 Ar + 0.0004 CO2
Incidentally, this gives the often-quoted molar weight of air (29 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 equal volumes oftwo different gases contain approximately equal numbers 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 fromits weight composition (or vice-versa).
Molar weights were the key to the finalclassification of the chemical elementspresented 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 individualatoms that compose it.
The modern notion of a chemical element was first proposed,on empirical grounds,byRobert Boyle in 1661. A chemical element is a species that cannot be obtained by combiningother chemicals.
The system of chemical symbols we currently use torepresent every element was devised byJacob 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...
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 byErnest Rutherford in 1911 (to explain the results of the notorious GoldFoil Experiment of 1909). More precisely, each element is identified by aunique integer called its atomic number which is usuallydenoted by the capitalized letter Z (initial of theGerman word Zahl for number ). The number Z corresponds to the number of elementary positivecharges (one such charge per proton) cointained in everyatomic 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 theymay contain different numbers of neutrons (a neutron has a mass nearly equal to that of a proton but noelectric charge at all). The total number of nucleons (i.e., protons and neutrons) in a nucleus is calledits mass number and is usually denoted bythe letter A. Nuclei that have the same value of Z but different values of A are said to be different isotopes of thesame element.
Isotopes have virtually identical chemical properties, except possibly forthe lightest elements (e.g., the different masses of protium and deuterium,the two stable isotopes of hydrogen, yield measurablydifferentionization potentials). Most elements below Uranium (Z = 92) have several stableor very long-lived isotopes. Some have only one, some have none.
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 contains only the two stable carbon isotopes: Nearly 99% of Carbon-12 (6 protons and 6 neutrons, whichserves for theabove modern definition ofthe mole) and 1% of Carbon-13 (6 protons, 7 neutrons). On the other hand, new carbon in living organismsis 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 (eitherdirectly by photosynthesis or indirectly by consumingcarbon compounds from other living organisms). Radiocarbon is constantly formedcosmogenicallyby 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 directlyon its age, defined as the time elapsed since thecreature 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 thatall traces of radiocarbon have long disappeared.
This modern view of chemical elements has replaced the antiquated doctrine of thefour 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 bothalchemy and chemistry for two millenia.
(2011-07-18) (3rd century AD) Purification by evaporation and condensation.
According to Egyptian mythology, Alchemy was founded by the goddessIsis. As Alchemy seemed similar to cooking, it wasonce 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 onrecord 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 alegendary nameas a pseudonym, signing Miriam the Prophetess, sister of Moses (amusingly, thiscaused 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.
Miriam devised the first true distillation apparatus by lettingthe vapor escape in pipes through a modified lid which is now calleda still-head (the learned term is alembic which is the Arabic namedenoting 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.
Fire, heater, oven.
Boiler, cucurbit, still.
Still-head, alembic.
Condenser.
Receiver.
If the condenser operates normally, the apparatus works at constant volume(no vapor escapes). Arguably, this key innovation marks the beginning of the slow transitionfrom ancient alchemy to modern chemistry.
(2011-07-19) (8th century AD) More than a simplified alembic.
Around 750 AD,Geber invented a simplifieddistillation 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 mostrecognizable symbols for alchemy or chemistry.
Although no longer as popular as it once was, this device remainsa great choice for crude high-temperature distillationor as a reaction vessel for chemical reactions where a gas is evolved.
(2011-07-18) 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 themto kill common bacteria and viruses before they infected the drinker. (In the Orient, the tradition of boiling water to make tea hadsimilar benefits.)
Even sour wine (vinegar) is fairly safe, because ofthe 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 thatmay or may not have been welcome... However, with only weak alcoholicbeverages available, those who sought that inebriation could not achieve itwithout consuming relatively large quantities of liquid fairly rapidly...
At a concentration of about 14% (by volume) alcohol inhibitsthe very enzymes (Zymase) that catalyze its production byanaerobic fermentation:
Under normal atmospheric pressure, ethanol (aqua vitae, C2H5OH) cannot be separated from water by distillation alone, because a mixture of95.629%alcohol and 4.371% water (by weight) actually forms what's called an azeotrope (a mixture whose vaporretains the same composition as the liquid). As the boiling point of that ethanol-water azeotrope (78.1°C) 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 alcoholby weight (unless the liquid itself was stronger than that to begin with).
The 190-proof grain alcoholEverclear made theGuinness Book of World Records in 1979as the World's most alcoholic beverage. Other brands ofneutral grain spiritsnow include Golden Grain, Gem Clear and Spirytus (rectified spiritfrom the former Polish state monopoly Polmos).
Some of those brands (includingEverclear) are alsosold in lesser grades, because full-strength rectified spirits cannotlegally be sold in several countries or states, including California. Typically, they are downgradedto 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 pressurecannot 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's possible to obtain nearly pure alcohol byvacuum distillations (other chemical methods are used industrially to produce water-free alcohol).
(2003-10-08) What is the composition ofblack powder ?
The French call it eitherpoudre à canon (gunpowder)orpoudre noire (blackpowder). The loose powder was calledserpentine. The nameblack powder is of relatively recent origin,as it appearedonly after other explosives were devised which lacked theblack luster of free carbon. Obviously, the stuff wasn't calledgunpowderbefore thegun was invented, around 1313.
Black powder was the first explosive ever devised,and it remained the only one for centuries. It is composed of the following threesolid ingredients:
Saltpeter: KNO3niter(or, more rarely, NaNO3Chilean 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 inferiormeal powder... To obtain what's now consideredproper black powder,the ingedients must be "incorporated" in adamp state. This allows the application of great pressure to form a dense cake,ultimately broken down into drygrains. This process is calledcorning,and it was first introduced in France in 1429.
Early forms ofblackpowder may have existed in China aroundAD 700, using crude recipes calling for equal weights of the three components... Such mixtures would only burn violentlywithout exploding... Also, explosion cannot occur if rawsaltpeter is used,and the refining of saltpeter is not mentioned before 1240 in a book onmilitarytechnology by the Syrian scholarHassan Al-Rammah, entitledal-furusiyya wa al-manasib al-harbiyya. The first Chinese author to describe an explosive formula was apparentlyHuo 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:
The Latin version of the pamphlet didn't appear until 1280 or 1300 and it maywell have been created at that time, although it was claimed to bean expanded translation by Spaniards of a more ancient Arabic text(dated AD 848)and/or a Greek version that didnot include the last four formulas.
Roger Bacon (c.1214-1292)investigatedblack powder before 1249, whenhe devised the recipe he communicated in 1268: 40% moresaltpeter thaneithersulphur or carbon (7:5:5 formula by weight). However, the first unmistakableblackpowder explosive compositionis 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 moderngunpowder composition seems to datefrom around 1800 and calls for 75% saltpeter (niter)oxidizer, with10% 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 followingsimplifiedreaction would correspond to about74.8% niter, 11.9% sulphur and 13.3% carbon (roughly 101:16:18):
2 KNO3 + 3 C + S + 3 CO2 + N2 + 572 kJ (505.8 cal/g)
The solid residue forms a thickwhite 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 ofblack powder would suffice (sulfur prevents wasteful carbonate production).
Newer propellants leave little or no solid residue when properly exploded. They are thus collectively known assmokeless powders. Thesimplest ideafor a smokelessdark powder is calledammonpulver (AP) and involvesammonium nitrate (AN) with 10% to 20% charcoal,although the stoichiometry of the following reactions translates into only7% 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 interestinclude the following propellants:
Guncotton,ornitrocellulose (also known as pyropowder, pyrocellulose,trinitrocellulose and cellulose nitrate) invented in 1845by the Swiss chemist Christian Schönbein (1799-1869).
Poudre B (flakes of nitrocellulose gelatinized with ether and alcohol)invented in 1884 byPaul Vieille (1854-1934; X1873)for the 1886Lebel rifle.
Ballistite(nitrocellulose & nitroglycerin, with diphenylamine stabilizer)invented in 1887 by Alfred Nobel (1833-1896).
(2003-11-14) How do we tell what a given initial composition will produce?
This may be tough, since the result of a chemical reaction isalways an equilibrium containing everything thatcould be produced(possibly only in minute quantities). However, for reactions involving chemical explosives, a decentruleof thumb is to use the following hierarchy of fictitious reactions and consider thateach occurs only when the previous ones have been completedto the fullest possible extent:
Metal + Oxygen
Oxide
C + O
2H + O
H2O
+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.
(2008-03-22) Thermite brings about thermal destruction chemically.
Thermite is a mix ofrustand powderedaluminumwhich can be ignited with a strip of magnesium to producealumina andiron. This popular reaction is ableto 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 gof aluminum. An excess of aluminum helps preventthe formation of hercynite (FeAl2O4 ).
The usual recipe calls for 8 grams of iron oxide for3 grams of aluminum.
This is the most popular special case of what's known as a Goldschmidtreaction (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 andglycol or by a burning ribbonof magnesium. When the difference in the reactivities of the two metalsis 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
(2003-10-09) How do we compute theenergy balance of a chemical reaction?
Theenthalpyof formation (H) of a chemicalcompound isroughlythe energyrequired to make it from its constituents[in theirstandard forms, as gases, liquids, or crystals]. Oncetabulated,this data can be used to work out the energy balancein a reaction involving such compounds.
Enthalpies of Formation ( H f < 0 for exothermic formation )
Substance (normalized to 298.15 K, 1 atm) s = solid, l = liquid, g = gas, d = dissolved
For example, the energy released in the combustion of CO isthe difference between the enthalpies offormation 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 liquidnitroglycerinin the following reaction:
Of particular theoretical and historical interest is the so-called heat of neutralization evolved in the aqueous neutralization of astrong acid and a strong base (e.g., HCl and NaOH). Remarkably, it doesn't depend on the natureof 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 equilibriumwhere 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 basedon that critical equilibrium and the disturbances caused to it by other reactionsthat involve either of the two relevant ions.
(2011-06-21) The crystallization of sodium acetate trihydrate is exothermic.
Here's the crystallization reaction for thehot icefound in the reusablePCMheating pads that have been widely available since 1978 (136.0796 g/mol).
Na+ + CH3COO + 3 H2O (NaCH3COO, 3H2O) + 38 kJ
The data from theabove 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 andsome 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 itinto a very warm solid object (which can later be returned to it metastableliquid form by heating the pouch in boiling wateruntil all traces of the crystals have disappeared).
(2007-11-21) The sign of G indicates thermodynamic stability.
A thermodynamically stable compound is indicated by a negative free energyof formation Gf
The change in entropy S 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 inthe entropy (disorder) which actually makes G negative, so the reaction is indeeda spontaneous one.
H and G are normally given in kilojoules (kJ) per mole, whereas S is usually given in unitsof 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 appliedin actual computations.
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 dissociatein substitution reactions in strict accordance to theso-called affinities ofpairs of chemical species for each other. This was thought to occur essentially to the fullest possible extent,regardless of the respective concentrations of the reactants involved.
(2007-11-21) Kinetics can make a compound not labile in spite of unstability.
Benzene is one compound which is unstable according to itsfree energy balance. Yet, the kinetics involved make the spontaneous decomposition ofbenzene into hydrogen and graphite so slow that it'snever 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) What is the composition of traditionalinks ?
Natural Ink
Sepia is the most lasting of natural inks, but it's not lightfast. It is a dark brown liquidconsisting of concentratedmelanin,secreted by Mediterraneancuttlefish and other cephalopods(it's stored inink sacs and ejected to confuse attackers).
India Ink (Chinese Ink)
As early as 2500 BC, writing inks werecarbon inksconsisting of fine grains of carbon black [from soot]suspended in a liquid. The Latin name for this wasatramentum librarium and it's now calledIndia ink orChinese ink. On the famousDead Sea Scrolls of Qumran(from the third century BC to AD 68),a red version of this ink is found which usescinnabar (HgS) instead of carbon. The idea is simple: When the liquid dries out, the solid pigment (C or HgS) remains whichleaves 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 ofcarbon black would aggregate under the action ofVan der Waals forces and formflakeslarge enough to fall quickly to the bottom of the container. Thisflocculation process can be prevented with an hydrophilic additivewhich minimizes Van der Waals interactions between the grainsby coating them (as was properly explained only in the 1980s). Early ink recipes may thus have called for variousplant juicesinstead of plain water. It turns out thatgum arabic acts this way to stabilizeIndia ink into acolloidal 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 neededby grinding aninkstick on aninkstone after adding a littlewater (theinkstone also acts as aninkwell). Chinese ink-sticks consist of apigment (usually soot from pine,oil or lacquer) and a solubleresin which holds the dry stick togetherand 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 Japanesename (Sumi ink) whereas bottled Chinese ink is called India ink. However, bottled Sumi ink is also available with features that some artistsswear by (seevideo review byweb comics artistBryan Christopher Moss).
Iron-Gall Ink, Indelible Ink,Encaustum
In the first century AD,Pliny the Elderdescribed a basic chemical demonstrationof 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 asan established writing ink around AD 420,in the encyclopedia of the 7 liberal arts by Martianus Capella. However, the latest analyses havedisproved dubious reports that this type of ink mighthave already been used on the famousDead 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 Greekenkauston, meaningpainted 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)...
Indelibleiron-gall ink is considered the most important ink in the developmentof Western civilization, up until the 20th century. The bestiron-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 ofmore sophisticated recipes with lesser chemical aggressivity.
Iron-gall ink normally includes what is effectively a"Chinese ink" component, which provides both body (fromgum arabic)and some initial coloring upon application of the ink. Otherwise, the main pigmentation of iron-gall ink comes paradoxically fromwater-solubleferrous 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 parchmentcollagen or papercellulose, in a totally indelible way. Some poorly balanced iron-gall inks have even been observed toburn holesthrough paper.
It has beenshownthat an excess of ferrous salt in iron-gall inkleaves permanent traces of active soluble salts(not properly oxidized into inert pigments) which will catalyzethe 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,theNetherlands Institute of Cultural Heritage (ICN) has introduced an interestingtreatment,which was first used on a large scale by the conservators of theNationaal 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 withcalcium bicarbonate,which creates an alkaline buffer and also leaves a phytate precipitate in the fibers,for continued oxidation protection.
Gum Arabic: True gum Arabic is exuded by theacaciasenegal 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 fromSudan.
The related products ofother trees of theAcacia 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 calledacacia 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 calledacacia.[info]CAS 9000-01-5: Gum acacia;Arabic gum oracacia 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 askankatum, greenvitriol orcopperas. (FeSO4, 7 H2O) iron sulphatein hydrated crystal form (278.01 g/mol).
Tannin: Tannic(orgallotannic) acid,extracted by water-saturated ether from crushed gallnuts ( galls,nutgalls, orgall apples ). It is an anhydrid ofgallic acid (next): COOH.C6H2(OH)2O.COC6H2(OH)3
Gallic acid: Produced (withglucose)by the hydrolysis oftannin in acid.Used incalotypephotography. C6(COOH)H(OH)3H (170.12 g/mol)
(2003-10-10) Chemicals traditionally used as coloring agents in paints, dyes orinks.
Most of these substances are fairly harmless butsome of them are too toxic for regular use, by modern standards at least...
At left is brazilin, (the expensivedye behind the lake pigment used for red velvet) frombrazilwood, the tree after which the country of Brazil was named.
Pigments:
Carbon Black : Lampblack, from soot. C (12.01 g/mol)
Manganese dioxide. MnO2 (86.937 g/mol)
Calledvermillion, or Chinese red. HgS (232.66 g/mol)
Lazurite (sodium aluminum silicate)not "lazulite".[supplier](Na,Ca) 8 (AlSiO4)6(S, SO4, Cl 2) especially: Na 8(AlSiO4)6 S.
Ferric ferrocyanide. Ferric hexacyanoferrate.Fe4[Fe (CN)6] 3 A chelating agent insoluble in water (Diesbach, 1704).
(2010-10-16) Waxes are long-chained esters, like myricin : C15H31COOC30H61
Crudebeeswax (raw beeswax) is secreted by young female worker bees (6 to 18 days old) from eight wax glands located on the inner sides of theirsternites, 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. Beekeeperswill typically harvest one pound of beeswax for 10 pounds of honey.
Refined natural beeswax has a deep gold color. It's available asyellow 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 usingnitric or chromic acid (traditional bleaching involved exposing for weeks thin slices of beeswaxto moist air and sunlight, next to the hives, possiblyremelting several times). White beeswax is cream-colored.
The wax made by bees is a complex mixture (of at least 284 distinct compounds) whose compositionvaries substantially from one batch to the next. In 1848,Sir Benjamin CollinsBrodie,Jr. (1817-1880) separated beeswax by means of alcohol into three mainconstituents, 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). It's formallycalledmyricyl 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% ofCerolein (dissolved by coldalcohol or ether) which melts at 23°C. It is cerolein which gives beeswax most of its odor and color.
Pure myricin is identified asTriacontanyl palmitate or Melissyl palmitate which is the long-chain fattyesterformed by palmitic acid and thelong-chain saturated alcohol variously called triacontanol, myricyl alcohol, melissyl alcohol or melissin.
Chinese wax (ceryl cerotate) is a wax-ester: C25H51COOC26H53
(2010-10-18)
Pine tar pitch can be obtained bydry distillationof resinous wood. It's a mixture ofresin 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
Also involved is pimaric acid, a close relativeof 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.
(2010-10-11) The magic bullet of ancient chemistry is not just for candy or ink.
Jerome A. Samounce is a minister in North Carolinawho tries to bring scripture to life by reproducing Biblical artefacts using ancient technology. On 2010-01-06, he approached me with a few technical questionsabout his latest project: Reproducing an authentic 3-cubit Judean javelin from theDavidic Dynasty...
The shaft of such a javelin was made ofash wood (finished withlinseedoil) 1" thick inthe 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 cedarpitch". Jerome had also found that archeological reports consistently mentiontwo other ingredients besides cedar or pine pitch: Beeswax and ground ash powder. (the presence of some inert powder should come as no surpriseto whoever has ever tried to optimize the mechanical properties ofthick 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 startwith 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 subsequentbackyard experimentsperformed byJerome Samounce et al (seefullreport).
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 themix 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.
(2011-08-02) 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 afterthe introduction of the copperstill 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 substantialamount 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 strongergrades of vitriolic acid appear darker and the Sumerians were tradingdifferent 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 willevolve a gas with the unmistakable corrosive smell of HCl (I just did that with some drain opener labeledCAS 7664-93-9, just to check how obvious this really is).
H2SO4 + NaCl 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.
(2003-11-01) Aqua regia, the "Royal Water" which dissolves gold and platinum.
Like silver,gold is impervious to strong acids like hydrochloric acid (formerly calledmuriatic acid, "marine acid" or "spirit of salt").
Unlike silver, goldcannot be oxidized by nitric acid (aqua fortis)...
However, early alchemists did discover that a mixture of nitricandhydrochloric acids was able to dissolve gold, the so-calledroyal metal. They dubbed the potent mixture "Royal Water",aqua regis oraqua regia. Aqua regia is already mentioned in the world'sfirstencyclopedia,published in AD 77 byPliny the Elder(AD 23-79).
The alchemical works of Ramon Llull (c.1232-1316)contain prominently the traditional preparations of aqua fortis (nitric acid) and aqua regia.
Aqua regia is a mixture of at least 3 moles ofhydrochloric acid per mole of nitric acid(too much hydrochloric acid is better than too little). It's used hot and concentrated for best efficiency. Aqua regia is also calledchloroazotic,chloronitric,nitromuriatic, ornitrohydrochloric 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 nitricacid would only result in aminute concentration of auric cations[Au], but inaqua regiathe concentration of auric ions is constantly depleted becauseauric cations combine quickly with chlorine anions to form complexchloroaurate ions:
Au+++ + 4 Cl AuCl4
Thespeed of the overall reaction is limited by the [Au+++ ]concentration in the relevant redox equilibrium. As this improves with temperature,aqua regia may be usedat 100°C or more (in a bath of boilingsalty water).
A more exotic compound (interhalogen compound) which readily dissolves gold byforming gold trichoride is iodine monochloride (ICl).
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 forany of the above!
CAS 13967-50-5: Potassium dicyanoaurate K[Au(CN)2].
Rheumatoid arthritis medicine:
CAS 15189-51-2: Sodium aurichloride (NaAuCl4, 2 H2O).
The combination ofgold trichloride with the chloride ofanother metal is called anaurochloride,aurichloride,chloraurate or [best]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 WillisandRobert Hooke demonstratedthat a powder of gold hydrazide explodes on a mere concussion,without the need for air or sparks (which were once thought to be requiredfor any kind of ignition).
Gold hydrazide (also known asaurodiamine) is a water-soluble substanceobtained by letting an ammoniacal solution react with anauric hydroxide precipitate(itself obtained from a gold solution prepared withaqua regia). Gold hydrazide has a dirty olive-green color (AuHNNH2 ).
Gold hydrazide is apparently only one of several explosive compounds which have been calledfulminating gold (aurum fulminans). Around 1603, another kind offulminating gold ("Goldkalck" or "Gold Calx")was described as the precipitate of gold by potassium carbonate.
In spite of its price,fulminating gold is said to have been used militarily in 1628.The discovery offulminating gold has been attributed to the legendaryalchemist Basil Valentine(Basilius Valentinus) a benedictine monk born in 1394 whosepersona was also used by other early chemists, possibly including Johann Thölde (c.1565-1624). His main work (The Twelve Keys of Basil Valentine) was first published in 1599. Basil Valentine has been regardedas the father of modern chemistry (seenext section).
(2003-12-03) 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...
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 ofRelativity Theorythat this fundamental conservation law would be proved to be only a firstapproximation, albeit an excellent one: Unlike what happens in nuclear reactions,the relative variation of mass involved in chemical reactions is so minutethat it can't be measured directly.
Willard Libby came to Princetonwith a little jar of crystals ofbarium xenate.
(2003-10-10) 
