Discovery of Bromine
Bromine compounds have been used since ancient times.
In the first century AD Pliny describes one of the world’s first chemical industries: dye factories making Tyrian purple. Tyrian purple (or royal purple) is an ancient purple dye obtained from a marine mollusk. A major component of the dye is the compound 6,6′-dibromoindigo.
Three people are significant in the story of the element bromine’s discovery.
First there’s German chemist Justus von Liebig, one of most famous chemists of his time. Liebig could have been credited with the independent discovery of bromine, but he squandered the opportunity.
In 1825 a salt maker sent Liebig a sample of salt spring waters from the German town of Bad Kreuznach, asking for an analysis.
The sample had a relatively high amount of bromine in it, which Liebig isolated. Without considering the substance too seriously, he concluded it was a compound of iodine and chlorine.
Only when bromine’s existence had been announced did an anguished Liebig return to the red-brown liquid to study it closely.
He then placed the bottle in his ‘mistakes cupboard’ to remind himself that preconceived ideas ruined his chance of discovering something new and to try not to make the same mistake again.
The next name in the story of bromine is Carl Lðwig (Loewig), who discovered bromine in 1825, while still a chemistry student at Heidelberg University, Germany.
Lðwig’s home town was Bad Kreuznach, where Liebig’s sample had come from. Lðwig had taken water from a salt spring in Bad Kreuznach and added chlorine to the liquid. He shook the solution with ether and found a red-brown substance dissolved in the ether. Lðwig evaporated the ether to leave a red-brown liquid: bromine.
His professor at Heidelberg asked Lðwig to prepare more of this substance for testing. By the time Lðwig had done this it was 1826 and a final name – Antoine Balard – had taken over the story of bromine’s discovery.
In 1824 Antoine Balard, aged 21, was studying the plant life in a salt marsh in Montpellier, France. He became interested in salt deposits he saw and began investigating them.
He took brine (sea water in which salts have been concentrated by evaporation of water) and crystallized salt from it. He took the remaining liquid and saturated it with chlorine.
He then distilled the solution to leave a dark red liquid.
Alert to the possibility that he had found something very interesting, Balard gave the French Academy of Science a sealed envelope containing his initial results in 1824.
He finally published his results in 1826, providing evidence that the substance he had discovered was a new ‘simple body’ – i.e. an element, not a compound.
As first to publish, he became bromine’s discoverer. Ironically, like Liebig, his first idea was that the substance was a compound of chlorine and iodine.
The French Academy named the new element after the Greek bromos for ‘stench’ because bromine, quite simply, stinks.
Geber, Jabir ibn Hayyan, born in Persia (Iran) in the 6th Century A.D. Geber systemized and brought experimental methods to alchemy. He believed all metals were based on mercury mixed in different proportions and different purities with sulfur. If the mercury and sulfur were perfectly pure and mixed in perfect proportions, they would form gold.
The periodic table we use today is based on the one devised and published by Dmitri Mendeleev in 1869.
Mendeleev found he could arrange the 65 elements then known in a grid or table so that each element had:
1. A higher atomic weight than the one on its left. For example, magnesium (atomic weight 24.3) is placed to the right of sodium (atomic weight 23.0):
"If all the elements are arranged in the order of their atomic weights, a periodic repetition of properties is obtained. This is expressed by the law of periodicity."
Dmitri Mendeleev, Principles of Chemistry, Vol. 2, 1902, P. F. Collier, p17.
"We have here a proof that there is in the atom a fundamental quantity, which increases by regular steps as one passes from one element to the next. This quantity can only be the charge on the central positive nucleus, of the existence of which we already have definite proof."
Henry Moseley, Philosophical Magazine, Vol. 26, 1913, p1030.
"The chemistry of an atom depends only on the number of electrons, which equals the number of protons and is called the atomic number. Chemistry is simply numbers, an idea Pythagoras would have liked. If you are an atom with one proton, you are hydrogen; two, helium;....."
Carl Sagan, Cosmos, 1980, Random House, p223. Photo: NASA.
Discovery of Mercury
Mercury or quicksilver has been known since ancient times. We do not know who discovered it.
Mercury was known to the ancient Chinese, Egyptians and Hindus and has been found in Egyptian tombs dating back to about 1500 B.C.
In the fourth century B.C. we find Aristotle refers to mercury in writing as ‘hydro-argyros’ – which translates as liquid-silver or water-silver.
The Romans modified the Greek name slightly, referring to mercury as Hydragyrum, from which we get mercury’s modern chemical symbol Hg.
Our modern name for the element was provided by alchemists. Alchemists observed the element’s rapid, liquid flow, and likened it to the fastest moving planet, Mercury. (The planet had been named after the fast moving Roman messenger of the gods, Mercury.)
Alchemists believed mercury was the most important of all substances because it encompassed solid and liquid, earth and heaven, and life and death. They also believed it offered the path by which base metals could become gold and represented the quintessential property of fluidity. They were wrong, of course!
Chinese emperors used mercury to prolong their lives – although in all probability it had the opposite effect. (Despite the fact that mercury is now known to be highly toxic, some traditional Chinese medicines still appear to contain high levels of mercury.)
In 1759 Adam Braun and Mikhail Lomonosov working in St. Petersburg, Russia obtained solid mercury by freezing a mercury thermometer in a mixture of snow and concentrated nitric acid. This provided strong evidence that mercury had properties similar to other metals.
In 1772 and 1774, Swedish scientist Carl W. Scheele and English chemist Joseph Priestley heated mercury oxide and found it yielded a gas that made a candle burn five times faster than normal – they had discovered oxygen.
Priestley discovered several gases, such as nitrous oxide (laughing gas) because he collected them over a bath of mercury instead of the more usual water. Unlike water, the mercury did not dissolve the gases, leaving them available for discovery.
English chemist Humphry Davy used mercury in other discovery work. For example, Davy isolated calcium for the first time, using a mercury electrode to form an amalgam with the calcium
Discovery of Tungsten
In 1779 Irish chemist Peter Woulfe deduced the existence of a new element – tungsten – from his analysis of the mineral wolframite (an iron manganese tungstate mineral).
Tungsten was isolated as tungstic oxide (WO3) in 1781, in Sweden, by Carl W. Scheele from the mineral scheelite (calcium tungstate). However he did not have a suitable furnace to reduce the oxide to the metal.
Tungsten was finally isolated by brothers Fausto and Juan Jose de Elhuyar in 1783, in Spain, by reduction of acidified wolframite with charcoal.
The element name comes from the Swedish words ‘tung sten’ meaning heavy stone.
The chemical symbol, W, comes from the original name of the element, Wolfram.
Discovery of Uranium
In ancient times uranium oxide was used to produce yellow colored ceramic glazes.
Uranium was formally discovered in 1789, in Berlin, Germany by Martin Heinrich Klaproth.
Klaproth was studying the mineral pitchblende, which was then believed to be a zinc/iron ore.
Klaproth dissolved pitchblende in nitric acid, then added potash to obtain a yellow precipitate. Adding excess potash dissolved the yellow precipitate. Such reactions were not characteristic of any known element and Klaproth concluded he had discovered a new element.
He named it after the recently discovered planet Uranus.
In 1841, French chemist Eugene-Melchior Peligot isolated uranium metal by heating uranium tetrachloride with potassium.
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