Herapathite, or iodo

quinine Quinine is a medication used to treat malaria and babesiosis. This includes the treatment of malaria due to ''Plasmodium falciparum'' that is resistant to chloroquine when artesunate is not available. While sometimes used for nocturnal leg c ...

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

, is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...

whose crystals are

dichroic In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with dispersion), or one in which light rays having different polarizations are ab ...

and thus can be used for polarizing light. It was discovered in 1852 by

William Bird Herapath Dr William Bird Herapath FRS FRSE FRCS (28 February 1820 – 12 October 1868) was an English surgeon and chemist known for his discovery of Herapathite. Life He was born in Bristol, the eldest son of William Herapath, Professor of Chemistry at ...

, a

Bristol Bristol () is a city, ceremonial county and unitary authority in England. Situated on the River Avon, it is bordered by the ceremonial counties of Gloucestershire to the north and Somerset to the south. Bristol is the most populous city in ...

surgeon and chemist. One of his pupils found that adding

iodine Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...

to the

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellular m ...

of a dog that had been fed

produced unusual green crystals. Herapath noticed while studying the crystals under a microscope that they appeared to polarize light. In the 1930s, invented a process to grow single herapathite crystals large enough to be sandwiched between two sheets of glass to create a polarizing filter; these were sold under the Bernotar name by

Carl Zeiss Carl Zeiss (; 11 September 1816 – 3 December 1888) was a German scientific instrument maker, optician and businessman. In 1846 he founded his workshop, which is still in business as Carl Zeiss AG. Zeiss gathered a group of gifted practica ...

. Herapathite can be formed by precipitation by dissolving quinine sulfate in

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...

and adding

iodine tincture Tincture of iodine, iodine tincture, or weak iodine solution is an antiseptic. It is usually 2 to 7% elemental iodine, along with potassium iodide or sodium iodide, dissolved in a mixture of ethanol and water. Tincture solutions are characterized ...

. Herapathite's dichroic properties came to the attention of Sir

David Brewster Sir David Brewster KH PRSE FRS FSA Scot FSSA MICE (11 December 178110 February 1868) was a British scientist, inventor, author, and academic administrator. In science he is principally remembered for his experimental work in physical optics ...

, and were later used by

Edwin H. Land Edwin Herbert Land, ForMemRS, FRPS, Hon.MRI (May 7, 1909 – March 1, 1991) was an Russian-American scientist and inventor, best known as the co-founder of the Polaroid Corporation. He invented inexpensive filters for polarizing light, a ...

in 1929 to construct the first type of

Polaroid Polaroid may refer to: * Polaroid Corporation, an American company known for its instant film and cameras * Polaroid camera, a brand of instant camera formerly produced by Polaroid Corporation * Polaroid film, instant film, and photographs * Polar ...

sheet polarizer. He did this by embedding herapathite crystals in a polymer instead of growing a single large crystal. Structurally, herapathite consists of quinine (in a cationic doubly-

protonated In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid, i ...

ammonium form),

counterions, and

triiodide In chemistry, triiodide usually refers to the triiodide ion, . This anion, one of the polyhalogen ions, is composed of three iodine atoms. It is formed by combining aqueous solutions of iodide salts and iodine. Some salts of the anion have bee ...

units, all as a

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was underst ...

. They combine as 4C₂₀H₂₆N₂O₂•3SO₄•2I₃•6H₂O, or sometimes other ratios and higher

polyiodide The polyiodides are a class of polyhalogen anions composed entirely of iodine atoms. The most common and simplest member is the triiodide ion, . Other known larger polyiodides include 4sup>2−, 5sup>−, 6sup>2−, 7sup>−, 8sup>2−, 9sup ...

References

Further reading