Test for zinc
Cobalticyanide paper (Rinnmanns test for Zn) can be used as a chemical indicator for zinc. 4 g of K3Co(CN)6 and 1 g of KClO3 is dissolved on 100 ml of water. Paper is dipped in the solution and dried at 100 °C. One drop of the sample is dropped onto the dry paper and heated. A green disc indicates the presence of zinc. History
Ancient use
The Charaka Samhita, thought to have been written between 300 and 500 AD, mentions a metal which, when oxidized, produces pushpanjan, thought to be zinc oxide. Zinc mines at Zawar, near Udaipur in India, have been active since the Mauryan period (c.  322 and 187 BCE). The smelting of metallic zinc here, however, appears to have begun around the 12th century AD. One estimate is that this location produced an estimated million tonnes of metallic zinc and zinc oxide from the 12th to 16th centuries. Another estimate gives a total production of 60,000 tonnes of metallic zinc over this period. The Rasaratna Samuccaya, written in approximately the 13th century AD, mentions two types of zinc-containing ores: one used for metal extraction and another used for medicinal purposes. Various isolated examples of the use of impure zinc in ancient times have been discovered. Zinc ores were used to make the zinc–copper alloy brass thousands of years prior to the discovery of zinc as a separate element.
Obstruction  may refer to:

Places
Obstruction Island, in Washington state
Obstruction Islands, east of New Guinea

Medicine
Obstructive jaundice
Obstructive sleep apnea
Airway obstruction, a respiratory problem
Recurrent airway obstruction
Bowel obstruction, a blockage of the intestines. Gastric outlet obstruction
Distal intestinal obstruction syndrome
Congenital lacrimal duct obstruction
Bladder outlet obstruction

Politics and law
Obstruction of justice, the crime of interfering with law enforcement
Obstructionism, the practice of deliberately delaying or preventing a process or change, especially in politics
Emergency Workers (Obstruction) Act 2006

Science and mathematics
Obstruction set in forbidden graph characterizations, in the study of graph minors in graph theory
Obstruction theory, in mathematics
Propagation path obstruction
Single Vegetative Obstruction Model

Sports
Obstruction (baseball), when a fielder illegally hinders a baserunner
Obstructing the field

See also
The Five Obstructions, a 2003 film
USS Obstructor, an American minelayer ship used in World War II