Wollaston wire is a very fine (less than .01 mm thick) platinum

Platinum

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...

 wire

Wire

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

 clad in silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 and used in electrical instruments. For most uses, the silver cladding is etched away by acid to expose the platinum core.

History

The wire is named after its inventor, William Hyde Wollaston

William Hyde Wollaston

William Hyde Wollaston FRS was an English chemist and physicist who is famous for discovering two chemical elements and for developing a way to process platinum ore.-Biography:...

, who first produced it in England in the early 19th century. Platinum wire is drawn through successively smaller dies until it is about 0.003 inch (0.0762 mm) in diameter. It is then embedded in the middle of a silver wire having a diameter of about 0.1 inches (2.5 mm). This composite wire is then drawn until the silver wire has a diameter of about 0.002 inch (0.0508 mm), causing the embedded platinum wire to be reduced by the same 50:1 ratio to a final diameter of 6E-05 inch. Removal of the silver coating with an acid

Acid

An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

 bath leaves the fine platinum wire as a product of the process.

Uses

Wollaston wire was used in early radio detector

Detector (radio)

A detector is a device that recovers information of interest contained in a modulated wave. The term dates from the early days of radio when all transmissions were in Morse code, and it was only necessary to detect the presence of a radio wave using a device such as a coherer without necessarily...

s known as electrolytic detector

Electrolytic detector

The electrolytic detector, or the bare-point electrolytic detector as it was also called, was a type of wet demodulator used in early radio receivers. This form of detector was in extensive use between the years 1902 and 1913, after which the superior vacuum tube diode became available...

s and the hot wire barretter

Hot wire barretter

The hot wire barretter was a demodulating detector, invented in 1902 by Reginald Fessenden, that found limited use in early radio receivers. In effect it was a highly sensitive thermoresistor developed to permit the reception of amplitude modulated signals, something that the coherer could not...

. Other uses include suspension of delicate devices, sensing of temperature, and sensitive electrical power measurements.