Thomas Clark (1801–1867) was a

Scottish Scottish usually refers to something of, from, or related to Scotland, including: *Scottish Gaelic, a Celtic Goidelic language of the Indo-European language family native to Scotland *Scottish English *Scottish national identity, the Scottish ide ...

chemist. He became known for the discovery of the phosphate of soda, and the process of

lime softening Lime softening (also known as lime buttering, lime-soda treatment, or Clark's process) is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and magne ...

hard water Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbo ...

the 'Clark process'. A ''Clark degree (°Clark)'' of water hardness is defined as one

grain A grain is a small, hard, dry fruit ( caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legu ...

(64.8 mg) of CaCO₃ per

Imperial gallon The gallon is a unit of volume in imperial units and United States customary units. Three different versions are in current use: *the imperial gallon (imp gal), defined as , which is or was used in the United Kingdom, Ireland, Canada, Austra ...

(4.55 litres) of water, equivalent to 14.254 ppm. and 10^5 parts of water

Life

Clark was born at

Ayr Ayr (; sco, Ayr; gd, Inbhir Àir, "Mouth of the River Ayr") is a town situated on the southwest coast of Scotland. It is the administrative centre of the South Ayrshire council area and the historic county town of Ayrshire. With a population ...

, the son of a shipmaster and a needleworker. He went to school at the Ayr Academy, and then was placed in the counting-house of

Charles Macintosh Charles Macintosh FRS (29 December 1766 – 25 July 1843) was a Scottish chemist and the inventor of the modern waterproof raincoat. The Mackintosh raincoat (the variant spelling is now standard) is named after him. Biography Macintosh was b ...

Glasgow Glasgow ( ; sco, Glesca or ; gd, Glaschu ) is the most populous city in Scotland and the fourth-most populous city in the United Kingdom, as well as being the 27th largest city by population in Europe. In 2020, it had an estimated pop ...

. After a few years he moved to the St. Rollox chemical works. In 1836 Clark became lecturer on chemistry at the Glasgow Mechanics' Institution. To improve his standing in the scientific world, he entered as a candidate for the M.D. degree of Glasgow in 1827, completing his curriculum in 1831; in the interval he became apothecary to the infirmary (1829). In 1833 he was elected professor of chemistry in

Marischal College Marischal College ( ) is a large granite building on Broad Street in the centre of Aberdeen in north-east Scotland, and since 2011 has acted as the headquarters of Aberdeen City Council. However, the building was constructed for and is on long- ...

, Aberdeen, after a competitive examination. He occupied the chair until the fusion of the Marischal College and University with King's College and University in 1860, when he was pensioned; but his career as a teacher had practically come to an end in 1843, due to bad health. He died on 27 November 1867. Clark took a seat in the university court of St. Andrews, as assessor appointed by the rector, John Stuart Mill, who had known him for many years.

Works

Clark wrote pharmaceutical papers in the '' Glasgow Medical Journal'' in the later 1820s. In 1832 he contributed an article to the ''

Westminster Review The ''Westminster Review'' was a quarterly British publication. Established in 1823 as the official organ of the Philosophical Radicals, it was published from 1824 to 1914. James Mill was one of the driving forces behind the liberal journal u ...

'' on weights and measures, and in 1834-5 two articles on the patent laws. In 1836 he discovered

sodium pyrophosphate Tetrasodium pyrophosphate, also called sodium pyrophosphate, tetrasodium phosphate or TSPP, is an inorganic compound with the chemical formula, formula Na4P2O7. As a salt, it is a white, water-soluble solid. It is composed of pyrophosphate anion an ...

. Clark is best known by his

tests and by his process for softening chalk waters. His soap test for hardness, patented in 1841, was quickly taken by the government for waters proposed to be supplied to towns. His other major invention was the process of softening waters rendered hard by the presence of

calcium bicarbonate Calcium bicarbonate, also called calcium hydrogencarbonate, has the chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing calcium (Ca2+), bicarbonate (), and carbonate () ions ...

in solution, a process that Thomas Graham took as exemplary applied science. Although the process was favourably reported on to the government in 1851 by Graham, Miller, and Hoffmann, it was opposed by the metropolitan water companies, and was adopted in only a few places. Clark was also a controversialist and pamphleteer. After he became unable to teach he studied English philology and grammar, and the gospels of the ''

Greek Testament (''The New Testament in Greek'') is a critical edition of the New Testament in its original Koine Greek, forming the basis of most modern Bible translations and biblical criticism. It is also known as the Nestle–Aland edition after its mos ...

''.

References

Attribution: * 1801 births 1867 deaths British chemists {{UK-chemist-stub