Jacobus Petrus van Zyl, agricultural chemist, was the son of Pieter Jacobus Willem van Zyl and his wife Janette, born Malan. He passed the matriculation examination of the University of the Cape of Good Hope in 1906 and continued his studies at Victoria College, Stellenbosch, receiving the BA degree in the natural sciences from the University of the Cape of Good Hope in 1909. He appears to have become a school teacher after graduating, as his address is given as the Public School, Adelaide, Eastern Cape for a number of years, until 1917. However, he went to Germany for further studies at the Georg-August-Universität zu Göttingen, probably before the outbreak of World War I (1914-1918). In 1916 he qualified as Dr. Phil. with a thesis entitled Über die Bodenlössung: ihre Gewinnung, Zusammensetzung und Anwendung bei der Schlämmanalyse (1916, 79p). In the thesis the author is said to be from Robertson, Western Cape. He returned to South Africa (probably only after the conclusion of the war) and joined the staff of the Division of Chemistry of the Department of Agriculture. The division's activities were so diverse, rendering service to many government departments and other clients, that its name was changed to the Division of Chemical Services in February 1935. The next year van Zyl was appointed as director of the division, succeeding St C. O. Sinclair*. He held this position until 1950. During World War II (1939-1945) most of the division's agricultural research was replaced by war-related work, which claimed all attention and finances available.
Van Zyl spent some of his time on laboratory work connected with the soil survey, the adaptation of methods for the chemical and mechanical analysis of soils and the salinity control of soils, and published papers on "Phosphorus deficiency in South African soils and vegetation" (South African Journal of Science, 1926) and "Variation of phosphoric oxide content of South African vegetation" (Journal of the South African Chemical Institute, 1928). He also undertook research at the Veterinary Research Institute at Onderstepoort (and was listed as a research officer at that institution) to investigate mineral deficiencies in soils and plants and develop analytical methods of use to veterinary science . This work was published in the annual Report of the Director of Veterinary Research and dealt with the composition of various samples of sodium arsenate, the determination of arsenic in dip washes and the oxidation of arsenical dipping tanks (9th and 10th Report, 1924), the decomposition of diluted polysulphide (11th and 12th Report, 1926), soil conditions related to lamsiekte and styfsiekte (13th and 14th Report, 1928) and the toxicity of arsenic to fowls (15th Report, 1929). During 1928-1936 he also wrote about ten reports dealing mainly with his investigations of the soils of various irrigation projects. In later years his reports dealt mainly with the work of the institute as a whole and were often published in Farming in South Africa.
Van Zyl became a member of the South African Chemical Institute in 1927 and was still listed as a member in 1958. He was a member of its council during 1931-1933 and 1936-1939, served as vice-president during 1939-1941, and as president during 1941-1942. He was married to Jacoba Johanna Potgieter.
