CLARK, THOMAS (1801–1867), Scottish chemist, was born at Ayr on the 31st of March 1801. In 1826 he was appointed lecturer on chemistry at the Glasgow mechanics’ institute, and in 1831 he took the degree of M.D. at the university of that city. Two years later he became professor of chemistry in Marischal College, Aberdeen, but was obliged to give up the duties of that position in 1844 through ill-health, though nominally he remained professor till 1860. His name is chiefly known in connexion with his process for softening hard waters, and his water tests, patented in 1841. The last twenty years before his death at Glasgow on the 27th of November 1867 were occupied with the study of the historical origin of the Gospels.