CLARK (Thomas). A new process for purifying the Waters supplied to the Metropolis by the existing Water Companies: rendering each water much softer, preventing a Fur Boiling Matter, separating Vegetating and Colouring Matter, destroying numerous Water-Insects, and withdrawing from solution large quantities of Solid Matter, not separable by mere Filtration.1841

London: Published by Richard and John E. Taylor, Red Lion Court, Fleet Street, First Edition, title slightly dusty,15, [1] pp., disbound. In 1841 the author patented his method of water softening ('Clark's process'). This removed what was called temporary hardness (hardness removable by boiling), which is due to the presence of calcium hydrogen carbonate (calcium bicarbonate). On boiling, this is converted to calcium carbonate which is deposited as scale or fur. Clark's method was to effect this precipitation by adding a calculated quantity of slaked lime, after first determining the degree of hardness. He published several works on this process, including A New Process for Purifying the Waters Supplied to the Metropolis (1841), and 'On the examination of water for towns, for its hardness, and for the incrustation it deposits on boiling' (Chemical Gazette). However, though the process was highly praised by Graham and others, it was several years before water companies made much use of it. Goldsmith, 32133.