On the spontaneous purification of Thames water

Abstract

In the report which the author made of the result of his exami­nation of Thames water to the Commissioners appointed by His Ma­jesty to inquire into the supply of water in the metropolis, one of the specimens, taken near the King’s Scholars’ pond-sewer, was de­scribed as in a state of extreme impurity. The water had remained in the laboratory unattended to ; but after an interval of some weeks it was observed to have become clear, while nearly the whole of the former sediment had risen to the surface, forming a stratum of half an inch in thickness, and still emitting a very offensive odour. In process of time this scum separated into large masses or flakes, with minute air-bubbles attached to them. At the end of two months longer these masses again subsided, leaving the fluid almost totally free from any visible extraneous matter. On analysis the water was found to contain lime, sulphuric and muriatic acids, and magnesia, in much larger quantities than in the specimens of Thames water previously examined, the proportion of saline matter being increased four-fold. The proportion of the muriates is nearly twelve times greater; that of carbonate of lime between two and three times, and that of sulphate of lime five and a half times greater. The water in its foul state had given very obvious indications of both sulphur and ammonia; but neither of these substances could be detected after its spontaneous depuration. The source of these new saline bodies is referrible to the organic substances, chiefly of an animal nature, which are so copiously deposited in the Thames. The depurating process may be denomi­nated a species of fermentation, in which the softer and more soluble animal compounds act as the ferment, and are themselves destroyed, while the salts that were attached to them are left behind. Hence, the more foul the water the more complete the depuration ; and it is on this principle that the popular opinion of the peculiar fitness of Thames water for being used at sea may be explained ; its extreme impurity inducing a sufficient degree of fermentation to effect the re­moval of all those substances which might induce any future renewal of that process.