Put a lump of zinc into the boiler of a steam-engine, and it will prevent the formation of ‘scale;’ that is, the stony crust which, as all engineers know to their sorrow, is very injurious and involves constant expenditure. The experiment having been successfully tried during four years by certain manufacturers in France, the Minister of Public Works appointed a Commission to inquire into and report upon it. From their Report, which was published last year in the _Annales des Mines_, we learn that the zinc is to be placed in the boiler as far as possible from the furnace, the quantity being a quarter-pound for every five square feet of boiler-surface if the water be soft, and a half pound if the water be hard. The boiler is then worked in the usual way; and when opened for the usual cleaning the appearances as the Commission describe will be—‘If the water be but slightly calcareous, the deposits, instead of forming solid and adherent scale, are found in a state of fluid mud, which is easily removable by simple washing. The iron being clean and free from rust, no picking or scraping is needed, whereby an important saving of time and labour is effected.’ On the other hand, if the water be strongly calcareous or hard, ‘the deposits are as coherent and strong as though the zinc had not been employed; but this strong coat does not stick to the iron. It can be pulled off by hand, or at the worst detached without much effort, leaving the iron clean. A simple washing clears it from the boiler; and in this case, as in the foregoing, picking and scraping are avoided.’ Here the question arises—What has become of the zinc? The answer given is, that it is not strictly correct to say it has disappeared, for it has been transformed into oxide of zinc, a white and earthy substance, which often preserves the lamellar texture of the metal, the central part sometimes continuing metallic and unattacked. At the same time it is worth remark that no trace of dissolved zinc is found in the water taken from the boilers.