one hour, as in the Barff process, to be presently described. By thus finishing the operation with steam a more uniform color is obtained, due probably to the oxidation of any protoxide of iron that might possibly have been produced during the last reduction, thus insuring a coating consisting only of magnetic oxide. Wrought-iron or steel, of course, requires no "pickling," as there is no sand to be removed. The furnace is heated to the same temperature as for cast-iron, and then the charge is run in and heated up with a strongly reducing flame until it reaches a bright red. The "gas" is then turned on for twenty minutes, and, when this time has expired, the chimney-damper and gas-valve are both closed tightly, and the steam-valve is opened into the combustion-chamber. The steam, in passing through this chamber, which is at a white heat, becomes highly superheated before reaching the charge in the oxidizing chamber. It is known that sufficient steam is being admitted, by the amount condensed on a cold iron bar held at one of the openings, through which the excess of steam and the hydrogen set free in the reaction escape from the furnace. The steam is kept on for from eight to ten hours, and then the charge is withdrawn. When polished work is to be treated, the furnace is not heated so highly as for wrought-iron, and, just as soon as the charge has been made, the gas is turned on for one hour, then steam is admitted, and the operation goes on the same as for the latter, with this difference, that the temperature in the furnace is kept very low—so low, in fact, that on looking into the furnace the charge is scarcely visible. If too high a heat is used, it causes the coating to scale. The steam is kept on for from eight to ten hours, and the charge is taken out. At first the articles treated are completely covered with soot when they come out, and do not look attractive, but, on rubbing with oil, which is the next step, the soot is removed, and leaves the articles a beautiful, lustrous blue-black.
| THE DEVELOPMENT OF MINERALS. |
By M. J. THOULET,
OF THE SCIENTIFIC FACULTY OF NANCY.
IN a lecture on "The Life of Minerals," which was published about a year ago, I tried to bring out a few principles which seem to assert themselves as each day's work contributes new facts and suggests new thoughts in science, and which seem to give a general direction to the labors of investigators. These principles were, in brief, that all the laws relating to the mineral kingdom are also applicable to the vegetable kingdom, which is, besides, governed by other laws special to it; all the laws of the vegetable kingdom are valid in the animal kingdom, and it has, besides, its own other special laws. One of the results of the progress of science has been gradually to
