THE DEVELOPMENT OF MINERALS. 397 



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 pos- 

 sibly 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, 

 w T hich is at a white heat, becomes highly superheated before reaching 

 the charge in the oxidizing chamber. It i3 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 hydro- 

 gen 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 kept on for from eight to ten hours, and then the charge is withdrawn.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, lus- 

 trous 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 sug- 

 gests 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 appli- 

 cable 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 



