62 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



quality of the iron. The smallness of the crystals, and the 

 height of the pyramids composing each element, are in pro- 

 portion to the quality and density of the metal, which are 

 seen also in the fineness of the surface. As the proportion 

 of the carbon diminishes in the steel, the pyramids have so 

 much the less height. 



In pig-iron, and the lower qualities of hard steel, the crys- 

 tals approach more closely the cubic form. Forged iron has 

 its pyramids flattened and reduced to superposed parallel 

 leaves, whose structure constitutes what is called the nerve 

 of the steel. The best quality of steel has all its crystals 

 disposed in parallel lines, each crystal filling in the interstices 

 between the angles of those adjoining. These crystals have 

 their axes in the direction of the percussion they undergo 

 during the working. Practically, good steel, examined under 

 the microscope, has the appearance of large groups of beau- 

 tiful crystals, similar to the points of needles, all parallel and 

 disposed in the same direction. 8 A, September 1, 168. 



PURIFICATION OF IRON BY SODIUM. 



A method recently suggested for freeing iron from its del- 

 eterious impurities consists in first forming an alloy of the 

 iron with one of the alkaline metals, either sodium or potas- 

 sium, which is done by forcing the vapor of either into a 

 mass of molten iron. To do this with the pure metal would, 

 of course, be inexpedient, on account of the expense; but the 

 same result may, it is said, be obtained by saturating the coal 

 or coke used to reduce the iron with a solution of carbonate 

 of soda, and drying it before it goes into the furnace, or by 

 adding common salt to the fluxing materials. Sodium will, 

 it is asserted, enter into combination with the iron in either 

 case. This, perhaps, is somewhat questionable. The alloy, 

 when prepared, is to be melted, and a current of moist air, or 

 moist carbonic oxide, sent through it. Decomposition en- 

 sues, and the alkaline metal combines readily with any met- 

 alloid, such as silicon, sulphur, or phosphorus, removing them 

 from their mixture, and leaving a pure iron under some cir- 

 cumstances, and pure steel under others. 8 A, July, 129. 



