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for zinc smelting; but a larger product is obtainedwhen it is raised to the melting point of magneticoxide of iron.
For large operations iron cylinders are used, whichare so arranged that they can be discharged and fedwithout removing them from the furnace, or extin-guishing the fire. The cylinders, made of wroughtiron (t, Fig. 4), are about 4 feet long, 5^ inchesinternal diameter, and half an inch thick. They areopen at one end, 0, and closed at the other end, P,except that this extremity is pierced with a circular
Fig. 4.
Fig. 5.
§!!i
aperture, to which an iron tube, L, is adapted, hav-ing a conical termination for connection with areceiver of the form already described. The openend, 0, is fitted with a wrought-iron cap terminat-ing in a hook. The iron cylinders must be pro-tected from the action of the fire by coating themwitli fire-clay, and inclosing them in tubes of refrac-tory earthenware.
The cylinders are heated in a reverberatory fur-nace, Figs. 4 and 5, the fire-place of which is dividedinto two equal parts by a wall of fire-brick IS inchesVOL. IT.
high, on which the middle of the cylinder rests.The fuel is introduced through it, and heaped on ashelf, M, so as to close the aperture while the pro-cess is going on. A wall, A, reaching a little abovethe cylinder, keeps the flame vertical, and the lowarch, v, causes it to circulate round the cylinders.
The soda mixture is introduced in paper or canvasbags, and the tube is closed by the cap and luted withfireclay. When tho process is finished a little wateris thrown on the cap; this cracks it off, and theresidue of the charge, which is a spongy mass of limeand charcoal mixed with caustic soda, &c., is with-drawn and washed with water to extract the alkali.
Properties. —The colour of sodium is a silverwhite; its lustre is more brilliant than that of lead,but scarcely equals that of silver. At the ordinarytemperature it is solid, but soft and ductile like wax.At —20° C. it is rather hard, at 0° C. very ductile,at 50° C. it is semi-fluid, and at 97'6° perfectly so.Though less fusible than potassium, it is more readilyvolatile, and hence a less intense heat is required inits preparation.. It crystallizes on cooling in oetaliedra.When exposed to the air it quickly becomes tar-nished, owing to the formation of a crust ofsoda; and if heated nearly to redness it inflames,and emits brilliant scintillations. The specificgravity of sodium is 0'97 at 50° C., and it isconsequently lighter than water; and if throwninto this liquid exposed to the air it swims about,presenting the appearance of a silvery-fusedglobule, constantly decreasing in size and pro-ducing a hissing noise, owing to the escape ofhydrogen gas. These phenomena continue untilthe whole is dissolved as soda.
Potassium under the same circumstancestakes fire, and continues to burn until dissolved;but sodium, in decomposing water, either pro-duces less heat or requires a higher tempera-ture to inflame it. If, however, the water bethickened with gum, so as to retard the move-ment of the sodium over the surface, or if there beonly a few drops of water, the metal then ignites.
Sodium dissolves in ammonia gas under pres-sure, forming a blue solution which, if evapor-ated slowly, yields crystals of the metal (Seeley,Chem. News, xxiii. 169).
The alloys of sodium are prepared by fusingit with the respective metals. Potassium andsodium alloy is fluid at ordinary temperatures.It can be prepared by melting the metals to-gether in a tube containing caoutchin (GrevilleWilliams) ; or by heating acetate of potassiumwith sodium (Wanklyn).
Sodium, like potassium, decomposes most oxides,metallic and non-metallic; also by far the greaternumber of salts, deoxidising not only the acid but thebase also, if it happen to be the oxide of a heavy metal.When thrown upon the surface of mercury, sodiumforms an amalgam, with the production of heat andlight; this does not take place with potassium. Sodiumis employed in the arts, principally in the preparationof aluminium, by the decomposition of the chlorideof that metal.
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