FUSING AND FREEZING POINTS are terms applied to the temperature at which solids assume the liquid form, and liquids become solid. The following table gives some of the best determinations of the fusing point: Mercury. —39° Alloy (1Sri,2B1). . 286°' Oil of vitriol .. —30° • " (3Sn,2Pb) .. 333° Bromine 9.°5 Tin 451° Oil of turpentine 14° Bismuth 512° Ice ... 32' Nitrate of soda 591° Lard Lead 620° Phosphorus 111.°5 Nitrate of potash 642' Potassium 136° Zinc 773' Yellow wax 143.°6 Antimony (about) 900° Stearic acid............ ..... 158° Silver 1773° Sodium 207.'7 Copper 1996° Fusible metal (5Pb,3Sn,8Bi) 212° Gold 2016° Iodine 226.'4 Cast iron 2786° Sulphur 239° I Wrought iron, higher than 3280° We see from this table that alloys may have a fusing-point far below that of any of the metals which enter into their composition. Similarly, mixtures of various silicates fuse • at a temperature far below that which is required to melt any one of them, and the same remark applies to mixtures of various chlorides, carbonates, etc.
, Most solids, when heated to their fusing-point, change 0 once into perfect liquids; but some—as, for example, platinum, iron, glass, phosphoric acid, the resins, and many others—pass through an intermediate pasty condition before they attain perfect fluidity, and, in these cases, it is difficult, if not impossible, to determine the exact fusing-point.
This intermediate condition is termed vitreous fusion, because it is a characteristic property of glass. It is in this intermediate state that glass is worked, and iron and platinum forged.
As a general rule, the freezing-point is the same as the fusing-point—that is to say, if a substance in the liquid form be cooled below the fusing-point, it again becomes solid; but there are cases in which we can cool a liquid several degrees below its fusing-point; thus, by keeping water perfectly still, we can cool it to 5°, or even to 1°.4 before it freezes. If, however, we drop a solid body into water in this condition, or if we shake the vessel containing it, congealation begins at once, and the temperature rises to 32°. This phenomenon is exhibited to a still greater degree in viscid fluids, like the oils. It is well known that the freezing-point of water is depressed by the presence of salts. Thus, sea-water freezes at about 26°.6, and a saturated solution of common salt must be cooled as low as 4° before freezing. Despretz has given the freezing-points of various saline solutions at different degrees of concentration in the fourth volume of the Comptes Rendus, p. 435.