Fusing-point

Schmelzpunkt, m. melting point, fusing point, -bestimmung,/. melting-point determination, -bestimmungsrohr, n. (or-rdhre,/.), melting-point tube-... 

Gil son it e or Uintoite. A black, brittle, lustrous, bituminous, mineral consisting of solidified hydrocarbons. Found only in the US, namely in, Utah and Colorado. Its sp gr is 1.05 to 1.10 (77°F) hardness (Mohs scale) 2 penetration 0 (77°F) fusing point (B R) 270-370°F. Behavior on heating in flame — softens and flows. It is soluble in carbon disulfide and mixes well with the fatty acid pitches in all proportions. Its numerous uses are listed in Ref 2, p 535-L Accdg to Ellem (Ref 3, p 98), it is a versatile inexpensive fuel and somewhat of a binder and compaction aid. ... 

The density in this cose is therefore greater than that of water, hut still it varies to a certain extent with the temperature at which the substance has been prepared thus the charcoal obtained between the temporaturcs 302" and 515° Ftthr. decreases in density from 1 507 to 1 402 while, on the contrary, that which is afforded between 618 and 602" increases from P402 to 1-600 and from this point the density continues to increase, till, at the fusing point of the vessel, it becomes double that of water. 

Zirconium nitride, Zr3N4. is made by ammoniating the tetrachloride to yield Zr(NlU)4Cl, which yields the nitride on heating. The nitride, like the bonde and carbide, are alloy-like in character, with high fusing points, extreme hardness, and subject to considerable variation in composition. Thus Zr3N4 may vary in composition to ZrN without material change in its properties. 

These phenomena are very sharply produced when the temperature does not exceed a certain limit, near the fusing-point of gold beyond this limit the two oxides exist in contact as a fused mass instead of forming two solid phases, th form but one liquid phase from mono variant the system becomes bivariant at a given temperature there can be no longer any definite dissociation tension. 

Under a given pressure and at a temperature equal to the fusing-point for this pressure, the freezing of a liquid sets heat free. 

For almost all solids whose fusion is accompanied by expansion, the fusing-point rises at the same time as the pressure supported by the system increases for solids, such as ice, whose fusion is accompanied by contraction, the fusing-point is lowered when the presstire increases. 

Application to fusion. Variation of fusing-point with pressure.—J. Thomson was the first to remark, in 1849, that a relation similar in all respects to equation (2) should apply to the curve which represents the variations of the fusing-point of a substance with the pressure. To pass from the preceding to the present case it suffices to substitute the word liquid for vapor and the word solid for liquid by this substitution L becomes the heat of fusion, V the specific volume of the liquid at the point of fusion 0 under the pressure P, 1/ the specific volume of the solid under the same conditions. 

If the specific volume of the liquid exceeds that of the solid (n—1/>0), the curve of fusion rises from left to right very steeply the fusing-point is the higher- as the pressure on the system increases but in order to attain an appreciable rise of the fusing-point, a very considerable increase must be given to the pressure. 

If the specific volume of the solid is greater than that of the liquid (t/—v>0), the curve of fusion rises from right to left with great rapidity the fusing-point is lowered with increase of pressure, but the lowering of the fusing-point is noticeable only with a great increase of pressure. 

This latter case is the same as that of the fusing-point of ice. 

TTo for atmospheric pressure by the fusing-point at the pressure let Afo be the point whose coordinates are do, Xo, and the point of coordinates dp in the right triangle M iMi we have... 

By means of this equation James Thomson showed that for an increase in pressure from 1 to 8.1 atmospheres the fusing-point of ice would be lowered by degrees Fahrenheit very precise experiments made by William Thomson gave a lowering of degrees. 

Almost all substances other than ice increase in volume upon melting for these substances the fusing-point rises with increase of pressure by a very ingenious method Bunsen verified quali tatively this prediction of theory for spermaceti and pan Sne various physicists have extended this verification to a great number of substances. 

Others have gone farther and sought a quantitative confirmation for formula (2) taking this formula as basis, they have calculated the increase that the fusing-point should have for certain substances for an increase of one atmosphere in pressure, and they have compared the number calculated with the number observed the foUowing table shows such a series of comparisons ... 

White solid phosphorus at ordinary temperatures and white liquid phosphorus above its fusing-point are transformed slowly into red solid phosphorus under the action of light at higher temperatures the transformation becomes more and more rapid and takes place even in the dark the inverse transformation of... 

Consider, at a temperature less than Oy a system formed of liquid water and vapor and suppose that the representative point is on the curve Vfi of tensions of saturated vapor from liquid water will the system be in equilibrium No, for the vapor, whose tension is greater than that of saturated vapor from ice at the same temperature, may condense into the form ice the liquid, whose temperature is less than the fusing-point for the same prei ure, may freeze. The system formed of liquid water and vapor is therefore not in equilibrium in the conditions which we have described, or at least, if it may be observed in equilibrium, it is one of those false equilibria to which we have called attention it is throu these false equilibria that we can trace, in certain cases, the line Vfi of tensions of saturated vapor from water in surfusion. 

Systems formed of ice and water it is necessary and sufficient that the representative point be on the branch (indicated by a full line) of the curve of fusing-points. 

A similar treatment may be given to a system where a single substance may exist in the three forms solid, liquid, vapor, and when the fusion is accompanied by an increase in volume. In this case the curve of fusing-points F F (Fig. 50) rises from left to right. 

Iodine, dissolved in liquid chlorine, may give iodine chloride, ICI, capable of being deposited in the solid state this solid chloride may exist in two allotropic forms denoted by the symbols IQa and ICl/j the first form has the fusing-point +27 .2 C., and the second the fusing-point +13 .9 C. Stortenbeker has shown that each of these two temperatures corresponds to an indiifer t point, the one for the solubility curve of Ida in liquid chlorine, the one for the solubility curve of Id in the same solvent. 

The temperature 0 is the fusing-point of a system which contains the two solids a and b at once. 

Guthrie/ who had observed with much care the formation of this solid of invariable composition, had at first regarded it as a definite hydrate for which 0 would be the aqueous fusing-point to this hydrate he gave the name cryohydrate. 

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