<P> The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid at atmospheric pressure . At the melting point the solid and liquid phase exist in equilibrium . The melting point of a substance depends on pressure and is usually specified at standard pressure . When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point . Because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance . When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point . </P> <P> For most substances, melting and freezing points are approximately equal . For example, the melting point and freezing point of mercury is 234.32 kelvins (− 38.83 ° C or − 37.89 ° F). However, certain substances possess differing solid - liquid transition temperatures . For example, agar melts at 85 ° C (185 ° F) and solidifies from 31 ° C (88 ° F; 304 K); such direction dependence is known as hysteresis . The melting point of ice at 1 atmosphere of pressure is very close to 0 ° C (32 ° F; 273 K); this is also known as the ice point . In the presence of nucleating substances, the freezing point of water is not always the same as the melting point . In the absence of nucleators water can exist as a supercool ed liquid down to − 48.3 ° C (− 55 ° F, 224.8 K) before freezing . The chemical element with the highest melting point is tungsten, at 3,414 ° C (6,177 ° F; 3,687 K); this property makes tungsten excellent for use as filaments in light bulbs . The often - cited carbon does not melt at ambient pressure but sublimes at about 3,726.85 ° C (6,740.33 ° F; 4,000.00 K); a liquid phase only exists above pressures of 10 MPa (99 atm) and estimated 4,030--4,430 ° C (7,290--8,010 ° F; 4,300--4,700 K) (see carbon phase diagram). Tantalum hafnium carbide (Ta HfC) is a refractory compound with a very high melting point of 4215 K (3942 ° C, 7128 ° F). At the other end of the scale, helium does not freeze at all at normal pressure even at temperatures close to absolute zero; pressure greater than twenty times of atmosphere of normal one is necessary . </P> <Table> <Tr> <Th_colspan="4"> hide List of common chemicals </Th> </Tr> <Tr> <Th> Chemical </Th> <Th> Density (g / cm) </Th> <Th> Melt (K) </Th> <Th> Boil (K) </Th> </Tr> <Tr> <Td> Water @ STP </Td> <Td> </Td> <Td> 273 </Td> <Td> 373 </Td> </Tr> <Tr> <Td> Solder (Pb60Sn40) </Td> <Td> </Td> <Td> 456 </Td> <Td> </Td> </Tr> <Tr> <Td> Cocoa butter </Td> <Td> </Td> <Td> 307.2 </Td> <Td> - </Td> </Tr> <Tr> <Td> Paraffin wax </Td> <Td> 0.9 </Td> <Td> 310 </Td> <Td> 643 </Td> </Tr> <Tr> <Td> Hydrogen </Td> <Td> 0.00008988 </Td> <Td> 14.01 </Td> <Td> 20.28 </Td> </Tr> <Tr> <Td> Helium </Td> <Td> 0.0001785 </Td> <Td>--</Td> <Td> 4.22 </Td> </Tr> <Tr> <Td> Beryllium </Td> <Td> 1.85 </Td> <Td> 1560 </Td> <Td> 2742 </Td> </Tr> <Tr> <Td> Carbon </Td> <Td> 2.267 </Td> <Td> 3800 </Td> <Td> 4300 </Td> </Tr> <Tr> <Td> Nitrogen </Td> <Td> 0.0012506 </Td> <Td> 63.15 </Td> <Td> 77.36 </Td> </Tr> <Tr> <Td> Oxygen </Td> <Td> 0.001429 </Td> <Td> 54.36 </Td> <Td> 90.20 </Td> </Tr> <Tr> <Td> Sodium </Td> <Td> 0.971 </Td> <Td> 370.87 </Td> <Td> 1156 </Td> </Tr> <Tr> <Td> Magnesium </Td> <Td> 1.738 </Td> <Td> 923 </Td> <Td> 1363 </Td> </Tr> <Tr> <Td> Aluminium </Td> <Td> 2.698 </Td> <Td> 933.47 </Td> <Td> 2792 </Td> </Tr> <Tr> <Td> Sulfur </Td> <Td> 2.067 </Td> <Td> 388.36 </Td> <Td> 717.87 </Td> </Tr> <Tr> <Td> Chlorine </Td> <Td> 0.003214 </Td> <Td> 171.6 </Td> <Td> 239.11 </Td> </Tr> <Tr> <Td> Potassium </Td> <Td> 0.862 </Td> <Td> 336.53 </Td> <Td> 1032 </Td> </Tr> <Tr> <Td> Titanium </Td> <Td> 4.54 </Td> <Td> 1941 </Td> <Td> 3560 </Td> </Tr> <Tr> <Td> Iron </Td> <Td> 7.874 </Td> <Td> 1811 </Td> <Td> 3134 </Td> </Tr> <Tr> <Td> Nickel </Td> <Td> 8.912 </Td> <Td> 1728 </Td> <Td> 3186 </Td> </Tr> <Tr> <Td> Copper </Td> <Td> 8.96 </Td> <Td> 1357.77 </Td> <Td> 2835 </Td> </Tr> <Tr> <Td> Zinc </Td> <Td> 7.134 </Td> <Td> 692.88 </Td> <Td> 1180 </Td> </Tr> <Tr> <Td> Gallium </Td> <Td> 5.907 </Td> <Td> 302.9146 </Td> <Td> 2673 </Td> </Tr> <Tr> <Td> Silver </Td> <Td> 10.501 </Td> <Td> 1234.93 </Td> <Td> 2435 </Td> </Tr> <Tr> <Td> Cadmium </Td> <Td> 8.69 </Td> <Td> 594.22 </Td> <Td> 1040 </Td> </Tr> <Tr> <Td> Indium </Td> <Td> 7.31 </Td> <Td> 429.75 </Td> <Td> 2345 </Td> </Tr> <Tr> <Td> Iodine </Td> <Td> 4.93 </Td> <Td> 386.85 </Td> <Td> 457.4 </Td> </Tr> <Tr> <Td> Tantalum </Td> <Td> 16.654 </Td> <Td> 3290 </Td> <Td> 5731 </Td> </Tr> <Tr> <Td> Tungsten </Td> <Td> 19.25 </Td> <Td> 3695 </Td> <Td> 5828 </Td> </Tr> <Tr> <Td> Platinum </Td> <Td> 21.46 </Td> <Td> 2041.4 </Td> <Td> 4098 </Td> </Tr> <Tr> <Td> Gold </Td> <Td> 19.282 </Td> <Td> 1337.33 </Td> <Td> 3129 </Td> </Tr> <Tr> <Td> Mercury </Td> <Td> 13.5336 </Td> <Td> 234.43 </Td> <Td> 629.88 </Td> </Tr> <Tr> <Td> Lead </Td> <Td> 11.342 </Td> <Td> 600.61 </Td> <Td> 2022 </Td> </Tr> <Tr> <Td> Bismuth </Td> <Td> 9.807 </Td> <Td> 544.7 </Td> <Td> 1837 </Td> </Tr> <Tr> <Td_colspan="13"> <P> Notes </P> <Ol> <Li> Jump up ^ Z is the standard symbol for atomic number; C is the standard symbol for heat capacity; and χ is the standard symbol for electronegativity on the Pauling scale . </Li> <Li> Jump up ^ Helium does not solidify at a pressure of one atmosphere . Helium can only solidify at pressures above 25 atmospheres, which corresponds to a melting point of absolute zero . </Li> </Ol> </Td> </Tr> </Table>

Which type of substance has the highest melting point