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We have already seen with salt eutectics that, given the curve of melting-points of a mixture in various proportions, we may predict the existence, composition, and melting-point of the eutectic alloy. As a matter of course, the same thing holds good for metallic eutectics.
In practice, the measurement of a quantity of heat is very often effected by means of the ice calorimeter, the use of which is particularly simple and convenient. There is, therefore, a very special interest in knowing exactly the melting-point of ice.
We should further expect this to have a constitution between PbSn and PbSn and a melting-point somewhat below 181°. On melting together tin and lead, and allowing the alloy to cool, we find our expectation justified; for by pouring off the fluid portion which remains after solidification has commenced, and repeating this several times with the portion so removed, we at length obtain an alloy which solidifies at the constant temperature of 180°, when the melting-point of tin is taken as 228°. On analysis 1.064 grm. of this alloy gave 0.885 grm.
Below us was a stream of lava, rolling and surging and beating against huge, precipitous, red-hot cliffs; and, higher up, suspended from other, also red or white hot overhanging cliffs, depended huge stalactites, like masses of fiercely glowing fern leaves waving about in the subterraneous wind; and here we saw how thin was in some such places the crust over which we walked, and how near the melting-point must be its under surface.
These groups of meteorites, already as dense as a swarm of bees, were then packed closer by the influence of gravity, and the contracting mass was heated by the pressure, even above the normal melting-point of the material, which was kept rigid by the weight of the overlying layers."
I felt, quite acutely, that it was a shame that he could not be for ever the central figure of a field of mud, kicking a ball into long and grandiose parabolas higher than gasometers, or breaking an occasional leg, surrounded by the violent affection of hearts whose melting-point was the exclamation, "Good old Jos!"
Further, it is well known that certain alloys can be prepared, the melting-points of which are lower than the melting-point of either of the constituent metals alone.
On the other hand, platinum, although found to be the best of all materials for the purpose, aside from its great expense, and not combining with oxygen at high temperatures as does carbon, required to be brought so near the melting-point in order to give light, that a very slight increase in the temperature resulted in its destruction.
Another black coating for ironwork, which is really a lacquer, is obtained by melting ozokerite, which becomes a brown resinous mass, with a melting-point at 140° F. The melted mass is then further heated to 212° F., the boiling-point of water. The objects to be lacquered are scoured clean by rubbing with dry sand, and are dipped in the melted mass.
A large part of the heat used in melting is known to be absorbed by the substance during the process of melting. This is indicated by the thermometer remaining at the temperature of the melting-point once this has been reached, until the whole of the melting substance has liquefied.
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