In most substances that are solid under ordinary conditions, by applying heat continuously we first liquefy and ultimately vapourize them.
"Creation and Its Records"
B.H. Baden-Powell
There may be fissures in the earth, or portions less dense than others which, by the general disarrangements of the adjacent parts, and by the enormous pressure exerted by the force of gravity, are contracted, and the movement causes such friction and intense heat as to liquefy the rock.
"The Wonder Island Boys: Exploring the Island"
Roger Thompson Finlay
The ice of its glaciers may enable its inhabitants to liquefy the gases with the least expenditure of mechanical force; and the heat of its volcanoes may supply the power necessary for their condensation.
"On the Economy of Machinery and Manufactures"
Charles Babbage