LXI
If we heat a vessel filled with snow over a light, the thermo
meter put into the snow, the temperature will rise up to 0°, but
at this point it will stop until all the snow is melted.
1 lb. of water at 80° C and 1 lb of water at of 0°C mixed to
gether are changed into 2 lbs. of water at 40°C, but
1 lb. of water at 80° C and 1 lb. of snow at 0°C mixed to
gether, yield 2 lbs. of water at 0°C. In this case the surplus of
heat is absorbed by the melting body.
§ 150. The same takes place and the same laws hold true
also for evaporation (the slow formation of vapours on the
surface of a liquid, which process goes on at any temperature in
an open vessel) and ebullition (a rapid production of vapour
in the mass of a liquid itself). 309.
§ 151. Aëriform bodies, which under ordinary circum-
stances are not produced by evaporation we call gases (but see
§ 167), vapour is invisible, only when commencing to liquify
can it be seen (mist).
§152. As to latent heat the amount of heat absorbed by a
body varies with different substances. Iron absorbs more than
lead; fusing and boiling point. 310. Melting substances absorb
heat, hence a thaw lowers the temperature in spring. 311. This
is the reason, why even in a hot country ice may be prepared; for
Freezing mixtures see: 312. 3 parts (by weight) of snow and
1 part of salt give a mixture of 0° to -17° C. Powdered sul
phate of soda (Glauber's salt) poured over by hydro-chloric
acid yield a mixture of +10° to -17° C. 3 parts of muriatic (hy
dro-chloric) calcium and 2 parts of snow -0°C to -28°C,1 part
of dilute sulphuric acid and 1 part of snow -7° to -51°C.
§ 152 Just the contrary takes place in Solidification.
(passage from the liquid to the solid state) or the Liquefaction
of gases and vapours (passage from the gaseous to the liquid