The latent heat of vaporization of mercury was found by Marignac to be 103 to 106.
The vaporization of a substance below its normal boiling-point can also be effected by blowing in steam or some other vapour; this operation is termed "distillation with steam."
A liquid boils when its vapor pressure equals the superincumbent pressure; consequently any process which diminishes the external pressure must also lower the boiling-point.
An objectionable feature of the system of allowing the vapour to escape from the still to the condenser through a loaded valve, viz: the irregularity of the distillation, is thus removed, and the benefits of regular vaporization and condensation under high pressure are obtained.
The substance is now placed on the support already mentioned, and the apparatus closed to the air by inserting the cork at D and turning the cock C. By turning or withdrawing the support the substance enters the bulb; and during its vaporization the free limb of the manometer is raised so as to maintain the mercury at a.
The difficulties arise in connexion with the determination of the quantities of ice melted or steam condensed, and in measuring the latent heat of fusion or vaporization in terms of other units for the comparison of observations.
Its specific gravity is 3.18828 (r), latent heat of fusion 16.185 calories, latent heat of vaporization 45.6 calories, specific heat 0.1071.
Thus the heat of fusion of ice (for H 2 O=18 g) is 1440 cal., and the heat of vaporization of water at 100°, for the same quantity, 9670 cal.
For theoretical considerations see Vaporization, and for the most important application see Steam Engine; also Water.
Again, pure sodium chloride melts at about 775° C., while sodium boils at 877° C., so that the margin of safety is but small if loss by vaporization is to be prevented.
Andrews's conception of the critical temperature of gases by defining the absolute boiling-point of a substance as the temperature at which cohesion and heat of vaporization become equal to zero and the liquid changes to vapour, irrespective of the pressure and volume.
The weight of steam condensed on the body gives a means of calculating the quantity of heat required to raise it from the atmospheric temperature up to ioo° C. in terms of the latent heat of vaporization of steam at zoo° C. There can be no appreciable gain or loss of heat by radiation, if the admission of the steam is sufficiently rapid, since the walls of the enclosure are maintained at too C., very nearly.
And L 1 are the latent heats of vaporization of the solid and liquid respectively, the difference of which is equal to the latent heat of fusion L1.
Another discussed conduction in curved sheets; a third the distribution of electricity in two influencing spheres; a fourth the deter mination of the constant on which depends the intensity of induced currents; while others were devoted to Ohm's law, the motion of electricity in submarine cables, induced magnetism, &c. In other papers, again, various miscellaneous topics were treated - the thermal conductivity of iron, crystalline reflection and refraction, certain propositions in the thermodynamics of solution and vaporization, &c. An important part of his work was contained in his Vorlesungen fiber mathematische Physik (1876), in which the principles of dynamics, as well as various special problems, were treated in a somewhat novel and original manner.
The extent of this loss is determined by the relation between the liquid heat and the latent heat of vaporization at the refrigerator temperature.
This is chiefly due to the fact that in the former the heat of vaporization acquired in the refrigerator is rejected in the absorber, so that the whole heat of vaporization has to be supplied again by the steam in the generator.
On the other hand, a great advantage is gained in the absorption machine by using the direct heat of the steam, without first converting it into mechanical work, for in this way its latent heat of vaporization can be utilized by condensing the steam in the coils and letting it escape in the form of water.