With this formula Smith calculates that at 15° the heat of vaporization
of water is equal to 588.73 calories; at 20°, 585.84 calories; at 25°,
582.93 calories; at 30°, 580.04 calories;[13] and at 35°, 577.12
calories. In all of the calculations in the researches herewith we have
used the value found by Smith as 586 calories at 20°. Inasmuch as all of
our records are in kilo-calories, we multiply the weight of water by the
factor 0.586 to obtain the heat of vaporization.