The Rate of Evaporation of Liquids in a Current of Air

The experiments were made in a large ventilating tunnel at Edgewood Arsenal near the end of a 280 ft straight section, 6 ft square. The liquid being studied was pumped continuously into a copper pan mounted flush with the floor, over the edge of which it overflowed into a lower pan. The amount of evaporation in several hours was determined by weighing the pans. Results were obtained for chlorbenzene, $M$-xylene, nitrobenzene and toluene, for winds from 0 to 15 miles per hr, 49 runs in all. The rate of evaporation is found to be a linear function of the wind velocity, and taking the values of vapor pressure given in the literature corresponding to the temperatures of the liquid surfaces, the relation suggested by DeHeen in 1891 is found to be correct; the number of gram mols evaporated per hour from a liquid surface 60 cm in diam. is given by $M=(0.1+0.10W)P$, where $W$ is the wind velocity in miles per hour and $P$ is the vapor pressure in millimeters of mercury. Due to variations in the wind velocity and uncertainty as to the exact temperature of the surface in some cases, the mean variation of observed values of $M$ from the computed values is about 10 per cent, but there is no evidence of a systematic deviation of the results for any one liquid, although the vapor pressures very from 0.3 to 30 mm.