Salt Crystals as Nuclei of Sea Fog Particles

Abstract

“On Sunday, April 29, 1928 (R.M.S.P. Demerara), we were a little south of Ushant, about 49 degrees north and 6 degrees west, when after a bright sunny morning a fog came on about 12.30 P.M. and remained till about 7 P.M. The sea was very smooth, no white caps or spray. A light breeze from west. The fog could be seen blowing in wisps across the ship. My cabin being on the west, the breeze was blowing into the port, and I placed a well-polished tumbler in the port hole so that fog particles blown in might hit it and stick. After about an hour visible spots were on the tumbler, and at about 5.30 P.M. the side facing the west was well covered with minute drops obviously liquid, when magnified. I removed the tumbler and filled it with hot water, when all drops disappeared, and in their place were whitish spots, such as one would expect if the droplets contained a soluble salt. On emptying the glass and allowing it to cool again, after about 10 minutes the whitish spots became converted into drops of liquid, evidently the soluble salt deliquescing. It seems, therefore, evident that the fog particles were formed round salt crystals, and that for such a fog to form the relative humidity need not rise much above 75 per cent, assuming, as is fairly certain, the salt present was sea salt, which deliquesces at 74 per cent or 75 per cent relative humidity."