A full moon is often thought of as an event of a full night's duration.
This is somewhat misleading, as the Moon seen from Earth is continuously becoming larger or smaller (though much too slowly to notice with the naked eye). Its absolute maximum size occurs at the moment expansion has stopped, and when graphed, its tangent slope is zero. For any given location, about half of these absolute maximum full moons will be potentially visible, as the other half occur during the day, when the full moon is below the horizon. [Wikipedia]
Salt is not separated simple because it gets dissolved in water and its molecules become more small, smaller than the pores on the filter paper and therefore, they pass.