The standard way to measure porosity of a rock is to get the pores completely saturated with water, then weigh the rock immersed in water and again in air (there are modified balances for this). Using Archimedes' principle, you then can determine the volume of the rock. Then you dry the rock completely and weigh it again (only in air). The water weight lost gives you the pore space in the rock. Divide this into the total volume and you get the porosity. A major source of error is that when you weigh the rock after taking it out iof the water you have to blot the outside surface dry. Not dry enough and you are weighing some exterior water. Too dry and you will suck some of the water out of the pores and the rock is no longer saturated. What I am looking for is a textbook or other publication that tells the amount of error to be expected from this source. Anyone with information or experience with this method is welcome to reply.