Plutarch Quaestiones Convivales 1.9.3

[3] Probable indeed, I replied, but not true; for I have observed that with ashes, gravel, or, if these are not to be gotten, with dust itself they usually thicken the water, as if the earthy particles being rough would scour better than fair water, whose thinness makes it weak and ineffectual. Therefore he is mistaken when he says the thickness of the sea water hinders the effect, since the sharpness of the mixed particles very much conduces to make it cleansing; for that opens the pores, and draws out the stain. But since all oily matter is most difficult to be washed out and spots a cloth, and the sea is oily, that is the reason why it doth not scour as well as fresh; and that it is oily, even Aristotle himself asserts, for salt in his opinion hath some oil in it, and therefore makes candles, when sprinkled on them, burn the better and clearer than before. And sea water sprinkled on a flame increaseth it, and is more easily kindled than any other; and this, in my opinion, makes it hotter than the fresh. Besides, I may urge another cause; for the end of washing is drying, and that seems cleanest which is driest; and the moisture that scours (as hellebore, with the humors that it purges) ought to fly away quickly together with the stain. The sun quickly draws out the fresh water, because it is so light; but the salt water being rough lodges in the pores, and therefore is not easily dried.