Paints, in discussing the number of coats of oil paint that must be applied to iron in order to secure efficient protection against rusting, says that in establishing a standard, preference must undoubtedly be accorded to paints requiring a large proportion of oil to make them work properly. He says: "It may be laid down as a normal standard, that presupposing the use of good paint, one bottoming coat and three subsequent coatings, laid on at suitable intervals, will be required to produce a layer of sufficient thickness on iron to keep moisture away from the metal and to protect the latter from rust for a certain time." The first, or prime coat upon a surface of steel, in a fit condition to receive paint, is of the greatest importance, especially as to its drying, hardening, adhesiveness, and impermeability to water.