Iron corrosion; anti-fouling and anti-corrosive paints . ds up itsoxygen to oxidise the iron, whilst the liberated hydrogenpresses up the paint and contributes to its destruction. Consequently the preservation of the hull, and especiallythe protection of the bottom from corrosion by rust, isattended with great difficulties ; and though a number ofcompositions have made their appearance there is none thatfulfils all requirements. Such paints must be insoluble in 218 mON-CORROSION AND ANTI-CORROSIVE PAINTS. water, and sufficiently elastic to give a little and thus preventcracking, but at the sam
Iron corrosion; anti-fouling and anti-corrosive paints . ds up itsoxygen to oxidise the iron, whilst the liberated hydrogenpresses up the paint and contributes to its destruction. Consequently the preservation of the hull, and especiallythe protection of the bottom from corrosion by rust, isattended with great difficulties ; and though a number ofcompositions have made their appearance there is none thatfulfils all requirements. Such paints must be insoluble in 218 mON-CORROSION AND ANTI-CORROSIVE PAINTS. water, and sufficiently elastic to give a little and thus preventcracking, but at the same time possess a certain degree ofhardness to oppose sufficient resistance to mechaijical conditions are best fulfilled by a thin layer of resin ;consequently many ships paints are compounded of varnishto which metallic oxides in the state of powder are added inorder to increase the oxidation and resinification of the oil(this is, however, an erroneous assumption). Such materialsinclude red lead, iron oxide, zinc white, and white lead, the. Fig. 62 (magnified).—Peeling anti-fouling composition after six monthsimmersion in water. resulting paints taking a long time—one to three days—todry. More extensively used are the spirit varnish paintsconsisting of volatile oils or hydrocarbon compounds (spirit)and dissolved resin, which latter forms a thin, elastic, lacquer-like film on the surface of the iron after the solvent hasevaporated. To this class belong the compositions made byRathjen, Heyl, IJr. Pfliug, Von Hcivelmg, and many others,which are widely used in the mercantile marine service. Asthey dry quickly, almost under the brush, the operation ofpainting takes up but little time. IRON-COEROSION AND ANTI-COREOSIVE PAINTS. 219 Coal tar, which contains solid and liquid hydrocarbonsand resinous matters, has also been found to behave well forships use when prepared as free from acid as possible, thoughit wears away under the influence of sea water somewhatquicker
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