254 TOWERS AND TANKS FOR WA TE A'- II'OA' A'.V. 



A small municipal water-supply plant in use in California has 

 two small galvanized tanks in service, which seem to have 

 given satisfaction. 



" Oxidized Plates. " Another method of treating steel 

 or iron plate for protection against corrosion, popularly called 

 '* oxidizing," has been accomplished in several ways with sat- 

 isfactory results, the effect being produced by heating the 

 metal, and afterwards subjecting it in a furnace to the action 

 of mingled steam and carbonic acid gas, resulting in the pro- 

 duction upon the metallic surface of a coating of the black 

 oxide of iron, Fe 3 O 3 FeO. 



It is claimed that the same result has been obtained by 

 coating the metal with a mixture of red oxide of iron, con- 

 taining an almost equal amount of silica and in a solvent of 

 resin-oil, and afterwards heating the metal to a bright red. It 

 is also claimed that the metal, heated to about 300 degrees 

 Fahr., and immersed in an asphaltum mixture of the same 

 temperature, will produce the same black oxide coating, but 

 in this case it would seem that the plate must first have com- 

 menced to rust naturally, to produce the change from red to 

 black oxide. In some of these processes, the change in the 

 strength of the material is not more than that which would be 

 produced by annealing, but in the first of these methods it is 

 certain that the iron or steel is permanently expanded, which 

 would be a certain advantage. The protective power of the 

 black oxide film or coating is shown from the record of an iron 

 column, said to have been erected at Delhi, India, about 900 

 B.C., and which is 60 ft. in height and weighs about 17 tons. 

 After the lapse of ages, the surface is free from rust and other- 

 wise unaffected by weathering. 



Japanned Plates. A permanent, hard and enamel-like 

 coating, capable of successfully resisting the effects of corro- 

 sion, is known as "japan," and is produced by treating the 

 article to be protected to a composition consisting of asphalt 



