RECENT WORK IN AGRICUETURAL SCIENCE. 



AGRICULTTJRAL CHEMISTRY. 



The preservation of iron and steel, A. S. Cushman (U. 8. Dcpt. Agr., Office 

 I'ub. Roads Bui. So, pp. JfO, i)ls. '/). — This is a continuation of studies previously 

 reported (E. S. R., 19, p. 306), and lias a direct bearing upon the preservation 

 of fence wire and other forms of iron and steel in general use. The controlling 

 factors which influence the more or less rapid corrosion of iron and steel are 

 discussed in the light of the electrolytic or autoelectrolytic theory of rust 

 formation. The various methods which are in common use, or which have been 

 proposed for the protection of iron and steel, are then considered with special 

 reference to the results of recent investigations, and principles are announced 

 to serve as a guide in the selection of paints for the prime or contact coatings 

 for steel. 



Iron combines so readily with other elements that commercial iron is not a 

 homogeneous pui-e metal, and the presence of small quantities of impurities 

 serves to change its physical characters. The ferroxyl test, which is described 

 in detail, affords a visible demonstration of electrolytic action taking place on 

 the surface of iron and causing rapid corrosion at the positive poles. 



" This electrolytic action, which is shown to take i)lace whenever iron rusts, 

 should not, however, be confused with the rapid destruction of steel in the 

 neighborhood of escaped currents from high potential circuits used for electric 

 lighting or tramways. In order to avoid such confusion of terms and ideas, it 

 has been proposed to speak of the underlying electro-chemical cause of corrosion 

 as autogenous electrolysis or, more briefly, autoelectrolysis." 



The electro-chemical explanation of the corrosion of iron is stated as follows : 



" Iron has a certain solution tension, even when the iron is chemically pure 

 and the solvent pure water. The solution tension is modified by impurities or 

 additional substances contained in the metal and in the solvent. The effect of 

 the slightest segregation in the metal, or even unequal stresses and strains in 

 the surface, will throw the surface out of equilibrium, and the solution tension 

 will be greater at some points than at others. The points or nodes of maximum 

 solution pressure will be electro-positive to those of minimum pressure, and a 

 current will flow, provided the surface points are in contact through a con- 

 ducting film. If the film is water, or is in any way moist, the higher its con- 

 ductivity the faster iron will pass into solution in the electro-positive areas, 

 and the faster corrosion proceeds. Positive hydrogen ions migrate to the 

 negative areas, negative hydroxyls to the positives. . . . The rusting of iron is 

 primarily due to attack, not by oxygen, but by hydrogen in its ionized condi- 

 tion. Nevertheless, the function of oxygen in carrying on the process of rust- 

 ing, although a secondary one, is absolutely essential to its progress, for in 

 the absence of oxygen rust is not formed. It is owing to these separate, though 

 coordinated, functions of hydrogen and oxygen that the formation of rust can 

 be inhibited by the addition to the water of certain oxidizing agents, as well as 

 by certain reducing agents, a seeming paradox that no other theory, attempts 

 to explain. The strong reducing agent pyrogallol will inhibit rusting by inter- 



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