. The Locomotive. ine structure,and a so-called fibrous texture is duemerely to a series of crystals pullingout of the mass when a fracture takesplace. The slower and more uniformiron and steel are heated and cooled,the smaller and more regular will bethe crystalline structure of the from the chemical and voltaiccauses, corrosion will vary according to the structure of the materialand the mechanical treatment it has received. Hard cast-iron is less corrodible than soft cast-iron of similarcomposition and it corrodes faster if cooled irregularly than if cooleduniformly and slowly. T
. The Locomotive. ine structure,and a so-called fibrous texture is duemerely to a series of crystals pullingout of the mass when a fracture takesplace. The slower and more uniformiron and steel are heated and cooled,the smaller and more regular will bethe crystalline structure of the from the chemical and voltaiccauses, corrosion will vary according to the structure of the materialand the mechanical treatment it has received. Hard cast-iron is less corrodible than soft cast-iron of similarcomposition and it corrodes faster if cooled irregularly than if cooleduniformly and slowly. The more porous the material the morerapidly will corrosion proceed and the deeper and more distinctivewill it be. Blowholes of any size invite rust. Metals of crystallinestructure are better conductors of electricity than amorphous,and this may account for the fact that some rolled sheets are moredurable than others. Those which have had careful annealing orheat treatment would have the more crvstalline A Corroded Stay. 138 THE LOCOMOTIVE. [January, It has been demonstrated that iron and steel are porous mi-croscopically speaking and under high pressure (as in hydraulicpressure cylinders), water may be forced through thin walls inamounts sufficient to show as beads of sweat. Gases are absorbedinto this porous structure. At high temperatures all metals absorbgases, losing part of them on cooling. Corrosion is aided by the mixture of impurities into iron and ascorrosion is one of the frequent causes of boiler explosions, some-times involving the loss of life and the destruction of thousandsof dollars worth of property, therefore only the best of materialsshould be used in the construction of boilers. The amount of stress on a piece of iron or steel effects its lia-bility to corrosion. Experiments have shown that in all classesof tests, tensile, torsional and flexional, the results will be similar;that is to say, that galvanometer readings show the strained partsto be
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