.S7/C WIl.UAM SIEMENS, F.R.S. 151 



either immediately transferred to the bath of the open-hearth 

 furnace, or are previously subjected to the processes of squeezing 

 and hammering for the removal of scoria, which otherwise carries 

 some of the impurities contained in the ore into the metallic bath, 

 and prevents the attainment of steel of a high quality. 



One of the drawbacks to the use of iron and steel for structural 

 purposes is found in their liability to rust when exposed to air and 

 moisture. The ordinary means of protection against rust consists 

 in covering the exposed surfaces with paint, and if this is renewed 

 from time to time, iron or steel may be indefinitely preserved from 

 corrosive action. Another mode of protection consists in dipping 

 articles of iron and steel while hot into a bath of oil, when some 

 of the oil penetrates to a slight depth into the pores of the metal, 

 while other portions become decomposed, and form a very tenacious 

 resinous coating. For the protection of iron and steel, when in 

 the form of thin sheets or wire, galvanizing, as is well known, is 

 largely resorted to. 



The protection in this case depends upon the fact that zinc, 

 although more oxidisable than iron, forms, with oxygen, an oxide 

 of a very permanent nature which continues to adhere closely to 

 the metal, and thus prevents further access of oxygen to the same. 

 This mode of protection presents the further advantage that so 

 long as any metallic zinc remains in contact with the iron in 

 presence of moisture, the latter metal forms with the zinc the 

 negative element of an electrolytic couple, and is thus rendered 

 incapable of combining with oxygen. 



Galvanising is not applicable in those cases in which structures 

 of iron and steel are put together by the aid of heat, or are 

 brought into contact with sea water, which would soon dissolve 

 the protecting zinc covering. But even in these cases the metal 

 may be effectually protected against corrosion by attaching to it 

 pieces of zinc, which latter are found to dissolve in lieu of the 

 iron, and must, therefore, be renewed from time to time. 



Captain Ainslie, of the Admiralty, has lately made a series of 

 valuable experiments, showing the relative tendency towards 

 corrosion of both iron and steel when in contact with sea water, 

 and of the efficacy of pieces of zinc in preventing this corrosion. 

 These experiments further show that mild steel is contrary to 

 the rfsults obtained by M. Gautier more liable to corrosion than 



