332 PRINCIPLES OF CHEMISTRY 



hardness. Electro- deposited iron is brittle, but if heated (after the 

 separation of the hydrogen) it becomes soft. If pure ferric hydroxide, 

 which is easily prepared by the precipitation of solutions of ferric 

 salts by means of ammonia, be heated in a stream of hydrogen, it 

 forms, first of all, a dull black powder which ignites spontaneously in 

 air (pyrophoric iron), and then a grey powder of pure iron. The 

 powdery substance first obtained is an iron suboxide ; when thrown 

 into the air it ignites, forming the oxide Fe 3 O 4 . If the heating in 

 hydrogen be continued, more water and pure iron, which does not 

 ignite spontaneously, will be obtained. If a small quantity of iron be 

 I fused in the oxyhydrogen flame (with an excess of oxygen) in a piece 

 of lime and mixed with powdered glass, pure molten iron will be 

 formed, because in the oxyhydrogen flame iron melts and burns, but 

 the substances mixed with the iron oxidise first. The oxidised im- 

 purities here either disappear (carbonic anhydride) in a gaseous form, 

 or turn into slag (silica, manganese, oxide, and others) that is, fuse 

 with the glass. Pure iron has a silvery white colour and a specific 

 gravity of 7 '84 ; it melts at a temperature higher than the melting- 

 points of silver, gold, nickel, and steel, i.e. about 1400-! 500 and 



spindles of looms, hammers, spades, hoes, &c. ; (4) very hard steel, carbon 0'5 to 0'65 

 p.c., tensile breaking weight 70 to 80 kilos, extension 5 to 10 p.c., does not weld, but 

 tempers easily ; used for small springs, saws, files, knives and similar instruments. 



The properties of ordinary wrought iron are well knowa. The best iron is the most 

 tenacious that is to say, that which does not break up when struck with the hammer 

 or bent, and yet at the same time is sufficiently hard. There is, however, a distinction 

 between hard and soft iron. Generally the softest iron is the most tenacious, and can 

 best be welded, drawn into wire, sheets, &c. Hard, especially tough, iron is often 

 characterised by its breaking when bent, and is therefore very difficult to work, and 

 objects made from it are less serviceable in many respects. Soft iron is most adapted 

 for making wire and sheet iron and such small objects as nails. Soft iron is characterised 

 by its attaining a fibrous fracture after forging, whilst tough iron preserves its granular 

 structure after this operation. Certain sorts of iron, although fairly soft at the ordinary 

 temperature, become brittle when heated and are difficult to weld. These sorts are 

 less suitable for being worked up into small objects. The variety of the properties of 

 iron depends on the impurities which it contains. In general, the iron used in the arts 

 still contains carbon and always a certain quantity of silicon, manganese, sulphur, 

 phosphorus, &c. A variety in the proportion of these component parts changes the 

 quality of the iron. In addition to this the change which soft wrought iron, having a 

 fibrous structure, undergoes when subjected to repeated blows and vibrations is con- 

 siderable ; it then becomes granular and brittle. This to a certain degree explains the 

 want of stability of some iron objects such as truck axles, which must be renewed after 

 a certain term of service, otherwise they become brittle. It is evident that there are 

 innumerable intermediate transitions from wrought iron to steel and cast iron. 



At the present day the greater part of the cast iron manufactured is converted into 

 steel, generally cast steel (Bessemer's and Martin's). I may add the Urals, Donetz 

 district, and other parts of Russia offer the greatest advantages for the development of 

 an iron industry, because these localities not only contain vast supplies of excellent iron 

 ore, but also coal, which is necessary for smelting it. 



