854 THE farmers' handbook. 



It is owing to the properties of iron when in the heated condition that it . 

 is so valuable. Thick bars can be made thinner, thin bars can be thickened, 

 it can be twisted into all conceivable shapes without impairing its strength, 

 and, finally, separate pieces can be welded into one so firmly that where the- 

 joint is made the iron is as strong as in any other part. 



When iron is being heated, one point must be borne in mind : — The right 

 heated condition can only be obtained in a fire where there is little or 

 no excess of air. A certain amount of air must be forced into the fire. If 

 insufficient is forced in, heating takes place slowly, whilst on the other 

 hand, if the blast is made too strong, burning takes place rapidly, but still the- 

 fire cannot use up all the air. The iron becomes very hot on the surface, 

 while the inner part is still comparatively cool. Now when its temperature- 

 becomes very high in the presence of air, iron burns. It is probably difficult 

 to realise that practically the same burning that takes place in wood can- 

 occur in iron. It is, however, the case, that when iron is heated to a very 

 high temperature and air is present burning does occur. 



This can be proved by placing a piece of iron in a fire and forcing in & 

 heavy blast. In a short time brilliant sparks begin to fly off, and in a little 

 while the iron is all burnt away. When such burning iron is removed from, 

 the fire, shooting sparks continue to fly off until it cools. 



If the substance composing the sparks is collected and examined after 

 cooling, it will be found very different from iron. It has a dull, slaty or 

 bluish appearance, and is very brittle. It is iron changed into oxide of 

 iron ; that is, the iron has combined with oxygen and formed a material 

 which has not the properties of the original metal. This oxide is seen in the- 

 scale found on and around the blacksmith's anvil. 



The burning of iron is one of the first difficulties with which the amateur 

 has to contend. So long as the fire cannot be so controlled that burning is- 

 prevented, good work is almost impossible. 



From what has been said it will be seen that burning is due to iron at 

 d,n intense heat coming in contact with air. The burning, therefore, can be- 

 . largely prevented by blowing in only just as much air as can be used by 

 the fire. If much over this is blown in, the iron commences to burn. The- 

 degrees of burning vary considerably ; in the hands of a raw beginner a con- 

 siderable portion of the iron may be burnt away, and even experienced work- 

 men cannot altogether prevent the formation of some scale. This is objec- 

 tionable in any class of work ; proper welding is interfered with, and in- 

 ordinary forging the iron is pitted and roughened. 



Fluxes are used to aid in preventing the formation of scale. Those- 

 generally used are sand or borax, either singly or mixed in the proportion of 

 3 of sand to 1 of borax. The flux should be sprinkled on the iron when it 

 has reached a yellow heat, using sufficient to cover the whole of the surface, 

 especially the parts to be welded. It melts under the heat, flows over the 

 eurface of the iron, and forms a protective covering or coat. This covering 

 prevents the air coming in contact with the iron, and burning does not 

 take place; or at least not nearly so easily. Besides this, the molten flux 

 causes any scale which has already formed to melt, and when a weld is being 

 made this fluid scale is forced from between the parts. The objectionable 

 features of scale are its hardness and brittlehess, and that when it covers- 

 the surface of iron, and an attempt is made to weld, it prevents perfect union. 



