STEEL AT WELDING TEMPERATURES. 595 
become the same as that of the molten iron. It is at this point that a freely floating 
ball would just appear at the surface. The expansion beyond this corresponds to the 
gradual rising of a free ball above the surface, the disturbances in the flotation due 
to the cooling of the emergent part of the ball, and to the interference of the floating 
scoria in the more crude experiment, are obviated by keeping the ball submerged. 
As the ball becomes hotter the curve flattens between C and D, the conduction of 
the heat into the ball becoming slower, until no further expansion takes place. 
Several balls, removed at this stage, were found complete in form, but so soft that a 
steel pin could be pushed right through them. ‘This plastic condition of the mass 
remains for a short time, when it quickly passes into the liquid condition, the metal 
of the ball joining the molten iron in the ladle. Of course, so soon as the melting of 
the ball begins, the pencil no longer registers measurable changes of volume, as a 
reduction of mass is taking place, but the maximum volume of the ball can be 
measured in the plastic condition, and the volume when it reaches the liquid con- 
dition being known, it can be stated with certainty that it passes rapidly from one 
condition to the other. The conducting power of iron is so good that little wasting 
of the surface takes place, until the whole ball from surface to centre is in a plastic 
condition, and then it very rapidly melts and joins the bath ; as shown by the sudden 
drop of the curve at E. 
The mean average of a number of experiments upon grey Cleveland iron led me 
to conclude that the 
Specific gravity of the solid iron at atmospheric temperature was 6°95 
That the specific gravity of the molten iron was. . . . . . 6°88 
That the specific gravity of the plastic iron was . . . . . . 6°50 
In other words, while cast iron passes from the solid to the liquid state its volume 
is at its minimum when the mass is solid. As the temperature rises the metal 
first expands 1°02 per cent., and then has the same specific gravity as the liquid 
metal, viz., 6°88. It then continues expanding until it reaches the plastic condition, 
when it assumes its maximum volume with a specific gravity of 6°5, the total increase 
of volume from the solid to the plastic state amounting to 6°92 per cent. 
After this, expausion by heat ceases and a quick centraction takes place, until the 
mass becomes liquid, when its specific gravity is, as before, 6°88. If this is expressed in 
terms of the volume of liquid iron, taken as 100, the volume of the solid iron at 
atmospheric temperature is 98°98. That of plastic iron is 105‘85, in which condition 
an increase of heat to the melting point reduces the volume to 100, representing 
its liquid condition. 
These changes of volume were much greater than was expected, and it was thought 
well to verify them by a converse series of experiments which enabled the changes 
in a cast iron ball in passing from the liquid to the solid state to be observed. Two 
: 4G 2 
