248 
Iron * 
If a 6-pounder shot is placed in the bottom of a 12- 
pounder mould, or of any size larger, and hot melted 
metal poured in till the mould is filled, apparently a per- 
fect shot is formed ; but a few blows upon the upper part 
of the sphere, around the gate or runner, detect the sur- 
face of the small shot. The thickness of the iron here 
will not exceed 1-X0th of an inch, while the bottom thick- 
ness will be nearly a full inch ; and if the mould exceeds 
in diameter that of a 12-pounder, the inequality of thick- 
ness is greater. It is evident from this, that six pounds 
of fluid iron float six pounds of solid iron in the state of a 
sphere. That this property is permanent, may be further 
understood from a continuation of the same experiment. 
If a short allowance of time is made after the mould is 
filled under the above circumstances, and this dexterous- 
ly inverted, a fair inclosure will be found, possessing re- 
gular and equal thickness of new metal on all sides of the 
minor balk 
This is easily accounted for upon the same principle. 
When the mould was full, the ball, as usual, occu- 
pied its place near the runner. The iron first run into the 
mould, meeting with the greatest degree of cold, would 
immediately consolidate upon the bottom : when the 
mould was inverted, the ball would naturally tend to ele- 
vate itself to what was formerly the bottom of the mould ; 
but its progress would be arrested by that portion of the 
iron now become a solid, and would remain stationary, 
more or less central in proportion to the fitness of the mo- 
xnent taken to perform the operation. 
That cast iron occupies a greater bulk of volume im- 
mediately after it passes into the state of a solid, may be 
learned " from observation as well as direct experiment. 
If a shot-mould is carefully separated at a certain period 
after filling, a metallic crust is formed, more or less thick, 
which is the natural progress, of consolidation, but which 
