Shrinkage and Expansion of Cast Iron, ^c. g 



continuation of the same experiment. If a short allowance 

 of time is made after the mould is filled under the above 

 circumstances, and this dexterously inverted, a fair mclo- 

 sure will be found, possessing regular and equal thickness 

 of new metal on all sides of the minor ball. 



This' is easily accounted for upon the same principle- 

 When the mould was full, the ball, as usual, occupied 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 elevate 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 pro- 

 portion to the fitness of the moment taken to perform the 

 operation. 



That cast iron occupies a greater bulk or volume imme- 

 diately 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 is at present 

 an envelope to a considerable portion of fluid contents. la 

 this state the expansion, if any has taken place in the shot 

 and mould, is nearlv the same; the former is easily extracted 

 from the under and upper parts of the latter. In about two 

 minutes alter, however, the expansion of the shot is more 

 rapid than that of the mould ; and at this period is difficult 

 to disengage. As the heat is communicated to the mould, 

 its dimensions enlarge, and the extraction of the shot is 

 attended with less violent et^orts. The mould is always 

 filled by the shot till cooling has so far taken place as to re- 

 duce the shot-mould to its former diameter. Beyond this, 

 however, the shot still continues to lessen its bulk, so that 

 when cold it will be found to have left its mould by nearly 

 l-6J(ith part of its diameter. In all cases where shot-moulds 

 are re-lilled bclore they have contracted, by cooling, to 

 their (original diameter, their product in shot will be various 

 as to dimensions. The eflccts of this, particularly in sum- 

 mer, are inconceivable, and, though seldom adverted to, 

 will account often tor shot being rejected as unserviceable 

 for not parsing the gauge. This subject I at one time paid 

 particular attention to, and, to ascertain the fact rigorously 

 made the following experiments : 



I selected seven pairs of shot-moulds, well seasoned, of 



the following sizes, 3j 4, C, 9, 12, 34, and 3'2-pounders, 



3 These 



