800

ON THE SHRINKAGE AND

which is the natural progress of consolidation, but whichis at present an envelope to a considerable portion offluid contents. In this state the expansion, if any hastaken place in the shot and mould, is nearly the same ;the former is easily extracted from the under and upperparts of the latter. In about two minutes after, how-ever, the expansion of the shot is more rapid than thatof the mould, and at this period is difficult to disengage.As the heat is communicated to the mould, its dimen-sions enlarge, and the extraction of the shot is attendedwith less difficulty. The mould is always filled bythe shot till cooling has so far taken place as to reducethe shot mould to its former diameter. Beyond this,however, the shot still continues to lessen its bulk, sothat when cold it will be found to have left its mould bynearly -^th part of its diameter. In all cases whereshot moulds are refilled before they have contracted, bycooling, to their original diameter, their product in shotwill he various as to dimensions. The effects of this,particularly in summer, are inconceivable, and thoughseldom adverted to, will account often for shot beingrejected as unserviceable for not passing the gauge.This subject I at one time paid particular attention to,and, to ascertain the fact rigorously, made the followingexperiments:

I selected seven pairs of shot moulds, well seasoned,of the following sizes, 3, 4, 6, 9,12, 24, and 32-pounders.These were cast or filled with the same quality of ironthree times successively. The first interval of pouringwas ten minutes, and the second fifteen minutes.

3-pounder shot,

1st

Inches.

cast measured 2*724

weighed

Lbs.

2

Grains.

6015

2nd

„ 2*730

yy

2

6031

3rd

„ 2*736

yy

2

6070