Iron . 
249 
is at present an envelope to a considerable portion of fluid 
contents. In this state the expansion, if any has taken 
place in the shot and mould, is nearly the same ; the for- 
mer is easily extracted from the under and upper parts 
of the latter. In about two minutes after, 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 ef- 
forts. The mould is always filled by the shot till cooling 
has so far taken place as to reduce 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-66th part of its 
diameter. In all cases where shot-moulds are re-filled be- 
fore they have contracted, by cooling, to their original 
diameter, their product in shot will be various as to di- 
mensions. The effects of this, particularly in summer, 
are inconceivable, and though seldom adverted to, will 
account often for shot being rejected 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 following experiments : 
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 iron three 
times successively. The first interval of pouring was ten 
minutes, and the second fifteen minutes. 
Measured. Weighed. 
Inches. 
Lbs. 
Grs. 
3 -pounder shot, 1st Cast 2*724 
2 
6015 
2d — 
— 2*730 
2 
6031 
3d — 
2*736 
2 
6070 
4-pounder shot, 1st — 
3*036 
3 
6125 
2d 
3*054 
3 
6234 
I I 
