246 
Iron • 
The following bomb-shell gauges were cast from very 
clean wood patterns ; the breadth of metal in the hoop 
was exactly 1*250 inches, and the thickness *450 inch. 
Diameter of Patterns. Diameter when cast. Contraction. 
1st Pattern 7*500 inches. 7*350 inches. *150 inch. 
2d 
5*950 
5*850 
3d 
5*500 
5*430 
4th — 
4*550 
4*490 
5th 
4*060 
4*020 
TOO 
*070 
*060 
• *040 
The relative proportion of contraction to the diameters 
will be as follows : 
Contraction of No. I. *15, equal to l-50th of the diameter. 
II. 
•10, 
— l-59£ 
III. 
•07, 
IV. 
•06, 
* 
V. 
•04, 
— . 1-1004 
It will be seen from this table, that the quantity of com 
traction is in a due relation to the diameter of the casting* 
No. IV. seems an exception, however, and appears to :J 
have shrunk more in proportion to its diameter than the 
other four. This may with safety be laid to the score of 
error in the moulding. In casting flat surfaces, the de- 
gree of contraction is in a just proportion to the length of' 
the article. 
Inches* 
A front pattern of polished tin measured exactly 24*5 
When cast of soft grey iron, and cold, measured 24*250 
a—— I — ' i 
Contraction *25 
Equal to T98th part the length of the pattern ; the height 
of which, or rather breadth, was 20 inches ; its thickness 
a quarter of an inch. 
The contraction of two ash-grate patterns was ascer- 
tained as follows : 
First pattern measured in length - 18*250 inches. 
When cast in soft iron - - 18*035 
Contraction *215 
Equal tQ i-84x 8 oVth part the length of the pattern® 
