Shrinkage and Expansion of Cast Iron, &c. 7 



castin>y by moving small iron rods up and down in the gate. 

 The metal is thus allowed to percolate into the chasm, if 

 any is formed, and prevents anv bad consequences likely to 

 ensue from the general shrinkage of the mass. 



It is impossible to convey an exact idea of the extent or 

 quantity of snrinkage that 'takes place in castings, or pro- 

 portion it to the weight or dimensions of the ongmal 

 mass. The subject of contraction is more withm the reach 

 of measurement, and in many cases may be ascertained with 

 great precision. 



The following bomb-shell gauges were cast from very 

 clean wood patterns ; the breadth of metal in the hoop was 

 exactlv 1-230 inches, and the thickness -450 inch. 



Diauiece- of Patf ■ . ?. Diaineicr when -ast. Contraction. 



l5t Pattern 7-500 inches. 7-350 inches. -150 inch. 



2d 5-950 5-850 '100 



3d 5-500 5-430 '070 



4th 4-5,50 4-490 '060 



5th 4-060 4-020 '040 



The relaiive proportion of contraction to the diameters 

 will be as follows : , n , i- 



Contraction of No. I. -15, equal to i -50th of the diameter. 

 II. -10, 1-597 



III. -07, l-7S-f'oV 



IV. -06, l-75fTfV 



V. -04, 1-100^ 



It will be seen from this table, that the quantity of con- 

 traction is in a due relation to the diameter of the casting. 

 No. IV. seems an exception, however, and appears to have 

 shrunk more in proportion to its diameter than the other 

 four. 'I'his may with safetv be laid to the score of error in 

 the moulding. In casting flat surfaces, the degree of con- 

 traction is in a just proportion to the length of the article. 



L'ches. 



A front pattern of polished tin measured exactly 24-5 

 When cast of soft gray iron, and cold, measured 24-250 



Contraction -25 

 Equal to 1 -9Sth part t^ie length of the pattern ; the height 

 of which, or rather breadth, was 20 inches ; its thickness a 

 quarter ot .ni inch. 



The comraction of two ash-grate patterns was ascer- 

 tained as folkjws : 



First pattern measured in length - 18-250 inclies 

 When cast in soft iron - - J8'^35 



Contraction -215 

 Equal to l-84fJ',Ttb part the length of the pattern. 



