Shrinkage and Expajision of Cast Iron, &c. 5 



than at any other period ; and that, when cold, and in pro- 

 portion to tlic absence of heat, so will the volume of the 

 metal be diminished. 



1st, then. Shrinkage appears to be dependent upon two 

 causes; the gravitation of the fluid metal, and the expan- 

 sion of the jiiould. The latter, I conceive, acts a very pow- 

 erful part : the immense quantity of caloric combined with 

 the iron is in part easily and almost instantaneously com- 

 municated through the sand to the iron box : this creates a 

 disposition to expand, in which it is greatly assisted by the 

 great pressure of fluid iron. That portion of the metal in 

 contact with the interior of the mould is the first to lose its 

 fluidity, and is acted upon and forced to give way in the 

 same ratio of expansion before the subtle and denser fluid. 

 The diameter of the shell of the gun is at this period in- 

 creased in every part ; the fluid iron in the interior descends 

 to occupy the enlarged space, and the head of the gun pre- 

 sents an increasing chasm like the concave of a sand glass. 

 In proportion as the cast iron resolves itself into a solid, a 

 diminution of pressure should take place upon the mould : 

 this would inevitably follow, were not its force replaced by 

 the increased volume of the metal passing into a solid state, 

 which is equivalent to that law which I have termed 



2d, Expansion. Of the extent of this operation we may 

 judge from the following facts : — All patterns of castings are 

 made somewhat larger than the piece of goods is wished to 

 be: in common cases l-8th of an inch to the foot is allowed, 

 but in many cases the allowance will be nearly 3-l6ths of 

 an inch. In the case of the gun, therefore, the mould would 

 be plus the allowance upon the pattern what space was 

 gained by beating the pattern to loose it from the sand, and 

 all the extra space acquired by the increased volume of 

 the consolidating iron. These, taken collectively, may 

 amount to l-4th or 5-lOths of an inch; and so much less 

 will the diameter of the gun be found when cold, to what 

 it would have measured at the climax of its expansion. 



3d, Coniraction immediately takes place of the metal 

 ceasing" to expand : to its eflects are chargeable the reduc- 

 tion of the increased diameter of the gun, and which seems 

 merely in consequence of the escape of the caloric. 



The acti(jn or effect of these separate laws will intimately 

 depend upon the quality and fluidity of the metal : with the 

 same quality of iron ditlercnt (dfects will be produced ac- 

 cording to the division of the fluid, and with the same de- 

 gree of division in the fluid the extent of the operation of 

 these linvs will be difiercnt with the diflercnt qualities of 

 A 3 crudv; 



