4 Fads illustratwe of the 



operated upon frequently explains, in a most satisfactory 

 manner, the whole niinutice. 



But this regards onlv the heating of certain substances 

 in temperatures short of fusing them. AVhen the object of 

 experiment is exposed to a heat sufficient to fuse it, it then 

 becomes subject to new laws as a fluid, and exhibits pheno- 

 mena entirely diiferent. By not taking the change of state 

 from that of a st)iid to a fluid into the account, some writers 

 have given an awkward and unsatisfactory account of the 

 laws which rciriilate iron in these two different states. Be- 

 fore I procccd^to detail some experiments made upon this 

 subject, 1 shall trace out the different states of shrinkage 

 and expansion, as observed in cast iron. 



In doing this I shall divide shrinkage into two distinct 

 operations : 1st, Shrinkage, properly so called, when a mass 

 of iron diminishes or shrinks withvn itself, and would ac- 

 tually displace a smaller quantity of water, and when no 

 dciiree of heat short of fusion would make it occupy its 

 tbaner bulk or volume. 2d, Contraction, or that diminu- 

 tion of superdcial meajuremeiit which any body undergoes 

 by evolving its caloric. The surface in this case is never 

 injured ; the casting will be found less than the pattern from 

 which it was formed, and simple heating will restore it to 

 its greatest original volume. 



The former of these properties cannot exist without the 

 latter, but this last may take effect in full force in many 

 minor operations without any appearance of .shrinkage. I 

 only say appearance ; for I believe, abstractly speaking, the 

 one never takes place without the other, though in such 

 various minute degrees that it is often difficult to form any 

 estimate of the quantity. 



In casting pieces of ordnance we arc enabled to judge, 

 of the conjoint effects of shrinkage, contraction, and expan- 

 sion. We shall suppose that a gun mould of any given 

 length is filled with fluid cast iron not subject to these law? ; 

 then the size and shape of the gun, when cold, would ex- 

 actly correspond to the dimensions of the mould. But 

 finding that the piece of easting was considerably altered, 

 that it had shrunk interiorly, was dnninished in point of 

 length, and had lessened its diameter, we inust seek for a 

 solution of these facts in the explanation of the causes re- 

 spectively. 



First assuming, what shall be hereafter proved by direct 

 experiment, that cast iron occupies less volume when fluid 

 than when solid j that in the act of the arrangement of the 

 fnoleculae towards cousf.lidatiouj it occupies a larger bulk 



than 



