FUSION AND SOLIDIFICATION 69 



trace connections between, for example, the 

 mechanical properties of metals and their micro- 

 scopic structure when solidified ; and, from the 

 complicated relations which declare themselves, 

 we may hope to throw light on the processes of 

 fusion and solidification, and construct a theory 

 that will hereafter prove of some use to the 

 enofineer and the metal-worker. 



In the first place it is well to remark that we 

 are seldom dealing with pure materials. Nearly 

 the whole of the phenomena we shall consider 

 depend on the admixture of two or more sub- 

 stances, one for the most part predominating. It 

 follows that the result of the inquiry is specially 

 applicable in all cases where traces of some 

 impurity are the determining factor ; that is, to 

 the majority of cases, since the attainment of 

 chemical purity is more often a pious hope than 

 an accomplished fact. 



Our investigations will lead us far afield, and 

 we shall pass in review combinations of many of 

 the principal metals. It is well, however, that 

 the starting-point should be on familiar ground ; 

 if, indeed, by such a term it is permissible to 

 indicate the ice that occasionally covers our 

 ponds and perpetually caps our globe. 



It is well known that sea-water remains liquid 

 at temperatures low enough to freeze ponds and 

 lakes, and, long ago, it must have been recognised 

 that this behaviour was due to the dissolved salt, 

 though it was not till the year 1788 that Blagden, 

 the first worker in the field, published a syste- 

 matic series of observations on the freezing-points 

 of salt solutions. 



