68 
ME. S. AY J. SMITH ON THE THEBMOAIAGXETIC ANALYSIS OF 
(containing GF per cent.). Hence any alloy containing more than GE per cent, and 
less than GB per cent, of Ni will be heterogeneous when completely crystallised at 
the eutectic temperature. 
(2 a) When the alloy contains GB. per cent, of Ni, the material will be, when 
completely crystallised at the eutectic temperature, a mixture in definite proportions 
of the two types of crystals, one relatively rich and the other relatively poor in nickel. 
(3a) The ultimate state, at the eutectic temperature, of an alloy containing more 
than GB per cent, of nickel will he different according as the percentage of nickel is 
less than or exceeds GF. 
If the alloy contains less than GF per cent, of Ni, the eutectic temperature will be 
reached before the whole of the solution has crystallised. The final crystals will 
form from a solid solution containing GB per cent, of nickel, and will be a mixture of 
the two types containing respectively GE and GF per cent, of nickel. When 
completely crystallised at the eutectic temperature the alloy will be heterogeneous. 
If the alloy contains more than GF per cent, of nickel, it will be crystallised 
completely before the eutectic temperature is reached, and will contain crystals of one 
type only, of which the percentage composition will be the same as that of the 
originally uncrystallised alloy. The alloy will be homogeneous at the eutectic 
temperature. 
In all the cases described above, with the exception of that in which the alloy contains 
GB per cent, of nickel, the composition of the crystals changes continuously during 
the process of cooling to the eutectic temperature. When the percentage of Ni is 
less than GB the crystals become continuously richer in nickel ; when the percentage 
is greater (but less than that represented by C) they become continuously poorer. 
If, however, the alloy contains the percentage of nickel represented by the dystectic 
point C, the crystals and the solid solution from which they form will be of the 
same composition from the beginning to the end of the crystallising process. 
§ 3. As stated above, the crystallised material is homogeneous at the eutectic 
temperature if the alloy contains originally less than GE or more than GF per cent, 
of nickel. This result need not apply, however, to lower temperatures if the equili¬ 
brium curves below the eutectic temperature are (as they may be by analogy with 
fluid solutions) of the form represented qualitatively by EE' and FF' respectively. 
Under such circumstances alloys containing slightly less than GE per cent, or slightly 
more than GF per cent, of Ni might become heterogeneous at temperatures not very 
far below the eutectic temperature. 
^ 4. There are various experimental data which are explained by the views above 
summarised of the relation between the structure and temperature of a nickel iron 
alloy of given composition. 
That the formation of crystals of varying composition can occur in an alloy has 
been proved by direct experiment, and that this crystallisation occurs in a way 
analogous to that in which it takes place in liquid solutions has also been shown. 
