TRANSACTIONS OF SECTION B. 357 
which chemists have been familiar, These are for the most part changes which 
are special to particular elements or compounds, and are usually classed with the 
chemical properties by which the substances may be distinguished from each other. 
Very different is the amorphous crystalline change, for although in particular cases 
it may have been observed and associated with allotropic changes, yet the causes 
of its occurrence are more deeply founded in the relations between the molecules 
sand the heat energy by which their manifold properties are successively unfolded 
-as temperature is raised from the absolute zero. At this transition point we find 
ourselves face to face with the first stirrings of a specific directive force by which 
‘the blind cohesion of the molecules is ordered and directed to the building up of the 
most perfect geometric forms. It is hardly possible any longer to regard the sta- 
bility of a crystal as static and inert, and independent of temperature ; rather must 
its structure and symmetry be taken as the outward manifestation of a dynamie 
-equilibrium between the primitive cohesion and the kinetic energy imparted by 
heat. ven before the discovery of a definite temperature of transition from the 
amorphous to the crystalline phase we had in our hands the proofs that in certain 
cases the crystalline state can be a state of dynamic, rather than of static, equ- 
librium. ‘The transition of sulphur from the rhombic to the prismatic form 
supplies an example of crystalline stability which persists only between certain 
narrow limits of temperature. Within these limits the crystal is a ‘living 
erystal’ if one may borrow an analogy from the organic world, It can still grow, 
and it will under proper conditions repair any damage it may receive. 
The passage of the same substance through several crystalline phases, each 
only stable over a limited range of temperature, strongly supports the general 
conclusion drawn from the existence of a stability temperature between the 
amorphous and crystalline phases, namely, that the crystalline arrangement of the 
molecules requires for its active existence the particular kind or rate of vibration 
corresponding with a certain range of temperature. Below this point the crystal 
may become to all appearance a mere pseudomorph with no powers of active 
growth or repair. But these powers are not extinct—they are only in abeyance 
ready to be called forth under the energising influence of heat. This temporary 
abeyance of the more active properties of matter is strikingly illustrated by 
the early observations of Sir James Dewar at the boiling-point of iiquid air, 
and more recently at that of liquid hydrogen. At the latter temperature even 
chemical affinity becomes latent. In metals it was found that the changes in 
their physical properties brought about by these low temperatures are not 
permanent, but only persist so long as the low temperature is maintained. During 
the past year Mr. It. A. Hadfield has supplemented these earlier results by making 
a very complete series of observations on the effect of cooling on the mechanical 
properties of iron and its alloys. The tenacity and hardness of the pure metal 
and its alloys at the ordinary temperature and at — 182° have been compared, 
and it has been found that these qualities are invariably enhanced at the lower 
temperature, but that they return exactly to their former value at the ordinary 
temperature. By the mere abstraction of heat between the temperatures of 18° 
and —182° the tensile strength of pure metals is raised 50 to 100 per cent. In 
pure iron the increase is from 23 tons per square inch at 18° C. to 52 tons 
at — 182°; in gold from 15:1 tons to 22°4 tons; and in copper from 19:5 tons 
to 26-4. This increase is not, I think, due to the closer approximation of the 
molecules, for the coefficient of expansion of most metals below (6° is extremely 
small, Neither is it due to permanent changes of molecular arrangement or 
ageregation, for Mr. adfield has obtained a perfectly smooth and regular cool- 
ing curve for iron between 18° and — 182°, and there appears to be no indication 
of the existence of any critical point between these temperatures. Turther, the 
complete restoration of the original tenacity on the return to the higher 
temperature shows that no permanent or irreversible change has occurred during 
cooling. Everything therefore indicates that the increase of tenacity which oceurs 
degree by degree as heat is remoyed is due to the reduction of the repulsive force 
of molecular vibration, so that the primary cohesive force can assert itself more and 
more completely as the absolute zero is approached, 
