360 REPORT—1905. 
the moment the action of the water molecules, it would appear that as long as the 
gold molecules are so numerous that a uniform distribution would bring them 
within the range of each other’s attraction, we can imagine that all submerged 
molecules would be in equilibrium so far as the attractions of their own kind are 
concerned, being subjected to a uniform pull in all directions. This condition 
would certainly make for uniform distribution. But when the distance between 
them exceeds the range of the molecular forces, it is evident that an entirely new 
condition is introduced, and it seems not improbable that the widely distributed 
molecules would tend to drift into clouds in which they are brought back within 
the range of these forces. The range of the cohesive forces in water and aqueous 
liquids is usually taken from 50 to 100 micro-millimetres, and I am disposed to 
think that ten times this amount would not be an excessive estimate of the range 
in the case of gold. If the range for gold be taken as 500 micro-millimetres, then 
the gold molecules of the dilute gold solution, which are spaced at 400 micro- 
millimetres apart, are just within the range of each other’s attraction, and their 
distribution is, therefore, likely to be uniform. But by a further dilution to half 
concentration, the equilibriuni would be liable to be disturbed, and denser clouds 
of gold molecules would be formed, with less dense intervals between them. 
In preparing the zinc boxes through which the gold solution is passed, very 
great care has to be exercised to ensure that the contact surface of the zinc is used 
to the best advantage. With this object the packing of the zinc shavings is so 
managed that the solution is spread over the zinc surface in as thin sheets as pos- 
sible. The object, of course, is to bring as many of the gold molecules as possible 
into actual contact with the zinc. The gold molecules found in the solution 
leaving the boxes are those which have not been in contact with the zine. Yet 
we have seen that these molecules are still so numerous that they are within 
sodoz Of an inch of each other. If these molecules are in a state analogous to the 
gaseous state, with diffusive energy of the same order as that of the gas molecule, 
it is difficult to imagine how they can escape without coming in contact with the 
zine surface during their tortuous passage through the boxes and being deposited 
there. Yet they do escape, even when the velocity of the solution in passing 
over the zinc snrfaces is so slow as 10 em, per minute or 1:6 mm. per second. 
We may regard the condition of these isolated gold molecules, or the more 
complex auricyanide of potassium molecules, as typical of that of the solute 
molecules in a dilute solution of any non-volatile solid. They are solid molecules 
sparsely distributed among a multitude of intensely active solvent molecules, the 
temperature of the solution being many hundred degrees below that at which 
they could of themselves assume the greater freedom of the liquid or gaseous 
state. These solute molecules have to a great extent been set free from the 
constraining effect of their cohesive forces, but it 7s important to remember that 
this freedom has not been attained by the increase of their own kinetic energy as in 
liquefaction by heat. Their freedom and the extra kinetic energy they have 
acquired have in some way been imparted to them by the more active solvent 
molecules; for, if the solvent could be suddenly removed, leaving the solute 
molecules still similarly distributed in ~ vacuous space, they would eventually 
condense into a solid aggregate. This must be the case, for the non-volatile solute 
has no measurable vapour pressure at the temperature of the solution. The 
kinetic energy of the solute molecules is of itself quite insufficient to endow them 
with the properties of the gaseous or even of the liquid molecule, even when 
their cohesive forces have been weakened or overcome by separation. 
Tf the energy employed in this separation is not intrinsic to the solute molecule 
then tt must in some way have been imparted by the solvent molecules. It therefore 
becomes important to compare the energy endowment of one set of molecules with 
that of the other. 
Compared with other solids, ice at its freezing-point has very little hardness or 
tenacity: the cohesion of its molecules has been much relaxed by the great absorp- 
tion of heat energy between the absolute zero and the freezing-point. If an average 
specific heat of 0'5 over the whole range be assumed, the heat absorption of one 
gram, amounts to 1:36;5, calories. In the transition to, the liquid state at 0° a 
