ME. CHAELES TOMLINSON ON SUPEESATUEATED SALINE SOLUTIONS. 57 
formed films, oil the under surface of which octahedral crystals of alum were 
formed. 
Experiments were also tried with supersaturated solutions of ammonia alum, of the 
magnesic sulphate, and the sodic acetate. Although these are not so well adapted as 
Glauber’s salt for the display of the phenomena in question, yet by carefully separating 
anomalous cases, as where a lens of old oil is not chemically clean, or where a mote 
from the air, in loosely covered vessels, produces crystallization, the result of a large 
number of experiments with a variety of liquids leads to the conclusion that liquids 
are nuclear in the form of films, and non-nuclear in the form of lenses, globules, or 
drops. 
In the form of films, as when a drop placed on one of the solutions spreads out 
and covers the surface with a display of colour, the surface-tension of the solution is 
so far diminished as to allow the film to come into contact, when that differential kind 
of action takes place whereby, the salt of the solution adhering more strongly to the 
film than the water of the solution does, the action of separation and crystallization 
thus once begun is continued and propagated. A similar action takes place with solid 
bodies that have contracted filmy nuclei by being drawn through the hand or touched 
or merely exposed to the air ; they are active, or nuclear, by virtue of the films of 
matter which more or less cover them. 
On the other hand, when a drop of oil, or many drops, is placed on the surface of a 
supersaturated solution, and it assumes the lenticular form, or even flattens down into 
disks, which more or less cover the surface, such lenses or disks retain their surface-ten- 
sion, and do not greatly interfere with the tension of the solution on which they rest. 
The adhesion is, indeed, very different from that of a film, as may be made manifest by 
pouring, say, thirty or forty drops of freshly distilled oil of turpentine on the chemi- 
cally clean surface of water in a shallow glass vessel about 3^ inches in diameter. The 
oil will nearly cover the surface of the water without being in contact, so to speak, with 
it ; for contact is prevented by the surface-tension at the boundary of the two liquids. 
If, now, upon the oil thus resting on the surface of the water some fragments of cam- 
phor be scraped, these will be immediately wetted by the turpentine and be covered with 
a solution of camphor in that oil. This solution of camphor will form a film with 
iridescent colours on the surface of the water ; a fragment of camphor will sail about, 
and being bounded on each side by nearly symmetrical films of iridescent colour, it has 
the appearance of a tropical butterfly. As it moves over the surface of the water it 
displaces the turpentine, and cuts it up into numerous lenses, until the surface-tension 
of the water is so far reduced, that no force is left to give rotation to the camphor. 
The lens of oil &c. is not then sufficiently in contact with the surface of the super- 
saturated solution to allow of that differential kind of action taking place whereby salt 
is separated. Even when, by shaking, the oil is broken up into globules, and these are 
submerged, the conditions of the case are not greatly altered, since a submerged globule 
and the solution moulded upon it are separated by surface-tension, which prevents actual 
mdccclxxi. i 
