MR. CHARLES TOMLINSON ON SUPERS ATURATED SALINE SOLUTIONS. 55 
film, and falling off, allow fresh portions of the solution to come into contact with the 
film, until at length a very fine crop of crystals is produced. This experiment was re- 
peated on the solutions in the other three flasks with the same result. 
Similar experiments were tried on solutions of Glauber’s salt of different strengths, 
with drops of ether, absolute alcohol, naphtha, benzole, oil of cajeput, oil of turpentine, 
and other volatile oils, herring-oil, sperm-oil, olive-oil, castor-oil, and some other fixed 
oils of animal and vegetable origin, with this general result, that, whenever the oil spread 
out into a film, it acted as a powerful nucleus. 
Experiment 2. A solution of two parts of Glauber’s salt to one part of water 6 was 
boiled and filtered into three flasks, which were covered with watch-glasses and left until 
the next day. A drop of castor-oil was then placed upon the surface of each : it formed 
a lens which gradftally flattened ; but there was no separation of salt, even when the flasks 
were shaken so as to break up the oil into small globules. 
The necks of some clean flasks were oiled inside with castor-oil, and the boiling solu- 
tion of Glauber’s salt filtered into them : the oil formed into globules, and some of it 
ran into the solution. Next day there was no separation of salt. The flask was turned 
round quickly so as to form a whirlpool, in which the globules of oil descended to the 
bottom and were broken up and diffused so as to form a kind of emulsion ; but by repose 
the solution became clear again, the oil collected into larger globules, and there was no 
separation of salt. 
If, while the flask is being turned round, a sudden jerk be given to it, so as to flatten 
some of the globules against the side into films, the whole solution instantly becomes 
solid ; or if by strong pressure with the finger against the interior of the neck a smear 
of oil be made, the solution crystallizes as soon as it is brought into contact with such 
smear. But if it be objected that the finger may introduce nuclear matter, then a catha- 
rized wire, which dipped into the solution is inactive, will, if rubbed against the side so 
as to flatten some of the small oil-globules, leave a number of minute crystals of a chalky 
white colour filling up the lines traced by the wire, and these serve as nuclei to the 
rest of the solution. 
Experiment 3. Stearine from sheep-tallow produced immediate crystallization in 
supersaturated solutions of Glauber’s salt. The solutions were gently heated and gra- 
dually raised to boiling. In cooling, the stearine, now catharized, collected into disks ; 
but it was no longer nuclear, even when the vessel was shaken. When the flask was 
uncovered, a nucleus from the air produced immediate crystallization. 
Of course, unless the oils be chemically clean, according to the definition, they induce 
crystallization, whether they form a lens or a film on the surface of the solution. 
Thus a specimen of sperm-oil placed on the centre of the surface of a supersaturated 
6 This solution, it will be seen, contained twice ‘as much salt as the solution used in Experiment 1, and 
hence was much more sensitive to the action of nuclei. This sensitiveness also increases as the temperature 
falls ; and at low temperatures the crystals are more rapidly formed, more crowded and hence less distinct, 
than when formed from weaker solutions and in summer weather, as in Experiment 1. 
