54 ME. CHAELES TOMLINSON ON SUPEESATUEATED SALINE SOLUTIONS. 
without any separation of salt due to nuclear action. Cases of this sort will be illus- 
trated experimentally. 
In preparing the flasks and other apparatus for the exhibition of the properties 
referred to, attention must be paid to cleansing, by means of caustic alkali, sulphuric 
acid, or spirits of wine, as insisted on in former papers ; but in the experiments on the 
action of nuclei the flasks are not to be plugged with cotton-wool, but merely covered 
loosely with watch-glasses. Solutions may thus be kept supersaturated in a quiet room 
during weeks, and even months. Cotton-wool answers admirably where the flasks have 
to be kept, as it were, in store, and then opened only once for the purpose of determining 
crystallization ; but when the flask is to be opened with a view to the insertion of a 
nucleus, cotton-wool is objectionable for several reasons, such as the liability to detach 
a few fragments in taking out the plug ; and this is certain to happen if in filtering 
the solution a little of it get into the neck and become entangled and crystallized 
with the fibres ; moreover, in taking out the cotton-wool, an equivalent volume of 
air enters the flask, and this is almost certain to deposit a nucleus on the solution. 
In the following experiments a solution of one, two, or three parts of Glauber’s salt 
to one of water was made in a large flask, and filtered while boiling into a number of 
three-ounce flasks made clean. Each flask received about two ounces of the solution, 
and was covered with a watch-glass, and left to cool during some hours, or until the 
next day. 
Experiment 1. Four ounces of Glauber’s salt in four ounces of water was boiled and 
filtered into four flasks, covered with watch-glasses and left till cold. A clean glass rod 
was dipped into a bottle of clear pale seal-oil, and the watch-glass being gently removed 
from off one flask, a drop of the oil was carefully delivered to the surface of the solu- 
tion ; the glass rod was withdrawn, and the watch-glass restored to its place. The 
drop of oil expanded into a well-shaped film, with a display of iridescent rings ; and 
immediately from the lower surface of the film there fell large well-shaped flat prisms 
with dihedral summits of the ten-atom sodic sulphate, being the normal salt. The 
prisms were an inch or an inch and a half in length, and three eighths of an inch across. 
The crystallization proceeded from every part of the lower surface of the film, and as 
one set of crystals fell off another set was formed, until the whole solution became a 
mass of fine crystals in a small quantity of liquid. This effect is entirely different from 
the usual crytallization which takes place when a supersaturated solution of Glauber’s 
salt is subjected to the action of a nucleus at one or two points in its surface, as when 
motes of dust enter from the air, or the surface is touched with a nuclear body. In 
such cases small crystalline needles diverge from the point touched, and proceed rapidly 
in well-packed lines to the bottom, the whole being too crowded and too rapid to allow 
of the formation of regular crystals. But in the case before us, where the whole surface 
of the solution, and the surface only, is subjected to nuclear action by the spreading of 
the oil-film, the action is not so rapid as in the former case, because it is not downwards 
but parallel with the surface ; the crystals mould themselves, as it were, upon the oil- 
