ME. CHAELES TOMLINSON ON SUPEESATUEATED SALINE SOLUTIONS. 63 
crystallization sets in from above and proceeds downwards, and the cauliflower masses 
become chalky white. Thus the presence of the two salts in solution affords a number of 
new phenomena which vary with the strength of the solution and the amount of reduc- 
tion in temperature, and also the old phenomena belonging to Glauber’s salt modified 
by the presence of the zinc salt. 
The ammonia and zinc sulphates mixed in atomic proportions, boiled with an ounce 
or two of water, and filtered into an evaporating-dish, form a definite compound with six 
equivalents of water. It forms supersaturated solutions of moderate strength, but very 
sensitive to the action of nuclei, a shower of brilliant crystals falling as soon as the tube 
is opened. Eighty grains of the salt in three drachms of water, boiled and filtered into 
a clean tube, and exposed to the temperature of 4° F., formed large feathery crystals 
with a central quill formed by the junction of two planes of crystallization, the effect 
being very lovely and striking. In snow and water at 32° the crystals balled, ascended, 
and quickly melted. These alternate effects of solidifying and melting were repeated 
three times, when the tube was opened and inspected to see if the whole contents were 
solid. On reinserting the cotton-wool and placing the tube in water at 32°, the solid 
quickly melted with immediate separation of the salt, the act of opening the tube having 
introduced a nucleus from the air. 
Nickel sulphate with 7 equivalents of water forms supersaturated solutions which resist 
a cold of 6°. Mixed with an equivalent weight of cupric sulphate with 5 equivalents of 
water of crystallization and one ounce of water, the mixture when hot is not to be distin- 
guished from the solution of nickel sulphate, but when cold a faint shade of blue comes 
over it. The salts separate in cooling in the air ; but the supersaturated solution is solid 
at 0° F., and produces the beautiful feathery crystals noticed in the case of the solution 
of the ammonia and zinc sulphates, and, like it, rapidly melts at 32° without any sepa- 
ration of salt, if nuclei be excluded. 
A very beautiful display of the leaf-like crystals, and also of the so-called tetrahedral 
crystals, is furnished by a solution of zinc sulphate in one of potash-cdum. The mixed 
solution, which contained the salts in atomic proportions, w r as evaporated to dryness, 
and 200 grains of the salt w 7 as boiled with 5 drachms of water and filtered into a clean 
tube. The solution was bright and viscous, but, as is usual in such cases, the viscosity 
became more equally diffused throughout the solution in the course of a few days. At 
4° F. tetrahedral crystals formed on the surface, and were propagated downwards until 
the whole was solid ; in snow and water it rapidly melted. The tube was left to repose 
during a week, when on examining it again it had thrown down a dense white powder, 
apparently of anhydrous zinc sulphate. On placing the tube in a freezing-mixture at 0°, 
the powder at the bottom increased in volume and formed acicular crystals, while in the 
solution above a series of large leaves resembling ivy gradually ascended to the surface 
of the solution, and even projected above it. In snow-water the ivy-leaves rapidly 
melted, and threw down small bright crystalline grains of alum, while the powder at the 
bottom remained. 
