672 ME. CHAELES TOMLINSON ON SUPEESATUEATED SALINE SOLUTIONS. 
Potassic chlorate, potassic ferrocyanide, baric nitrate, and plumbic nitrate gave similar 
results. 
Ammonium-nitrate solution gave apparently some signs of supersaturation ; but the 
observation is liable to error from the fact that at high temperatures ammonia is given 
off. According to Karsten, 100 parts of water at 64°5 F. dissolve 199 - 54 parts of the 
salt. A hot solution (2 salt to 1 water) was filtered into a clean flask moistened with 
a few drops of liq. ammon. Such a solution remained during an hour or so at 40°, when 
it suddenly crystallized. I may, however, remark that a number of authorities differ in 
their determination of the solubility of this salt. But if the observation be correct, the 
behaviour of this anhydrous salt resembles that of some salts that crystallize with only 
a small proportion of water of crystallization. Baric chloride (Ba Cl + 2 Aq) is a case in 
point. According to Brande’s Table, 100 parts water at 99 0, 5 F. dissolve 51 parts of 
the salt. This is equal to 244 grains of salt to one ounce of water. A solution of this 
kind cooled from the boiling-point to 100° without depositing salt, and it was not until 
the temperature had fallen to about 66° that the salt separated, and then it did so 
abundantly. 
VI. Summary. 
My experiments lead me to the conclusions, first, that the state of supersaturation in 
saline solutions is a real and not an apparent one, and is due in the majority of cases, 
where the solutions are kept in chemically clean flasks, to the absence of nuclei or other 
predisposing cause to crystallization ; 2nd, that in the few cases where salts of a lower 
degree of hydration are formed in such solutions, the effect is not due to a predisposing 
molecular change in the solution, but to the deposit of a portion of the anhydrous salt, 
or of a monohydrated salt, which, entering again into solution, forms a dense lower sub- 
stratum from which the modified salt crystallizes out ; 3rd, that anhydrous salts do not 
form supersaturated solutions. 
The salts examined in this memoir may be arranged into five groups according to 
their behaviour : — 
I. Salts of which the supersaturated solutions remain liquid at low temperatures. 
Examples : — Sodic acetate. 
Sodic sulphate. 
Sodic arseniate. 
Sodic succinate. 
Sodic borate. 
Sodio-potassic tartrate. 
Potash alum. 
Magnesic sulphate. 
Baric acetate. 
Calcic chloride. 
Cupric sulphate. 
