CHEMICAL AND PHYSICAL NOTES, _ 81 
of some of the salts in sea-water must be lower than this tempera- 
ture. The temperature of this mixture of ice and brine must be the 
freeing temperature of the brine and the melting temperature of ice 
in the brine. 
It has been said that above the cryohydric temperature crystals 
of the salt and of ice cannot be brought together without liquefaction. 
When air is saturated with moisture at temperatures below 0° C. 
the moisture is deposited as rime, which is ice. If the surface on 
which it is deposited is a soluble salt, and if the temperature is above 
the cryohydric temperature of the salt, liquefaction will take place at 
the point of deposit. Hence it follows that every salt is deliquescent 
at temperatures between 0° C. and tts cryohydric temperature. 
Numerical data regarding the freezing-points of saline solutions 
are to be found in collections of physical tables such as those 
published by the Smithsonian Institution. 
The following table gives the freezing-points of saturated solu- 
tions of a number of salts, as recently determined with the greatest 
care by L. C. de Coppet,* who was the first to prove and to clearly 
enunciate the relation which exists between the molecular weight of 
a salt and the freezing-point of its aqueous solution. 
Tasie I. 
Amount of 
Salt Freezing 
Salt dissolved. dissolved in Temperature 
100 grms. of Solution. 
water. 
grms. °C. 
Chloride of potassium . . . . . . KCl 24°6 —11°16 
Chloride ofsodium . . . ... . NaCl 29°6 —21°85 
Chloride of ammonium go A. Gh OS Be NH,Cl 22°9 —15°8 
Nitrate of potassium. ay Ue? Us “en Mb KNO,; 10°7 — 2°85 
Nitrate of sodium. ie ee Use Tan bas NaNO, 58°5 —18°5 
Nitrate of ammonium . : . .!| NH,NO, 70°0 -17°35 
Nitrate of barium . . . é . | Ba(No,), 4:5 -— 07 
Nitrate of strontium. . . oe Sr(NO,)- 32-4 — 5°75 
Nitrate oflead . . . » . . . | Pb(NO,), 35°2 - 27 
The meaning of this table is that if, for example, we take 
29°6 germs. of common salt (NaCl) and dissolve it in 100 grms. of 
water, which will take some little time, and we then expose it to an 
Antarctic temperature such as — 25° C. or — 30° C., the temperature 
of the solution will fall until it reaches — 21°°85 C., when it will 
* Zoits. f. Phys. Chem., vol. xxii. p. 239. 
a 
