CHEMICAL AND PHYSICAL NOTES. 107 
quantity W, of water, then the value of the product W» (¢, — T,) is 
constant for some salts; in the case of others it increases as Wg, or 
the amount of water, increases ; in the case of others again it decreases 
as dilution increases. 
The product of a mass into a temperature is a quantity of heat. 
Therefore, the expressions W; (Ty — t-) and Wz (¢, — T,) represent 
quantities of heat.* The physical meaning or interpretation of the 
statement that either of these products is constant, when the propor- 
tion between the factors in it varies, is that water can contain more 
heat without boiling, and less heat without freezing, im proportion to 
the amount of salt dissolved in it. 
This is a general law of which Blagden’s law of freezing is a 
particular case. 
The phenomena accompanying the freezing and the boiling of 
saline solutions have always been perplexing. Salt-water ice melts 
at a lower temperature than fresh-water ice, and it is impossible to 
prepare pure water from it; therefore it was held by some that the 
salt must belong to the ice. But by skilfully managing the melting, 
the temperature may approach very near to 0°C., and the water 
prepared from it may contain very little salt, and may be drinkable; 
therefore it was held by others that the salt belonged to the brine. 
The available experimental data did not conclusively prove either 
that the salt belongs exclusively to the ice or to the brine. The 
proof that the salt does not belong to the ice was furnished by 
showing that snow or other pure ice, of independent origin, which 
contains no salt, behaves in a saline solution in exactly the same 
way as the alleged ice formed by freezing the solution. 
Again, regarding the boiling of saline solutions, it was observed 
that the boiling temperature of a saline solution is higher than that 
of pure water, that the steam produced by it is pure steam, and that 
a thermometer in the steam above the boiling solution shows the 
same temperature as it would if immersed in steam above pure 
boiling water. The question which vexed many minds, was: When 
the steam is just quitting the solution, has it the temperature in- 
dicated by the thermometer immersed in the steam alone, or has it 
that of the thermometer immersed in the boiling solution? It was 
held by some that the temperature of the thermometer immersed in 
steam must be held to prove that the steam leaves the solution at the 
temperature of pure boiling water. Others contended that, although 
we have no means of knowing at what temperature steam would 
condense on perfectly dry glass, the moment there is the slightest 
* ‘Steam and Brines,’ p. 544. 
