146 Proceedings of Royal Society of Edinburgh. [mar. 21 , 
containing 11*87 per cent., 70 per cent, of the water in it must be 
removed. Hence in sea-water freezing at a final temperature of 
- 7° *2 C. there is formed 70 per cent, of ice, and there remains 
liquid 30 per cent, of brine. Freezing began at the mean temperature 
— 8°*7 C., and the latent heat of pure ice at this temperature is 75. 
Calculating the latent heat of this mixture from the heat liberated 
in the calorimeter during freezing, and assuming that the whole 
mass had solidified, Pettersson’s results give the mean latent heat 
of this sea- water as 52*1. Calculating the apparent latent heat on 
the assumption that 70 per cent, of the mass solidifies into pure 
ice and that 30 per cent, remains liquid, we get the number 51*5. 
On all grounds therefore we must conclude that pure ice is the 
primary product in freezing sea- water and saline solutions of mode- 
rate concentration. 
The plasticity of ice and the motion of glaciers receive a simple 
and natural explanation when we see, as in Table IX., that, if the 
water from which this ice is produced contains no more than 7 
parts of chlorine per millon, it will, in the process of thawing, 
when the temperature has risen to - 0°*07 C., consist to the extent 
of 1 per cent, of its mass of liquid brine or water. The water 
considered in Table IX. is certainly not less free from foreign 
ingredients than rain or snow. It follows, therefore, that a glacier, 
in a climate where the temperature is for the greater part of the 
year above 0’° C., must have a tendency to flow , owing to the power 
of saline solutions to deposit ice and to dissolve it at temperatures 
below 0° C. 
The verification of thermometers by comparison with the air 
thermometer is always troublesome. It results from the above 
investigations that, if the temperature at which ice melts in solu- 
tions of a salt, such as chloride of calcium of different degrees of 
concentration, were once and for all carefully determined by means 
of a standard air thermometer, a thermometer could be indirectly 
hut satisfactorily compared with the air thermometer at temperatures 
below 0° C. by immersing it in a mixture of ice and chloride of 
calcium solution, and taking a series of readings of the thermometer 
and samples of the brine simultaneously. By determining the 
chlorine in the samples the concentration of the brine is ascertained, 
and the comparison with the standard effected. 
