42 ROYAL SOCIETY OF CANADA 
touching one another. The length of these tubes allowed the solution to 
be well submerged in the protection bath, and, therefore, almost freed it 
from the influence of the outside temperature. 
In the determination of the freezing-point of a solution these tubes 
were surrounded by a mixture of salt water and pieces of ice contained in 
a vessel of glass 35 cm. high and 11 em. in diameter (called the protection 
bath). The cover for this vessel was one taken from the protection bath 
of a Beckmann apparatus. This vessel stood in a large earthenware jar (J) 
which was filled with water and ice at the temperature 0°, and over both 
these vessels, which were of the same height, was placed a covering of 
thick felt. The protection bath could, with these surroundings, be kept 
at a constant temperature, within a fiftieth of a degree, for at least fifteen 
minutes. This constancy of temperature was found necessary in order to 
obtain consistent determinations of the freezing-point. 
The bath was kept continually stirred, and any change of tempera- 
ture was quickly recorded by means of a thermometer (P) graduated to 
a fiftieth of a degree. The temperature of the bath could be raised by 
the addition of water at the temperature of the room, or lowered by the 
addition of pieces of ice,—snow, when obtainable, being preferable. 
The plantinum stirrer for the freezing-tube was of the common ring 
shape, having wound around its ring a thin platinum wire which would 
rub against the wall of the tube and thereby prevent the formation of an 
ice sheath. With constant stirring there appeared no tendency for the 
ice to mass itself together and float to the surface, but it could be seen 
moving through the whole solution in tiny, glistening particles. The 
stirrer for the protection-bath was of thick brass wire, with two rings, 
one for the upper and the other for the lower portion. Both these stir- 
rers were worked mechanically by means of the hot-air motor mentioned 
above, which required only a small Bunsen burner to drive it, and was 
placed at a distance of about 3 metres from the freezing-point apparatus. 
By means of a light belt this motor turned a wooden wheel (W) placed 
over the protection-bath. A connecting-rod (À) connected this wheel to 
a slider on a vertical guiding rod ; and to this slider also were attached 
the two stirrers. Any range of stroke could be obtained by varying the 
distance of the connecting-rod from the centre of the wheel. As about 
70 cc. of solution were used, a stroke of 11 cm. was required to cause the 
ring of the stirrer in the freezing-tube just to touch the bottom of the 
tube and reach to within } cm. of the surface of the solution. Thus all 
solutions were throughout uniformly stirred, and as the stroke of the 
engine was quite constant, every solution was stirred in exactly the same 
manner. 
Another glass vessel of the same dimensions as the protection bath 
contained salt water and ice at a temperature of about—10° C. (called the 
freezing-bath). The purpose of this bath was to reduce the solution in 
the freezing-tube to about 0°3 degree below the freezing-point. 
