470 
DR. J. H. VINCENT ON THE DENTSTY AND COEFFICIENT 
1ms been tabulated as three times tlie linear, but the legitimacy of this procedure is 
open to grave doubt in the case of a l)ody like ice Avbich is endowed with hexagonal 
symmetry of structure. 
Principle of the Afethod employed. 
Since the question of the density of ice was still, in spite of all the labour that had 
been spent upon it, in a far from satisfactory state, and since a direct determination 
of the Cubical Coefficient of Expansion had not been attempted since 1852, 1 aa'us 
desirous of employing a method which should yield both results. In order that the 
work should have any value, it AAms necessary to employ some device f)ther than any 
which had been used previously. 
Tlie method of weighing ice in mercury was one whicli naturally sugge.sted itself 
Eor the })urpose of a sinker tAvo metals are aAmilahle, tungsten and platinum. 
Tungsten is difficult to Avork, but is readily procurable in any amount ; if mercuiy 
attacks tungsten this could be avoided l;)y protecting it by an iron shell. Although 
this direct method AA'asnot employed, I helieA’e that the use of a platinum or tungsten 
sinker for AA-eio’hino- ice in mercurv Avoidd he Avell Avorth the attention of future 
Avoi’kers. 
The necessity of a sinker can Ije done aAA'ay Avith if the buoyancy of the ice is 
obtained by determining the tension of a Avire Avhich moors it to the bottom of the 
A'essel. The tension of the Avire may he found l)y passing it through a small hole in 
the l)ottom of the mercury-containing A’essel, Avhich latter must l)e closed at the top 
so that the mercury Avill not pour out of the hole through Avhich the AA’ire comes. 
This method olndates the use of a l)alance, for a scale jjan may he hung on the Avire, 
and equilibrium oljtained by suitably adjusting the suspended Aveights. Joly has 
used this principle in the construction of a l)alance (Joly, ‘Phil. Mag.,’ September, 
1888), and my apparatus differs from his, in that I introduce the material Avliose 
density is to l)e determined and use it as the float. 
The adA’antao’es to he deriA’ed from the use of mercury are seA’eral. It can easilv 
l)e obtained quite pure, is Avithout soE'ent action upon either AA'ater or ice, and its 
coefficient of expansion is of the same order of magnitude as tliat of ice. Further, 
this coefficient is known Avith greater accuracy. Tlie use of a liquid Avhose coefficient 
of expansion is near that of ice is lielpful in determining the density at 0° (A, and 
also in the determination of the coefficient of culiical expansion. 
In order to determine the density at 0° C. it Avould he sufficient under ideal 
conditions of temperature to find the liuoyaiicy of an iiiA'erted A’essel in mercury, to 
introduce air-free Avater into this Amssel, to determine the liuoA’ancA" of the A’essel and 
also that of the Avater in its liquid and solid state. The experiments Avere performed 
liy equilibrating the ice at temperatures heloAv zero, and to find the density at these 
temperatures we must alloAv for the contraction of the mercury and of the vessel 
containing the ice. The equilibration of the Avater aauis always performed at zero. 
