Tlif Density and Coefficient of Cubical Expansion of Ice. 423 



Two tables are given showing in the first all the results which have 

 been published concerning the density and coefficient of cubical expan- 

 sion of ice, and in the second the same results tabulated separately 

 according to the variety of ice used. The mean result for the density 

 of natural ice at freezing point is 0-9176, while that of artificial ice 

 is 0*9162 gramme per cubic centimetre. Only one estimation of the 

 dilatation of natural ice is available. It is 0-0001125 for the cubical 

 coefficient per degree C. The mean of three available results for 

 artificial ice is 0-000160. 



It was thought desirable to use a method of experiment which 

 would yield a result both for the density and for the coefficient of 

 cubical expansion, and in order that the work should have any value it 

 was necessary to employ some device other than any which had been 

 used previously. 



The method consisted in weighing a quantity of water in mercury. 

 The water was weighed both as liquid at C., and as solid at several 

 temperatures below freezing point. If we assume values for the 

 density of water and mercury at C., the density of ice at C. can 

 then be calculated, if we also assume that the densities of ice and 

 mercury are linear functions of the temperature. The coefficient of 

 cubical expansion of ice can also be calculated from these results, but 

 it will depend on the law assumed for the contraction of mercury, and 

 upon the accuracy of the thermometry. 



Instead of using a sinker to keep the vessel containing the water or 

 ice under the surface of the mercury, a modification of Joly's Hydro- 

 static Balance was employed.* 



Ten values of the density of ice at different temperatures below 

 C. were obtained in this way. The specimens of water were four in 

 number, and the temperatures ranged from - 10'02 to - 0'37 C. The 

 whole of the weighings taken with the final form of apparatus are 

 included in these determinations. 



In one experiment the values obtained show unmistakably that 

 the same specimen of water may assume different densities on 

 freezing. 



The ten values of the density are set out as functions of the tempera- 

 ture on a chart, and a graphical method is used to extrapolate for five 

 values of the density of C. These five values have weights 

 assigned to them proportional to the number of separate determina- 

 tions of the density from which they are derived. The numbers thus 

 obtained and the weights to be assigned to them are set out in the 

 following table. 



* July, ' Phil. Mag.,' September, 1888. 



