1902.] Expansion of Ice, etc., at Low Temperatures. 



243 



there is no distinction between the solid and liquid forms of water. 

 At temperatures below this limit no amount of pressure would trans- 

 form ice into water. We are thus relieved from a difficulty that would 

 follow but for this demonstration of Clausius, namely, that the appli- 

 cation of enormous pressures to ice, even at temperatures below that 

 of liquid hydrogen, might cause the transformation of ice into water. 



Carbonic Acid. — Two experiments were made with this substance, 

 the masses in each case being about 20 grammes. These were com- 

 pressed cylinders ; the former was compressed dry, while the latter 

 was slightly moistened with ether. The data and results are given in 

 Table III. 



The density of solid carbonic acid at its boiling-point was formerly 

 given as 1*5,* but the mean of my results at the time came to 1*53. Ee- 

 cently the same value has been found by Behn. Taking this value and 

 1*6267, the mean of the above results at - 188 *8 C, and using the 

 formula d T = d T {l -f cc (T - T)} we get a. = 0-0005704. 



This is a very large coefficient of expansion, being greater than that 

 of any substance recorded in Table I, and comparable with that of 

 sulphur between 80° and 100°, which, according to Kopp, is 0*00062. 

 The coefficient of liquid carbonic acid at its melting-poiut taken from 

 the recent observations of Behnf is 0-002989, so that the rate of 

 expansion of the liquid at its smallest value is very nearly five times 

 that of the solid. 



Solid Mercury. — One experiment was made with solid mercury, of 

 which the details are given in Table I. 



Mallet determined with great accuracy the density of solid mercury 

 at -38°'85, his result being 14*193; coupling this with the density 

 found for the liquid-air temperature, we find the value of the 

 coefficient of expansion between the melting-point and - 189° C. is 

 0*0000887. For fluid mercury above 0° C. the mean value is about 

 0*000182, so that in the solid state this coefficient is about half of that 

 in the fluid state. 



Notes on the Results of Table I. . 



Sodium, extending down to low temperatures, has a coefficient about 

 the same as that of mercury at the ordinary temperature. The coeffi- 

 cient for sulphur is about half of that between 0° and 100°, being 

 '0002 2 37, and that of iodine is not far removed from the value 

 0-000285 given for the solid at ordinary temperatures. The rate of 

 expansion of liquid iodine is about three times this value Paraffin 

 ought to have a value of 0*0004633 from Fizeau, but Bodwell's 

 coefficient between 0° and 38° is 0*00035. The value found for 



* See ' Proc. Roy. Inst.,' 1878, " The Liquefaction of Gases." 

 t ' Chem. Jour./ 1901. 



s 2 



