422 Professor Sir James Deivar [Jan. 16, 



sudden cooling. That the expansibility is being diminished at very 

 low temperatures may be inferred from the fact that clear pieces of 

 ice that have been slowly cooled to the temperature of liquid air when 

 dropped into liquid hydrogen do not crack, although the relatively 

 sudden drop in temperature is actually in this experiment greater than 

 in the similar experiment with liquid air. The limiting density of ice 

 at low temperatures may be determined from observing that it floats 

 upon the surface of liquid oxygen, while it sinks in liquid nitrogen, 

 the density of the former liquid being 1-13 and the latter 0*81. 



Solid Carbonic Acid at Low Temperatures. 



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

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

 Recently the same value has been found by Behn. Taking this 

 value and 1-6267, the density found at —188-8° 0., the mean coeffi- 

 cient of expansion is found to be - 0005704. This is a very large 

 coefficient of expansion, being greater than that of any substance 

 recorded in Table I. on page 423, and comparable with that of sulphur 

 between 80° and 100°, which, according to Kopp, is 0-00062. The 

 coefficient of expansion of liquid carbonic acid at its melting-point 

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

 rate of expansion of the liquid at its minimum value is very nearly 

 five times that of the solid. When solid carbonic acid was subjected 

 to pressure in the same steel cylinder as was used in the ice ex- 

 periments, a wire of the solid, composed of a series of adhering disc- 

 like plates, was easily formed. 



Coefficients of Expansion ; Hydrated Salts ; Organic Bodies, 

 ETC., AT Low Temperatures. 



A general summary of the values found for the coefficients of 

 expansion between 17° and — 188° of a number of substances is given 

 in Table I. on page 423. 



In the solid state mercury has a coefficient about half of that in 

 the fluid state, while sodium has about the same value as that of 

 mercury at the ordinary temperature. The coefficient for sulphur is 

 about half of that between 0° and 100° C.,-and that of iodiue is not far 

 removed from the value given for the solid at ordinary temperatures. 

 The rate of expansion of liquid iodine is about three times this value. 

 The value found for naphthalin is about half that of the liquid near 

 its melting-point. 



With the exception of carbonate of soda and chrome alum, 

 hydrated salts have a coefficient of expansion not differing greatly 

 from that of ice at low temperatures. It will be noted that iodoform 

 is a highly expansive body like iodine, and that oxalate of methyl has 



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

 t Chem. Jour., 190i. 



