Liquid Carbon Dioxide

Carbon dioxide was first liquefied by Faraday, in 1823, at a little below 0° C. under a pressure of 36 atm. Faraday's apparatus was simple. Sulphuric acid acted on ammonium carbonate in one limb of a sealed, bent tube, and the gas was liquefied under its own pressure in the other limb, which was immersed in a freezing mixture.

The same principle was employed by Thilorier on a larger scale, in 1839, the apparatus being made of cast-iron. Mareska and Donny improved on Thilorier's apparatus, with which fatal accidents had occurred, by employing two lead cylinders surrounded by copper and connected by a narrow tube. The carbon dioxide was produced and liquefied in the generator, and then distilled into the receiver.

Natterer and Bianchi compressed carbon dioxide by means of powerful pumps, so that it was liquefied in wrought-iron pear-shaped vessels. A similar method is still employed, cylinders of mild steel being substituted for wrought-iron vessels. Carbon dioxide derived from fermentation or from mineral springs is similarly compressed. Liquid carbon dioxide is employed as a refrigerator, for producing high pressures, and in the manufacture of mineral waters.

The vapour pressures of the liquid at different temperatures have been measured by Faraday (1845), Regnault (1862), Cailletet (1878), Amagat (1892), Villard (1897), Kuenen and Robson (1902), and Onnes and Weber (1913). Zeleny and Smith have obtained the following values for the vapour pressures of liquid carbon dioxide:

Temperature ° C	Pressure atm.	Temperature ° C	Pressure atm.
-65.5	330	-40	9.88
-60	435	-30	14.31
-56.4 (triple point)	511	-20	19.52
-50	673	-10	25.83

The constats a and b are those in van der Waals' equation:



Liquid carbon dioxide is colourless; it is soluble in alcohol and ether, but does not mix with water; it dissolves various substances, among which are naphthalene and camphor, carbon disulphide, some hydrocarbons, boric acid, phosphorus pentachloride, arsenic and antimony tribromides, and yellow phosphorus; but iodine and bromine are only slightly soluble, and inorganic salts are insoluble in liquid carbon dioxide.

The density of liquid carbon dioxide at various temperatures compared with that of the gas with which it is in equilibrium is shown by the following results obtained by Amagat:

Temperature ° C.	Liquid density.	Gas density.
0	0.914	0.096
10	0.856	0.133
20	0.766	0.190
30	0.598	0.334
30.5	0.574	0.356
31	0.536	0.392
31.35	0.464	0.464

It will be observed how these values approach each other towards the critical temperature at which, of course, they become identical.