LIQUEFACTION OF GASES. It is somewhat uncertain when the idea that gases could be liquefied first arose. Lavoisier certainly expressed the view that if the earth were cooled to the temperature of outer space, part, at least, of its atmosphere would liquefy, but he made no attempt to liquefy any known gas. His associates, Monge and Clouet, were actually the first to succeed in this direction, liquefying sulphur dioxide by passing it into a glass tube cooled with a mixture of ice and salt. About the same time van Marum and Paets van Troostwyk (179o), compressing ammonia to see whether it obeyed Boyle's Law, found that when a certain pressure was reached the volume suddenly decreased rapidly, and drops of liquid appeared. In the year 1799 Guyton de Morveau liquefied ammonia by cooling the gas to the temper ature of a mixture of ice and calcium chloride. In 18o5 Northmore compressed gases mechanically up to 15 atmospheres, and he appears to have liquefied chlorine.
No further ex perimental investigations can be traced till the year 1823, when papers were read before the Royal Society by Sir H. Davy and his assistant M. Faraday (Phil. Trans., 1923), describing experiments carried out at the Royal Institution. In Faraday's first experiments chlorine hydrate, obtained by cooling chlorine water, was heated in a sealed tube to Too° C, when "chlorine was evolved from it under such pressure that it assumed the liquid form, appearing of a bright yellow colour, and sinking in the warm water without any tendency to mix with it." In a second paper he describes experiments with the apparatus shown in figure T. Compounds which lib erated such gases as chlorine, or sulphuretted hydrogen, were placed in the short limb of the .
glass tube, which was her metically sealed. The substance was heated, and the long limb of the tube was cooled in ice or in a freezing mixture, and in it the gases liquefied. A few weeks later Davy described the liquefac tion of sulphuretted hydrogen, and hydrochloric acid by compres sion, giving data for the pressures required to liquefy these gases at different temperatures. His paper is of importance, as it shows that in 1823 Davy had already installed apparatus for the compression and liquefaction of gases at the Royal Institution.
Ill health prevented him from continuing his researches in this direction.
In 1834 Thilorier developed a method already in vogue for the manufacture of soda water, and applied it to the condensation of carbon dioxide in large quantity. Two stout metal vessels, at first made of cast-iron, but, after an accident, of copper, and lined with lead, served as the generator and receiver in Faraday's experiments. One of these was fitted with a cap which could be removed, and a cock, and in it was placed solid bicarbonate of soda and a vessel containing sulphuric acid. The other vessel was fitted with a stop-cock only, and the two vessels were joined by a connecting tube which could be detached. The generator was charged, and closed, and then rotated, so as to mix the acid and soda. It was then con nected with the receiving vessel, which was cooled in ice, and in this the gas liquefied. The stop-cocks were then closed, the vessels were separated, and, by re-charging the generator a second and third charge of gas could be condensed in the receiver. Thilorier observed that the liquid expanded rapidly when heated. He also found that when the liquid was allowed to escape through a jet into a box lined with non-conducting material a snow-like solid was formed. His observation that this solid carbon-dioxide mixed with ether was a much more efficient refrigerant than the solid alone was a valuable contribution to the experimental side of the subject.
The first to apply the results of Thilorier's work, which was carried out from a technical standpoint, to scientific investigations, was Faraday. His method of investigation was as follows. The mixture of solid carbon dioxide and ether was contained in an earthenware vessel of Too cu.cm. capacity, which fitted into a larger earthenware vessel, three or four folds of dry flannel intervening. The temper ature measured by an alcohol thermometer was —78° C, but by placing the apparatus under the receiver of an air pump, and reducing the pressure to 1.2 in. of mercury, a temperature of — I
C was reached.