Advanced inorganic chemistry / by G.H. Bailey ; edited by William Briggs.

  • Bailey, G. H.
Date:
[1898]
Catalogue details

Licence: Public Domain Mark

Credit: Advanced inorganic chemistry / by G.H. Bailey ; edited by William Briggs. Source: Wellcome Collection.

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    It will be noticed that the five gases in the table have very- low critical temperatures ; these gases and hydrogen were until recently called permanent gases, because until 1879 all attempts to liquefy them had failed owing to the temperatures employed being above the critical point. Hydrogen and helium have the lowest critical temperatures of all gases and have only recently been hquefied by Dewar. The boiling point of hydrogen is as low as — 238° 0, liquid hydrogen is only ^^ih. the density of water. Various methods have been employed in liquefying gases. Faraday was able to liquefy a large number of gases by means of their own pressure in glass tubes. To liquefy chlorine in this way the yellow crystals of chlorine hydrate, CI2 8 HjO, arc brought into a glass tube of about 1 cm. in diameter, and closed at one end. The tube is then bent at right angles at about its middle point and sealed. If now the sealed end be placed in a freezing mixture, whilst the other end containing the hydrate be gently warmed, a comparatively large volume of chlorine ia liberated, and the pressure of the accumulated gas together with the low temperature employed is sufficient to bring about its liquefaction. If silver chloride be saturated with ammonia gas, it forms the compound 2 AgCl. 3 NH3, and this body treated in the same way evolves ammonia in such a quantity as to liquefy by its own pressure. Diffusion of gases.—The particles of gases possess a much greater freedom of motion than do those of liquids or solids, for the excursions which they may make are confined in the case of tbe latter to the space occupied by the liquid or solid itself; in the case of gases, however, the extent of these excursions is only limited by the walls of the vessel in which they are contained. Furthermore, if the walls are loose and open in texture, that is, porous, then it is possible for the gaseous particles to traverse them. If a quantity of ammonia be discharged at one end cf a room, the odour of the gas will, after a short time, be perceptible at the other end, even though the temperature of the room is constant throughout and the air still and free from currents.