August 1, 1892.] 



KNOWLEDGE. 



141 



^C^ AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: AUGUST 1, 1892. 



CONTENTS. 



By Vauohan Cornish, 



The Liquefaction of Gases 

 M.Sc, F.C.S 



Bee Parasites — II. By E. A. Butler 



On the Cause of Earthquakes. By tin- Eev. II. N. 

 HtTciiiNsox, B.A., F.Cx.S. ... 



Planetary Nebulae. By Miss A. M. Clkrke 



Lightning Photographs. By A. C Eantaru 



Letters :—F. H. Glew; W.H.S. MoNCK 



Notice of Book ... 



Ruminants and their Distribution. Bv R. Lydekker, 

 B.A.t'antiib 



The Currents of the North Atlantic. By Richard 

 Bia-xoN, F.R.G.S " 



The Face of the Sky for August. By Herbert 

 Sadlkk, F.R.A.S 



Chess Column. By C. D. Locock, B.A.Oxon 



141 

 143 



145 

 148 

 149 

 150 

 151 



152 



155 



158 

 159 



THE LIQUEFACTION OF GASES. 



By Vaughan Cornish, M.Sc, F.C.S. 



THE commou liquids, such as water, rock oil, mercury, 

 and so on, can be readily converted into gases ; 

 but many of the commou gases, on the other hand, 

 for instance oxygen, nitrogen, and hydrogen, can 

 only be brought into the liquid conclition by the 

 use of special methods and powerful agencies. Tempera- 

 ture and pressure are the two factors on which it depends 

 whether a body remains in the state of gas or assumes the 

 liquid condition. Low temperature and high pressure are 

 the conditions favourable to liquefaction. 



The history of experiments on liquefaction of gases is 

 mainly a record of devices for producing high pressure and 

 low temperature. Sulphurous acid gas is condensed at the 

 temperature of an ordinary freezing mixture, or at the 

 pressure which can be obtained by a hand-worked piston in 

 a tube or barrel. It had been prepared in the li(iuid state 

 before the year 1800 a.d. Chlorine was condeused by 

 Northmore in 1805, but his experiments attracted little 

 attention till years later, when Faraday had made a 

 speciality of the liijuefaction of gases, and the atten- 

 tion of the scientific world was drawn to the subject. 

 Then, as usually happens, forgotten records were found of 

 earlier work on the same lines. The later, but indepen- 

 dent, observation by Faraday (1823) of the liquefaction 

 of chlorine is, however, the commencement of the 

 systematic study of the subject. Faraday has the only 

 kind of priority which is of real importance in scientific 

 discovery— that, namely, of baing the first to make the 



subject fruitful, and the first to make its importance 

 generally understood. Faraday had been experimenting 

 on the solid hydrate of chlorine which separates out in 

 yellowish crystals when ice-cold water is saturated with 

 chlorine gas. Sir Humphry Davy, to whom at that time 

 Faraday acted as assistant, suggested that the crystals 

 should be sealed up in a glass tube and heated. Davy 

 gave at the time no reason for his suggestion, and 

 Faraday himself did not know what to anticipate from 

 the experiment. The crystals of the solid hydrate were 

 placed at one end of a A-shaped glass tube, which was 

 then closed by sealing up the glass in the blow-pipe fiame. 

 The crystals being warmed to 60° F., underwent no 

 change, but at 100° F. " the substance fused, the tube 

 became filled with a bright yellow atmosphere, and on 

 examination was found to contain two fluid substances ; 

 the one (chlorine water), about three-fourths of the whole, 

 was of a faint yellowish colour, having very much the 

 appearance of water ; the remaining fourth was a heavy 

 bright yellow fluid, lying at the bottom of the former 

 without any apparent tendency to mix with it." At 70' F. 

 the pale portion congealed {i.e., the hydrate separated out), 

 although even at 32° F. the yellow portion did not solidify. 



Heated up to 100° F., the yellow fluid appeared to boil, 

 and again produced the bright coloured atmosphere. It 

 was found that by heating to 100° F. the yellow liquid 

 (fluid chlorine) could be distilled from the pale coloured 

 liquid (chlorine water) so as to get them in difierent limbs 

 of the bent tube. " If, when the fluids were separated, the 

 tube was cut in the middle the parts flew asunder as if 

 with an explosion, the whole of the yellow portion dis- 

 appeared, and there was a powerful atmosphere of chlorine 

 produced ; the pale portion, on the contrary, remained, and 

 when examined proved to be a weak solution of chlorine in 

 water with a little muriatic acid." 



The paper from which the above extracts are taken was 

 read before the Royal Society by Sir Humphry Davy in 

 1823. In a note at the end of Faraday's paper, Davy says 

 that " in desiring Mr. Faraday to expose the hydrate of 

 chlorine to heat in a closed glass tube, it occurred to me 

 that one of three things would happen : that it would 

 become fluid as a hydrate ; or that a decomposition of 

 water would occur (forming hydrochloric acid) ; or that 

 the chlorine would separate in a condensed state." Further 

 on he remarks, " I cannot conclude this note without 

 observing that the generation of elastic substances in close 

 vessels, either with or without heat, oft'ers much more 

 powerful means of approximating molecules than those 

 dependent upon the application of cold, whether natural or 

 artificial, for as gases diminish only about ^-J-^ m volume 

 for every degree of Fahrenheit's scale, beginning at ordinary 

 temperatures, a very slight condensation only can be pro- 

 duced by the most powerful freezing mixtures, not half as 

 much as would result from the application of a strong 

 flame to one part of a glass tube, the other part being of 

 ordinary temperature, and when attempts are made to 

 condense gases into fluids by sudden mechanical compres- 

 sion, the heat, instantly generated, presents a formidable 

 obstacle to the success of the experiment, whereas in the 

 compression resulting from their slow generation in close 

 vessels, if the process be conducted with common pre- 

 cautions, there is no source of difficulty or danger, and it 

 may easily be assisted by artificial cold, in cases where 

 gases approach near to that point of compression and 

 temperature at which they become vapours." 



This " bent tube " method was successfully employed by 

 Faraday in the liciuefaction of a number of other gases. 



In 1822, the year preceding Faraday's experiments on 

 chlorine, C'aignier de la Tour had examined the effects 



