594 



NATURE 



• [October i6, 1890 



cation to the current number of Liebtg's Annalen (Band 

 259, Heft I, p. 100). 



The work includes the determination of the vapour- 

 tension of liquid chlorine at temperatures from - 88° C. 

 to 146° C. (its critical point), a complete examination of 

 its behaviour near the critical point and the determina- 

 tion of its specific gravity and coefficient of expansion 

 for a range of temperature between — 80° and + 80°. 



Liquid chlorine generally appears to possess a yellow 

 colour. When, however, the colour of a long column is 

 examined, it is found to have a distinctly orange tint. 

 The absorption spectrum does not exhibit any character- 

 istic bands, but the blue and violet portions of the spec- 

 trum are completely absorbed, the transmitted spectrum 

 thus consisting of the red, orange, yellow, and green. 



Vapour-Tension of Liquid Chlorine below its 

 Boilittg- Point. 



The apparatus used for this determination consisted of 

 a kind of distilling flask, whose side tube was connected 

 by means of a piece of strong-walled caoutchouc tubing 

 with a wide manometer tube. The flask was about half 

 filled with liquid chlorine, and was immersed in a bath 

 also containing liquid chlorine whose temperature could 

 at the same time be kept equal throughout, and be very 

 finely regulated by means of a current of air driven in 

 through a tube passing to near the bottom of the bath. 



In commencing a series of determinations the chlorine 

 in the flask was first made to boil, thereby driving out the 

 air remaining in the apparatus. The neck was then 

 closed by means of a caoutchouc stopper well coated 

 with glycerine, and the open end of the manometer 

 was allowed to dip into a vessel containing concen- 

 trated sulphuric acid. As the flask became cooled 

 by immersing it in the cold chlorine in the bath, 

 sulphuric acid was drawn into the manometer until it 

 attained a height of 3-5 cm., when the caoutchouc con- 

 nection was momentarily pinched while the open end of 

 the manometer was transferred to the mercury trough. 

 The small column of sulphuric acid thus standing above 

 the mercury column effectually protected it from the cor- 

 roding action of the chlorine. The bath was then cooled 

 gradually, and a series of readings taken of the tempera- 

 ture of the bath, by means of an alcohol thermometer, 

 and of the position of the meniscus of the mercury in 

 the manometer. The small column of sulphuric acid was 

 of course calculated to its equivalent height of mercury, 

 and added to the measured height of the mercurial column. 

 By careful use of the current of dry air the liquid chlorine 

 of the bath was found capable of being reduced in tem- 

 peratlire as low as —60° C. The lower temperatures, 

 down to —88°, were attained by mixing more or less solid 

 carbon dioxide with the chlorine. The results obtained 

 are given in the table at the end. 



Determinatioft of the Pressure of Liquid Chlorine frojn 

 its Boiling- Point to 40° C. 

 The data at present existing upon this subject are very 

 meagre and conflicting. Davy and Faraday found the 

 pressure at 15° C. to be 4 atmospheres, whilst Niemann 

 gives the pressure at 0° C. as 6 atmospheres, and at 

 I2°"5 C. as 8 atmospheres. As this is a most important 

 point in regard to the storage of liquid chlorine in metal- 

 lic bottles, great pains have been taken to arrive at unim- 

 peachable results, and as the most certain method of 

 measuring the pressure a high column of quicksilver 

 was employed. 1 he apparatus consisted of a U-tube, one 

 limb of which was narrower than the other, and pro- 

 longed upwards to a height of over 8 metres. The other 

 and wider limb was joined at the top by means of a capil- 

 lary tube to a cup, serving the purpose of a funnel for intro- 

 ducing the liquid chlorine. In commencing an experiment, 

 a convenient quantity of mercury was first poured in so 

 as to stand in the wider limb at about a quarter its height. 



NO. 1094, VOL. 42] 



A column of sulphuric acid was then introduced into the 

 wider limb so as to protect the mercury, and finally the 

 liquid chlorine was introduced through the funnel by a pro- 

 cess of alternately warming and cooling ; the cooling was 

 effected by pouring a little liquid chlorine over a piece of 

 cotton wrapped round the limb and evaporating it by a 

 strong current of air. When the limb was quite full, the 

 chlorine occupying the capillary tube was evaporated by the 

 warmth of a small blowpipe flame, and the capillary fused 

 up. The apparatus was then immersed, until the wider 

 limb was covered, in a bath of liquid sulphur dioxide for 

 temperatures up to 0°, in ice for the determination at o', 

 and in water agitated by a current of air, and either cooled 

 by ice or warmed by a small flame for temperatures up to 

 40°. For the comparatively higher of these temperatures 

 it was of course necessary to pour mercury into the longer 

 limb so as to prevent the mercury in the wider limb being 

 driven round the bend. Complete results are given at 

 the end, but it may be remarked in passing that the 

 pressure at 0° is 3-66 atmospheres ; and at 15°, 575 

 atmospheres. 



Determination of the Pressure at Higher Tetnperatures. 

 For these yet more dangerous and difficult experiments 

 a metal apparatus was employed, similar in principle to 

 that just described, except that the pressures were measured 

 by a metal gauge manometer, which had previously been 

 completely tested and its readings verified. It was found 

 important in these experiments not to employ too much 

 chlorine, as owing to the immense coefficient of expansion 

 the whole space might become full of liquid, and further 

 heating would cause the generation of dangerously high 

 pressures. For temperatures up to 100° a water-bath 

 was employed, and for the higher temperatures up to the 

 critical point 146° an oil-bath, both kept in circulation by 

 a rapid current of air. The pressure at the critical 

 temperature of 146° C. was found to be as high as 93*5 

 atmospheres. 



Critical Point of Liquid Chlorine. 

 The critical point was determined in a separate ex- 

 periment, and some very interesting results were obtained, 

 the yellowish green colour of chlorine perhaps assisting 

 in rendering the appearance of what has sometimes been 

 termed the fourth state of matter between the liquid and 

 the gaseous more distinct than usual. A hard glass tube 

 of 8 mm. diameter was about one-third filled with re- 

 distilled dry liquid chlorine and sealed. A small thermo- 

 meter, whose readings commenced at 140°, was attached 

 to it by platinum wire, and the whole very slowly heated 

 in a bath of vaseline. The observations were made with 

 the naked eye, the observer being protected from any 

 possible explosion by a thick glass plate. At 140° ex- 

 tremely small bubbles began to be developed throughout 

 the mass of liquid. At 144° the hitherto sharp meniscus 

 began to disappear, and at 145° the presence of a liquid 

 was only evident by the more intense yellow colour and 

 higher refractive power of the lower portion of the tube. At 

 146° the contents of the tube were homogeneous through- 

 out, the critical point being attained, and the liquid con- 

 verted into gas. On allowing the tube to cool slowly, the 

 condensation always commenced below 146°, with the 

 formation of a cloud and a fine rain of minute yellow 

 spheres of liquid chlorine. The rain was generally ap- 

 parent throughout the whole of the upper portion of 

 the tube. Sometimes, however, the liquid meniscus 

 again appeared without any previous manifestation of 

 precipitation. 



Specific Gravity and Expansion of Liquid Chlorine. 



It is a curious fact that many gases when compressed to 

 the state of liquid expand enormously when heated as com- 

 pared with ordinary liquids, the amount of expansion some- 

 times exceeding that of the gas itself. Liquid chlorine is no 



