Indian Journal of Chemical Technology Vol. I 0. March 20m. pp. 22:l-23(i

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Louis Paul Cailletet-The liquefaction of the permanent gases

Jaime Wi sniak '1'

Department of Chemical Engi neering. 13cn-G urion Universi ty or the cgcv. Bccr-Shcva. Israel R4 1 0.')

To Louis Paul Ca illetct ( l lD 1- 1913) we owe the rea l ization of the liquefaction of permanent gases using a free expan­sion process. A bri lli an t analysis of an ex perimental mishap led him to achieve thi s possib ility. The priority or oxygen lique­faction was and continues to be a matter of di scuss ion. The life and sc ientific work or Caillctet arc descri bed toget her w ith detai ls about the prior ity polemic.

Mankind has been interested in quantifying the differ­ence bet ween hot and cold si nee very old times. The ori gi nal apparatus, ca lled thennoscopes, served merely to show the changes in the ten~perature of its surroundings. Eventuall y th e need arose for quanti­fying these observati ons and the eli fferent thermome­ters began to be developed. Astronomers built most of these instruments , particularly for measuring low temperatures 1• Development of thermometri c sca les such as those of Reaumur, Fahrenheit and Celsius, led in a natural way to the question whether there was a lower I i mit to tempera ture, and corresponcli ngly, to the behaviour of materia Is u ncler those circumstances.

While study ing the proper way to ca librate an ai r thermometer Guillaume A montons ( 1663- 1705) no­ticed that wh en the temperature was changed between the boiling point of water and ambient temperature, equal drops in temperature resulted in equal decreases in the pressure of the air. From these results he con­cluded that on further coo ling the air pressure would become zero at a finite temperature, which he es ti­

mated as - 240°C. Since the pressure of the gas could not become negative, it fo llowed that there must ex ist a lowest temperature beyond which air, or any other substance could not be cooled. Amonton s also con­sidered that air might be a body of high vo latility, ca­pable of liquefacti on or even so lidifica ti on by suffi-. I 1. o , ctent y strong coo mg-·· .

In 18 15 Joseph-Lou is Gay-Lussac ( 1778- 1850) made a large number of observati ons of the cooling effect produced by the evaporati on of liquids and re­marked that under certain conditions the heat of va­pouri za ti on would be eq ual to the heat transferred

*For correspondence (E-ma il : wisniak @bgumai l.bgu.ac.il )

through the wai Is of the vesse l4 . However, if the I iq­uid evaporated into a vacuum surrounded by a freez­ing mi xture the cooling effec t could be increased in­definitely as long as the liquid exerted an appreciable vapour pressure. John Leslie ( 1766-1 832) not on ly had been able to freeze water by absorbing its vapour at the same rate it was produced ; he had also been able to reach a temperature almost as low as the melting point of mercury (234 K) by evaporation of ether. Gay-Lussac reported that he had succccdccl in freezing mercury by evaporating water in a vessel surrounded by a freezing mi xture. Gay-Lussac had no doubt that with a vo latile li quid it would be possible to obtain even lower temperatures.

According to Gay-Lussac, if the liquid evaporated in a perfectly dry gas instead of a vacu um th e cool ing would not be so great because the gas press ing the liquid would retard the evaporat ion process. The co ld achievab le had a max imum value correspond ing to the equilibrium between the caloric (heat) absorbed by the vapour and the ca loric los t by the air. Gay­Lussac then proceeded to develop the fo llow ing for­mula describing the degree of cold x (deg rr:e dcfi"oid) produced by evaporati on:

. . . ( I )

where, 8. C.. H , and c are the dens ity, hea t of va­pourization, and heat capac ity of the vapour at the temperature t in question, and P0 and P the vapou r pressure and the pressure, both in atmospheres.

In the case of water the above equat ion became

pO (T) = 0_76 (I 0 oot5~5-17.r-o .oooo625X26• ' ) ... (2)

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Gay-Lussac also prepared a table comparing the expenmental results obtained by wetting the bulb of the thermometer with a cloth (wet bulb temperature) with those predicted by Eq. 2 for the case of air at atmosphe ri c pressure.

In a later publication5 Gay-Lussac analyzed the production of cold by the expans ion of a gas. He re­alized that coo ling by evaporat ion was limited and poi nted out that the minimum temperature achi eved was only - 80°C. He believed that it was possible to achieve lower temperatures by using the equ ivalence between coo li ng caused by the expansion of a gas and heating ca used by compress ion. It was known th at compress in g the air to one-fifth of its original volume increased the temperature to 300°C and Gay-Lussac thought that the temperature mi ght be increased to I 000°C or even 2000°C, if the process was rapid . I r air was first compressed to five atmospheres, then allowed to cool to atmosrhcric temrerature, and fi­nally allowed to expand , it shou ld absorb as much heat as was given out in its compression and its tem­perature should be lo wered by 300°C. From these re­sul ts he believed that "en prenant une nwsse d'air

con1pri111ee par cinquante, cent. etc .. atnwspheres, le .fi'oid produit par sa dilatation instantanee 11 'a ura point de lin1it" (if we take a mass of compressed air to 50, I 00, etc .. atmospheres, the cold produced by its in stantaneous ex pansion will have no limit). In other words, it would be possible to achieve unlimited cold by the ex pansion of gases.

Gay-Lussac conc luded hi s paper stating: "S 'il est incontestable que, par Ia dilatation des ga z., on pettl {Jroduire un .fi'o id i flilllit e, Ia deter111ination du z.ero ahsolu de clza feur doil para/Ire 1111 e question tout-cl­fa it cltiiii Prique" (If it is undi sputabl e that ex pansion nr a gas can produce an unlimited amount of co ld , then the determination of the absolute zero of heat must seem a complete fantasy).

Later on, Charles- Bernard Dcsormes ( I 777- 1862) and Nicolas Clement ( 1779- 1842) argued that there was an absolute zero and that Gay-Lttssac had shown what thi s temperature was. According to Gay-Lussac the coeffici ent of expans ion of gases was 1/266.66 per degree Celsius, hence, Clement and Desormes argued that there was a limit o f co ntract ion at - 266.66°C, which was the absolute zero('.

Early works on the liquefaction of gases The possible effect of the low temperatures yet to

be achieved, were described in a prophetic way by

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Indian J. Chem. Techno ! .. M:11·ch 200~

Antoine Laurent de Lavoisier ( 1743-17<)4) in his hook E/e/1/ e/1/S oj" Chentist rv , r ub li shed in 17X97 La voisier wrote: " If the earth were sudden ly tran sport ed in to a very co ld reg ion , the water which at present composes our seas, rivers, and springs, and probably th e greater number of lluids we arc acquain ted wilh , would be converted into solid mountains and hard rocks at first diaphanous and homogeneous , like roc k crystal, but which, in time, becoming mi xed with foreign and het­erogeneous substances would became opaque stones of va ri ous co lours. In thi s case, the air, or at least part o r the aeri form fluid s which now comrosc the mass of our at mosphere, wou ld doubtless ly lose its elastic ity for want of a temperature to retain it in that stal e: it would return to the liquid state of existence, and new liquids would be formed, of whose properties we can­not, at present, form the most distant idea. Sol idity, liquidity, and aeriform elasticity are on ly three diller­cn t sta tes or ex istence of the same matter, or three rarticula r modifications which almost all substances are susceptibl e or ass uming successi vely, and which so lely depend upon the degree of temperature to which they arc exposed, or. in other words, upon the amount of ca loric wi th which they are penetrated".

Starting in the late 1700 ' s many sc ientists looked for ways of reaching lower and lov:er temperatures and liquefying gases. In 1799 Martinus Van Marum ( 1750-1 837) and van Trovstwyk performed ex peri­ments trying to determine if the Boyle-M ariotte 's law was applicable on ly to air or for all gascsx. For thi s purpose he chose ammonia and proceeded to com­press it in a system piston-cylinder. When the pres­sure reached about seven atmospheres he noted that although the vo lume of the gas continued to decrease, the pressure did not change. Van Marum understood that he had liquefied ammonia by a sim ple compres­sion process without resorting to coo li ng . He al so ob­served that reduct ion of the gas volu me was accom­panied by an increase of the liquid vo lume. In the same year, Louis-Bernard Guyton de Morveau ( 1737-18 16) I iquefi ed ammonia by simple coo li ng to about -50°C with a freezin g mixture of ca lcium chl oride and ice~ while Antoine-Franc;ois Fourcroy ( 1750- 1809) and Louis Nicolas Vauquel in ( 1763-1 f\29) failed to liquefy hydrogen chloride, hyd rogen su lphide, and sulphur dioxide 10 In 180 I Gaspar Monge ( 1746-18 18) and Jean Franc;ois Clouet ( 175 1-1 80 I) suc­ceeded in liquefy ing sulphur di ox ide by passing a stream of S02 through an U-tube submerged in a re­frigerant mixture of ice and salt ; they noticed that the

Wisni ak: Louis Paul Caille tet- T he liquefaction of the permanent gases Educator

tube fill ed up littl e by littl e with a co lourl ess and high mobile I iquid , s imil ar to water 11

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Thereafter, many sc ienti sts tri ed to liquefy gases by a compress ion process. The nex t important step were the results obtained in I R23 by Michae l Faraday ( 1791-1 867), while in ves ti gating the int1uence o f heat on chl o rine hydrate 12 He introduced hydrate crystals in one of the ex tremes o f an in verted V- tube closed o n both ends and proceeded to hea t them w ith a wate r

bath at I oooc. Faraday noticed that the c rys ta ls first melted and then rek ased a yellow gas th at o n cooling y ie lded a heavy bright ye ll ow fluid fl oating o n top of a so li d ph ase. Faraday understood that chl o rine gas had separated fro m the hydrate and condensed under its own pressure.

Faraday's ex periment in fac t, presented an altern a­tive method fo r liquefy ing gases, in stead of generat­ing the m in a separate apparatus, fo llowed by the ir compress ion with the he lp o f pumps, of co mplicated des ign, operati o n, and no nfl exibl e, the gas was now prod uced in an enc losed space, in increas ing amounts by a chemi ca I react io n that served to generate the necessary pressure in a coo led c losed tube .

In the course of the same year ( 1823), Faraday's procedure was used to lique fy hyd rogen sulphide pro­duced by the reac ti o n between hydrogen chl o ride and iro n sulphide; so2 produced by the reac tio n between mercury and sulphu ric ac id ; nitrous ox ide from the decom pos iti on of ammo nium ni trate; cyanogen, and C02.

Faraday's eq ui pment was limited to the producti o n of a very sma ll amounts of liquefied gas ; in 1834 a very smart modi f icati o n by C harles Sainte-Ange Thilo ri er allowed inc reas ing subs tanti a lly the amo unt of I iquefied gas, parti cul arl y I iqu id C0 2

13. T hi lo ri er' s

ap paratus was composed o f two large vesse ls co n­nected by a tube. T he firs t vesse l, built of copper lined w ith lead, was used as the reactor. Thi s vesse l hung fro m two pi vots so tha t it could be osci ll ated to in­c rease the mi xing of the reagents (fo r example, sul ­phuri c ac id and sodi um bicarbonate). T he react io n produced large amounts of gas, w ith the correspond­ing increase o r the press ure in side the vesse l. No liq­uefact ion took pl ace on account of the temperature increase, whi ch took place due to the heat of react io n. A va lve was now opened o n the top of the vesse l and the gas was a ll owed to f low in to the second vesse l, he ld at room tempera tu re, where liquefac ti o n now took p lace. Opening of a valve located o n top of the second vesse l re leased the pressure and res ulted in a

vio lent evapo rati o n o f the liquid w ith the corre­spo nding intense cooling and solidifi cati o n of th e re­maining liquid into a white snow.

Thilori e r studied also the pro pe rti es of liquid C0214

and found that it had a very large coef fic ient o f ex ­

pansio n, fro m 0 to 30°C its vo lume increase fro m 20 to 29, which was fo ur times larger that the ex pansion of a ir in the same te mperature range. Simil arl y , in the same temperature range the vapour pressure of the liquid increased fro m 36 to 73 atmospheres, that is , one atmosphere fo r each degree. Liquefied C0 2 was soluble in a ll pro po rti ons in a lcoho l, ether, naph tha, turpentine, and carbo n di sulphide, and insoluble in water.

Afterwards, it was found that a mi xture of solid C0 2 and vo latil e liquids such as ethe r (Thilo ri er's mi xtures) were capabl e o f produc ing very low tem­

peratures (be low -80°C). In 1845, Faraday combined the two liquefy ing me thods (coo ling and compres­sio n) into one by taking advantage o f Thilo ri er 's mi xtures to produce low temperatures. He now used a reg ul ar U-tube submerged in a Thil o ri er mi xture that

a llo wed reduc ing the temperature to - li0°C, and connected to two pumps operating in seri es tha t a l­lowed increasing the pressure up to 50 atmospheres. With thi s new apparatus it was poss ible no t onl y to lique fy gases such as HC I, HBr, SiF4, PH 1, As H1, and ethylene but also to so lidi fy othe rs such as H2S, N20 , and HCIO. He was unsuccess ful to liquefy hydrogen , nitrogen, oxygen, carbo n mo nox ide, and, meth ane at

50 atmospheres and - II0°C 15.

By mid-ni neteenth century, a ll but s ix of the known gases had been liquefi ed , and temperatures be low 170 K had been achieved by evaporating a Thilorier mix­ture o f so lid C0 2 and di eth y l ethe r. The s ix re main ing gases (oxygen, nit rogen, carbo n mo nox ide , nit rous ox ide, methane, and hydrogen) were ca lled pernwnenl gases and beli eved to be no n-condensabl e. He lium was no t considered then because thi s gas was d iscov­ered o nl y in 1869 w hile observing the sun and identi­fi ed by a bri ght ye llow line in a spec trum analysis or the sun ' s coro na. Ramsay di scovered the firs t depos its in the earth in a sampl e of pitchblende. a dark rock conta ining rad ium and uranium .

George Aime ( 18 1 0- 1846) tri ed, w itho ut success, to liquefy oxygen and nitrogen by immers ing recipi­ents co ntaining a ir in the sea, to a depth correspo nd­ing to more than 200 atmosphe res 16

. In 1844 Johann August Natterer ( 182 1- 1900) succeeded in prod ucing large quantities of liq uid nitrous oxides but later on he

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failed to liquefy air by compress ing it to pressures bet ween 1300 to 2800 atmospheres 17

In 1850 Victor Regnault ( 18 10- 1878) 18 made ex­tensi ve measurements of the velocity of sound in dif­ferent gases and of the heat absorbed during the ex ­p~ul s i o n of the gas through an orifice in a vessel, through capillari es, and when the gas was suddenly stopped . In some of hi s experiments on the discharge of a gas th rough a capi llary tube he observed a small coo ling effect but di smi ssed them as experimental errors. Two years later, James Prescott Joul e ( 1818-188t)) and Willi am Thomson ( 1824-1907 , Lord Kel-

. I') II v1n ) wou c report the same result and understand its signifi ca nce ( the Joule-Thomson effect).

Based on hi s findinQs on the behav iour of the com-·b·l · ,. R~ I ,. d' 0 press1 1 1 ty o · gases egnau 1 prec Jete - , as was later

demonstrated. that application of insuffi c ient pressure was the onl y obstac le for th e liquefacti on of oxygen and nitrogen. Also. th at if hydrogen was coo led, it would show enough compress i bi I i ty to he I iqucfied. On December 24, 1877. Regnault sa t for the las t time in a sess ion o f the Academic. he was already very ill ~llld would cli e a few weeks later. On that opportunity Dumas read Ca ill etct 's communica ti on on th e lique­fac ti on of oxygen (mentioned below) . A week later, Ca ill etet announced that he had also succeeded in liq­uefying nitrogen.

Joule and Thomson performed a seri es o f ex peri­ments of throttling air at pressures up to 4. 11 atm and

temperatures up to 171 °F through a pipe blocked at one end by a piece of calf-skin lea th er and found " there is a final coo ling effect prod uced by air rushing

th rough a sma ll apertu re at any temperature up 170° F, and that the amount of thi s th ermal cffect decreases as the temperature is increased". Not only thai , thei r re­sults indi ca ted that in th e case of sa turated steam the density va lues used by Regnault were lower by a fac­tor 1.01 9 from the rea l ones1

'J.

It was found empiricall / 3 that the Jou le-Thomson

coo ling effec t 6.T was proporti onal lo th e pressure

drop !J.P and in verse ly proporti onal to the square of the abso lu te temperature T, according to follow ing equation,

,j 273 )" 6.T = 116.. l T . .. (3)

where 11 is a constant characteri stic for each gas ( for <.ur 11 = 0.276), T is in kel vin s, and P is in atmos­pheres.

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Indian J. Chc:m. Tech no!.. M ;udl 2003

It took the experiments or Andrews IO understand the reason of th e failure2122 .

Thomas A ndrews ( 18 13- 1885) stud ied the behav­iour o f gases under high pressures and different tem­peratures and was able to formulate the concep t o r coex istence of the vapou r-liqui d equ i l ibrium and the constancy o f temperatu re during a phase change (A n­drew's isotherms). A ndrews demons trated that for every gas there ex ists a temperature (ca lled the criti­cal te111perature) above which it was impossible to condense the gas, no matter how hi gh a pressure was applied . For thi s purpose he used C0 2 partl y becau se o r the facility with wh ich it can be produced in a pure state (by the act ion o f boiling sulphuri c ~tc id over marble, and dried by pass ing through sulphuric acid)

and its criti ca l temperature being 31 °C. Prev ious ex­perimenters 1 x had shown that C0 2 dev iated sensibl y from Boy le's law. even at temperatures we ll above the criti ca l one.

Andrews found that on partl y li qucl'y ing C02 by pressure all1ne, and rai sing simultan eously the tem­

peratu re to 8R°F, the surface of demarcation between the liquid and gas phases disappeared grad ually . AI

tem perature above ggoc there was no apparent l iq ue­facti on of the gas, on ly one phase was visible, even al pressures as hi gh as 400 atmospheres21 . He usee! the concept o f critical temperature to di stingu ish between a vapour and a gas, a di stincti on that was based previ­ously on the boi li ng point. a clearly arbitrary clcfini ­ti on. Andrews proposed calling v<~ pou r any gas that was at a temperature be low the criti ca l one, and gas if it was above this temperature. Acco rding to hi s defi­niti on a vapou r could be changed into a li quid by a simple increase in pressure and the two phases cou ld coex ist in equilibrium.

Another important ex perimental result was that the gaseous and liquid form s o f matter could be tran s­fanned into one another by a seri es o r continuou s and unbroken changes 21 . In 1873 the cont inuity o f the gas and liquid state wou ld be the subject o f Johannes D id­erik van der Waals' ( 1837-1923) doctora l th es is (Over de continuYteit van de gas-en v loeistoftoestand )2

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In what foll ows we desc ribe the I i l'e and works of Loui s Paul Cailletet ( 1832- 1931 ), the fi rst to show that permanent gases could be l iq uefi ed, and the events that accompan ied thi s achievement.

Lou is Pau l Cailletct Lou is Paul Cailletet (Fig. I ) was born in Chatill on­

sur-Sei ne, Core-d-Or, France, on September 2 1, 18:12.

Wi sniak: Loui s P<ILI I Ca illelel- The liquefaction of !he permanent gases Educator

into a well-to-do famil y engaged in metallurgy. He did hi s first studi es at the co ll ege of Chatillon-sur­Seine, completed hi s secondary studi es at the Lycee Hen ri IV in Pari s, and then enroll ed for two years as an auditeur /ihre at the Ecole des Mines in Pari s. While in Pari s he used to visit the chemi stry labora­tory of the Ecole No mwle Superieure, directed by the Henri Saint-Claire Dev ill e ( 181 8-1 88 1) who had in­vented the industrial process for the production of aluminum in 1855 , and with whom he became a close fri end . After finishing his studi es Cailletet returned to Chari li on and at the age of twenty-eight took over the management of hi s father's metal working mills , Forges de Saint-Marc. He became parti cularly inter­es ted in the operati on of the blast furnaces, interest that led to hi s first investigations in metallurgy. He studi ed the operati on of forges. the process of ce­mentati on, the mechanism of iron purification, the permeability of hydrogen in iron , and developed pro­ced ure for improving the combustion process in blast furnaces. He did also ex tensive work on the behavi our of gases at hi gh pressures and their liquefaction. For so me unknow n reasons, he also had a short interest in plant physiology.

Other of Cailletet ' s accomplishments includes the installation of a 300-meter man ometer on the Eiffel Tower. It was built of a 4.5-mm internal diameter tube con nected every three meters to a projecting pipe with a coc k and glass tube, permitting pressure readings at different heights. The apparatus allowed reaching a pressure of almost 400 atmospheres . He also used the Eiffel Tower to study the effect of air resistance on the fall of bodi es. Cai ll etet worked on the constructi on of devices, such as automatic cameras and air sample coll ectors, for the study of upper atmosphere by weather balloons, as well as the des ign of a liquid­oxygen respiratory apparatus designed for hi gh­altitude ascents. These in ves ti gati ons led to Cailletet being chosen president of the Aero Club de Fran ce.

Cai lletet was elected correspondant of the Acadenrie des Sciences on December 17, 1877 and became acadenricien fibre on December 27, 1884.

Loui s Paul Cailletet died in Pari s, on January 5, 191 3, at the age of 8 1.

Scientific activ ities

Plant physiology Caill etet publi shed several works related to pl ant

. 0 4 -0 7 phystology- - . It was then known that the green parts of a plant decomposed carbon di oxide when

ex posed to sunli ght and released an equival ent quan­tity of oxygen when in darkness . Cailletet decided to study the influence of rays of different colours (radia­tion of different wavelength) on the decomposition of C02 by pl ants and for thi s purpose he enclosed se v­eral varieties of plants in a box built of a co loured g lass that could be submitted to the direct action of sunli ght and did not allow an increase in temperature, a side phenomena important in the case of a red glass. Hi s results indicated that similar to the chemical rays. the heat rays did not affect the decompos iti on of car­bon dioxide, which seems to be the most under the influence of ye llow rays. In addition, he observed that green li ght exerted a totall y unex pected action; in­stead of helping ass imilate C0 2 it acted like total darkness. Plants illuminated by green li ght cracked and oxidized, while los ing carbon di ox ide24 Caill etet results where later confirmed by Pau l Bert 's ( 1833-1886) experiments28

.

Another phenomenon studi ed by Ca i ll etet was the poss ibility that leaves could absorb liquid water25

. For thi s purpose he constructed an apparatus that allowed introducing a leaved branch of a plant into a glass probe full of water and prov ided with a manometer. Hi s res ults indicated that a plant grow ing in a humid soil would not absorb water though its leaves. When so il humidity was in suffici ent the leaves would absorb a large amount of water to maintai n the plant viable (these results are known today to be wrong).

Another work was related to the origin of the car­bon fix ed by a green plant26

. The prevalent idea was that plants growing in an almost dry soil that did not contain the elements of ash (potass ium carbonate), obtained all their carbon from the air. It had not been proved if part of the carbon ori gin ated from carbon diox ide di sso lved in water that was then assimilated by the roots. Cailletet studied the behaviour of differ­ent well-developed plants (co lza, lentil , and passi­flora) under an atmosphere devoid of carbon dioxide. He found that in thi s situati on plants ceased their de­velopment; the lower leaves became yell ow and fell and the upper part of the trunk dried and eventually died. When the pl ant was almost dead, passing air through water charged with carbon dioxide reani­mated the plant and reiniti ated its development. From these ex periments Cailletet inferred that atmospheric carbon dioxide was indi spensable for the life of green plants.

In another study27 Cailletet found that there were substantial differences between the ashes of mush-

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rooms and chlorophy ll plants . He analyzed the ashes of a piece of tree on which mushrooms grew and found that the largest majority of the minerals had been absorbed by the latter. To him, thi s fact ex­plained why a tree subject to the act ion of cryptogams deteri orated seri ously. In additi on he found that sili­con that const ituted about 70% of the weight o f fern s and graminae, was not present in mushrooms. The ashes o f the latter were poor in ca lcium ox ide and magnesium ox ide, but very ri ch in alkali and phos­phoric acid.

Metallurgy Operators o f blast furnaces were aware th at they

had to do th eir work carefull y to avoid ex plosions. Similarly, it was known that mechanical work of cast iron might result in its catching fire. A series of acci­dents o f thi s nature in his factory moved Ca illetet to study their origin .

Jacques Joseph Ebelmen ( 18 14- 1852) and other chemists had occupied themse lves with th e analys is of the gases produced in the blast furnace, by aspirating them with a long iron tube containing an intern al por­ce lain tube, and under conditions that resulted in their coo ling. Ca illetet rejected their results because on coo ling the dissoc iating compounds recombined aga in, as predicted by the dissoc iation phenomena discovered by Sai nt -Cia i re De vi li e. In order to avoid thi s prob lem Cail letet designed hi s equipment to sam­ple the gases from the midst of the furnace (operating at a temperature we ll above the fu sion point o f plati­num) followed by sudden coo ling (q uenching) . Hi s results indicated that the gas compos ition was sub­stan tiall y different from that reported by Ebelmen and others: Carbon diox ide and other tlammabl e gases such as hydrogen, carbon monoxide were present in very small amounts. The gas mi xture was opaq ue be­cause it carri ed a large amount o f fine ly di v ided car­bon in suspension that required a long time to settl e2

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It was a well-known fact that when using cas t iron for fabri cating molded pi eces the melt released com­bustibl e gases while it so lidified. The large amounts of gas released required special precautions to avoid an exp los ion. Many theori es had been proposed to try to exp lain the ori gin of the gases di sso lved in the cast and in molten steel s. In foundri es it was believed that the gases ori ginated from the decomposition of the water occ luded in the molding earth by the metal at high temperature. Cail letet believed that the gases were ac tuall y furnace gases th at had di sso lved in the liquid metal, before it 's being discharged from the

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Indian J. Chcm. Techno !. . M;1rch 200.1

furnace. To prove hi s point he cast th e liquid melt in water-j acketed molds made of metal to avoid the presence of humidity . A nalysis of the gases released indicated that instead of water it was a mi xture of hy-1 . I I d. . I lll 1 1 c rogen, n1trogen, anc canon I OX IC e· ·· .

Cailletet did also work on the permeability of dif­ferent gases, particu lar ly hydrogen, oxygen, and car­bon monoxide, and usc hi s results to ex plain the fail ­ures that occurred during the tempering of incom­pletely forged pieces o f iron of large dimensions and also during cementation . In the latter case. he found that the pulls contained hydrogen and ca rbon mon­ox ide and that th ey accumulated in those areas where the meta l sponge was incompletely forged12

.13

It was known that metals like iron . platinum and aluminum hardly ama lgamated with mercury . A l­though the same phenomenon was observed if mer­cury was replaced by a dry ama lgam of sod ium or ammonia, add ition of water resulted in amalgamati on and rel ease of hyd rogen gas. Cailletet performed an ingenious experiment to demonstrate that amalgama­ti on took place together with hydrogen release: He used an electro ly tic ce ll that had a sheet o f iron, plati­num, or aluminum as the negat i ve electrode and a layer of mercury under an elec trol y ti c hath made of acid or basic water. Dropp ing the metal sheet into th e mercury resulted in the immediate arpari ti on o f hy­drogen bubb les and thi s was enough to obta in amal­gamation. When a few drops of a lead or copper sa lt were added to the elec troly te hydrogen generati on stopped and the metal used as negati c pole was un­able to ama lgamate.

Cailletet used this procedure to produce amalgams of the metal s known to amalgamate with diffi culty and to stu dy their properti es. He remarked that the amalgam of mercury and aluminum was unusual in its b.l . d ~ a 1 1ty to ecompose pure water· .

Liquefaction of gases The most important researches of Cai lletet are re­

lated to the behav iour of gases under pressure and their li quefac ti on, particularl y oxygen. Between the end of 1877 and the beginning of 1878 Ca illetet lique­fi ed all the gases considered permanent.

In hi s first work he studied the val idity of Mari ­otte's law (ideal gas) at high pressures, using a piece of equipment which was a prototype o f the one he would use later to liquefy gases35 His fi rst results in ­dicated that at high pressure hydrogen and air did not behave ideall y, the compressi bi I ity of hydrogen de­creased regu larl y with increased pressure, while that

Wi sniak: Louis Paul Cai lle te t- The lique fac ti on of the permane nt gases Educator

of air first increased to a maximum value at about 80 atm and then it decreased more rapidly than that of hydrogen. Further work with nitrogen indicated th at thi s gas did also not behave idea ll y and that its com­press ibility presented a maximum value at I5°C and about 92 atm'r' .

He then used hi s equipment to liquefy carbon di ­ox ide under temperature and pressure conditions not reported by other inves tigators. Cailletet found that liquid C02 was co lourless and very mobile, did not conduct electricity, and th at electricity produced a burst of brilliant induction sparks, in the midst of a very volatile liquid. Liquid C02 was not attacked by sod ium. did not di sso lve sulphur or phosphorus but mi xed with ether in all proportions. Iodine gave it a violet tint. Caill etet thought that since C02 and water had a similar structure th ey would di ssolve the same sa lts. Contrary to hi s expectati ons liquid C02 did not disso lve NaCI , Na2S04 , or CaCI 2 . Liquid C02 di s­solved partiall y in water; the less dense layer being C0/ 7

Next, Cai lletct studi ed then th e co mpress i bi I ity of acetylene at hi gh pressures and found that the gas be­haved according to the law of Mariotte (i deal gas)'g Caill etet built hi s equipment essentiall y along the same lines as those used by Andrews for hi s experi­ments with C02 (Fig. I). The central pi ece was an inverted probe (TT) , opened at its bottom and con­nected to a hydrauli c pump through a layer of mer­cury (tube TU). The upper part of the probe was fu sed to a thick capillary tube containing the gas to be studi ed . The capillary was in side a liquid bath (P) contai ning water or a refrigerating mixture, as desired. The bath was made of glass and was surrounded by a bell jar (C) th at offered protec ti on in case of a burst. The capillary was subj ected on the outside to atmos­pheri c pressure and on the inside to an internal pres­sure that determined liquefac ti on. The probe was subjected to the sa me pressure, inside and out. The glass constructi on permitted observation of what was happening inside the capillary ".

Prev ious to building hi s eq uipment, Cailletet had d I d . I W-4" F eve ope the necessary ancii ary elements· -. or example, he studi ed the res istance of glass tubes to rupture' '1 and the building of manometers for the measurement of high pressures~0-~ 1.

Acetylene was chosen first because it had been suggested that at room temperature a pressure of about 600 atm might be sufficient to liquefy it38

. In October 1877, during a routine verification of acety-

Fig. !- Lou is Pau l Ca ill e te t ( 183 1- 1913) (By permi ss io n of Ed­gar Fahs Smi th Collec tio n. Un iversity of Pcnnsy lva.nia Library).

lene, an incident took pl ace: Before the liquefacti on pressure could be reached the apparatus sprang a leak and the compressed gas escaped. The sudden re lease of the gas resulted in a considerable drop in tempera­ture and appearance of a thick mi st (brouillard epais) . At first , Cailletet thought that hi s gas was impure and what he had seen was condensation of humidity. Cailletet had now the brilli ant idea of repeating hi s experiment using a sample of very pure acetylene prov ided by Marcel in Berthelot ( 1827- 1907) and agai n observed the formation of mi st. Cai!l etet under­stood that the liquefaction had been achieved by the intense cooling produced by the sudden release of press ure and that he had now in hi s hands a new tech­nique for gas liquefacti on.

Ca i ll elet observed that compression of acetylene. initially at I8°C, to a pressure of 83 at m, res ulted in the formation of many drops drippi ng on the walls of the vessel. Reduction of the press ure by several at­mospheres resulted in vapouri zation of the vessel and the tube being filled with a fin e mist.

The liquid acetylene obtained was co lourless. hi ghly mobil e, and apparently very refringent. It was li ghter than the water and di ssolved in a large propor­tion into it. It dissolved paraffin and greases . Cooling the liquid to 0°C in the presence of water and lin seed oil produced a white snowy substance, which decom­posed rapidly on sli ght heating or lowering of the pressure, generating a large amount of gas bubbles.

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Cailletet determined the following pressures and temperatures at whi ch acetylene was liquefied -' 8 :

t°C atm

4X

2.5 .'iO

10 63

IR R:l

2.'i 94

31 103

Compari son of the above va lues with those re­ported by Din4

' for the liquid- vapour saturati on dome of acety lene shows th at Ca ill etet reported the condi­tions upstream the throttling process and not those of the vapour-liquid equilibrium.

Caill etet used th e sa me eq uipmen t to liquefy eth­ane, and found that at 4°C the required pressure was about 46 atm, that is , sl ightl y larger than that required for acetylene.

Cailletet c losed hi s paper with the remark that hi s liquefact ion equipment was very simple and easy to operate and th at he intended to tes t it with other gases.

In Caill etet's experimen t the discharge (expansion) of the gas may be considered adiabat ic. hence, as­suming as a first approx imati on idea l behaviour, it is poss ibl e to ca lcu late the final temperature with the re lation

.. . (4)

where i and f indicate the initi al and final conditi on, respec ti ve ly. According to Eq. (4) the final tempera­ture depends on the va lue of y , th at is, on the gas in

ques ti on. y is about 1.67 for monatomic gases and

about 1.40 for diatomic gases like H2, 0 2• N2, CO, and 0. Assuming I 03 atm and 304. 1 S K as init ial cond i­

tions, a drop to atmospheric pressure corresponds to a fina l temperature of about 8 1 K. The cooling effect is due to the external work done by the gas in expanding agai nst the down stream press ure. The actual cooling wi ll be less because of the cooling effect of the wall s of the vesse l, and heat losses to the env ironment.

In a followin g pub li cat ion Cailletet reported that he had used hi s eq ui pmen t to li quefy nitrogen dioxide at 104 atm and - II 0 C. At to 8°C N02 remained in ihe gaseous state at pressu res up 270 atm4

"'. He also ob­served th at when methane was compressed to 180 atm

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Indian J. Chcm. Tcchnol. . March 200]

at 7°C, a sudden release of the press ure produced a mist simil ar to the one observed with carbon dioxide: for thi s reason he believed he would be abl e to liquefy meth ane. This publication carried a comment by Ber­thelot about the importance of Cai llete t' s finding s because so far it had been imposs ible to liquefy gases that behaved accord ing to Mariote's law . Berthelot menti oned that in the las t years Andrews had shown that the reason fo r the failure was that every vapour had a critical temperature, above wh ich the vapour could not be transformed into li qui d, no matter how much a pressure was appli ed to it.

According to Berthelot, Cailletet's experiences showed th at the criti cal point of nit rogen dioxide was between 8 and - II 0 C. He also be lieved that Ca il ­letet's procedure wou ld soon lead to the liquefaction of oxygen and carbon monox ide.

Liquefaction of oxygen Liquefact ion of oxygen represen ts a sensa ti onal

sc ientifi c accomplishment th at was achieved in 1877 almost simultaneously by Cai ll etet and Rao ul Pictet ( 1846- 1929) using completely different experimental techniques. This achi evemen t was also accompanied (and con tinuous to be) by much discuss ion regarding priority to the discovery.

Caill etet and Pi ctet' s resu lts were com muni cated to the Academic des Sc iences by the Pe rmanent Secre­tary, Jean Baptiste Andre Dumas ( 1800- 1884) during the sess ion held on December 24, 1877, and appear in Co111p1. Ren(/ti , 85, 12 12. 1877 .

It is important to g ive a detailed accou nt of thi s partic ul ar session in order to understand the reasons of the priority polemic that followed the announce­ment.

Dumas opened the sess ion reading the prophetic words of Lavoi sier, written a lmost one- hu ndred years before, regarding the new liquids that could be pro­duced by liquefact ion (see above).

Cai llete t' s note "De Ia Condens(/( ion de I' Oxygene et de I 'Oxyde de Carbone" was read immediately thereafter"'5 In it Caill ete t reported that if oxygen or carbon monoxide were put in his apparatus"'" (b ioxide. REF) at 300 atm and cooled to -29°C with boiling sulphur dioxide, both gases rema ined as such. If the gases were then released sudden ly they wou ld cool, according to Poi sson ' formula , to a temperatu re :woo below the initi al, and immediately an intense tnist (brouill ard intense) woul d be seen , caused by the liq­uefaction and perhaps the solidification of oxygen or

Wisniak: Louis Paul Ca ill e tet- The liquefact ion of the pe rmanent gases Educator

carbon monoxide. The same phenomenon was ob­served when the gas was carbon diox ide, nitrous ox­ide. and nitrogen di ox ide. This mi st was produced when compressed oxygen was released after it had coo led to room temperature. Ca ill etet indicated that he had demonstrated this fact during experi ences he had performed on Sunday, December 16. in the chemi stry laboratory of the Ecole No r/1/al Superieure, in the presence of various in vest igators and professors, some of them members of the Academic.

Caill etet added that to authenticate th at oxygen or carbon monoxide were in the liquid or so lid state it was enough to perform an optical tes t. which unfortu­nately was easier to say than to do because of the shape and thic kness of the tubes in hi s apparatus. Several certain chemi cal reactions had allowed him to bear out that oxygen had not transformed into ozone during the compression .

Caill etet fini shed hi s repo rt indi cat ing that he had app lied the same operat ing co nditi ons to hydrogen wi thout observing the presence of mi st and that he intended to apply them to try to liquefy nitrogen.

Afte rwards, Mr. de Loynes46, the Pari s representa­

tive of the firm Raoul Pictet & Co., read the telegram sent by Pictet and received on December 22 at 8 PM , report ing the liquefaction of oxygen in the following words: "Oxvgene !iqtu!{ie aujord'!tui sous 320 atnws­p!tere.\ et - 140 de _fi-oid par ocide su/p!tureux et ca r­!Jonique accmtples''. The telegram had been followed by a document describ in g in detail the eq uipment and proced ure utili zed for ach iev ing the condensat ion (Fig. :?.) .

Q and R are double-effect aspiration pumps. R op­erates on liquid anhydrous sulphur dioxide contained in tu be Cat - 65°C. The gaseous S02 generated in C is directed to the condenser D, operating with refriger­ated water, where it liquefies at - 25°C and about 2.75 atmospheres. The diameter of pipe k is sma ll enough to produce the req uired backpress ure to co ndense soc

Simila rl y, pumps R operated on liquid C02 con­tained in the annular space H, held at the proper pres­sure to evapo rate the liquid at - 140°C. The gaseous C02 produced is direc ted to the condenser K sur­rounded by a tu be contain ing liquid S02 at -65°C and 5 atmospheres . The diamete r of pipe d is sn:all enough to produce the required backpressure to con­dense C02. The liquid C02 return s to H through the connector k.

Fi g. 2- Sc he mc or Ca i lletet"s equipmcnt 1'

L is a flask made of forged iron, capable of sus­taining a pressure of 500 atmospheres, used to gener­ate pure oxygen by heating potass ium chl orate with a heat source. The quantity of salt added to the flask determines the oxygen pressure achieved. The gas thus produced accumulates in the internal tube of H, maintained at - 140°C. After several hours of opera­tion oxygen achieves the conditi ons of 320 atmos­pheres and - 140°C.

Opening the cock at N results in a strong expansion of the compressed and co ld oxygen and a large part of it liquefies and fi ll s the tube M.

After de Loyens ' words, Dumas read a letter sent on December 2 by Cailletet to Sainte-Claire Dev ille that the latter had deposited the nex t day in the hands of the Secretary of the Academic, in a scaled enve­lope, which he now proceeded to open and read: "I hasten to in form you, and you first without losing a moment that I have liquefied this day both carbonic ox ide and oxygen. I am perhaps wrong in sayi ng li q­uefied, because the temperature I obtained by evapo­rating sulphurous acid. is at -29°C and under 200 at­mospheres pressure. I did not see any liquid. but a fog so dense that I was able to in fer the presence of a va­pour very close to its point of liquefact ion. I have

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written today to Mr. Deleuil to ask him for some pro­toxide of nitrogen. by means of which I sha ll doubt­less ly be able to see carbonic and oxygen flow .

P.S . I have just carried an experiment. whi ch sati s­fies me completely. I have compressed hydrogen to 300 atmospheres, and after cooling it down to - 28°C, I ex panded it suddenl y. There was no trace o r mi st in the tube. My gases (CO and 0 ) are. therefore. cer­tainly at the point o f liquefaction , as thi s mi st is only produced by vapours close to liquefaction. The fore­casts o f M. Berthelot are completely verifi ed" .

After Dumas finished reading Cailletet's letter Sainte-C laire Dev ill e rose to add more detail s. He said that on Sunday December 16. Cai ll etet had repeated his ex peri ences on the condensation of oxygen at the laboratory of the Eco le Nonnale and that they had success full y duplicated the results he had reported in his previous note. Ca illetet had not wish to publi sh them because he was a candidate to the positi on of Correspondant of the Academic, pos iti on that he was awarded on the session of December 17, an d he did not want that the di sc uss ion of hi s merits for the posi ­ti on included a pi ece of work that its res ult s and not been repeated in front of appropriate judges. He did not want to publi sh such an important achievement exac tl y on the day of his election. Fortunately. on De­cember 3, Sainte-C laire Dev ille had put the letter, properly sealed , in the hands of the Permanent Secre­tary. For these reasons Sainte-Claire Dev ille believed that the priority of the discovery belonged to Cailletet. He al so added that the remarkabl e work of Pictet had hardly been quoted; hi s operating procedure being completely different from that of Cailletet.

Afterwards, several members ex pressed thei r views that both methods were proof that oxygen had been liquefi ed or solidifi ed. Jules Jamin ( 18 18-1 886) indi­cated that the real confirmation of the actual state would be the ability to maintain liquid oxygen at its boiling tem perature, as had been done with li quid ni­trous ox ide; or at the solid state, as had been done with carbon dioxide.

For their in vest igat ions on the liquefaction of oxy­gen Cailletet and Pi ctet recei ved the Davy Medal from the Roya l Society of London (November 1878) and the Prix Lacaze from the Acade111ie des Sciences ( 1883). The se lecti on committee members were Ber­thelot , Auguste Cahours ( 181 3-1 89 1 ), Michel Eugene Chevreul ( 17R6-1889, Henri Debray ( 1827-1888), Jean Baptiste Andre Dumas ( 1800-1884), Edmond Fremy ( 18 14-1894 ), Charles Friedel ( 1832-1 899),

232

Indi an J. Chem. Tc:chnol. . March ~003

Fig. 3- Sch..:mc of Pi clc!· s equi pmc: r11 13

Loui s Pasteur ( 1822- 1895). and Charl es-Adolphe WUrtz ( 18 17- 1884) .

A year later after the presentati on at the Academic, Pi ctet publi shed an ex tensive memoir giving many details about hi s equipment and the re~ ults of the nu ­merous experi ences he had done~ 7 .

The polemic about priority

Although the proceedings of the sess ion of the Academic des Sciences indicate that Cailletet reported the liquefact ion of oxygen ahead of Pictet. there has been much argument about how well do they present the facts as they really too k occurred.

Kurti 48 did a thorough study of all the documents related to the proceedings of the Academic and fou nd several discrepancies. For example. Dumas om itted part of the letter that de Loy nes, had sent to justify hi s employer claims. In the paragraphs omitted , de Loy­nes indicated that Pictet's was well-known for manu­fac turing so2 anhydrous, a criti ca l element fo r achieving the liquefaction of oxygen in both Ca il­letet's and Pi ctet's procedures . In addition, Sainte­Claire De vill e had ex plained that the reason why he had not reported before to the Academic the res ults achieved by Cailletet was that the latte r was a candi ·­date to membership and did not want that thi s impor­tant achievement be part of the argument, before it had been endorsed by competent judges. According to

Wisn iak : Louis Pau l Cai lletet-T he li quefaction of the permanen t gases Educator

Kurti, there is nothing in Caille tet 's le tter indicating th at he did not want his results to be known by the Academi e before the e lec ti on. Kurti went to archi ves of the Academi e, located the orig ina l letter and on reading it found that when reading it to the Academi e Dumas had cut three parag raphs fro m the o ri ginal. In the mi ss ing materi a l it is c learl y stated th at Caille tet thought that hi s prelim inary results would he lp him achi eve membership .

Kurt raises the questi on: " Why did Sainte-C la ire Deville insist on Caill etet 's pri ority over Pi ctet. Was it chauvini sm - France versus Switzerl and?"

8 I 4'! . h enaroc 1e ratses o t er arguments based o n pho-tocopi es of the criti ca l documents present in the a r­chi ves of the Academie: (a) According to Sainte­C laire-Dev ille he depos ited Cailletet's letter o f De­cember 2, on December 3, in a sealed enve lope, in the hands o f the Secretary of the Academie. There is no record in the Acade mi e (as ex isted for othe r similar letters) that thi s letter was deli vered , (b) Sainte-C laire­Deville claimed th at Cailletet was candidate as corre­spondant for the e lecti o n he ld on December 17 . Cail­letet's name does not appear in the li st of candidates th at was posted in the sess ion held o n December I 0 , as was the usual procedure, (c) the most curi ous fact is that the letter that was supposed to be received o n December 3, was actuall y received o n December 2, (d) the post-script in Cailletet's letter to Sainte-Claire­Dev ill e (de li vered o n December 23) , was dated De­cember 2, and hence it was not poss ible that the post­sc ript was de li vered on December 3, and fin ally (e) It is c lear that in the letter fro m Sainte-C laire-Deville to Dumas the date has been correc ted .

Benaroche is not sure if all these inconsistencies represent a chain of c le ri cal e rrors or othe r moti ves.

In thi s contex t we can menti on the accusati ons of pl ag iari sm that Karl DUhring ( 1833- 192 1) made agains t Paul de Mondes ir in hi s book Neue Grundge­setze m r Rationalle11. Physik und Chemie ("Funda­mental Laws of Phys ics and C hemi stry"), publi shed in two vo lumes. The second vo lume c loses with a two-page s tatement entitl ed "About Pl ag iari sm of the first vo lume of Fundamenta l Laws of Phys ics and Chemi stry". In it DUhring makes a bitter attack on several peopl e he accuses of copyi ng his ideas about the corresponding temperatures of bo il ing liqui ds. In parti cul ar he singles o ut Winke lmann fo r the papers he publi shed in Allnalell der Physik and de Modesir for the paper he publ ished in Comptes Re11.du. In the mi dd le of the second vo lume there is a lso a copy of

the lette r sent on December 5, 1880, by Ulrich DUhring to the Permanent Secretary (Dumas) of the Academie des Science, reques ting that the Academy publi sh an attached document entitl ed Reclamation de la loi des temperatures d'ebullitioll correspondents (C ia i m regarding the law of corresponding bo i I i ng po ints). Ulrich pointed o ut that on the sess ion he ld by the Academi e Febru ary 23, 1880. Sa in te-C lai re Devill e had read a communicatio n by Paul de Mode­sir regarding a compari son between the temperatu res at which pure components exerted the same vapour pressure. De Modesir 's communicati on was pu bli shed in Compte.\· Rendu, 18RO, 90, 360-367. Ulrich Di.ihring po inted o ut th at hi s fa the r had already pub­li shed the law "di scovered" by de Modes ir in essen­tia ll y the same terms and using the same vapour pres­sure measurements made by Regnault. More than that, hi s fathe r had not on ly publi shed the law and ex­pl ained it theore ti ca ll y, he had a lso sugges ted its prac tical applicati ons and its re lation to the che mical s tructu re of the molecules. Di.ihring's book reports that the Academi e publi shed onl y an extrac t of Ul­rich 's letter ( Comptes Relldu, volume 91 ) under the titl e Reclamation de priorite au suject de la loi des temperatures d' ebullition correspondents. Exu-ait d'une lettre de M. U. Diihrillg . The way that the orig inal letter was reduced in length caused another bl ast of Di.ihring aga inst the sc ienti fic es tabli shment and its journals50

.

Liquefaction of other gases In the same year that he liquefied oxygen ( 1877)

Caille tet reported that he had been able to lique fy ni­trogen, and air, and probabl y hydrogen51

. To liquefy nitrogen he f irst compressed the dry gas to about 200

atm at l 3°C ; after a sudden re lease of the press ure the fo rmati on o f large liquid drops was observed, which d isappeared in contact w ith the wall s o f the vessel , fo rming a sort of liquid column a lo ng the ax is of the tu be. The to ta l pheno meno n lasted for abo ut three seconds. On December 30. 1877, he repeated the ex­

perience at -29°C, in the presence o f several me mbers of the Academi e, amo ng them Jean-B apti ste Bouss in­gault ( 1802-1 887).

Cailletet used the same techniq ue to liquefy air, ab­solute ly dry and free of C0 2 and co mmented that thus Lavoisie r's prophe tic words had been confi rmed : pro­ductio n of substances with new and un known pro per­ties. He a lso remarked th at hyd rogen had a lways be­ing considered the mos t non-condensabl e gas because

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or its low density and mechanica l properties almost identi ca l to those of ideal gases. Anyhow, he per­fo rmed his experiments of sudden expansion from 280 at m, in the presence of Berthelot. Sainte-Claire­Deville, and Eleuthere Mascart ( 1837- 1908), and all had had the experi ence of observi ng a very fine and light mist, suspended in all the mass of the gas, that disappeared very fast.

In a following work. Ca illetet was able to liquefy eth y lene under various pressure and temperature con­

ditions5~ . For example, at I 0°C the pressure required

was 60 atm while at I °C it was 45 atm. From hi s many measurements he es timated the critical tem­

perature of ethy lene to be about I 3°C (actual ly 282.4

K ) in compari son with 3 1 °C for carbon dioxide. In a footnote he indicated that determinati on of the criti ca l temperature was difficult because it vari ed strongly with small amounts o f impuriti es.

The low value of ethyl ene's cri ti ca l temperature suggested Ca illetet the poss ibility of using boiling ethylene instead of boiling nitrous ox ide (N 20 , Tc = 309.6 K ) to achieve lower temperatures. He repeated hi s experiments on the liquefact ion of oxygen using this time liquid ethylene at - 105°C as the coldest

source, instead of liquid Nc.O at - 88°C and found that there were substanti al eli rrerences between the two liquids. With Nc.O, the free expansion produced onl y a thin mist of very short life while w ith liquid ethy lene a defin ite amount o f liquid oxygen was produced th at boil ed vigorously for a long period of time. Cailletet remarked th at liquid ethy lene was not on ly capab le of producing lower temperatures , it also had the advan­tage of being transparent, in con trast wi th liquid C02

and liquid Nc.O, which were opaque.

Cailletet and Hautefeuille5' did some interes ting

work on the behaviour o f gases near their criti ca l point. Small temperatures changes around the critical point gave place to observab le striat ion and undul a­tions and the question was if the liquefied gas was co lou rl ess, had a colour, or cou ld a colour be added arti ficia ll y . Ca illetet and Hautefeu ille found that al­though it was very easy to co lou r liquid C02 by addi­ti on of either iod ine or ozone, these were not appro­priate because iodine attacked mercury and the prop­ert ies of ozone made observat ions of the phenomena occurring near the critical point difficult. After trying many so lutes they conc luded that the best one was blue oi l of galbanum ( ote I ). A small drop of the oil was enough to colour the gas w ith a li ght blue tint. The co lourati on allowed the changes that took place

234

Indian J. Chcm. Tcchnol. . March 20()]

when the liquid passed into gas, at temperatures above the critica l one. According to Cai l letet ancl Haute­feuille the disappearance of the meni SC US WaS llOt necessaril y synchronous with the al tai nment o f the critical temperature.

Cai ll etet and Bordet54 discovered that when phos­phine WaS compressed in the presence of Watel· it would liquefy and lloat on top of the water layer. I f the pressure was suddenl y released a white crysta lline body would form that would di sappear i f the press ure was reduced further. The formation and decomposi­ti on of th e crysta l occurred at fi xed pressures ancl

temperatures: for example at 2.2°C ~llld 2.8 atmos­

pheres. and 20.0°C and I 5. 1 atmospheres. The cri ti cal

temperature of fo rmati on (congruent point) was 28°C. Ca illetet and Bordet believed that the crysta ls were composed of phosphine hydrate, although they were unable to determine its compos ition.

They repeated th e experi ence with other wet gases and found similar resu lts. For example, the compres­sion of equal vo lumes of wet C02 and phosphine re­generated a wh ite crysta lline solid, wi thout leav ing a gaseous res idue th at was assumed to be a mixture of the hydrates of the two gases. Hydrogen sulphide also combined w ith water y ielding a hydrate having a

criti ca l temperature of 29°C.

Cailletet and Mathias55 des igned a very simple ap­paratus made ou t o f g lass to measure the density or the vapour and liquid phases of a pure compound as it approaches its critica l point. A plot of their experi­mental results o f th e dens ity for N::> O, ethy lene, and C02 , showed that the mean densi ry of both phases decreased linearl y with the temperature and that the st rai ght line drawn through the midd le point of the chords went through the critical point. They suggested employing thi s fact to determine the criti ca l tempera­ture and density of a gas, usi ng measu rements be low the critical point.

This finding is known today as the Cailletet­M athias rul e. Mathematically

Pa vcragc = 0.5 (pl. + Pc; ) = (/- bT ... (5)

where pL and pG are the densi ti es of the liquid and

gas phase, respect i ve ly. Applying Eq . (5) to the va l­

ues T = 0 and T = Tc we get a = 0.5p, and

PL = Pc = Pc , where P, is the density of the so lid

phase at 0 K and Pc the density at the criti cal point.

Hence,

Wi sniak: Louis Paul Cnilletet- The li quefaction o f the permanent gases Educator

T P~. + Pc; = P, - (p, - 2pr ) T

c

Epilogue

. .. (6)

The ex istence of liquid oxygen have a picturesque angle in Jonathan Swift 's book "Gulli ver's Travels" 56

and in Jules Verne's book " Le Doeteur Ox"57 (REF). In chapter V of "A Voyage to Balnibarbi ", Lemuel Gulliver describes hi s visit to the Grand Academy of Lagado and the projects its sc ienti sts are engaged: "I had hitherto seen only one side of the Academy, the other being appropriated to the advancers of specula­tive learning, o f whom I shall say something when I have mentioned one illu strious person more, who is ca ll ed among them ' the universal artist' . He to ld us ·he had been thirty years employing his thoughts for the i mprovemcnt of human I i fe'. He had two large rooms full of wonderful curiositi es, and fifty men at work. Some were condensing air into a dry tangib le substance, by extract ing th e nitre, and letting the aqueous or fluid particl es perco late ... "

In " Le Doctcur Ox" Doctor Ox and hi s assistant Ygene come to the small quiet community of Quiquendone located in Flanders. He promi ses to light thi s town with a network of oxyhyd ri c gas pipes. During the construction of thi s network , th e quiet community becomes quite exc itable, to the point where they arc ready to go to war against a neighbor­ing communit y. But what is the cause of this change in the nature of the good people of Quiquendone? Perhaps it is something in the air, but only Doctor Ox and hi s assistant Ygene know for sure.

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235

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57 Verne J. Le Docteur Ox (Doctor Ox) Hetzel. Paris. 18!l3

Notes I . Ga lbanum is a resinous oil th at was imported from the Middle East and used for medicina l purposes and incense offerings. It also mentioned in the Bible. Exodus :10::14 under the name o f che f !Jonah .