Revista Brasileira de Ensino de F¶³sica, v. 33, n. 2, 2601 (2011) www.sb¯sica.org.br Hist¶oriada F¶³sicae Ci^enciasA¯ns Liquefaction of gases and discovery of superconductivity: two very closely scienti¯c achievements in low temperature physics (Liquefa»c~aode gases e a descoberta da supercondutividade: dois feitos cient¶³¯cos na f¶³sica de baixas temperaturas intimamente relacionados) Sim¶onReif-Acherman1 School of Chemical Engineering, Universidad del Valle, Sede Mel¶endez,Cali, Colombia Recebido em 15/11/2010; Aceito em 15/3/2011; Publicado em 3/6/2011 Liquefaction of helium and the discovery of superconductivity are two of the most striking developments in low temperature physics. The fact that both were carried out in the laboratories of Kamerlingh Onnes at Leiden is not mere coincidence; the ¯rst one was indispensable for the researches that led to the second one. On the same way, liquefaction of helium was the consequence of several decades of e®orts addressed to the process for liquefy the so-called then `permanent gases'. A whole study of this remarked subject must then include developments that extended, in his decisive step, more than a half of a century and that connect researches of many scientists throughout several European countries. Keywords: liquefaction, superconductivity, electrical conductivity, electrical resistance, helium, electron theory. A liquefa»c~aodo h¶elioe a descoberta da supercondutividade s~aodois das mais surpreendentes desenvolvimen- tos da f¶³sicade baixas temperaturas. O fato que ambas ocorreram no laborat¶oriode Kammerlingh Onnes em Leiden, na Holanda, n~ao¶emera coincid^encia:o primeiro foi indispens¶avel para que os pesquisadores pudessem chegar `asegunda. Do mesmo modo, a liquefa»c~aodo h¶elioculminou ap¶osd¶ecadasde esfor»cosem liquefazer os chamados \gases permanentes". Um estudo mais completo deste assunto requer a discuss~aode estudos que se estenderam por mais de 50 anos, ligando pesquisadores de diferentes pa¶³seseuropeus. Palavras-chave: liquefa»c~ao,supercondutividade, condutividade el¶etrica,resist^enciael¶etrica,h¶elio,teoria de el¶etrons. 1. Introduction One of the most important sources for those changes was helium, the chemical element ¯rst detected by the French astronomer Pierre-Jules-C¶esarJanssen (1824- The study of the remarkable properties exhibited by 1907) in 1868 in India through a bright yellow line he the matter in the vicinity of the absolute zero became observed in spectroscopic study of the chromosphere one of the main research subjects carried out in the during a total eclipse of the sun [1], and latter recog- second half of the XIX century and the ¯rst decades of nized as di®erent to those then known by the as- XX century in low temperature physics. The discov- tronomer Joseph Norman Lockyer (1836-1920), in col- ery of new phenomena derived from these researches laboration with the English chemist Edward Frankland decisively contributed to the dramatic changes that af- (1825-1899) [2]. Once some the ¯rst sources of helium fected and characterized a wide group of scienti¯c and were identi¯ed in earth, and along the full century, its technological disciplines on the following times. Super- unique physical and chemical properties, such as low conductivity, whose ¯rst centenary is commemorated boiling point, density and solubility, and inertness, re- this year, is, very probably, the most striking of them. spectively, progressively allowed a lot of remarked de- The observation of the abrupt drop in the electrical velopments in so diverse ¯elds, as for example astron- resistance of mercury wire to an immeasurably small omy, cryogenics, medicine, electronics, power genera- value as it is cooled below at a certain temperature was tion, communications, energy storing and transporta- the culminating development of a entire research pro- tion systems, among others. gram carried out by the by the Dutch physicist Heike Kamerlingh Onnes at his cryogenic laboratory at Lei- The liquefaction of helium by ¯rst time on July 10, den, which had begun about three decades earlier. 1908 not only put end to a race that involved scientists 1E-mail: [email protected]. Copyright by the Sociedade Brasileira de F¶³sica.Printed in Brazil. 2601-2 Reif-Acherman from di®erent countries with the same objective, but ammonia and sulfur dioxide at that time, because of opened up a whole new ¯eld of research. The ¯rst part their hazardous or toxic nature, had began to arouse of this article is mainly concentrated in the researches scienti¯c interest to turn the attention to utilize new carried out at the University of Leiden, and focuses on compounds for this just purpose, which coincide with the di®erent details that characterized the initial steps the recent discovery of those we now know as noble of the whole program of liquefaction of those so-called gases. The possibility to evaluate quantitatively di®er- `permanent' gases and how each chapter of the full story ent properties of substances for con¯rming or rejecting contributed in di®erent measure to the successful ob- emerging or established scienti¯c theories, or for imple- taining of liquid helium at Leiden. It is subsequently menting new and more accurate measuring instruments shown the way how the apparatuses, cryogenic facil- for each one of them, became an additional motivation ities and strategies developed along this program be- for studying these new ranges of temperature. Electri- came the indispensable infrastructure that three years cal resistance, as it is shown below, was one of these later would lead to the discovery of the phenomena of properties [6]. superconductivity. The de¯nitive step had happened in 1877 with the practically simultaneous but independent liquefaction of the ¯rst \permanent" gas, oxygen, by the French 2. The basic facts and the state-of-art mining engineer Louis Paul Cailletet (1832-1913) [7] of liquefaction of gases in the begin- and the Swiss physicist Raoul Pierre Pictet (1846- nings of XX century 1929) [8], using two di®erent methods. Whereas Cail- letet's involved high compression, then mild cooling, As whatever successful technology, the closed relation- and ¯nally a sudden decrease in pressure, Pictet's con- ship between academic research and industrial innova- sisted of a series of stages during each of which a dif- tion, besides appropriate communication and commer- ferent gas was lique¯ed by exploiting the correspond- cial good sense, were the ingredients for the early de- ing thermodynamic properties of the preceding stage. velopments on low temperature physics. The underly- Very quickly other European scientists, as the Polish ing basic motivations can then be looked from di®erent Zygmunt Wr¶oblewski(1845-1888) and Karol Olszewski viewpoints. (1846-1915) at the Chemistry Department of the Jagiel- Several elements contributed to the increasing in- lonian University in Cracow, took interest in the same terest on the very particular behavior of substances at subject, tried some improvements in the equipment and low temperatures at the end of the XIX century and its the operating techniques, and extended the whole ¯eld possible applications. Liquefaction of gases was then of research. Although di®erent gases were studied, the the most important experimental tool and source of interest was mainly focused in two of them: hydrogen information to get it. Initial trials with ammonia by and helium. the Dutch chemist Martinus van Marum (1750-1837) in 1769 [3], and others with chlorine by the English chemist and physicist Michael Faraday (1791-1867) in 3. The liquefaction of hydrogen as 1823 [4], showed the possibility to liquefy a gas only starting point and a false claim of by compression, and varying both pressure and tem- priority perature, respectively. The works carried out on the concept of critical temperature, ¯rst on its existence The liquefaction of oxygen put end point to the concept by the French physicist Charles Cagniard de la Tour of \permanent gases", and after that nobody doubted (1777-1859) in 1822-1823, and four and half decades about the possibility to turn other gases into the liq- later by the Irish physician and chemist Thomas An- uid state. Hydrogen was the following step. The e®orts drews (1813-1885) on the clari¯cation of its nature and were then focused on substantial improvements over the hence the relationship between the gaseous and liquid original Pictet's method, then known as the cascade states of matter, supplied a theoretical basis to previous process. The researches followed then two simultane- successful trials of liquefaction [4]. ous and dependent on each other lines: the quest of From a practical viewpoint, the each time more ob- each time more lower temperatures, and investigation served necessity about the use of cold in di®erent areas of properties of substances in these new ranges. of preservation of foods, as for example fermentation of The main protagonists of the hydrogen's chapter, some brewing industries and intercontinental shipment that by ¯rst time -although mistakenly- involved he- of meat, together with the growing concern about the lium, were the Dutch professor of experimental physics utilization of natural ice from frozen polluted sources of and meteorology at the University of Leiden Heike water, had stimulated the development of new equip- Kamerlingh Onnes (1853-1926) - Fig. 1 -, and the Scot- ments for making arti¯cial ice, such as vapor compres- tish professor of chemistry at the Royal Institution in sion and absorption refrigerators [5].On the other hand, London -later Sir- James Dewar (1842-1923). They had the increasing unpopularity of known refrigerants as the same ultimate objective, but great di®erences in Liquefaction of gases and discovery of superconductivity: two very closely scienti¯c achievements in low temperature physics 2601-3 their investigative attitudes and motivations. di®erent properties of matter was his main objective.