PARA QU ITARLE EL POLVO La química en la historia, Development of the concept of para la enseñanza absolute zero temperature Jaime Wisniak* Resumen and night, shall not cease” (Genesis 8:22). Later on, La posibilidad de un cero absoluto de la temperatura the allegory of the vision of the prophet Ezekiel fue introducida en una etapa temprana del desarrollo contains a symbol of extreme cold: “And over the científico. La existencia del Primum Firgidum, un heads of the living creatures there was the likeness cuerpo supremamente frío, fue objeto de mucha of a firmament, like the colour of the terrible ice, discussion entre filósofos y científicos hasta el siglo stretched forth over their heads above” (Ezek. 1:22). diecisiete. Aun cuando científicos famosos como Observations of various natural and man-made Gay-Lussac negaron la posibilidad de un cero abso- phenomena led the ancients to postulate theories luto, la idea prendió de a poco y un gran número de that led to our modern concepts about the nature of valores diferentes fueron propuestos para su ubica- heat and heat transfer. Thermometry started from cion bajo el punto de congelación del agua. Hubo the recognition of the need to quantify these differ- que esperar hasta el trabajo funamental de Lord ences more precisely than by adjectives like hot and Kelvin para establecer la escala absoluta de tempera- cold. The original apparatus, called thermoscopes, tura que llevó al valor aceptado hoy en día de served merely to show the changes in the tempera - —273.15 C. ture of its surroundings. Eventually the need arose for quantifying these observations and the different Abstract thermometers began to be developed. Astronomers The possibility of an absolute zero temperature was built most of these instruments, particularly for introduced very early in the development of science . measuring low temperatures (Wisniak, 2000). Devel- The existence of the Primum Frigidum, a body su - opment of thermometric scales such as those of premely cold, was the subject of much discussion Réaumur, Fahrenheit and Celsius, led in a natural among philosophers and scientists well up to the way to the question whether there was a lower limit seventeenth century. Although famous scientists to temperature, and correspondingly, to the behav - such as Gay-Lussac negated the possibility of an iour of materials under those circumstances. Simul- absolute zero, the idea took ground little by little and taneously, many scientists devoted part of their ef- a large number of widely different values were pro- forts to understand the nature of heat and cold as well posed for its actual location below the freezing point as to find the laws that described them. Already by of water. It took the seminal work of Lord Kelvin to the seventeenth century detailed memoirs had been establish an absolute scale of temperatures that led published describing all the available information to the accepted value of —273.15 C. and the theories about the nature of heat, the most famous (and lengthy) ones being those of Francis The physiological sensation of heat and cold has Bacon (1561-1626) ( Bacon, 1651, 1955) and Robert accompanied mankind from the very beginning. Boyle (1627-1691) (Boyle 1999). Later on, scientists Heat and cold are mentioned in the Bible in the book such as Isaac Newton (1642-1727), Antoine-Laurent of Genesis as natural phenomena that existed before Lavoisier (1743-1794), John Dalton (1766-1844), the deluge and that will continue to occur afterwards: Joseph Fourier (1768-1830), Pierre-Simon Laplace “While the earth remaineth, seed time and harvest, (1749-1827), Joseph-Louis Gay-Lussac (1778-1850), and cold and heat, and summer and winter, and day Sadi Carnot (1796-1832), James Prescott Joule (1818- 1889), and William Thomson (Lord Kelvin, 1824- 1907) would develop the mathematics of the phe- nomenon and the concepts of absolute temperature *Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel 84105. and absolute zero that accompany us today. [email protected] Francis Bacon (1561-1626) dealt extensively with Recibido: 12 de agosto de 2004; aceptado: 15 de octubre de the concept of heat and cold, as seen in his major 2004. works Novum Organum (Boyle, 1955) and Sylva Syl- 104 Educación Química 16[1] PARA QUITARLE EL POLVO varum (Boyle, 1651). The latter contains an entry among Naturalists, the various candidates being the entitled Experiments in Consort Touching the Production earth, water, air, or nitre. Although there was argu- of Cold, where Bacon writes: “The production of cold ment about its nature, all agreed that there must exist is a thing worthy of the inquisition both for the use a body that by its own nature was “supremely cold” and disclosure of causes. For heat and cold are and that its participation in a phenomenon led other nature’s two hands whereby she chiefly worketh, and bodies to obtain that property. Boyle believed that heat must have in readiness in respect of the fire, but before arguing about the nature of the factor, scien- for cold we must stay till it cometh back or seek it in tists should first discuss (and agree) if it existed or not. deep caves or high mountains, and when all is done According to him “ it is disputable enough, whether we cannot obtain it in any degree, for furnaces of fire cold be a positive quality, or a bare privation of heat, are much hotter than a summer sun, but vaults and and till this question be determined, it will be some- hills are not much colder than a winter’s frost.” He what improper to wrangle solicitously, which may be went on to describe what he believed were the seven the Primum Frigidum. For if a Body being cold, means of producing cold, or its causes (the inside of signifies no more, then its not having its insensible the earth, the contact of cold bodies, the primary parts so much agitated there will be no cause to bring nature of all tangible bodies, the density of bodies, a in a Primum Frigidum. In the mean time, having quick spirit enclosed in a cold body, the chasing and discoursed thus long against admitting a primum driving away the spirits, and the exhaling or drawing frigidum, I think it not amiss to take notice once out of the warm spirits). The first mean is particularly more, that my design in playing the Sceptik on this interesting because it reflects some of the wrong subject, is not so much to reject other men’s probable ideas prevalent at that time: “The first means of opinions, of a primum frigidum, as absolutely false, producing cold is that which Nature preferenth us as it is to give an account, why I look upon them, as whithal; namely the expiring of Cold out of the doubtful.” inwards parts of the Earth in Winter, when the Sun Between 1703 and 1704 Guillaume Amontons hath no power to overcome it; the Earth being, as (1663-1705) published several papers (Amontons, has been noted by some (Primum Frigidum). This has 1703a,b, 1704) where he reported the phenomena he been asserted, as well as by Ancient, as by Modern had observed while studying the proper way to Philosophers such as Parmenides, Plutarch, andTele - calibrate an air thermometer. The greatest climatic sius” (in other words, the inside of the earth was the cold on the scale of units adopted by Amontons was source of the maximum cold). marked 50 and the greatest summer heat 58, the In 1682 Boyle read a paper to the Royal Society value of boiling water being 73, and the zero being on “New Experiments and Observations Touching 51.5 units below the freezing point. He noticed that Cold, or an Experimental History of Cold” (Boyle, when the temperature was changed between the 1999) where he described the many experiments he boiling point of water and ambient temperature, had done on frigorific mixtures, and the general equal drops in temperature resulted in equal de- effect of such upon matter. His multiple experiments creases in the pressure of the air. Since degrees in his led him to conclude that cold was a privation of that thermometer were registered by the height of a local motion of the particles of bodies which was column of mercury, “which the heat was able to requisite to constitute heat, and was not a positive sustain by the spring of the air”, it followed that the entity at all. He said: “if a body being cold signify to extreme cold of the thermometer would be that more than its not having its sensible parts so much which reduced the air to have no power of spring. In agitated as those of our sensorium, it suffices that the there must be a lowest temperature beyond which sun or the fire or some other agent, whatever it were, air, or any other substance could not be cooled. that agitated more vehemently its part before, does According to Amontons, this lowest temperature either now cease to agitate them or agitates them but represented a greater cold than what we call “very very remissly, so that till it be determined whether cold’, because his experiments showed that when the cold be a positive quality or but a privative it will be “spring of the air” (pressure) at the boiling point of needless to contend what particular body ought to water was 73 inches, the degree of heat which re- be esteemed the primum frigidum” (Boyle, 1999). mained in the air when brought to the freezing point According to Boyle the dispute about the actual of water was still very great, for it could maintain the identity of the Primum Frigidum was well known spring of 5.5 inches.