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Recebido em 5/1/10; aceito em 29/4/10; publicado na web em 1/9/10The formulation of the so-called law of rectilinear diameter for the determination of the critical volume of substances in the concluding decades of the nineteenth century became in a very useful and acceptably exact alternative tool for researchers in the field of critical phenomena. Its corresponding original expression, and even those of its early few modifications, were so mathematically simple that their use did not limit to exclusively contribute to remove the by then experimental obstacle for the estimating of this critical parameter, but also extended along several decades in the increasing applications of the principle of corresponding states.

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Recebido em 13/2/11; aceito em 1/8/11; publicado na web em 20/9/11 A very little known aspect of the scientific career of Regnault is his contribution to the emerging organic chemistry in the first half of the nineteenth century. The purpose of this article is not only to describe two of his most important researches in this field, as were the discovery of two series of halogenated derivates of certain organic compounds and the precise identification of some of the then recently discovered alkaloids, but also the main features that identified his research method. With the involvement in these subjects, Regnault unintentionally positioned himself in the midst of some of the polemics about the classification of organic compounds that characterized this age of science.

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 first 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 efforts 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 liquefação do hélio e a descoberta da supercondutividade são dois das mais surpreendentes desenvolvimentos da física de baixas temperaturas. O fato que ambas ocorreram no laboratório de Kammerlingh Onnes em Leiden, na Holanda, nãoé mera coincidência: o primeiro foi indispensável para que os pesquisadores pudessem chegarà segunda. Do mesmo modo, a liquefação do hélio culminou após décadas de esforços em liquefazer os chamados "gases permanentes". Um estudo mais completo deste assunto requer a discussão de estudos que se estenderam por mais de 50 anos, ligando pesquisadores de diferentes países europeus. Palavras-chave: liquefação, supercondutividade, condutividade elétrica, resistência elétrica, hélio, teoria de elétrons.

Studies on the temperature dependence of electric conductivity for metals in the Nineteenth Century: a neglected chapter in the history of superconductivity (Estudos sobre a dependência com a temperatura da condutividade elétrica de metais no século XIX: um capítulo menosprezado na história da supercondutividade)Simón Reif-Acherman Two different lines of research had significant contributions to the discovery of superconductivity: the liquefaction of gases and the studies of the temperature dependence of the electrical conductivity, or resistance, of pure metals and alloys. Different publications have described and discussed the achievements in the first one of these subjects. The second subject had not received, however, the same attention. This article tries to fill this gap by presenting an account showing details of the evolution of the ideas, the first essentially experimental contributions to the subject and their corresponding responsible persons. Keywords: superconductivity, electrical resistance, temperature, dependency relation, history, metals, alloys.Duas diferentes linhas de pesquisa deram significativa contribuiçãoà descoberta da supercondutividade: a liquefação de gases e os estudos da dependência da condutividade ou resistência elétrica com a temperatura, em metais puros ou ligas. Diferentes artigos descrevem e discutem as conquistas da liquefação ao passo que a segunda não recebeu, contudo, a mesma atenção. Este artigo busca preencher esta lacuna, apresentando um histórico detalhado da evolução de idéias, das primeiros resultados experimentais e dos pesquisadores nelas envolvidos. Palavras-chave: supercondutividade, resistência elétrica, dependência com a temperatura, história da supercondutividade em metais e ligas. IntroductionThe traditional accounts about the discovery of superconductivity, whose first century is commemorated this year, show it as a consequence, in some way accidental, of the experimental researches on the liquefaction of the by then so called 'permanent' gases. A previous article on this subject is mainly focused on the historical evolution of these events [1]. This conception is, however, historically incomplete, since parallel achievements developed in a different line of research made equally significant contributions to the identification of the new phenomenon. The necessity for disposing of appropriate thermometric instruments for the each time more extreme and limited regions of low temperature in order to replace those, by then, unpractical gaseous ones, forced the carrying out of researches focused on the application of different physical principles and materials in order to fill this objective. The studies on the electrical conductivity, or resistance, of pure metals and alloys and their temperature dependence aroused the interest of scientists of different nationalities in the second half of the nineteenth century and the first half of the twentieth century, and contributed not only to the understanding of the electrical properties of those materials but also to t...

Heike Kamerlingh Onnes , born a century and a half ago, was a major protagonist in the so-called Second Golden Age of Dutch Science. He devoted his career to the emerging field of low-temperature physics. His particular concern was to test the theories of his older compatriot Johannes Diderik van der Waals (1837-1923) by creating a style of research that was characterized by meticulous planning, precise measurement, and constant improvement of techniques and instruments. He made numerous contributions to low-temperature physics, but I focus on his liquefaction of helium, for which he received the Nobel Prize in Physics for 1913, and on his discovery of superconductivity. He became known internationally as le gentleman du zéro absolu.

Recebido em 17/7/08; aceito em 10/2/09; publicado na web em 3/7/09Cryoscopy is considered one of the foundations of the modern theory of solutions and of physical chemistry. This paper shows in order the first regularities pointed out by several scientists on the subject, in the first chapter of its birth as a scientific discipline. The study is focused on the identification of the different steps that helped, first qualitatively and then quantitatively, to adjust the different classes of possible solutions, including those that formed hydrates, to a basic formulation that the French scientist François-Marie Raoult would later generalize in the law that bears his name.Keywords: cryoscopy; history; freezing point.The excessively brief style used by most textbooks to present the historical events associated with the emergence, development, and discussion of laws, theories and hypotheses related to scientific concepts, usually tends to create in the reader a distorted or incomplete version of the real facts. The history of cryoscopy's birth as a scientific discipline constitutes a good example of this situation.Cryoscopy is usually defined as the branch of science that studies the solutions founded on the determination of their corresponding freezing points. It allows, just like the other colligative properties, the determination of the molecular weight of a an unknown or unidentified substance based on the principle that the freezing point of a solution compared with that of the respective solvent varies according to the amount and nature of the solute dissolved in it. The origins of cryoscopy (from Greek roots, κρυος ice, and σκοπεω I examine) have been generally associated, in an almost exclusive way, with the name of the French professor of chemistry François-Marie Raoult (1830-1901. Through a very accurate and systematic experimental work on this subject, he was able to formulate a freezing point law that holds not only for water but also for other solvents, which include solutes of both, organic and inorganic nature. The very little cited information included in textbooks on physical chemistry about the different colligative properties seems to show that Raoult was gifted with the relevant information. According to that, it wouldn't be possible to know that the subsequent evolution of the subject was the result of many trials, successes, failures, approximations, and mistakes. Although it is true that he was responsible not only for the quantitative generalization of the connection between the lowering of freezing point of a solution and its corresponding concentration, but also for the proposal of the name for this branch of chemistry, the first observations about this subject go back to more than a century before Raoult's researches.The purpose of this article is show in order the first regularities pointed out by several scientists on the subject, which would later lead to the formulation of what could be considered one of the foundations of the modern theory of solutions and of physical chemistry. The spe...