264 



NATURE 



\Jan. 31, 1878 



means of their calorimeter based on the method of cool- 

 ing, and obtained data sufficiently accurate to warrant the 

 establishment of their law that the product of the specific 

 heat of an element and its atomic weight is a constant. 

 Regnault, after having submitted their method to careful 

 examination, found it useless for the exact determination 

 of the specific heat of solids, and invented in its place 

 the calorimeter bearing his name. It is based on the 

 method of mixtures, viz., of heating a known weight of a 

 substance to a known temperature, immersing it in a 

 known weight of water at a known temperature, and 

 determining the temperature of the mixture. With this 

 apparatus, which is of a somewhat complicated character, 

 in order to reduce to a minimum the possibilities of 

 error, Regnault determined the specific heat of the 

 liquid and solid elements, and of a great variety 

 of compounds. From the comparison of these results 

 he deduced the general law that for all compounds 

 of the same formula and similar chemical constitution 

 the product of the specific heat and the atomic 

 weight is the same. He also confirmed, by his experi- 

 ments, the hypothesis of Wostyn, that the elements 

 require the same amount of heat to be raised to a certain 

 temperature, whether free or in combination, and showed, 

 by his more exact results, the general truth of Dulong 

 and Petit's law. In order to overcome the difficulties of 

 determining the specific heat of gases, Regnault contrived 

 aningenious apparatus in which the gases passed through a 

 spiral inclosed in a known weight of water. The volume 

 of gas, its temperature on entering and leaving the appa- 

 ratus, and the alteration in the temperature of the water 

 supplied the necessary data. By this means he experi- 

 mented with about thirty-five of the principal gases and 

 vapours, and established the two important laws, i, that 

 the specific heat of any gas at constant pressure, whether 

 simple or compound, is the same at all pressures and tem- 

 peratures ; and 2, that the specific heats of different 

 simple gases are in the inverse ratio of their relative 

 densities. Regnault prepared also an interesting table of 

 the specific heats of various substances in the solid, 

 liquid, and gaseous forms, from which it appears that the 

 specific heat of the same Isody is commonly greater in the 

 liquid than in the solid state, and always greater than in 

 the gaseous state. 



. In his experiments upon heat Regnault was led to 

 devise methods of measuring high temperatures accu- 

 rately, and invented the well-known air thermometer, 

 which can be used at all temperatures below that at 

 which gas softens, and the mercury and hydrogen pyro- 

 meters, the latter of which permits the determination of 

 the temperature in a furnace at any instant. In this con- 

 nection he carried out also an elaborate series of experi- 

 ments on the density and absolute expansion of mercury 

 from 1° to 360°, the results of which, as tabulated, are of 

 primary importance in the correction of thermometers 

 and barometers, as well as in a multitude of physical 

 experiments conducted with this liquid. Still more ela- 

 borate and exhaustive are the extensive series of deter- 

 minations in connection with water, its specific heat at 

 various temperatures, the tension of its vapour at various 

 temperatures, and the latent heat of its vapour at various 

 pressures, all of which were designed to serve as funda- 

 mental facts upon which to base the action of heat on 

 water for industrial purposes. The specific heat of water 

 was found to increase from I at 0° to i'oi3 at 100° and 

 I '056 at 230°. For the determination of the tension of 

 steam Regnault contrived a simple apparatus based on 

 the fact that the maximum tension of steam at the boiling- 

 point is equal to the external pressure, by the aid of which 

 he was able to construct his table of tensions from 

 o"32 mill, at 32° to 20926 mill, at 230°. 



The experiments with this apparatus were extended to 

 a number of volatile liquids with the design of testing the 

 truth of Dalton's supposition that the tension of the 



vapours of all liquids is the same at temperatures equally 

 distant from their boiling points, and the results showed 

 that although not a law, it was very nearly correct 

 for small intervals of temperature in the neighbour- 

 hood of the boiling point. A variety of interesting 

 results were also obtained from mixtures of gases and 

 vapours, including the laws that a liquid does not give off 

 a vapour of so high a tension in the presence of a perma- 

 nent gas as in a vacuum, and that while the tension of 

 the vapours of a mixture of liquids not dissolving each 

 other is equal to the sum of the tensions of its liquids at 

 the same temperature ; on the contrary, the tension 

 arising from a mixture of mutually solvent liquids is less 

 than the sum of the individual tensions. 



Perhaps the most important of Regnault's experimental 

 investigations was that on the coefficient of expansion for 

 air and other gases, as well as on the compressibility of 

 gases. Dalton, Gay-Lussac, and Rudberg had obtained 

 numbers for the coefficient of expansions differing widely 

 from one another. It was reserved for Regnault to esta- 

 blish by the most delicate experiments the number "03663 

 as the coefficient of expansion of air, and to show in 

 addition that the law of Dalton and Gay-Lussac with 

 regard to the regularity of expansion among gases was 

 only approximately correct. A similar result was obtained 

 in his investigations on the accuracy of Boyle and 

 Mariotte's Law, on the compressibility of gases. 



In addition to the chief lines of research alluded to, 

 Regnault made a variety of interesting experiments on 

 the phenomena produced by heat, and his hypsometer and 

 hygrometer should be mentioned, on account of their 

 simple and practical qualities. Some valuable investiga- 

 tions on the phenomena of respiration were made by him 

 in connection with Reiset, and, together with Dumas, he 

 carried out a lengthy research on illuminating gas. 



His most valuable experimental results are collected 

 together in vol. xxi. of the Memoires of the French 

 Academy, and a continuation is to be found in vol. xxvi. 

 Regnault published, in 1847, a treatise on chemistry, 

 which has survived numerous editions in France, and 

 been translated into German, English, Dutch, and Italian. 



In 1854 he was appointed director of the famous porce- 

 lain manufactory of Sevres, and since that date much of 

 his time has been devoted to improvements in ceramic 

 processes. During the Franco- Prussian war he received 

 a sad blow in the death, on the battle-field, of his second 

 son, Henri Regnault, a promising artist, and universal' 

 favourite in Paris. He returned to his laboratory at 

 Sevres, after the declaration of peace, to find that the 

 results of his last great research on the phenomena of 

 heat accompanying the expansion of gases, derived from 

 over6oo observations, had been destroyed. The announce- 

 ment of this loss was his last communication to the 

 scientific world. Since then, oppressed by grief and a 

 victim to increasing infirmities, he has been forced to 

 renounce his wonted pursuits. On the day when the 

 gay artist world of Paris was celebrating the battle of 

 Buzenval by laying wreaths on the grave of the young 

 patriot-painter, the father was released from a long and 

 painful illness by the hand of death. 



As a scientific investigator, Regnault did not possess 

 the brilliant originality of many of his fellow-physicists. 

 It is as the patient, thorough, conscientious observer that 

 he has won his way to the foremost rank. Possessing a 

 wonderful ingenuity in the invention of mechanical 

 appliances for the purposes of observation and a perfect 

 familiarity with the mathematical department of physics, 

 he has been enabled by means of his unflagging 

 enthusiasm and unbending resolution to place the modem 

 physicist and chemist in possession of an invaluable col- 

 lection of constants, which at the present stage of science 

 are in daily use not only in the laboratory of research, 

 but for a large variety of industrial purposes. 



T. H. N. 



