Thomsen, Julius

Thomsen, Julius. Untersuchung fiber die Warmtdn-ung beim Auflosen verscheidener fester flfissiger und Ififtfonniger Kdrper in Wasser. 

Danish chemist Julius Thomsen, regarded the heat evolved in a chemical reaction as a measure of chemical affinity, on the grounds that heat represented the work done by chemical forces. Thomsen and Berthelot similarly defined affinity as the force that unites the component parts of a chemical compound and that must be overcome by an equivalent force, the quantity of which can be measured by heat evolved. 52... 

Marcellin Berthelot, Essai de mecanique chimique fondee sur la thermochimie, and Julius Thomsen,... 

Kragh, Helge. "Julius Thomsen and Classical Thermochemistry." BJHS 17 (1984) 255272. 

At present, there are not sufficient data available for the change of enthalpy by formation of hydroxo complexes which are further complicated by precipitation and polynuclear behaviour. However, some of Julius Thomsen s calorimetric measmrements seem to indicate that heat frequently is evolved with hard central atoms in contrast to formation of the corresponding fluoro complexes. On the other hand, sulphate and carboxylates behave like F according to Ahrland. 

Hafnium had lain hidden for untold centuries, not because of its rarity but because of its dose similarity to zirconium (16), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, C. F. Rammelsberg, A. E. Nordenskjold, J.-C. G. de Marignac, and other experts on the chemistry of zirconium, he found that they contained from 1 to 5 per cent of the new element (26, 27). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (24, 28). Some of the minerals were of nepheline syenitic and some of granitic origin (20). Hafnium and zirconium are so closely related chemically and so closely associated in the mineral realm that their separation is even more difficult than that of niobium (columbium) and tantalum (29). The ratio of hafnium to zirconium is not the same in all minerals. 

The standard temperature selected for the values given in this book is 18° Centigrade, following the procedure of the thermochemistry section (Bichowsky1) of the International Critical Tables. The authors have been reluctant not to use the almost universally accepted standard temperature of 25° Centigrade for thermodynamic calculations but the selection of 18° as the standard temperature is practically necessary in this case because all of the monumental work of Julius Thomsen and of Marcellin Berthelot was done at or near 18° and there are not now available sufficient heat capacity data with which to make accurate conversion to 25° (this is especially important for reactions involving substances in aqueous solution where the temperature coefficient is usually very large). In later years, as the data on heat capacities become available, or as the heats of many of the reactions, which have until the present time been measured only by Thomsen or Berthelot or both, are redetermined, it will be quite feasible to use 25° as the standard temperature. 

H. Kragh, Julius Thomsen and classical thermochemistry , Brit. J. Hist. ScL, 1984,17, 255-272. 

His most famous achievement was the discovery of the -> endothermic galvanic cells in 1897 [i,ii]. It was the first evidence that endothermic reactions can proceed spontaneously. Therefore, it supplied a verification of the concept of -> Gibbs and -> Helmholtz regarding the nature of affinity, i.e., the Gibbs free energy of reaction is of importance and not the heat of reaction (enthalpy) as claimed by Pierre Eugene Marcellin Berthe-lot (1827-1907) and Hans Peter Jorgen Julius Thomsen (1826-1909). 

A particularly interesting classification was the one with horizontal groups and vertical periods proposed by the Danish thermochemist Hans Peter j0rgen Julius Thomsen (1826-1909) in 1895 (Figure 23) (Thomsen, 1895). Such a pyramidal/ladder form representation had already been proposed by the English scientist Thomas Bayley in 1882 (Figure 24), but... 

FIGURE 23 Julius Thomsen s pyramidal periodic table (1895). Reproduced from Thomsen (1895). 

The first conscious attempt in this direction is due to Julius Thomsen, who repeatedly stated as early as 1852, in his Contributions to a System of Thermo-chemistry, that vigorous manifestations of chemical affinity were accompanied by vigorous development of heat, and that chemical processes associated with an absorption of heat were of rare occurrence. Hence he arrived at the following conclusion When a body falls it develops a certain mechanical effect which is related to its weight and to the distance traversed. In chemical reactions which take place in their normal direction, a certain effect is again produced, but in this case it appears as heat. In the development of heat we have a measure of the chemical force developed in the reaction. ... 

Using such a calorimeter (from the Latin for heat-measure), Berthelot ran careful determinations of the quantity of heat evolved by hundreds of different chemical reactions. Independently, the Danish chemist Hans Peter Jorgen Julius Thomsen (1826-1909) did similar experiments. 

At the end of last century, the most urgent question to answer about the Periodic Table was how many lanthanides there are. An interesting attempt to answer this question was made by Julius Thomsen (1895a) describing a set of vertical series containing 1, 7, 7, 17, 17 and 31 elements, each series starting with an alkali-metal... 

Niels Bjerrum (Copenhagen ii March 1879-30 September 1958), a pupil of Julius Thomsen and later of Nernst, was professor in the Royal Veterinary and Agricultural College, Copenhagen (1914). ... 

For more complicated atoms Bohr, by ingenious methods, arrived at a scheme for the structure of atoms which corresponds with the periodic table. He assigned incomplete inner groups of electrons to the atoms of the so-called transitional elements , which explained the anomalous behaviour of the rare-earth elements. This had been foreshadowed in a periodic table proposed by Julius Thomsen, in which the transitional elements occur in the middle of long rows, and was suggested by Rudolf Ladenburg (son of the chemist Albert Ladenburg), professor of physics in Breslau. Successive electrons added to the atomic structure of such elements fill shells below the valency electrons, and hence the chemical properties remain fairly constant as the atomic numbers increase. 

Further thermochemical measurements were made in the 1850s and 1860s by the Danish chemist Julius Thomsen (1826-1909) and the Frenchman Marcelin Berthelot, who had earlier made such important contributions to organic synthesis (Chapter 10). It was Berthelot who introduced the terms endothermic and exothermic and invented the bomb calorimeter for the accurate determination of heats of combustion. Berthelot suggested that all spontaneous reactions occur with the evolution of heat, and that the reaction which actually occurs in a given situation is the one which is accompanied by the greatest evolution of heat. These conclusions are erroneous, and it was not until the new discipline of thermodynamics was more fully developed that the criteria for spontaneous chemical change were properly understood. 

But why cryolite Why would these two young men, one a metallurgist in Europe, the other a chemist in North America, choose a mineral from Greenland with which to experiment The answer may be related to an 1850 connection between the Pennsylvania Salt Manufacturing Co. in the U.S., and the Kryolith Co. of Denmark, to a process invented by Julius Thomsen of that company ( ), and to the earlier discovery of cryolite on Danish soil in Greenland. The Kryolith Co. used Thomsen s process to... 

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