Petit, Alexis-Therese

Petit Alexis-Therese (1791-1820) Fr. phys., co-developed methods of determining thermal expansion and specific heats of solid bodies Philolaos ofTarentum ( 500 BC) Ger. phil., held the earth is not center of universe but that is stars and planet circle about central fire... 

Dulong was also an associate of Berthollet and a member of the Societe d Arcueil. His 1819 paper on heat capacities of elements in collaboration with Alexis-Therese Petit was widely interpreted as support for the atomic hypothesis. They noted that the product of specific heat times atomic weight was very nearly the same for a large number of sohd elements. They recognized that the quantity in qnestion represents the heat capacities of the atoms—or in modem terms, molar heat capacities. And they generalized the resnlts, asserting that, atoms of all simple bodies have exactly the same capacity for heat. (7)... 

Calorimetric studies of the type done by Lavoisier and Laplace (Figure 212) were continued by others including Pierre Louis Dulong (1785-1838) and Alexis Therese Petit (1791-1820). They discovered the law that bears their names the product of the specific heat and the atomic weight of solid elements (e.g., lead, gold, tin, silver, and sulfur) is constant. This really implies that all atoms (independent of their identities) have the same capacity for heat. This result was later extended to solid compounds and ultimately cleared up confusions such as whether the binary oxides of copper were really CuO and CUO2 or CU2O and CuO. 

Dulong and Petit s law /doo-long and pe-teez / The molar thermal capacity of a solid element is approximately equal to 3R, where R is the gas constant (25 J moh ). The law applies only to elements with simple crystal structures at normal temperatures. At lower temperatures the molar heat capacity falls with decreasing temperature (it is proportional to T ). Molar thermal capacity was formerly called atomic heat - the product of the atomic weight (relative atomic mass) and the specific thermal capacity. The law is named for the French physicists Pierre-Louis Dulong (1785-1838) and Alexis-Therese Petit (1791-1820). 

Fortunately, there were other keys to correctness in atomic weights. In 1818, for instance, a French chemist, Pierre Louis Dulong (1785-1838), and a French physicist, Alexis Therese Petit (1791-1820), working in collaboration, found one of them. They discovered that the specific heat of elements (the temperature rise that follows upon the absorption of a fixed quantity of heat) seemed to vary inversely with the atomic weight. That is, if element x had twice the atomic weight of element y, the temperature of element x would rise by only half as many... 

Alexis Therese Petit (Vesoul, 20 October 1791-Paris, 21 June 1820) entered the ficole Polytechnique in 1807 and became professor of physics in 1815. After an exceptionally brilliant career he died at the age of 29. Dulong and Petit in collaboration investigated the expansion of solids, liquids and gases, and the laws of cooling of solids in gases. ... 

Two major developments then followed that permitted better atomic weight determinations. They were the law of Pierre-Louis Dulong and Alexis-Therese Petit and the law of isomorphism. 

Stanislao Cannizzaro s method for determining atomic weights was not easy to apply to the metallic elements, as it required volatile compounds. Instead, other methods continued to be used for metals. One important way of obtaining atomic weights was through the 1819 law of Pierre-Louis Dulong and Alexis-Therese Petit. As discussed in chapter 2, these authors had found an approximate relationship between the specific heat and atomic weight of a sohd element to be ... 

Dulong-Petit law A chemical law proposed in 1819 by French physicists and chemists Pierre Louis Dulong and Alexis Therese Petit stating the classical expression for the specific... 

Berzelius also used the law of Pierre Louis Dulong (1785-1838) and Alexis Therese Petit (1791-1820). These two Frenchmen noticed in 1819 that for a number of elements the product of the atomic weight and specific heat (the atomic heat) was constant. They had hoped that this would provide an accurate method of determining atomic weights, but the constancy of atomic heats proved to be only approximate. However, Berzelius was able to use this approximate constancy to confirm the formula MO for the oxides of several metals (e.g. Mg, Ca, Ba) in preference to the formula MO2 which he had used earlier. 

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