54 6 THE POPULAR SCIENCE MONTHLY. 



rious rare metals, by means of which the molecular weights of various 

 compounds have been satisfactorily ascertained. 



M. Deville's highest title to honor, says M. Wiirtz, rests upon 

 his having introduced to science the idea of dissociation as a particu- 

 lar method of decomposition, the understanding of which has ren- 

 dered the grandest services to theoretical chemistry. Decomposition 

 was believed, previous to his researches in this line, to be a simple 

 phenomenon, taking place and being repeated with each body at a 

 fixed temperature. M. Deville has shown that it is not always so, but 

 that decomposition is accomplished in certain cases by degrees, within 

 certain limits of temperature, in such a manner that it is arrested at 

 a given temperature, by the establishment of an equilibrium between 

 the decomposing body and the products of its decomposition. The 

 principle explains a variety of occurrences among thermal phenomena 

 that have hitherto not been accurately accounted for, and may be de- 

 fined, says " Nature," " as the property of many compound bodies to 

 undergo partial decomposition under the influence of heat in confined 

 spaces, until the liberated gas or vapor has attained a certain tension, 

 greater or less, according to the temperature. So long as this temper- 

 ature remains constant, no further decomposition takes place, neither 

 does any portion of the separated elements recombine. If the temper- 

 ature be raised, decomposition recommences, and continues until a 

 higher tension of the liberated gas or vapor, definite for that par- 

 ticular temperature, is attained. If the temperature falls, recompo- 

 sition ensues, until the tension of the residual gas is reduced to that 

 which corresponds with the lower temperature. The enunciation of 

 this simple but far-reaching principle has thrown light upon a number 

 of phenomena, such as the formation of minerals, the apparent vola- 

 tilization of solids, etc. ; and has been the fruitful source of countless 

 novel discoveries." 



Other researches with which M. Deville's name is associated are 

 those on boron, which he prosecuted in company with Wohler in 1857, 

 on the preparation of silicium and its compounds with copper (1863), a 

 new calorimeter, on the changes attendant upon the mixture of liquids 

 (1870), and the examination of a large variety of minerals and natu- 

 ral products. A few years ago he was appointed on the commission 

 to prepare the international normal standard of the measure of a 

 metre, and acquitted himself of the task allotted to him with charac- 

 teristic devotion to the interests of science. 



His simplicity was the predominant quality in M. Deville's char- 

 acter, and distinguished him alike in his social relations and in his sci- 

 entific labors. He kept away from the theoretical disputes in which 

 many of his colleagues were too prone to indulge, finding abundant 

 employment for his own resources " in attacking the still unsolved 

 problems of inorganic chemistry " ; and he is said to have gone so far 

 as to declare the whole theoretical tendency of modern chemistry, the 



