476 EEPORT— 1888. 



By examination of a number of well-known minerals lie arrives at tV.e 

 following general conclusion : ' The specific heats of bodies of similar 

 chemical composition are inversely as their stochiometric quantities.' 

 As examples the following are adduced : calc spar, CaCOa ; bitter spar 

 (CaMg)C03 ; magnesite (MgFe)C03 ; spathose iron ore, FeCOs ; ^"d 

 calamine, TmCO-^. These are bodies of similar chemical composition ; 

 the stochiometric quantities are the quantities found thus (taking, for 

 example, magnesite) : find the value assigned to CO3, according to the 

 atomic weights of C and O, and add the amounts of magnesium and iron 

 according to the proportions of these metals found on analysis of the 

 mineral. 



The product of the specific heat and the stochiometric quantity is 

 found to be approximately the same for all the above minerals. Simi- 

 larly for the minerals heavy spar, anhydrite, celestin — BaS04, CaSOj, 

 Sr£04 — also for magnesium-, mercuric-, zinc-, oupric-, calcium- oxides; 

 for cinnabar HgS, realgar AsS, lead glance PbS, blende ZuS ; and for 

 ferric oxide, minium, chromic oxide, in the case of each of -which he 

 remarks that two [stochiometric] parts (antheile) are combined with 

 three of oxygen. 



The above examples are reproduced here principally to show in what 

 sense Neumann meant the words ' similar chemical composition ' to be 

 applied. 



Eegnault's Determinations ' — Elements and Compounds, 



In his first memoir- Regnault deals with solid elements, making fresh 

 determinations of those examined by Dulong and Petit, and on -which 

 they founded their law, and in addition finding the specific heats of a 

 number of elements which they had not determined ; on pp. 61-64 of this 

 memoir he gives a table of his results. Comparing the atomic weights 

 •with that of oxygen as 100, the atomic -weights of the elements examined 

 by him vary from 200 to 1400, while the atomic heats vary only from 

 88 to 42, with the exception of that of carbon, which is too small unless 

 its atomic weight is doubled ; he halves the then received atomic weight 

 of silver, thereby bringing it in harmony with the law and bringing the 

 formula of its sulphide from that adopted before (AgS) to Ag2S, whereby 

 the isomorphism of this sulphide with cuprous sulphide is represented by 

 giving to the two similar formulae. With the exception of carbon and pos- 

 sible exceptions of a few elements of which he had not at the time pure 

 specimens in sufficient quantity, including boron and silicon, Regnault 

 concludes that Dulong and Petit's law applies to the elements generally 

 with fair approximation, but not with accuracy, even allowing for experi- 

 mental errors. He expresses the opinion that possibly their law may be 

 true quite rigorously if each element were examined at a definite point 

 of the thermometric scale appropriate to it, and if the specific heat were 

 obtained free from admixture with the heat which is used up in expand- 

 ing the body, and if the body is at a temperature so far removed from the 

 temperature of fusion that no portion of the heat effusion enters into the 

 observed number representing the specific heat. 



In his second memoir ^ on the specific heat of simple and compound 



' Regnault, Ann. adm. 2, 73, 1840, p. 5 ; 3, 1, 1841, p. 129 ; 9, 1843, p. 322 ; 3, 38, 

 1853, p. 129 ; 46, 185G, p. 257 ; 63, 1861, p. 5 ; 67, 1863, p. 427 ; 4, 3, 1864, p. 495 ; 

 7, 1866, p. 450. 



■' Ann. Chim. (2), 73, 1840, p. 5. ' IKd. (3), 1, 1341, p. 129. 



