478 REPORT — 1888. 



has a specific heat rapidly rising with the temperature, the mean between 



— 78° and +10° being -1740, and between +10° and +30° being -1887; 

 that solid mercury has between —78° and — 40° a mean specific heat 

 •3192 ; that of solid bromine between — 78° and —9° is -087, and between 



— 78° and —20° it is '082, the melting-point of bromine being taken to 

 be not lower than —9°. [As a fact, the melting or the solidifying point 

 of bromine has been the subject of a considerable number of determina- 

 tions, and the temperature has been estimated by diflerent experimenters 

 at points varying from —72° to — 25° ; the most recent values and the 

 most trustworthy, however, are about -7-2°.] 



It is seen that mercury and bromine in the solid state obey the law 

 of specific heat, while the atomic heat of phosphorus is somewhat small. 

 The specific heat of red phosphorus ' is only slightly less than that of 

 ordinary phosphorus, the difference being perhaps due to the remoteness 

 of red phosphorus from its melting-point. The two varieties are con- 

 sidered by Regnault to have a difference which is inconsiderable. 



It will be noticed that the specific heat is always greater at higher 

 than at lower temperatures. 



In two subsequent papers Regnault ^ makes determinations of various 

 metals, including those accompanying platinum, cobalt, and nickel 

 whose specific heats he finds nearly equal ; manganese, magnesium, 

 which all fall into line with Dulong and Petit's law ; sodium (by sur- 

 rounding the tube containing the metal with a freezing mixture at 



— 34°), atti'ibnting to it half the then accepted atomic weight by which 

 change sodium is found to be in complete accord with the law ; lithium 

 chloride, from which he found that the molecular heat was only slightly 

 less than that of sodium chloride, which was slightly less than that of 

 potassium chloride, from which facts he infers that lithium chloride must 

 have a similar atomic composition to these others, thus halving the 

 atomic weight of lithium to make the formula of lithium chloride LiCl 

 (instead of LiClo). In confirmation of this view he says (t. 46, p. 278) : 

 ' For bodies of the same chemical composition the product of the sjjecific heat 

 by the molecular iveight is smaller the smaller the molecular iveight.' Thus 

 for RClo — e.g., CaCl2 and BaClo — the molecular heats are 114'72 and 

 116"44 ; again each of these numbers is quite different from those for 

 R0CI2, as LioCU, NaoCU, KgClo, which are 148-09, 156-97, 161-19. For 

 aluminium he finds the atomic heat somewhat smaller than for most of 

 the others. 



Just as in the case of the two varieties of phosphorus, so he finds for 

 the vitreous and metallic varieties of selenion examined at low tempera- 

 tures sensibly the same specific heat agreeing well with Dulong and 

 Petit's law, and mentions the fact (t. 46, p. 288) that the vitreous and 

 porcelain modifications of arsenious oxide have the same specific heat ; 

 but remarks on the unexpected result that the enormous evolution of 

 heat accompanying the transformation of vitreous into metallic selenion 

 has no appreciable effect on the specific heat of this body ; a similar 

 result he obtains afterwards for silicon (t 63). By direct determination 

 he afterwards obtains a specific heat for lithium, which agrees with the 

 formula LiCl, and includes lithium among the elements conforming to 

 Dulong and Petit's law. For boron and silicon he tries, by using a 

 different atomic weight for each from that then used, to place these 



» Aim. Chim. (3), 38, 1853, p. 129. 



- Ibid. (3), 46, 1856, p. 256 ; and 63, 1861, p. 5. 



