190 
PROFESSOR KOPP ON THE SPECIFIC HEAT OF SOLID BODIES. 
accordance with Dulong and Petit’s law, are approximately equal, the average being 6‘4. 
I do not think that all these elements have really the same atomic heat, but think that 
some of them will subsequently be considered as exceptions to the above-mentioned 
law, as it will in the sequel be proved that several elements have an atomic heat differing 
from 6 ’4. But for none of the previously mentioned elements are the present data, 
and the presumed deviation of the atomic heat from that of other elements, sufficient to 
justify their being separated from them. 
To the elements just mentioned chlorine must be associated from the close agreement of 
the corresponding chlorine, bromine, and iodine compounds (§ 84), and of the compounds 
K Cl 0 3 , 24*8, and K As 0 3 , 25’3 (§ 88). To the atomic heats of these latter compounds 
those of individual salts KN0 3 approximate closely; the latter gave (§ 88) 21*8-24’4, 
mean 2S , 0, which on the whole agrees sufficiently closely with those found for the 
metallic oxides, B 2 0 3 (§ 85). I count nitrogen also among the elements whose atomic 
heat may be assumed at 6'4, like that of most other elements; without, however, con- 
sidering the determination of the atomic heat of this element as very trustworthy. To 
deduce the atomic heat of this element with certainty, compounds are wanting which 
contain, besides nitrogen, elements whose atomic heat has been directly determined. 
The fact that the atomic heat of the nitrates, R 2 N 2 © 6 , was found (§ 88) in the mean 
to be 38T, a third of which, 12‘7, is somewhat less than the average atomic heat 
found for the oxides of heavy metals of the formula R 0 2 , might be a reason for assign- 
ing to nitrogen a smaller atomic heat ; while, on the other hand, the atomic heats of 
other nitrogen compounds, in which it is true other elements enter whose atomic heat is 
only indirectly determined, do not favour this view. 
In the class of elements with the atomic heat about 6 '4, barium , calcium , and 
strontium may be placed from the agreement in the atomic heats of their compounds 
with the atomic heats of corresponding compounds of such elements as have been 
found by the direct determination of their specific heat in the free solid state to belong 
to that class (compare the atomic heats of the compounds RC1 2 in § 84, R©0 3 in 
§ 86, R S0 4 in § 87, and SN 2 G 6 in § 88); further, rubidium (compare the atomic 
heats of the compounds B Cl in § 84, and R 2 € 0 3 in § 86) ; then also chromium (from 
the agreement in the atomic heats of Cr 2 0 3 and ¥e 2 0 3 , § 84), and titanium (from the 
agreement in the atomic heats of Ti 0 2 and Sr 0 2 , § 84). To place zirconium in the same 
class has no other justification than that on this assumption the atomic heat of zircon 
may be calculated in accordance with that deduced from the observed specific heat of 
this mineral. 
101. According to direct determinations of the specific heat, sulphur and phosphorus 
do not belong to this class. The more trustworthy determinations (for sulphur the last 
two, for phosphorus the last three of the numbers in § 82) assign to these elements the 
atomic heat 5 '4. That sulphur has a smaller atomic heat than the elements discussed 
in the last paragraphs follows from the atomic heats of sulphur compounds, compared 
