1864. | Physics. 697 
purpurin, and rubiacin; and in a piece of the dry material no larger 
than a pin’s head all three substances were distinctly recognized. 
The poisonous nature of the green colouring-matters in general use 
has led to numberless attempts to substitute for them pigments of less 
danger. At the recent meeting of the Société Stanislas at Nancy, a 
proposition was made to employ the beautiful green manganate of 
barium as a pigment. Although very beautiful and comparatively 
inexpensive, this pigment would still labour under the disadvantage 
of being poisonous, whilst at the same time it is likely to be deficient 
in permanence. 
Hzat.—One of the most important investigations in this branch 
of science has recently been communicated by Dr. Kopp to the Royal 
Society. He has been engaged in the determination of the specific 
heat of an immense number of solid and liquid bodies, and has devised 
a very simple method of performing the experiment, thus bringing the 
determination of specific heat out of the restricted sphere of the 
physical cabinet, with its complicated apparatus, within reach of the 
ordinary appliances of the chemical laboratory. Dr. Kopp has arrived 
at the result that each element in the solid state, and at an adequate 
distance from its melting-point, has one specific or atomic heat; and 
that for each element it is to be assumed that it has essentially the 
same specific or atomic heat in the free state and in compounds. The 
author discusses the applicability of Dulong and Petit’s law, and shows 
that it is not universally applicable. He concludes his memoir 
with some considerations on the nature of the chemical elements, and 
shows that chlorine, bromine, and iodine (which are even now regarded 
by some as peroxides of unknown elements), if compound at all, are 
not more so than the other elements to which Dulong and Petit’s law 
is considered to apply. If this law were universally valid, it might 
be concluded that the so-called elements, if they are really compounds 
of unknown simpler substances, are compounds of the same order, and 
have the same degree of composition; but with the proof that this 
law is not universally true, the conclusion to which this result leads 
loses some of its authority. In a very great number of compounds, the 
atomic heat gives however, more or less accurately, a measure for the 
complication of the composition, and the conclusion appears legitimate 
that for the so-called elements the directly or indirectly determined 
atomic heats are a measure for the complication of their composition. 
Carbon and hydrogen, for example, “if not themselves actually simple 
bodies, are yet simpler compounds of unknown elements than are 
silicium or oxygen,” and still more complex are the large number of. 
elements which may be considered as following Dulong and Petit’s 
law. With reference to the nature of the so-called elements, the 
author states that it must not be forgotten that his conclusions only 
give some sort of clue as to which of the present undecomposed bodies 
are of more complicated and which of simpler composition, but they 
tell nothing as to what the simpler substances are which are used in 
the construction of the compound atoms. But even if these conclusions 
are not free from uncertainty and imperfection, they are well worthy 
