18 Recent Developments of Chemical Science. [January, 
the colour of chemical compounds, viewed as a function of 
the atomic weights of their component elements. In a 
memoir on this subject communicated to the “ Berichte der 
Deutsch. Chem. Gesell.” (vol. xvii., p. 2151), he remarks 
that the colour of chemical compounds depends on at least 
three conditions, namely, — 1, the temperature ; 2, the quan- 
tity of the eledtro-negative element ; and 3, on the atomic 
weights. 
The two former of these conditions have been especially 
studied by Ackroyd (“ Chemical News,” xxxiv., p. 76). Long 
previously a paper on the second of these conditions was 
read before the Chemical Sedtion of the Manchester Philo- 
sophical Society. This took place between the autumn of 
1849 and that of 1853 ; but as we cannot give the precise 
date, and have no means of referring to the original docu- 
ment, we suppress the name of the author. His conclusions 
agreed very closely with those reached by Mr. Ackroyd 
under the second head. 
The conclusions of the latter chemist are — 
I. All the chrome compounds change their colour in a 
fixed succession, in the order of the spedtral colours, 
and in such a manner that the colour, as the temper- 
ature rises, approximates more and more to the red 
end of the spedtrum, and passes ultimately into 
brown and black if the heat is sufficient. The 
transition of colour is generally diredt from white to 
a pale yellow, violet, indigo, — blue and green being 
overleapt. 
II. In binary compounds an increase of the proportion of 
the eledtro-negative element involves a modification 
of colour towards the red end of the spedtrum, and 
finally into brown and black. Thus PbO is yellow, 
Pb 3 0 4 red, and Pb 0 2 brown. 
III. Prof. Carnelley’s law as to the influence of the atomic 
weight is as follows : — In certain series of compounds, 
A# Ry, Bx Ry, Cx Ry, &c., in which R is an element 
or group of elements, whilst A, B, C., &c., represent 
elements belonging to the same sub-group of the 
periodic classification, the colour passes either entirely 
or partially through the following scale : — White or 
colourless, violet, indigo, blue, green, yellow, orange, 
red, brown, black, — or, in other words, the higher the 
atomic weight of the elements A, B, C, &c., the 
more the colour of the compound approaches the red 
end of the spedtrum, passing in certain cases into 
brown and black. 
