670 
MESSRS. T. E. THORPE ARE J. W. RODGER OH THE RELATIOHS 
As the numbei’ of hydrogen atoms displaced by the halogen increases, the differences 
augment at an increasing rate. 
If the values of carbon and hydrogen be taken as normal in these compounds, on 
introducing the value of chlorine obtained from monohalogen compounds the following 
numbers represent the respective effects on the molecular viscosity work of 1, 2, 3, 
and 4 atoms of chlorine when linked to one carbon atom. 
Effect upon molecular 
viscosity -work. 
Difference. 
Cl 
89 
do 
164 
i 0 
Cl, 
214 
50 
C 14 
258 
44 
It is instructive to note that the magnitudes of several of the other physical 
properties of these and similar substances exhibit the same kind of relationships. 
From determinations of the heats of formation of halogen compounds at constant 
volume, Thomsen concludes that the respective thermal effects wdiich may be attri¬ 
buted to the fixation of different numbers of chlorine atoms in the same molecule are 
as follows :— 
Thermal effect. 
Diffei’ence. 
Cl 
138 K 
1 QO 
Cb 
330 K 
144 
CI 3 
474 K 
126 
Cb 
600 K 
Here, precisely as in the case of molecular viscosity work, the differences diminish 
at a decreasing rate. 
The numbers given in the following table indicate also a parallelism between the 
magnitudes of the boiling-points, specific molecular volumes, and magnetic rotatory 
powers of the chlormethanes and the values of the molecular viscosity work. 
Critical temperatures might also be included in the comparisons, but the values for 
the higher chlorinated compounds, especially that of methylene chloride, are untrust¬ 
worthy, as the observations were made over heated mercuiy, Avhereby the substances 
are partially decomposed. The value for the molecular viscosit}^ Avork of methyl 
chloride is calculated from that of monohalogen compounds. 
