554 
MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
dibromides, for although the curves for acetylene, ethylene, and isobutylene bromides 
follow in the order of the molecular weights of the substances, that for propylene 
bromide lies to the left instead of the right of the curve for ethylene bromide. From 
such data as can be obtained on this point, the divergence is more probably due to the 
difference in symmetry between the structure of the molecules of ethylene and propylene 
Ijromides than to any possible difference in the complexity of the liquid molecules 
of these substances. It is significant that the curves for substances of which the 
molecules contain two atoms of bromine have such a different shape from those of 
mono-derivatives. Bromine itself, as shown by the similarity of its curve to that of 
acetylene bromide, behavms like a dibromide. This fact may be held to indicate 
the diatomic nature of its molecule. 
Cl dor idea. 
Four monochlorides were examined, viz., isopropyl chloride, propyl chloride, 
isobutyl chloride, and allyl chloride. Fig. 10 represents the results obtained. The 
Fig. 10. 
Older of the curves for the monohalogen compounds shows the same regularity as is 
exhibited liy the paraffins. The curve for the allyl compound is nearer the isopropyl 
than the normal propyl curve. It is therefore evident that although in the case of 
monohalogen compounds the allyl curve always lies between the propyl curves, there 
is a regular alteration in its relative position. It is nearer the normal curve in the 
case of the iodides, but nearer the iso curve in the case of the chlorides. At the 
boiling point the saturated mono-chlorides have, as in the case of the parent paraffins, 
almost the same viscosity coefficient. 
DicJdorides. 
Three dichlorides were investigated, viz., methylene dichloride, ethylene dichloride, 
and ethylidene dichloride. The results obtained are represented in fig. 11, in which 
the curves for propyl and isobutyl chloildes are inserted for the sake of comparison. 
