55G 
MESSRS. T. E. THORPE AND .]. W. RODGER ON THE RELATIONS 
tlian that of the curves for the di- and tri- compounds, and points to the fact that the 
effect produced bj the introduction of a chlorine atom into the molecule of a com¬ 
pound depends on the number of chlorine atoms already present. 
Pig. 12. 
The comparison of the curves for tetrachlorethylene, CgCl^, and tetrachlormethane, 
CCfj,, is significant, as illustrating the effect of constitution in counteracting that of 
molecular weight, and also the effect of temperature on the relative viscosities of two 
substances. At low temperatures the compound of higher molecular weight has the 
lower viscosity, but, as-the temperature rises, the curves cross, and the viscosity at the 
same temperature is in the order of the molecular weights. No crossing of the curves 
takes })lace in the case of any of the strictly comparable compounds which have 
hitherto been considered. 
Sulphur Compounds. 
Four compounds containing sulphur were investigated, viz., methyl sulphide, ethyl 
sulphide, carbon disulphide, and thiophen. The results obtained are represented in 
fig. 13. The curves for methyl and ethyl sulphides exhibit the same regularities in 
shape and position as other homologous compounds. 
Carbon bisulphide gives a somewhat steeper curve than the alkyl sulphides, but 
the position of the curves for the three substances is in accordance with their molecular 
weights, 
