between the ahscosity of liquids and theie chemical nature. 561 
connection with them is the anomalous course of the benzene curve. At 0° benzene 
has a greater viscosity than ethyl benzene ; at about 10° the curves cross and for the 
greater part of its course the benzene curve lies between those of ethyl benzene and 
toluene. At about 80° however, it cuts across the toluene curve, so that at the 
boiling point of benzene the viscosity constants of benzene, toluene, and ethyl benzene 
are in the order of the molecular weights. The curve for toluene is uniformly to 
the left of that for ethyl benzene. Another striking point is the disposition of the 
curves for the three isomeric xylenes. The curves for the meta- and para-isomers 
lie between those of toluene and ethyl benzene, and thus uniformly to the left of the 
curve for the latter. The curve for the ortho-isomer howmver, is Avidely separated 
Fig. 17. 
from the other two and lies considerably to the right of the curve for ethyl benzene. 
It is also interesting, as em])hasising the similarity between the meta- and para- 
compounds and the separation from them of the ortho-compound, that although at low 
temperatures para-xylene gives slightly larger coefficients than meta-xylene, yet 
between 110° and the boiling-point the two curves for the meta- and para-isomers 
are practically identical. 
The peculiar course of the benzene curve might at first sight appear to indicate 
molecular complexity; an extensive series of surface-energy measurements made 
by Ramsay and Shields would appear to show hoAvever that this disturbing factor 
does not here exist. If we accept this conclusion, then difference in chemical constitu¬ 
tion must be taken to be the cause of the peculiarity, for it is easy to conceive that a 
mdcccxciv.—A. 4 c 
