between the viscosity of liquids and their chemtcal nature. 553 
has hitherto been. x4.1though the scale Iras thus been reduced, the general shape of 
the curves, since both ordinates and abscissae have been altered in the same ratio, is 
the same as it would have been on the previous scale. 
The marked effect of replacing an atom of hydrogen in a monobromide by an atom 
of bromine, is evident on comparing the curves of ethyl, propyl, and isobutyl iDromides 
with the corresponding dihalogen compounds; at 0°, for example, ethylene bromide 
has a coefficient five times as great as that of ethyl bromide. Indeed, the entire 
rig. 9. 
shape of the dihalogen curves differs from that of the mono-derivatives. For the 
latter, the slope of the curve varies little from member to member, and is comparatively 
speaking small. The slope, of course, is drjjdt and is the measure of the rate of 
change of the viscosity coefficient with temperature. In the case of the mono¬ 
derivatives, drjidt is not only small but varies little as the temperature rises. For 
dihalogen derivatives the slope is considerably increased, and with it, its variation 
with temperature. 
It is also apparent that constitution exercises a marked effect in the case ol the 
MDCCCXCIV.—A. 4 B 
