BETWEEN THE VISCOSITY OE LIQUIDS AND THEIR CHEMICAL NATURE. 403 
increase in the time of efSux. This increase in efflux-time is greater when the 
increment of CH 2 takes place in an alcohol radicle than when it takes place in an acid 
radicle. 
3. An increase in the transpiration-time also accompanies an increment of CHOH, 
of Ho, and of 0. 
4. A decrease of efflux-time accompanies an increment of C. 
5. Metameric bodies have, in general, different efflux-times. These are nearer 
together, the nearer the boiling-points of the liquids. 
6. Substances containing double-linked carbon have a greater efflux-time than those 
of equal molecular weight containing single-linked carbon. 
7. An increase or diminution of velocity of transpiration corresponds with an 
increase or decrease of boiling-point without being a simple function of the latter. 
8. In any particular homologous series it is possible to determine the direction of 
the alteration in transpiration-velocity on passing from a lower to a higher member, 
but not the magnitude of the change. 
Guerotjt (‘ Compt. Rend.,’ vol. 81, p. 1025, 1875 ; and vol. 83, p. 1291, 1876) also 
determined the value of K in Poiseuille’s formula K = VL/HD*^ (taking H as the 
height of a water column) at ordinary temperatures (13°-15°) for a number of the 
liquids investigated by Rellstab, and from the data Pribram and Handl have 
calculated the “ specific viscosities ” for equal volumes so as to make the results more 
directly comparable with those of Rellstab. The numerical values thus given by the 
two observers are, for the most part, widely different, although certain of their general 
conclusions are in agreement. Both find that, as a rule, in an homologous series, an 
increase of molecular weight is accompanied by an increase of transpiration-time, and 
Guerout confirms the exceptions in the cases of formic and acetic acids. Guerout’s 
numbers are, wdth one exception, considerably higher than those of Rellstab. In 
the series of the alcohols the difference is as high as 40 per cent, in the case of butyl 
alcohol, and is about 20 per cent, in most of the others ; in the series of the acids the 
discrepancy amounts to 5 or 6 per cent. It is impossible to determine exactly to 
what these divergencies are due, since Guerout gives no details either of the character 
of his preparations or of his method of observation. 
Guerout found that isomeric esters give the same value for K, but Rellstab’s 
observations lend no support to this conclusion. 
The most extensive investigation hitherto published on this subject is that by 
Pribram and Handl (‘ Wien. Ber.,’ Part II., vol. 78, p. 113, 1878 ; Part II., vol. 80, 
p. 17, 1879; Part II., vol. 84, p. 717, 1881), who have determined the “specific 
viscosity ” of a large number of lic[uid substances at different temperatures. Their 
methods, in principle, were identical with that of Poiseuille, although it must be 
admitted that their apparatus was hardly capable of furnishing results at all com¬ 
parable in point of accuracy with that of their predecessor. Indeed, the test-observa¬ 
tions which they adduce difter among themselves by from 2 to 3 per cent., and, under 
3 E 2 
