BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 401 
how far determinations of viscosity may be taken as the measure of such dissociative 
changes; up to the present no simple expression for the relation of the viscosity 
coefficient of a mixture to those of its components has been deduced. 
A point of more immediate importance is that in this Memoir, Graham, for the 
first time, directed attention to the desirability of studying the transpirability of 
homogeneous liquids in connection with their other physical properties, and in respect 
to their chemical nature. He determined the transpiration-times of a number of 
such liquids at the uniform temperature of 20° C., and compared the observed times 
with that of water in the same apparatus, at the same temperature. From obser¬ 
vations made on methyl, ethy], and amyl alcohols ; on acetic, butyric, and valeric 
acids, and on the ethyl esters of these acids he found that the transpiration-time of 
an alcohol, ester, or acid, increases as its boiling-point under ordinary pressure 
increases, from which he inferred that a connection exists between transpirability 
and molecular weight of a kind analogous to that which subsists between boiling- 
point and composition, and he suggested the advisability of determining the trans¬ 
piration-times of homologous series of substances at a fixed and relatively high 
temperature. 
In 1868, PtELLSTAB (‘ Ueber Transpiration homologer Fliissigkeiten, Inaug.- 
Dissert.,’ Bonn, 1868) attempted to develop the subject in the manner indicated by 
Graham, and at the same time to determine the influence of temperature on the 
effiux-times of the liquids studied. Poiseuille, as already stated, had traced this 
influence in the case of water; Graham had repeated the observations on water, and 
had further studied the case of ethyl alcohol. Rellstab’s method was essentially 
that of Poiseuille, the main difference being that the effective pressure was established 
by means of a column of mercury instead of by compressed air, and that the observa¬ 
tions were made, as a rule, at various temperatures between 10° and 50°. The 
intermediate values for every 5° were obtained by graphical interpolation, and the 
times were compared with that occupied by water at 0° in flowing through the same 
apparatus under the same pressure {circa 500 millims.). The experiments gave 
directly what Pribram and Handl subsequently designated {vide suprct) by the 
somewhat arbitrary term specific viscosity of the liquids at the temperature of 
observation. Calling the specific viscosity Z, it is expressed by the formula Z = ^ lOO/G, 
in which t is the time of flow of the constant volume of liquid at the temperature of 
observation, and is the time occupied by the same volume of water at 0°, the 
pressure which determines the flow being the same in both cases. PtELLSTAB was 
of opinion that the connection between composition and transpiration would be 
best traced by comparing the efflux-times of “ equivalent amounts ” instead of the 
efflux-times of equal volumes of liquids. The efflux-times of equivalent amounts were 
assumed to be obtained by multiplying the observed efflux-times of equal volumes 
by the molecular weight, and dividing by the density; in other words, multiplying the 
mdcccxciv.—A. 3 p 
