BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 447 
Stephan .' Wied. Ann./ 17, 680 (1882). 
Wagner . ..‘ Wied. Ann./ 18, 259 (1883). 
Slotte .‘ Wied. Ann.,’ 20, 262 (1883). 
Konig .‘Wied. Ann.,’ 25, 620 (1885). 
Traube ..." .‘ Ber.,’ 19, 871 (1886). 
Noack .‘Wied. Ann./ 28, 666 (1886). 
In order to compare our results with those of our predecessors, we have made a 
careful critical examination of certain of these memoirs, and more particularly of 
these in which the observations extend over a moderate range of temperature, which 
are expressed in absolute measure, and which, so far as can be judged, were made 
Avith sufficient care. In all cases where the values are given in gravitation measure 
they have been reduced to dynes, and when a correction for kinetic energy is 
necessary, the more accurate values deduced from the expression of Couette and 
Finkener have been substituted for those obtained by the formula of Hagenbach. 
PoTSEUiLLE.— The observations made by Poiseuille in 1846 are still regarded as 
the standard data from which the coefficients of viscosity of water for the temperature 
range over which the experiments extended, viz., from 0° to 45°, may be deduced. 
Poiseuille found the number of milligrams of water which could be driven through 
tubes of different dimensions under definite conditions of temperature and pressure. 
From four sets of observations in tubes of different diameters, 0. E. Meyer (‘ Wied. 
Ann.,’ 2, 387) has calculated the values of the viscosity-coefficients at the difierent 
temperatures of obseiwation, and, by graphical interpolation, has found from each set 
the values at the same temperature 5° apart. The numbers obtained for the different 
sets are in close agreement, and from these the mean values of the coefficients are 
calculated. 
On plotting these mean values as ordinates against temperatures as abscissae on the 
same sheet as that containing the curve for our observations, the agreement between 
the two series is seen to be remarkably close. Poiseuille’s observation at 0°'6 lies 
exactly on our curve, that at 0°'5, which is not cjuite concordant with that at 0°‘6, is 
somewhat larger than our observation at that temperature. From 5° to 30° the 
observations lie slightly to the right of our curve ; from 30° to 40° they are coincident 
with it, and the observation at 4 5° lies slightly to the left. In no single case does the 
difference between our observations and those of Poiseuille at the same temperature 
exceed 1 per cent. Comparing observations at intervals 5° apart at temperatures 
between 0° and 45°, the mean difference between our observations and tliose of 
Poiseuille is less than 0’4 per cent, Poiseuille’s values being, on the average, 
greater by this amount. 
We have examined the values of the coefficients, as calculated by Meyer, from 
Poiseuille’s observations, in order to ascertain if they lend any suppoi’t to the 
correction for friction-efiects outside the tube, as given b}’- Couette. ’fhe coefficients 
