75561 str (130)

20

CHEMICAL CONSTITUTION

tures for senes in which the successive members differ by CH₂.

To compare different compounds at a single temperaturę would be unfair, and yet it is difficult to find a method of choosing temperatures for comparison. It was necessary to solve a similar problem in the case of the parachore, in which molecular volumes are compared at constant surface tension, and in Chapter VI it will be shown how a similar idea is used in measuring flow-plasticities by comparing yield-values at constant adhesions.

Thorpe and Rodger compare viscosities at boiling points, and also choose arbitrary identical values of drjjdt. Bingham points out that for unassociated liąuids, <j>/t curves are nearly straight; and that distances between them for the different members of a senes give a measure of the effect of each added CH₂ or other group. Dunstan and Thole show, as a very generał relation, except for the lowest members of the senes, that

log r) = aM -f- b,

where a is a generał constant, b is characteristic of each senes, and M the molecular weight.

Ali kinds of shapes are found in the curves for viscosities of liquid mixtures: steady rise, fali, I maxima, minima, or morę complex curves. In some cases maxima are taken as evidence of com-1 pound formation in the liąuid.

BI BLIOGRAPH Y

Akdrade. Naturę, 1930, CXXV., 580.

Bikgham. " Fluidity and Plasticity," 1922. McGraw-Hilll Book Co.

Bridgman. Proc. Nat. Acad. Scis., 1925, XI., 603.

Cunningham, J. Phys. Chem., 1931, XXXV., 796.

Dcnm. Trans. Farad. Soc., 1926, XXII., 401.

Ebbecke. Arch.f. ges. Physiol., 1936, CCXXXVIII., 429.

Farr and McLeod. Proc. Roy. Soc. (A), 1920, XCVII., 80. Lederer. Petroleum, 1937, XXXIII., 2; Koli. Beih., 1932 XXXIV., 270.

Leon'teva. Russ. J. Phys. Chem., 1938, XI., 310.

Sheppard. J. Rheol., 1930,1., 349.

Thorpe and Rodger. Phil. Trans., 1894, CLXXXV. (A), 397.