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i    KI NI' 1'iC ENERGY CORRECTION

when* /> i the presKurt* Bn for (wrcoming wllffii reifltnnco and l‘ is tht* totaJ pressure.

Ilteie hfis l)ct*n Jiuicli dilCUllion uboul the fuctor A iminbri ul authori ifldependently deriyed .simiJai r*tju;i(ions, wilii ynrioua factor». TJiu fuctor, which B gcncrally called " m," bas hcen variou,sIy ryaJuidfd as foliowa

m i

Couctte and (indcpcndantly) Willn-rforce i:*oo Hagenbach ,    ,    ,    ,    o'79 I

Reynolds ......    0*50    I

Boussinescj .....    1*12    I

The dif/erenccs are realJy due to diffcrunt ways of I accounting for disturbances in thc transition of the I materiał from comparative rest in the reservoir to I the condition of " streamline " (».«., teiescopic) flow I in the tubę.

The Poiseuille eąuation, corrected both for kinetic I energy and for the so-called " end-effect/' may be I written:—

łrR⁴P    ttipV    .

^v ~ 8V(L + wR) “ 87r(L -f »R) ' ' • ^

m and n¹ are constants, and may be evaluated from experimental data in any given instrument. Perhaps I the best experimental data on m are those of I Riemann, who, working with water, gets m — I 1-124 i o-ooó. This was with very narrow tubes I (R = order of 0-005 cm.). For perfectly sąuare-1 ended capillaries, the value of n is about o-8. It is I important to notę that no one has the least idea of I the value of " m " for materials which do not obey I Poiseuille’s law. Those interested in the physics of I

KINET1C ENERGY CORRECTION

13

this question are recommended to read Barr’s i Monograph on Viscometry." The industrial chemist is advised not to under-estimate the importance of these kinetic energy and end-effect corrections, to try if po*sible to arrange experi-mental conditions ² so that the effects which they bring about are rnade less tiian the experimental error, and to avoid the uho of »o-called theoretieal cqnations derived for truć fhiids in experimcnts dealing with complex system*.

BIBLIOCRAPHY

Altar, J, Appl. Phyi., *937, V., 377.

Anorade, Phil, Mag,, 1934, XVII., 31I, 698.

Barii. "Monograph on Vl*cometry,” 1931. Pub. Oxlord Unłversity Pres*.

Bernac. Trans, Parad, Soc., 1937, XXXIII., 17.

Bingham, " Flufdlty and Plasticity," 19*2. McGraw-HiU Book Co.

Dorsby. Phys, Reoiew, 1926, XXVIII., 833.

Ewbll. /, Chem. Phys., 1937, V., 571 ; J. Appl. Phys., 1938. IX., 252.

Ewbll and Eyring. J. Chem. Phys., 1937, V., 726.

Eyring. J. Chem. Phys., 1936, IV., 283.

Hatschek. " Viscosity of Liquids," 1928. Pub. Bell. Hirschfbldbr, Stbvenson and Eyring. J. Chem. Phys., 1937. V., 896.

Houwink. '3 Elasticity, Plasticity and the Structure of Matter," 1937. Pub. Cambridge University Press.

Katz. Cer. Chem., 1937, XIV., 382.

Riemann. J. Amer. Chem. Soc., 1928, L., 46.

Stewart. Phys~Review, 1928, XXXII., 558.

Stonb. J. Rheol., 1930, I. (3), 240.

Taylor. Proc. Roy. Soc. (A), 1937, CLXIII., 319.

Ward. Trans. Farad. Soc., 1937, XXXIII., 88.

1

n here should not be confused with the shear modulus for which it will be used in a later chapter.

2

The most important being to keep the velocity smali.