str (126)

28 MAGMO IDS

the expression has not become popular. At the present time (1938), it is in vogue to refer to dough_s and pastes as “ magmoids,” a term used by Dutch workers.

BIBLIOGRAPHY

AU the early papers are ąuoted in Hatschek’s " Viscosity of Liąuids,” and not listed here.

Bincham and Grekn. J. Amer. Soc., Test. Mats., 1919. Blsinimger. J. Ind. Eng. Chem., 1920, XII., 436.

Cook. J. A trier. Ceram. Soc., 1924, VII., 651.

Crowhll and Saundkrs. J. Phys. Chem., 1925, XXIX., 1267. Drostb. Farbemeit., 1932, XXXVII., 619, 655, 694.

Evans and Rbid. Trans, of Mining and Geol. Inst. of India 1936, XXXI., 1.

Harrison. J. Amer. Ceram. Soc., 1927, X., 970.

Jbbbns and Rhodks. J. Phys. Chem., 1931, XXXV., 383. Moness and Gibsy. J. Phys. Chem., 1925, XXIX., 1282. Rhodbs and Wells. J. Ind. Eng. Chem., 1929, XXI., 1273. Richardson. J. Agric. Sci., 1933, XXIII., 176.

Schobield and Scott Blair. J. Phys. Chem., 1930, XXXIV., 248.

Scott Blair and Crowther. J. Phys. Chem., 1929, XXXIII., 321.

Shbarbr. J. Amer. Ceram. Soc., 1928, XI., 542.'

Sheppard and Carver. J. Phys. Chem., 1925, XXIX., 1244. Talwalker and Parmelee. J. Amer. Ceram, Soc., 1927, X., 670.

Trouton. Proc. Roy. Soc. (A), 1906, LXXVII., 426.

Trouton and Andrews. Phil. Mag., 1904, VII., 347 ; Proc.

Phys. Soc. Lond., 1909, XIX., 47.

Volarovitch (Wolarowitsch) and co-workers. Koli. Zeits., 1935, LXX., 165, 280 ; 1935, LXXI., 22, 159, 276 ! ^:£935. LXXIII., 339 ; 1936, LXXVI., 338 ; 1936, LXVII., 93-Wilson and Hall. J. Ind. Eng. Chem., 1922, XIV., 1120.

CHAPTER IV

Modlfications of BingharrTs Equatlon. Buckingham-Reiner Equation. Pług Flow. Wall Effects. “ Sigma " Phenomenon in the Paint and Ceramlc Industries. Orlentatlon. Electric Fields. Chronophotographic Methods.

Bingham’s treatment of the flow curves, which was described in the last chapter, leaves several ąuestions still unanswered. For a single capillary tubę, it is quite satisfactory to subtract a “ yield-value ” pressure from the total pressure, in order to obtain a mobility; but it is not elear how such mobilities are to be compared with those derived for the same materiał flowing through capillaries of different dimensions. The ąuestion also arises as to how this change in the eąuation of flow will affect the original hypothesis of Newton, relating shearing stress to velocity gradient, on which the Poiseuille eąuation is based.

Buckingham and Reiner ąuite independently worked out the fuller implications of Bingham's idea, as applied to capillary flow. They start by assuming a modification in the Newton eąuation, by which a certain critical shearing stress (S₀) has to be subtracted from the total stress, before the eąuation is applied. Writing /x for mobility, this now readsr

!=-f(s-s.)    . . . . (x|

For a capillary tubę, S == TrfeL (compare with

39