340 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Fig. 5. Calibration of Flowmeter. Fig. 7. Non-liquefied Zones Liquefied Zones Fig. 8.

INTRODUCTION TO THE RHEOLOGY OF DISPERSE SYSTEMS 341 Thus the application of a very small pressure to the capillary is exerted exclusively in inducing a velocity gradient close to the thin wall layer only, and insufficient to register on the scale of the rheological diagram, whilst in the rotary instrument the torque exerted by the small annulus sheared is too small to be recorded unless a special technique be used. The curvilinear part of the rheological line represents the transition or growth from the early to the final stages of shear where the whole content of capillary or cylindrical annulus is in differential velocities. This process of a change from what is virtually a solid body at rest, even though it be of a low modulus o! rigidity, to one which under shear behaves as a fluid is known as deflocculation. The internal change which a rigid plastic undergoes during shear may be seen by observing the difference in field ot a dispersion of carbon black in liquid paraffin under the microscope. At rest it will be seen that the system is solid (Fig. 9) by reason of its skeletal ""':'•:' " ....... •"': :'..L: ..-.• .•'...• •- . • . ..-. '/..:j ? •.::: •: :-- •:. - • .... L.• .• .... ß .. '-i-'-:...:.. . :. •.• ..- ....... : ... . . .- .:, ::.• • :• '- ? :.. , . . • .... •. : •.' .:•. • -?•.: .. .... . , .- .-:. • , .'•: .. :,.:...., ...... ,.• •.- •?•:•. 4 ::::-,:: h:g •- •.:...::..•&• .•"'.• ... ,•?.• . ½ • :: .• ?5'" .?')'":"':-,•--.•'•:• "'•- :.'::,•. .. - ',•...': .•-. . ....... :"':'•' •' ' ':• ...... -. : . . • • '•:..' . ...::'• . . :.... • • .. .. • . • • •: 7'..". .: . ..". :. • .. ß ..• :• . .. ,- -.: .. -•: .. . :. .. .. •:•. • ....?.:'"..:.::... - . •. .. • . , :... ... ["ff t' ....•,¾:.'•. ':"-':•'-:• - .'.. '•'•' "-' :'" • : •".•' •. -: •.,.'•.•. ." , -:(.:?':, ' :--?..•. • ('..'L.• :'--.. .... ":--"L• •: .,'" :.• :.'•'"':"• .': --:: • ("'r• ":. --: ". •- ?i. :,,.•::! . i•,..': •' ................ •" •-_. . • .......• .• . .,• . •:•%.•:,.• • •-. .• •. ..• : • • • • • • - ,• •. -: ... • :•. •. • •'. . .• •,•. ".:..% ' •.•...• - .... ... - Q' ' . ß :.::•. '- •?..- .•:.- .... :...• •. ß .-.•-: •:•:. k •. .z. •..•. :- Fig. 9. A fiocculate. (Carbon black in Liq. Paraffin.) structure, whilst when immediately obeyed alter rubbing the cover slip over the slide, complete transparency devdops temporarily, the visible skeletal structure re-appear•g after an interval of rest. This is knom as defiocculation by shear and is a completely reversible change.