INTERPRETATIONS AND APPLICATIONS OF FLOW MEASUREMENTS 607 flow curves as shown to the right of Program B. Two plastic viscosities U• and U,2 are obtained from the inverse slope of the straight lines of the two down curves. To obtain U• shear was applied to the sample over a time 0• while U,2 was obtained after shear was applied to the same sample over a time 02. This assumes that the time required to produce the down curve does not contribute to the breakdown in structure. The coefficient of thixotropic breakdown B is then calculated as B - (10) In (02/01) In the automatic viscometer (5, 6) the time 0 that it takes to change the rate of shear from zero to a preset maximum could be chosen to be 240, 120, 60, 30 or 15 seconds. Thus, one of the advantages of the automatic viscometer is its rapidity of flow curve measurement, since a flow curve record extending over rates of shear from zero to 4000 seconds-1 can be pro- duced in fifteen seconds. At all encircled points of speed changes the automatic programs are set up so as to permit the operator either to wait or to continue immediately with the sequence. This is done, so that the time-dependency of the material can be studied, and is, for instance, necessary to obtain the sequence that yields the coefficient B. INTERPRETATIONS OF FLow MEASUREMENTS A few flow measurements were made with the automatic viscometer on '7' PROGRAM A TEMPERATURE 23 ø C 0:50 SEC 15-MINUTE REST PERIOD BEFORE RUN • 2000 HEASUREHENT 1500 IOOO 500 1500 2 3 4 0 0 0 0 5 POISES DYNES/CM 2 I I 1500 3000 SHEARING STRESS, r, DYNES/CM 2 Figure 4.--Flow curves of an all-purpose cream.

200 150 I00 50 PROGRAM A TEMPERATURE 25 ø C 8=50 SEC //• IST 2ND RUN RUN 7.6 5.4 POISES 600 500 DYNES/CM 2 6.0 4,.2 POISES 500 500 DYNES/CM z TD MEASUREMEMADEMEASUREMENT IMMEDIATELY AFTER IST 500 I000 1500 SHEARING STRESS. z', DYNES/CM 2 PROGRAM A TEMPERATURE 25 ø C 200 3RD MEASUREMENT AFTER A I0 MINUTE REST PERIOD 8=50 SEC ! .-/- LL o 150 I00 50 U2= •.6 POISES f2 = 500 DYNES/CM z i = 6.3 POISES f• = 500 DYNES/CM 2 I o 500 IOOO 15oo SHEARING STRESS, T, DYNES/CM 2 Figures 5(a) and 5(b).--Flow curves of an all-purpose cream.