178 



BINGHAM.* PLASTIC FLOW 



pressure through capillaries of different dimensions and measure 

 the rates of flow. Some of the values obtained are shown in 

 figure 2. For medium pressures the volume of flow is given 



50 



100 



150 200 



PRESSURE 



250 



3O0 



Fig. 2. The flow (in cc.) of 50 per cent clay suspension in water containing 

 0.1 per cent of potassium carbonate in solution, for pressures (g. per sq. cm.) 

 as shown, and at 25 °C, except one series of experiments with Capillary No. 1 

 which was made at 40°C. The following are the numbers and dimensions of 

 the capillaries used: 



by the formula v = k (P — /), where P is the pressure em- 

 ployed and / is the " friction, " i.e., the force required to start 

 the flow. Putting (P — /) in place of P in the ordinary Poiseuille 

 formula for calculating the fluidity, we have a means for cal- 

 culating the "mobility" of plastic substances, analagous to the 



