Determination of coefficient of friction between two spherical particles

[snow]

I have some very small spherical particles with diameter of 1 mm and i would like to know coefficient of friction between them. Can anyone suggest an experiment/device that would help me?

In order to get friction between a plate and particle i can use tilt test and measure the angle at which a group of connected particles slips.

 

[cragar]

maybe glue a bunch on piece of paper then slide them down a plane made of that material , and use the tilt test like you said.