It is desired to determine the size of pulverized coal particles by measuring the time it takes them to fall a given distance in a known fluid. It is found that the coal particles $(S G=1.35)$ take a time ranging from $5 \mathrm{~s}$ to $1000 \mathrm{~min}$ to fall $23 \mathrm{~cm}$ through a column of methanol $(S G=0.785, \mu=0.88 \mathrm{cP})$. What is the size range of the particles in terms of their equivalent spherical diameters? Assume the particles are falling at their terminal velocities at all times.