_v_ = Q(4)/(πD²) centimeters. Since the velocity in the elutriating cylinder v is directly as the quantity of water overflowing so is _v_ : _v_ₙ = √(_h_ − C) : √(_h_ₙ − C); then _v_ₙ = √(_h_ₙ − C) (_v_)/(√(h − C)) and _h_ₙ = _v_ₙ²((_h_ − C)/(_v_²) + C. The constant (_h_ − C)/(_v_²) is obtained from the means of a number of estimations; for example as illustrated in the following data: Observed Corresponding velocity quantity of in elutriating cylinder Constant. Observed height, outflow, cubic of 4.489 centimeters (_h_ − centimeters. centimeters. diameter, millimeters. C)/(2) 1.6 0.406 0.0257 621 1.8 0.484 0.0306 652 80.0 5.530 0.3490 647 100.0 6.130 0.3870 660 ——— Mean 645 Then are obtained the following values of _h_ₙ and _v_ₙ: _h_ₙ = 645(Vₙ²) + 1.19 centimeters. and _v_ₙ = √(_h_ₙ − 1.19) × 0.0394 centimeters. In order to be able easily and rapidly to judge under what pressure the outflow has taken place in any particular instance, a larger number of values are computed with the help of the formula given and placed together in tabular form. As an example the following table may serve which was computed for one of the apparatus used. Usually it will be sufficient to test the apparatus for four different heights and then to interpolate the values for all the others. The numbers marked with a star in the table are those which were determined by experiment; the others were calculated.