In the mechanical analysis of the soil, after separation of the stones and fine gravel by means of sieves, the remainder of the finer earth is subjected to various processes of sifting and deposition from water with a view of determining the relative proportions of sand, silt and clay present in it.
In the wider compartments are placed sieves having sixteen holes to the square inch and bearing zinc turnings.
Some engineers have the sand separated from the stones by screens or sieves and then remixed in definite proportions.
The disintegrated ground is then brought back in the trucks and fed through perforated cylinders into the washing pans; the hard blue which has resisted disintegration on the floors, and the lumps which are too big to pass the cylindrical sieves, are crushed before going to the pans.
Internally, each purifier is filled with ranges of wooden trays or sieves A, made in the form of purifiers.