The excess of heat received in equatorial regions expands the water, but at the same time excess of evaporation concentrates it, so that the density increases.
The magnetic concentrates contain enough zinc to be well adapted to the manufacture of zinc oxide.
Thus the election is virtually an electiov by states, and the struggle concentrates itself in the large states, where the great parties are often nearly equally divided, e.g.
square, with free access to the river bank; the gravel and sand were washed in cradles provided with screens of perforated metal, and the concentrates were sorted by hand on tables by means of an iron scraper.
These are shallow cylindrical troughs containing muddy water in which the diamonds and other heavy minerals (concentrates) are swept to the rim by revolving toothed arms, while the lighter stuff escapes near the centre of the pan.