def clear(self):
self.solid_density = <NUM_LIT:1.0><EOL>self.H2O_mass = <NUM_LIT:0.0><EOL>self.size_class_masses = self.size_class_masses * <NUM_LIT:0.0><EOL>
Set all the size class masses and H20_mass in the package to zero
and the solid_density to 1.0