  A lattice calculation shows that the Casimir scaling hypothesis is well
verified in QCD, that is to say that the potential between two opposite color
charges in a color singlet is proportional to the value of the quadratic
Casimir operator. On the other hand, in a bag model calculation for the same
system, a scaling of the string tension with the square root of the quadratic
Casimir operator is obtained. It is shown that, within the same formalism but
with the assumption that the width of the string is independent of the color
charges, the string tension is proportional to value of the quadratic Casimir
operator. Some considerations about the color behavior of the total interaction
are given.
