Sometimes it is desirable to be able to determine the weight percent of one element, C1, that will produce a specified concentration in terms of the number of atoms per cubic centimeter, N1, for an alloy composed of two types of atoms. This computation is possible using the following expression:

where
NA = Avogadro's number
ρ1 and ρ2 = densities of the two elements
A1 and A2 = the atomic weights of the two elements
Derive Equation 4.19 using Equation 4.2 and expressions contained in Section 4.4.