Section 17.2 Example of Mass Diffusivity at Low Density: Ar & O2
>  restart;
>  eq := p*DAB/((pcA*pcB)^(1/3)*(TcA*TcB)^(5/12)*(1/MA+1/MB)^(1/2))=a*(T/sqrt(TcA*TcB))^b;  eq 17.2-1

>  MA:= 39.94*g/mol: TcA:=151.2*K: pcA:=48*atm: properties of argon
>  MB:= 32.00*g/mol: TcB:=154.4*K: pcB:=49.7*atm: properties of oxygen
>  T:= 293.2*K: p:=1*atm: temp and pressure
>  a:=2.745e-4: b:=1.823: constants for the nonpolar pair
>  DABu:=simplify(solve(eq,DAB),assume=positive); solve for DAB and tell Maple how to simplify the result.

>  DAB:=.1886791089*cm^2/s; The same numeric value but the correct units.
>  aun:=DAB/DABu;

>  a:=a*aun;

>  DAB:='DAB';
>  simplify(solve(eq,DAB),assume=positive);