A body of density d1 is counterpoised by Mg of weights of density d2 in air of density d. Then the true mass of the body is
M(1−dd2)(1−dd1)
Let MO=mass of body in vacuum.
Apparent weight of the body in air = Apparent weight of standard weights in air
Actual weight of the body - upthrust due to displaced air
= Actual weight of the weights- upthrust due to displaced air
⇒M0g−⟮M0d1⟯dg=Mg−⟮Md2⟯dg⇒M0=M[1−dd2][1−dd1]