Time and again one comes across various authors using the sentence "" by the principles of propellant chemistry"", in order to determine the ratios of the complexant (fuel, like glycene, citric acid etc) and the metal salt, in preparatioin of ferrites by sol gel technology. Say for example in case of NiFe2O4 when metal nitrates as Ni(NO3)2, Fe(NO3)3 and citric acid are used, the total valences are – 10, – 15 and + 18, respectively. Hence the stoichiometric composition by the principles of Propellant chemistry requires that – 40 + 18n = 0 or n = 2.22 mol of citric acid. 1)How does it work out to -40? 2)what is this principle of Propellant chemistry?