According to Lorentz theory of electrons

Lambert law an d Beer′s law

a theoretical model of the corresponding relationship between the solution concentration and its refractive index in a certain concentration rang e was proposed.The experiment mainly used Abbe refractometer to study the relat ionship between concentration and refractive index

combining with the linear le ast squares method and graphical method.The regression equation was established.The experimental results indicate that an empirical formula of the relationshi p between the concentration and the refractive index of the Na2CO3 solution and starch solution is obtained.The suitable measuring concentration range of t he two solutions by the Abbe refractometer is estimated.The error of the experi mental results of the theoretical model and the results of actual measurement is within 5%.These empirical formulas have an important reference value in the pr oduction and experimental work.