Refractive indices of different concentrations (5 ppm up to 200 ppm) of reference chemical solution (Fe(NO3)3) Nonahydrate were determined with an accuracy of plusmn10-5, the Brix of these chemicals were measured by using Digital multi-wavelengths (refractometer DSR-lambda). Practically, the refractive indices of these solutions have been measured as a function of temperatures in the spectral visible range 0.4-0.7 microm with increasing wavelengths and with increasing temperature the refractive index decreased monotonically. The refractive indices are increasing with increasing concentrations. Also, the Brix of this solution have been measured as a function of temperature (20 omicronC up to 30 omicronC) with wavelengths in the same visible spectral range. The Brix values are used as a tool of concentration of these chemicals samples. The empirical formula between the concentration and the Brix of these chemical are applied.