Abstract：A new method for measuring the refractive index of micro-quantity liquid using glass capillary is introduced. the method based on imaging principle of a Coaxial Spherical Surface Optical System

the refractive index is obtained by measuring the focal position of a capillary filled with the liquid to be measured through a reading microscope

and then doing a calculation with an analytic formula deduced by us. Four liquid mediums

water

ethanol

ethylene glycol and glycerin have been measured

the required sample is less than 0.002 ml

the precise of obtained refractive index is better than 0.0003 for water and ethanol

and 0.0007 for ethylene glycol and glycerin. The method is characterized by using micro-quantity sample

simple equipment

easy to operate and high measurement accuracy

which is adapted to measure the refractive index of transparent or translucent micro-quantity liquid sample. Based on the deduced formula for calculating refractive index of liquid medium

we have analyzed the influence of the parameters (n0

R

r) of a capillary and the refractivity index to be measured (n) on the sensitivity of refractivity index (△d/△n) and the real image depth (Teff). The calculation results show that (1) either the decrease of r or the increase of R and n0 can enhance △d/△n effectively

however

Teff is also increased; (2) both Teff and d/n decrease with the refractivity index to be measured

and (3) the cross point of curves Teff (n) and △d/△n (n) determines the measurement range and precise of liquid refractivity index. The theoretically analyzed results provide an effective way to improve measurement precise and extend measurement range of liquid refractivity index.