Au particle of the size in the range of 10-189 nm has been prepared by sodi
um citrate procedure. The resonance scattering spectra of Au particle have
been studied. The nanoparticle solutions of the size in the range of 10-95
nm exhibit red in colour, Their maxmum absorption wavelenth are in the rang
e of 517. 8-533. 3 nm. The absorption peak shifts to the red with the size
increasing. The maxmum resonance scattering peak is at 580 nm. The cube roo
t of the intensity at 580 nm is proportional to the size of Au particles.