English

ON THE SHAPE OF ULTRAMICROSCOPIC GOLD PARTICLES

THE COLOR APPEARANCES OF METALS IN THE COLLOIDAL STATE ARE CLARIFIED BY A THEORETICAL STUDY. IT IS SHOWN THAT THE OPTICAL CONSTANTS OF THE METAL CONCERNED AND THE PARTICLE SIZE ARE THE COLOR DETERMINING FACTORS, AND THAT A RESONANCE PHENOMENON IS NOT CORRECT. THE ABSORPTION CURVES FOR COLLOIDAL GOLD SOLUTIONS ARE CALCULATED, WITH THE ASSUMPTION THAT THE PARTICLES ARE SPHERES WHOSE REFRACTIVE INDEX AND ABSORPTION COEFFICIENTS POSSESSED THE SAME VALUES, FOR INDIVIDUAL WAVELENGTHS, AS THOSE FOR METALLIC GOLD. THE RESULT IS THAT VERY SMALL GOLD PARTICLES GIVE RUBY-RED SOLUTIONS AND, THAT WITH INCREASING PARTICLE SIZE, THE SOLUTIONS TAKE ON DEEPER BLUE COLORS.

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