The Purple of Cassius is a colloidal solution that is associated with gold. It is formed when a colloidal gold solution is mixed with a small amount of stannous chloride (tin chloride). This colloid displays a characteristic purple color, which is why it's known as the Purple of Cassius. This reaction is often used historically for the detection of gold and its analysis due to its distinct color.
In chemistry, colloids are materials that are dispersed throughout another substance, where one takes the form of fine particles. The Purple of Cassius is a specific type of colloidal gold, notable for its use in qualitative analysis and its historical significance in decorative arts and forensic science.
