Colloids and some of their biological relations

Summary

• (a) The diffuse scattering of light in Tyndall’s experiment is to be referred to material particles.

• (b) Investigations of colloidal metallic solutions by the ultra-microscope show that the largest particles in the coarser hydrosols have magnitudes corresponding approximately to 60-80μμ linear dimensions.

• (c) Colloidal metal-sols can be prepared which exhibit scarcely any sign of inhomogeneity, and can hardly be distinguished from crystalloid solutions. There are innumerable intermediate grades.

• (d) The smaller metallic particles in hydrosols possess a persistent and lively oscillatory and translatory movement which, in several respects, differs from typical Brownian movement.

• (e) In many reversible colloids, and in solutions of dyes the material particles are accessible to direct observation.