Determination of the Size and Internal Structure of Colloidal Particles Using X-rays.

P. Scherrer. Bestimmung der Grösse und der inneren Struktur von Kolloidteilchen mittels Röntgenstrahlen. Nachrichten v. d. Kön. Gesellschaft d. Wiss. zu Göttingen. H. 1, p. 98, 1918.

The internal structure of colloidal particles has not yet been established. P. Scherrer, applying the method of interference of X-rays from randomly arranged particles, investigated the internal structure of typical inorganic and organic colloids.

Two cases are possible:

1) The colloidal particles possess a crystalline structure. Then we should expect an X-ray photograph with a large number of interference bands arranged in a way characteristic of the given crystal lattice. Moreover, the position of these bands does not depend at all on the size of the individual crystalline particle, but is determined exclusively by its space lattice; the width of the interference band, however, depends on the size of the individual crystallites.

2) The colloidal particles are amorphous. Then the X-ray photograph will give one or two very weak maxima near the incident X-ray beam, and in this case it is difficult to say anything about the internal arrangement of the atoms.

Considering from this point of view the X-ray photographs of various colloids obtained by him, Scherrer found that:

1) Colloidal particles of gold and silver are crystalline and have exactly the same space lattice as macroscopic crystals of gold. It is noteworthy that even particles invisible in the ultramicroscope possess the same space lattice.

2) Gels of silicic and stannic acids, along with signs of amorphous bodies, give an extremely vivid interference pattern, so that these bodies may be regarded as bodies “ready for crystallization.”

3) Typical organic colloids (egg albumin, gelatin, casein, starch, etc.) are amorphous. It is most probable that the particles of these colloids consist of a separate molecule, or of a number of molecules arranged disorderly.

T. Molodoy.