Calcium (Ca++) and other diffusible ions cannot be preserved for x-ray microanalysis if specimens have been preserved by fixation using formaldehyde, glutaraldehyde or other fixatives. Atoms, such as Ca, are not diffusible when they are bound to something insoluble, such as bone or hard granules in cells which are sometimes mechanisms for detoxifying. Ions, loosely bound elements and other components such as sugars and amino acids are leached out during chemical fixation and dehydration by solvents. This problem was recognized over a hundred years ago by Richard Altmann. An alternative to wet chemical processing is the purely physical method that involves rapidly freezing the specimen and then removing the frozen water by the process of freeze drying, which is the subject of this article.