Iron is found in tissues as a constituent of hemosiderin, a metabolic product of hemoglobin breakdown. It is present in the ferric state, and may be demonstrated with Perls' Prussian blue reaction. It may otherwise be found in tissues of people coming into contact with iron containing dusts, e.g., miners who inhale iron containing ore particles. These deposits may be present in the ferric or ferrous states. Perls' prussian blue is effective for this as well, except that the concentration of acid may need to be increased, and the temperature elevated to free the iron from its compounds. Ferrous iron may be demonstrated similarly using Tirmann Schmeltzer's Turnbull's blue.

Iron salts, usually in the ferric form, are some of the more useful compounds in histotechnology. Ferric iron is a very important mordant for hematein, producing intense black staining of many tissue components with Heidenhain's method or procedures similar to Heidenhain's. There are also simpler formulations, such as Wiegert's or Janssen's, now mostly used for nuclear staining when greater resistance to extraction by acids is required than is given by aluminum hematein. The commonest application is likely their use with trichrome methods.

During the 1970's hematoxylin was in quite short supply. Several dyes were recommended as replacements, particularly for hemalum staining of nuclei in the H&E. Most of these techniques specified iron alum or ferric chloride as the mordant, although one dye (phenocyanin TC) required a ferrous salt.

Ferric ammonium sulphate (iron alum) forms complexes with some dyes, often fuchsin or victoria blue homologues. Based on Weigert's iron resorcin fuchsin, these techniques are invaluable for the progressive demonstration of elastic fibres and have also been used for staining the rough endoplasmic reticulum of hepatitis infected liver cells (the "ground glass" cells).

In colloidal suspension, iron is also used in Hale's and Mowry's methods to bind to acid mucosubstances. It is subsequently demonstrated with Perls' Prussian blue, thereby colouring the mucosubstances blue.

Schmorl's technique for reducing substances depends on the reduction of ferricyanide to ferrocyanide, the ferrocyanide being trapped with a ferric salt to produce Prussian blue. This is used in a method for aldehydes after their reducing capability has been enhanced with thiosemicarbazide.



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