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Zinc Chloride

Fixing Agent

Zinc Chloride


Chemical Formula:


State: White powder
Concentration: Varies, perhaps 2-5%
Fixation Time: One or more hours
Aftertreatment: None
Acid Dyes: Some improvement
Basic Dyes: Some improvement
Additive: Yes
Coagulant: Yes
Hardens: Yes

Before You Begin

Please consult the following guide to safe working with this chemical fixing agent, including how to safely clean up spills.

Safety Note

Zinc chloride is not an especially dangerous chemical, although it is a skin and respiratory irritant, and strong solutions are corrosive. The normal precautions that should be used in laboratories while handling any chemical powder are sufficient for safe handling, provided that a fume hood is used to ensure that inhalation does not occur and that gloves are worn when weighing out the powder.

Spilled powder may be cleaned up by brushing excess powder into a plastic bag, then wiping any residue with water soaked cloth or paper towels, then washing out the cloth and wiping down the area with a wet cloth. Other than sufficiently large quantities of water being used, no further treatment is necessary. Ensure that gloves are being worn when this is done to avoid skin contact from a strong solution on the wet cloth.

Spilled solutions may be cleaned up by absorbing into a cloth or paper towels. It may then be treated as a powder spill, washed down with water etc.
Zinc chloride is not as toxic to the environment as many other compounds, such as mercuric chloride for which it often substitutes, but it should still be disposed of in a manner that does not contaminate our living space and which is consistent with local regulations.

How it Fixes


Fixation with zinc chloride is probably similar to that with mercuric chloride. They are both group 12 elements in the periodic table, along with cadmium, but the mechanism does not appear to have been commented on apart from that.

It had been recommended long ago as a fixing agent, but was not popular. Most likely this was because it is inferior to mercuric chloride and microscopists preferred the results from using that. Recently, however, as mercuric chloride began to be criticized as a fixing agent because of its toxicity and the effect of disposal on the environment, a search for possible substitutes led to zinc chloride, which, it was claimed at first, was as good as the former and a lot less toxic. It is true that it is a lot less toxic, but it does not live up to the claims initially made in its favor. It is a good fixing agent but it falls short of what has been claimed for it. What is needed is a thorough, objective evaluation of its fixation characteristics so that some definitive information is available.


The preservation is good, although inferior to mercuric chloride. Staining is not quite as bright and clear, although quite acceptable.


Anecdotal statements are that solutions containing zinc chloride as a substitute for mercuric chloride require approximately 50% longer for the same degree of fixation. There does not appear to be any objective information.

Simple Solution

It is not used alone, but usually as a substitute for mercuric chloride in mixtures.


No specific aftertreatment.


  1. Kiernan, J.A., (1999)
    Histological and histochemical methods, theory and practice. Ed. 3,
    Butterworth, Heinemann, Oxford, UK.