Zenker’s classic fixative solution is named for its inventor, the 19th-century German Histologist Konrad Zinker. The classic formulation uses mercury chloride, which produces excellent results in protecting chromatin and connective tissue fibers, and some cytoplasmic features. It does not preserve mitochondrial features for which Zenker’s slightly different formulation, called Helly’s fixative solution, is preferred. The mercury chloride component is highly toxic, including toxicity by absorption through the skin, and all appropriate safety measures should be used, such as gloved hands. The potassium dichromate component is also toxic. Refer to the relevant safety data sheet(s). Hempstead Halide® produces both the classic formulation and a mercury-free alternative using Zink Chloride. The fixation time is 4-24 hours, depending on the thickness and toughness of the specimen. The stock solution requires the addition of 5% by volume of glacial acetic acid shortly before us. In addition to the stock solution, Hempstead Halide® sells a self-mixing syringe version that combines the two components as they are needed.