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Armstrong's mixture is a highly sensitive primary explosive, often found in various pyrotechnic toys.
Armstrong's mixture consists of red phosphorus and potassium chlorate. Other formulae use potassium perchlorate. Sulfur is used to substitute for some or all of the phosphorus to slightly decrease sensitivity and lower costs. Calcium carbonate may also be present in small proportions, as desensitizer. Mixtures, in which the chlorate is replaced by bromate exceed those in sensitivity and are even more unstable and sensitive.
Armstrong's mixture is found in paper caps in toy cap guns and in party poppers. The amount is very small, a few milligrams, and it's mixed with glue for better stability. Due to the high dangers of this mixture, it's extremely risky to extract this mixture.
Armstrong's mixture can be prepared by extremely carefully mixing powdered red phosphorus and potassium chlorate. This is always done underwater or under a non-flammable liquid. The mixture is then let to dry in open air.
Safety and handling
Armstrong's mixture is highly sensitive and can explode if heated or impacted. Due to extreme sensitivity to friction, mixing dry potassium chlorate and red phosphorus will most likely lead to an explosion, hence the ingredients are usually combined in a slurry with water, formed into the final product (for example, single drops onto paper for "paper caps") and allowed to dry. To decrease sensitivity, oil can be added.