|The patterned fabric at the bottom was created using rongalite (Source)|
In the early 20th century, sodium formaldehyde sulfoxylate was identified as an antidote for acute mercury poisoning (e.g. a one time ingestion of a bunch of corrosive mercuric chloride). An intense treatment regimen from 1942 called for (1) immediately swallowing a bunch of it, (2) injecting it into a vein, (3) irrigating the colon with it twice daily, (4) swallowing and injecting a bunch more of it twice a day for two days, and (5) rising the mouth out with it. Even with this effort, the antidote was eventually determined to only be effective if administered immediately (i.e. within minutes) after mercury exposure, which isn't at all practical in most poisoning cases. Presumably it worked by adding electrons to mercury cations in the stomach and intestines, reducing them to the less harmful elemental form of the metal.
In the 1930s, sodium formaldehyde sulfoxylate was demonstrated to be capable of curing mice intentionally infected with disease-causing bacteria. It's unstable in water or aqueous solutions (like, say, body fluids), decomposing to produce formaldehyde and a bunch of sulfur compounds (sodium sulfite, sodium sulfide, sulfur dioxide, and hydrogen sulfide). Formaldehyde is really good at killing things, so at first glance it appears to be responsible for the curative effect. However, sodium formaldehyde sulfoxylate only ended up working against one of the thirty two types of bacteria tested, so there was probably something else going on.
Sodium formaldehyde sulfoxylate has also seen use as a photographic developer and as a relatively environmentally friendly reagent for adding sulfur+oxygen groups to various organic molecules and doing other useful chemical synthesis stuff.
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