The Short Version
The claim correctly identifies mercuric chloride's extreme toxicity and the general trend toward restricted use, but overstates how narrow its current applications are. A 2023 New Jersey government hazardous substance fact sheet lists ongoing uses beyond laboratory research and industrial catalysis, including wood preservation, embalming, photography, fabric printing, and disinfection. While these may be declining, their documented presence in authoritative sources undermines the "primarily restricted to" framing.