Calomel
2 of the 7 encyclopedias on this shelf carry an entry for Calomel. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
Important: Safety Warning This page contains a formula or preparation using substances now known to be dangerously toxic, such as arsenic, mercury, lead, or cyanide compounds. Exposure to these substances can cause severe poisoning, permanent injury, or death. In addition, this page presents medical treatment from an era before modern medicine. The remedies described are ineffective against the conditions named, and some of the ingredients or doses are harmful. Do not use them to treat any illness; consult a qualified medical professional. This information has been left in for historical purposes but should not be acted upon. a white powdery compound of mercury and chlorine. It is without smell or taste, and cannot be dissolved in water, alcohol, or ether. It is prepared by heating corrosive sublimate with mercury and common salt. The drug is highly poisonous. In minute doses it is used extensively in medicine for inflammation of the serous membrane, and as a substitute for Epsom salts. Veterinary surgeons use it as a caustic to cleanse wounds, and for thrush in the frog of a horse's foot. See Mercury ; Medicine
Collier's New Encyclopedia (1921)
Important: Safety Warning This page presents medical treatment from an era before modern medicine. The remedies described are ineffective against the conditions named, and some of the ingredients or doses are harmful. Do not use them to treat any illness; consult a qualified medical professional. This information has been left in for historical purposes but should not be acted upon. mercury sub-chloride, HgCl2. For its preparation see MER- CURY. It is insoluble in water, and blacked by ammonia. It is used in liver complaints, and in any of the complaints for which mercury internally administered is indicated. Care should be exercised in its use, as it is likely to induce salivation. It should be tested to see if it contains any mercuric chloride (corrosive sublimate), which is soluble in boiling water. Calomel is a translucent or subtranslucent mineral. It occurs in Germany, Austria, Spain, and other countries.