This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
In this malady, the sulphate has been considered by some physicians so valuable as to be almost a specific. I cannot place great reliance upon it, though I have sometimes observed it relieve the cramps, the retching and purging, and strengthen the weak intermittent pulse, and assist in warding off collapse. The careful observations of Gutmann have rendered improbable any specific action of the drug.
Some prophylactic power against cholera has been claimed for copper, for the neighborhood of towns where large copper-works are situated, such as Swansea, Birmingham, Rio Tinto, has been markedly free from the disease, but other circumstances, and other components of the vapor, such as sulphurous acid, must be taken into consideration (Medical Times, ii., 1854, ii., 1871). A similar immunity is recorded at the large powder factory at Madras, where the mixed chemicals are said to be exposed to a temperature of 500° F., which would be sufficient to develop sulphurous acid from the sulphur (Mr. Parker: Lancet, ii., 1873). More important is the fact, that among more than 5,000 copper-workers in Paris, not one was attacked by cholera, during an epidemic which affected other workmen in the proportion of about 1 in every 140; and of the former, not one died of cholera in the course of five epidemics (Burq: Lancet, ii., 1873). Dr. Clapton also remarked that the copper-workers seemed to have almost complete immunity from cholera and from choleraic diarrhoea, when it was very prevalent among the neighbors, and the same observation has been made by others. Still, such prophylactic virtue of copper is not usually recognized, perhaps because it is difficult to understand, but Dr. Clapton suggests as some explanation, the disinfectant power of the metal, and its destructive action upon fungi; the subject deserves further investigation.