John Snow's theory of rickets
In Archives of Diseases in Children, 89(2):147, archivists  (I would love to know who it is) makes a comment on John Snow’s theory of rickets.
Unfortunately he, and those who may have written commentaries on this, are quite wrong in saying that alum is potassium aluminium phosphate. It is quite clear from various books on chemistry and the Encyclopaedia Britannica – copy enclosed – alum is the name commonly applied to a hydrated double salt, usually consisting of aluminium sulphate, water of hydration and the sulphate of another element. The latter may be ammonia iron. In more specific chemical terminology, alum refers to a whole series of hydrated double salts resulting of the hydration of the sulphate of any one of a number of triple valency ions.
If the alum used in bread was not the phosphate, but was the sulphate, this destroys the archivists theories. I am surprised this was not checked more carefully.
Obviously I will have to look more carefully at some of the articles and perhaps write to you.
1. Archivist article. John Snow’s theory of rickets Arch. Dis. Child. 2004; 89: 147.
It was the Broad Street (currently Broadwick Street) pump that John Snow had the parish elders remove the handle of, not Bond Street.