Number V To Make the Artificial Bolognian Stone
“Calcine some common oyster-shells, by keeping them in a good coal fire, for half an hour; let the purest part of the calx be pulverised and sifted. Mix with three parts of this powder, one part of flowers of sulphur. Let this mixture be rammed into a crucible of about an inch and a half in depth, till it be almost full; and let it be placed in the middle of the fire, where it must be kept red hot for an hour at least, and then set it by to cool: when cold turn it out of the crucible; and cutting or breaking it to pieces, scrape off, upon trial, the brightest parts; which, if good phosphorus, will be a white powder.”