Dr Papin's experiment 'upon petrified Wood calcined applying to the Lodestone or tinging with Galls' That parts of the petrified wood and bark were calcined to see if they were magnetic (only the bark proved positive); observations of the effects of powder of gall on uncalcined bark; carried out same experiment with iron rust Details about how to make plaster of Paris transparent by adding turpentine Figure page 176 16 April 1684