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.
By exposing the bones of animals to a red heat without access of air. Thus prepared, it contains 10 to 20 per cent. of charcoal, the remainder being mostly phosphate and carbonate of lime, with some iron sulphuret. It may be obtained from any animal substance, a good quality being procured from dried blood.