The ingredient is an extract of the cedar tree with antibacterial properties. They were found in "chunks of embalming tar, found with the 2,500-year-old mummy of Saankh-kare," according to MSN's article (www.msnbc.com/news/983621.asp) Secrets of mummy-making revealed.
The preservative is called Guaiacol.
Pliny had written about this ingredient, albeit centuries later, but it would have saved millennia if scientists had read him: "The team extracted the cedar oil using a method mentioned in a work by Pliny the Elder, a Roman encyclopedist who wrote of an embalming ointment called 'cedrium'."

