In the manufacture of white lead by the Dutch process, stable-litter was universally used as the source of heat and of carbon dioxide until 1787, when the use of spent tan-bark is mentioned. Richard Fishwick obtained a patent in that year for the use of spent tan-bark instead of stable-litter. The patentee claimed that the bark communicated a more certain and equal degree of heat to the vinegar and the lead.3,,3 Abridgments of Specifications, etc., p, 12.