have been puzzled by the accounts that Theophrastus and later authors have given, because no mention is made of the source of the carbon dioxide necessary for the formation of basic lead carbonate. It has been suggested that either the ancient processes were always performed near fires or some extraneous fermenting material was present, and that the ancient authors simply failed to mention these sources of carbon dioxide. What has been generally overlooked is that the air itself and the water used in the washing operations provided enough carbon dioxide to produce basic lead carbonate by the small-scale processes used by the ancients. This was verified by performing in miniature the process here described by Theophrastus. Lead blocks were supported just above a five per cent acetic acid solution in an open vessel, and the white crusts that were formed on the blocks by corrosion were scraped off at intervals of about ten days. The product was found to be a lead acetate containing only a small proportion of lead carbonate; but when it was dissolved in tap water, a turbidity due to the formation of basic lead carbonate was observed almost immediately, and after the solution had stood for a few hours it absorbed enough carbon dioxide from the air to cause the precipitation of a considerable amount of carbonate. The statements of Theophrastus suggest that, in the process he describes, white lead formed in just this way. Either the successive scrapings of the white crusts were thrown into a mortar along with a little water until all the lead was consumed, and then the total product was ground, washed, and separated, or else the individual scrapings, as they were collected, were ground with water for a considerable time before the product was washed and separated by decantation. Another source of the carbon dioxide may have been the so-called vinegar used in the process. If this was merely a spoiled grape juice undergoing both alcoholic and acetous fermentation, ample carbon dioxide would have been available. That this could have been the main source of the carbon dioxide is suggested by the statements in the next section, where Theophrastus describes how verdigris is prepared by the use of grape-residues and says that the process is similar to the one used for making white lead. The other ancient writers who describe methods of preparing
