purpose of treating garments with such earthy substances was probably to whiten the discolored cloth, but it is also possible that whole cloth was likewise treated with these earths in order to "weight" or stiffen it, just as certain kinds of cloth, especially silk, are weighted with inorganic substances at the present time.
67. It seems to be far superior to other earths for taking impressions.
This translation of άπομάγματα as "impressions" is supported by a passage in the Causes of Plants51* which contains the phrase τα άπομάγματα των δακτυλίων ("the impressions of signets"). Though this alludes specifically to impressions of signets or finger rings, in the present passage the word appears to have a more general significance and probably means impressions or molds in general. Obviously, the kind of gypsos used for such a purpose could only have been calcined gypsum.
68. It is also clear from the following example that it has a fiery nature; for once a ship loaded with clothes was itself burnt when the clothes became wet and caught fire. Although this story has obviously been condensed, the meaning seems clear enough. The argument seems to be that the clothes carried on the ship had been treated with gypsos, a substance that generates heat on contact with water; that water somehow had come into contact with the gypsos on the clothes, so that heat was generated and the clothes set on fire; and that this caused a general fire that destroyed the vessel. It is unlikely that this story is true, because the sort of gypsos used for cleaning or whitening clothes was ordinarily a natural earth that did not generate heat on contact with water. Even if dehydrated gypsum had been used for whitening the clothes, no heat would have been generated on contact with water, since the gypsum would probably have been completely hydrated while the clothes were being cleaned. Moreover, even if dehydrated gypsum had been present in the clothes or as a separate cargo on board the ship, no fire could have been started because it does not generate enough heat on contact with water to ignite organic materials. Furthermore, even if the clothes
518 VI, 19, 5.
