7. _White paints._ All the ancient white paints examined by Davy were carbonates of lime.[72] We know from Pliny that white lead was employed by the ancients as a pigment; but it might probably become altered in its nature by long-continued exposure to the weather. [72] Phil. Trans. 1814, p. 97. III.--GLASS. It is admitted by some that the word which in our English Bible is translated crystal, means glass, in the following passage of Job: “The gold and the crystal cannot equal it.”[73] Now although the exact time when Job was written is not known, it is admitted on all hands to be one of the oldest of the books contained in the Old Testament. There are strong reasons for believing that it existed before the time of Moses; and some go so far as to affirm that there are several allusions to it in the writings of Moses. If therefore glass were known when the Book of Job was written, it is obvious that the discovery of it preceded the commencement of history. But even though the word used in Job should not refer to glass, there can be no doubt that it was known at a very early period; for glass beads are frequently found on the Egyptian mummies, and they are known to have been embalmed at a very remote period. The first Greek author who uses the word glass (ὑαλος, _hyalos_) is Aristophanes. In his comedy of The Clouds, act ii. scene 1, in the ridiculous dialogue between Socrates and Strepsiades, the latter announces a method which had occurred to him to pay his debts. “You know,” says he, “the beautiful transparent stone used for kindling fire.” “Do you mean glass (τον ὕαλον, _ton hyalon_)?” replied Socrates. “I do,” was the answer. He then describes how he would destroy the writings by means of it, and thus defraud his creditors. Now this comedy was acted about four hundred and twenty-three years before the beginning of the Christian era. The story related by Pliny, respecting the discovery of this beautiful and important substance, is well known. Some Phœnician merchants, in a ship loaded with carbonate of soda from Egypt, stopped, and went ashore on the banks of the river Belus: having nothing to support their kettles while they were dressing their food, they employed lumps of carbonate of soda for that purpose. The fire was strong enough to fuse some of this soda, and to unite it with the fine sand of the river Belus: the consequence of this was the formation of glass.[74] Whether this story be entitled to credit or not, it is clear that the discovery must have originated in some such accident. Pliny’s account of the manufacture of glass, like his account of every other manufacture, is very imperfect: but we see from it that in his time they were in the habit of making coloured glasses; that colourless glasses were most highly prized, and that glass was rendered colourless then as it is at present, by the addition of a certain quantity of oxide of manganese. Colourless glass was very high priced in Pliny’s time.