When Solomon speaks of the action of vinegar upon nitre, the chemist understands that the salt referred to is a carbonate, but when the nature of the action or application is not given, we have no idea what particular salt is meant. There is no doubt, however, that the ancients were well acquainted with the alkaline salts of potash and soda, and applied them in the arts. The metallic salts of iron, copper, and alumina were well known, and their application to dyeing was generally the same as at the present day. That they were used both as mordants and alterants is evident from several references. A very suggestive statement is made by Pliny about the ancient Egyptians. "They began," says he, "by painting or drawing on white cloths with certain drugs, which in themselves possessed no color, but had the property of attracting or absorbing coloring matter, after which these cloths were immersed in a heated dyeing liquor; and although they were colorless before, and although this dyeing liquor was of one equable and uniform color, yet when taken out of it soon afterwards, the cloth was found to be wonderfully tinged of different colors according to the peculiar nature of the several drugs which had been applied to their respective parts, and these colors could not be afterwards discharged by washing." Herodotus states that certain people who lived near the Caspian Sea could, by means of leaves of trees which they bruised and steeped in water, form on cloth the figures of animals, flowers, etc., which were as lasting as the cloth itself. This statement is more suggestive than instructive. Persia was much famed for dyeing at a very early period, and dyeing is still held in great esteem in that country. Persian dyers have chosen Christ as their patron; and Bischoff says that they at present call a dye-house Christ's workshop, from a tradition they have that He was of that profession. They have a legend, probably founded upon what Pliny tells of the Egyptian dyers, "that Christ being put apprentice to a dyer, His master desired Him to dye some pieces of cloth of different colors; He put them all into a boiler, and when the dyer took them out he was terribly frightened on finding that each had its proper color." This or a similar legend occurs in the apocryphal book entitled "The First Gospel of the Infancy of Jesus Christ." The following is the passage: