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THE CHANGES UNDERGONE BY ANTIQUITIES IN EARTH AND IN AIR.
The greater number of those objects of antiquity which are composed of inorganic materials, such as limestone, earthenware, and metals, owe the commencement of any alteration in their character to the situation in which they are discovered, since they are buried in ground which has been at some period damp or wet, and has contained, moreover, salts soluble in water. Amongst these salts the most usual is sodium chloride (common salt), but this is mostly accompanied by potassium chloride, potassium sulphate, magnesium chloride, and calcium sulphate; in short, by those soluble salts which are found in sea-water. In the fine pores of Egyptian antiquities, especially, such salts occur, and their presence is readily explained by the fact that the land of Egypt was originally a sea-bottom.
The presence of salt in the soil of Egypt has been known for a considerable period. Thus Karabacek[3], quoting from Volney's "Travels in Syria and Egypt" (Jena, 1788, I. p. 13):
"Wherever one digs one finds brackish water containing soda, sea-salt, and a small quantity of saltpetre. Indeed, when a garden has been flooded for irrigation purposes, crystals of salt make their appearance on the surface after the water has evaporated or has been soaked up by the soil."
In the dry climate of Egypt, objects saturated with salt keep better after their removal from the ground than in our climate, where the variations in the temperature and in the hygroscopic condition of the air produce a partial deliquescence in wet weather, and in dry weather a re-formation of crystals. The continued alternation of these processes gradually loosens the surface of limestone or earthenware, or induces certain chemical changes in objects of metal and in both cases leads to their destruction.
The series of changes are particularly well illustrated by the Egyptian grave of Meten[4], the stones from which are now in the Royal Museum in Berlin. The three illustrations here given show: (1) an undecayed block of limestone, (2) a block with pitted surface, and (3) a block the surface of which was formerly covered with hieroglyphics, but which is now totally destroyed by flaking. The blocks of the latter kind were found in the lowest layer, or lowest but one, while those blocks which were above were the best preserved. As the amount of salt present scarcely varied, these specimens offer a striking illustration of the greater influence of moisture in the deeper soil than at the higher levels.