[99] Matthew v. 13.--“Ὑμεις εστε το ἁλας της γης· εαν δε το ἁλας μωρανθη, εν τινι ἁλισθησεται· εις ουδεν ισχωει ετι ει μη βληθηναι εξω, και καταπατεισθαι ὑπο των ανθρωπων.”
Asphalt was one of the great constituents of the Greek fire. A great bed of it still existing in Albania, supplied the Greeks with this substance. Concerning the nature of the Greek fire, it is clear that many exaggerated and even fabulous statements have been published. The obvious intention of the Greeks being, probably, to make their invention as much dreaded as possible by their enemies. Nitre was undoubtedly one of the most important of its constituents; though no allusion whatever is ever made. We do not know when _nitrate of potash_, the nitre of the moderns, became known in Europe. It was discovered in the east; and was undoubtedly known in China and India before the commencement of the Christian era. The property of nitre, as a supporter of combustion, could not have remained long unknown after the discovery of the salt. The first person who threw a piece of it upon a red-hot coal would observe it. Accordingly we find that its use in fireworks was known very early in China and India; though its prodigious expansive power, by which it propels bullets with so great and destructive velocity, is a European invention, posterior to the time of Roger Bacon.
The word _nitre_ (רתנ) had been applied by the ancients to _carbonate of soda_, a production of Egypt, where it is still formed from sea-water, by some unknown process of nature in the marshes near Alexandria. This is evident, not merely from the account given of it by Dioscorides and Pliny; for the following passage, from the Old Testament, shows that it had the same meaning among the Jews: “As he that taketh away a garment in cold weather, is as vinegar upon nitre: so is he that singeth songs to a heavy heart.”[100] Vinegar poured upon saltpetre produces no sensible effect whatever, but when poured upon carbonate of soda, it occasions an _effervescence_. When saltpetre came to be imported to Europe, it was natural to give it the same name as that applied to carbonate of soda, to which both in taste and appearance it bore some faint resemblance. Saltpetre possessing much more striking properties than carbonate of soda much more attention was drawn to it, and it gradually fixed upon itself the term _nitre_, at first applied to a different salt. When this change of nomenclature took place does not appear; but it was completed before the time of Roger Bacon, who always applies the term _nitrum_ to our nitrate of potash and never to carbonate of soda.