No trace of saltpetre has hitherto been found anywhere before the thirteenth century. The Greek alchemists of preceding centuries are silent. There is no saltpetre in the earliest recipe we possess for Greek fire, No. 26 of the _Liber Ignium_,[20] ascribed to one Marcus Græcus, either as given in the Paris MSS. of 1300, or in the Munich MS. of 1438. It is true that the phrase _sal coctus_ in this recipe has been translated by _saltpetre_ in M. Hœfer’s untrustworthy _Histoire de la Chimie_, but as MM. Reinaud and Favé remark: “Rien n’autorise à traduire ainsi; le sel ordinaire a été souvent employé dans les artifices.”[21] There is no instance in Latin, I believe, of saltpetre being designated otherwise than by _sal petræ_ (or _petrosus_), or by _nitrum_, singly or in combination with some other word, as _spuma nitri_. The substitution of _sal petræ_ for _sal coctus_, in later editions of the recipe, only shows that when the valuable properties of saltpetre became known it was employed instead of common salt. The very fact of the change having been made by most of the later alchemists, proves that to them _sal coctus_ did not mean _sal petræ_, but something else. If _sal coctus_ had meant _sal petræ_, what need was there for the change? This change, however, was not universal. In the version of recipe 26, given in the _Livre de Canonnerie et Artifice de Feu_, published in Paris in 1561, but written long before by a fire-worker well acquainted with saltpetre, we find: “prenez soufre vif, tarte, farcocoly (sarcocolla), peghel (pitch), sarcosti (sal coctum), &c.”[22] The word _coquo_ (to boil or evaporate) was necessarily connected with the preparation of common salt by evaporation,[23] and _coctus_ would correctly distinguish evaporated or artificial salt from natural or rock salt. In his “Natural History,” xxxi. 39 (7), Pliny tells us that salt is found round the edges of certain lakes in Sicily which are partially dried up in summer by the heat of the sun; while in Phrygia, where much greater evaporation takes place (_ubi largius coquitur_), a lake is dried up (and salt is deposited) to its very middle. _Sal coctus_ was salt recovered from salt water by natural or artificial heat, as distinguished from natural, or rock salt, which was dug out of the ground.[24]