Turf frequently contains phosphoric acid; for bogs or morasses, and bog-iron ores abound, more or less with it, in different states of combination. The _siderite_ of Bergmann which he supposed to be a peculiar metal, and found in bog-ore, is a phosphate of iron. The native Prussian blue, which also occurs in such localities, is generally admitted to be a combination of phosphoric acid iron and alumina. _Sec. XII. Of Naphtha, Petroleum, and Asphaltum._ Naphtha, petroleum, and asphaltum are all modifications of bituminous oil; and as they are all inflammable, naphtha being the most so, they have been used in the preparation of fire-works. It will be sufficient to remark, that naphtha or rock oil is a yellow or brownish bituminous fluid, of a strong, penetrating odour, and so light as to float on spirits of wine. By exposure to the air, it acquires the consistence of petroleum. It takes fire on the approach of a lighted taper, and burns with a bluish flame, yielding a thick smoke. Plutarch and Pliny both affirm, that the substance with which Medea destroyed Creusa, the daughter of Creon, was naphtha. She sent a dress to the princess, which had been immersed in, or covered over with the oil, and which burst into flames as soon as she approached the fire of the altar. Plutarch relates that Alexander the great, was amused and astonished with the effects of naphtha, which were exhibited to him at Ecbatana. On the shores of the Caspian sea, it is burnt in lamps, instead of oil. There are copious springs of this oil in that neighbourhood, and it is sometimes obtained by distilling bituminous substances. Hanway (_Travels through Russia into Persia_, i, 263,) mentions the naphtha of Baku, and remarks that the earth is strongly impregnated with it; for, he adds, by taking up two or three inches of the surface, and applying a live coal, the part which is so uncovered, immediately takes fire, almost before the coal touches the earth. Eight horses were consumed by the fire from naphtha, being under a roof where the surface of the ground was turned up, and, by some accident took fire. A cane, or tube, even of paper, set two inches in the ground, and the top of it touched with a live coal, and blown upon, immediately emits a flame, without hurting either the cane or paper, provided the edges be covered with clay. Three or four of these lighted canes will boil water in a pot. Pinkerton, (_Petralogia_ ii, p. 148,) speaks of the naphtha of Baku, which exists on the western side of the Caspian sea, being carried to Constantinople, "where it formed the chief ingredient of the noted composition called the Grecian Fire; which, burning with increased intensity under water, became a most formidable instrument against an inimical fleet." See _Greek fire_.