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LEFT PETBEL 210 PETROLEUM Venice, and, in 1370, removed to- Arqua, in the Euganean Hills. His works are partly in Italian and partly in Latin. His Italian "Sonnets," "Canzoni," and ''Triumphs," all sweet, exquisite, glow- ing variations on one theme, Laura, have placed him as one of the most cele- brated of poets. He modeled the Ital- ian sonnet, and gave to it, and to other forms of lyrical poetry, an admirable polish, diction and melody. After long continued ill health, he died sitting among his books, July 18, 1374. PETREL, a popular name for any individual of the family Procellariidse, small oceanic birds of dusky plumage, nocturnal in habit, widely distributed, but most abundant in the Southern Hemi- sphere. They are considered by sailors as the harbingers of stormy weather. Many of them nidificate in holes and the majority lay but one egg, usually white. (Est7'elata hesitata, the capped petrel whose habitat is the West Indian Islands, has been met with in Hungary. Procellaria (Thalassidroma) pelagica is Mother Carey's chicken, or the storm petrel ;_ Cymochorea leucorrhoa is the fork-tailed, or Leach's petrel ; and Ocean- ites oceanicus is Wilson's petrel. PETRIE, WILLIAM MATTHEW FLINDERS, an English Egyptologist, grandson of Captain Flinders, the Aus- tralian explorer; born June 3, 1853. He made measurements of prehistoric monu- ments in Great Britain (1875-1880); discovered and excavated the Grseco- Egyptian city of Naukratis, in the Delta ; and examined the interior of the pyra- mids at Hawara and Illahun. The re- sults of his researches are found in "Stonehenge: Plans, etc." (1881); "Pyra- mids and Temples of Gizeh" (1883); "Tanis" (1885-1888) ; "Ten Years' Dig- gings in Egypt" (1892), a popular sum- mary of his Egyptian work; "Six Tem- ples at Thebes" (1897); "Researches in Sinai" (1906); "Arts and Crafts in Egypt" (1909); "Egypt and Israel (1911); "Tools and Weapons" (1917). Professor of Egyptology, University Col- lege, London. PETRIFACTION, the act or process of petrifying or changing into a stone; the state of being petrified; conversion of any organic matter, animal or vege- table, into stone, or a substance of stony hardness. A "petrifaction" is not, strictly speaking, a transformation of the original animal or plant into stone. It IS merely a replacement of the organic tissue by mineral substance. As each particle of the plant or animal decays and disappears its place is taken, usually in water or mud, by a particle of mineral matter deposited from the water which has held it in suspension. Thus the perishable original is changed into im- perishable stone. By such means have the skeletons of animals millions of years old been preserved in the rocks of the everlasting hills. In the same way whole forests of trees in the Yellowstone re- gion and elsewhere are changed into agate and other forms of stone, the hol- low logs of the forest primeval being often found filled with beautiful crystals of quartz and amethyst. PETROGRAD, the name given St. Petersburg, the capital of the Russian Empire, following the outbreak of the World War in 1914. The estimated popu- lation in 1920 was 600,000. PETROGRAPHY, the art of writing on stone. Also the study of rocks; a scientific description of or treatise on rocks ; that branch of geology which deals with the constitution of rocks; petrology. PETROLATUM. Vaseline, petroleum jelly. A pale yellow to amber colored, oily,^ translucent, semi-solid substance, obtained by purifying the residue from the distillation of petroleum. Soluble in all common oil solvents, slightly soluble in alcoholj insoluble in water. Used in medicine, in the manufacture of shoe and metal polishes, and as a lubricant. ^ Liquid Petrolatu'in is a colorless, oily liquid, obtained from petrolatum, and consists of the fraction distilling be- tween 330° and 390° C. It is chiefly used in medicine as an emollient. PETROLEUM, a natural oil found in the earth, composed mainly of hydro- carbons. Its existence has been known since earliest times, but it was found in large quantities only following its dis- covery in Pennsylvania in 1850. Since that time there has been rapid develop- ment in its production. There was a dis- covery of oil fields in the United States, in Mexico, in Russia, and in Rumania. These are the chief producing countries, although oil is found in many other places on the earth's surface. The chief feature in recent years has been the development of new oil fields in the mid-west part of the United States and in California. In 1919 377,719,000 barrels of petroleum were marketed. The total production in 1919 was 380,- 000,000 barrels. Of this over 100,000,- 000 barrels came from California, 116,- 000,000 barrels from the Oklahoma- Kansas fields, 68,000,000 barrels from the central and north Texas fields, and the remainder from the Gulf Coast and Rocky Mountain fields. The consump- tion of domestic crude petroleum in 1919