Py rb eliometer 



for measuring 



radiation of beat 



from the sun 



PYRENOMYCETACEAE 



the capital. Be- 

 fore the Revolu- 

 tion the depart- 

 ment was partly 

 in Roussillon 

 and partly in 

 Languedoc. Pop. 

 210,000. 



Pyrenomyce- 

 taceae. Sub- 

 order of fungi, of 

 the natural 

 order Ascomy- 

 cetes, in which 

 the spore- bear- 

 ing surface is 

 contained in 

 flask-shaped 

 bodies embed- 

 ded in the ex- 

 ternal surface, and opening when 

 the spores are mature. Some of the 

 species are black, hard, and woody. 

 Others, like the Truffles (Tuber) and 

 Hart-truffles (Elaphomyces), are 

 fleshy and grow underground. See 

 Hart-truffle ; Truffle ; Tuberaceae. 



Pyrethrum. Garden name for 

 several species of Chrysanthemum, 

 especially the gold feather (C. 

 praealtum). A native of the 

 Caucasus, it was introduced to 

 Britain in 1804. It is a perennial 

 herb, about 2 ft. high, with aroma- 

 tic yellow leaves cut into incised 

 lobes, and daisy-like white flowers 

 with yellow centres. It is largely 

 used for carpet bedding and 

 edgings, and is grown, therefore, 

 as an annual to obtain small plants, 

 which are frequently nipped to keep 

 them dwarf and prevent flowering. 

 After flowering the plant turns 

 green. See Chrysanthemum. 



Pyrgi. Ancient port of Etruria, 

 Italy. It stands on the Tyrrhenian 

 Sea, 9 m. S.E. of Civita Vecchia, 

 and was the port of Caere (q.v.) of 

 prehistoric origin. Scanty ruins of 

 its walls are still extant. It was 

 sacked by Dionysius, tyrant of 

 Syracuse, in 384 B.C., and after- 

 wards became subject to Caere. 

 Colonised by Rome about 192 B.C., 

 it became a summer resort for 

 opulent Romans. 



Pyrgos. Town of Greece. Situ- 

 ated on the N. of the Gulf of Ar- 

 cadia, W. Morea, it is about 50 m. 

 S.W. of Patras, with which it is 

 connected by rail. The local pro- 

 ducts, currants, grapes, and 

 oranges, are exported through 

 Katakolon by rly. 12 m. E. are the 

 ruins of Olympia. Pop. 14,000. 



Pyrheliometer. Instrument 

 lor measuring the radiation of heat 

 from the sun. In a typical instru- 

 ment two blackened strips, the first 

 of which is to receive the heat of 

 the sun, and the second of which is 

 heated electrically, are placed side 

 by side. They are connected by a 

 detached electric thermo-couple, 



643 i 



which records when the two strips 

 are of the same temperature. The 

 amount of heating given to the 

 second strip can be precisely esti- 

 mated, so that the amount re- 

 ceived by the first strip from the 

 sun becomes known. See Sun. 



Pyridine. Hydrocarbon formed 

 by the destructive distillation of 

 bones. The tarry matter known as 

 Dippel's oil, which is obtained 

 when bones are distilled, contains 

 j>yridine, this base with others 

 being separated by shaking the oil 

 with sulphuric acid to form sul- 

 phates, decanting, and adding al- 

 kali to obtain the free bases. Pyri- 

 dine in the crude state is employed 

 on the Continent as a denaturant 

 for alcohol, on account of its per- 

 sistent, disagreeable taste. Pure 



Pyrenomycetaceae. Candle-snuff 

 fungus (Xylaria hypoxylon) grow- 

 ing on an old stump 



pyridine is used in asthma in doses 

 of from two to ten drops, and also 

 as an inhalation. 



Pyrites. Disulphide of iron, 

 FeSj. Brass-yellow in colour, 

 with a metallic lustre, it is very 

 widely distributed, being found in 

 practically every period of geo- 

 logical time, either disseminated 

 throughout a rock, as concretion- 

 ary masses, in veins, as lenticular 

 masses, or forming a layer between 

 two different types of rocks. When 

 heated in air it yields sulphur di- 

 oxide and ferric oxide, a fact made 

 use of in the preparation of sul- 

 phuric acid. The mineral usually 

 contains impurities, often valuable, 

 as gold and silver and copper. 

 Pyrites is also used in the manu- 

 facture of red paints, and varieties 

 are cut and polished as gem stones. 



The word pyrites is occasionally 

 used for other minerals, as copper 

 pyrites or chalcopyrite, one of the 

 chief ores of copper ; magnetic py- 

 rites, FeS, and arsenical pyrites, 

 FeS.As. See Iron; Mineralogy 



Pyrmont. Town of Germany. 

 It is 32 m. S.W. of Hanover, and is 

 the capital of the little state of 

 Waideck-Pyrmont. Picturesquely 

 situated in a wooded valley at 



PYROGRAPHY 



the foot of the hill called the Bom- 

 berg, it is celebrated for its mineral 

 springs, which have been used 

 since the 16th century. The chief 

 buildings are the Kurhaus, the- 

 atre, and the palace, which until 

 1918 was the residence of the 

 rulers of Waideck-Pyrmont. 



Pyrocatechin. A phenol first 

 obtained by the dry distillation of 

 catechin. It is also known as cate- 

 chol and brenzcatechin. Pyrocate- 

 chin is best obtained from guaiacol, 

 separated from beechwood-tar 

 creosote by passing through it a 

 current of gaseous hydriodic acid, 

 and then separating the catechol 

 by fractional distillation. Pyro- 

 catechol is used as a photographic 

 developer, and is also an ingredient 

 of kachin. 



Pyrocollodion. Variety of ni- 

 trocellulose smokeless powder. 

 Mendeleev, working on behalf of 

 the Russian government, was able 

 between 1891 and 1895 to produce 

 nitrocellulose containing 12'44 p.c. 

 of nitrogen which was completely 

 soluble, and this product contains 

 sufficient oxygen to convert the 

 whole of the carbon to carbon 

 monoxide and the hydrogen to 

 water. This nitrocellulose was 

 termed pyrocollodion. See Collo- 

 dion Cotton ; Explosives ; Gun- 

 cotton ; Nitrocellulose ; Poudre B : 

 Smokeless Powder. 



Pyrogallol. Aphenol, commonly 

 known as pyrogallic acid, or pyro. 

 and much employed as a photo- 

 graphic developer. It is prepared 

 by heating gallic acid in an auto- 

 clave or bronze digester, fitted 

 with a means for allowing the car- 

 bon dioxide to escape. The result- 

 ing solution of pyrogallol is boiled 

 with animal charcoal, filtered, 

 evaporated, and allowed to crys- 

 tallise. Pyrogallol occurs in two 

 forms, one being a light-weighing 

 white powder, and the other a 

 heavier product. The photographic 

 developing properties of pyrogallol 

 were discovered by Maddox in 

 1871. 



Pyrography (Gr. pyr, fire; 

 graphein, to write). Art of burning 

 a design on wood, leather, or other 

 substances. The design is burnt on 

 in a number of ways, the simplest 

 being by means of heated metal 

 skewers, but this is laborious, and 

 has been replaced by electrical and 

 other methods. One of the best is a 

 hollow needle heated over a spirit 

 lamp, and kept hot by forcing 

 through it a jet of burning vapor- 

 ised benzine. The needle is used 

 exactly like a pencil, and burns 

 lines on the surface of varying 

 depth according to the tempera- 

 ture, which can be regulated, gen- 

 erated by the benzine. Repeated 

 designs are often burnt by means 



