762 



PYRITES PYHOPHORUS. 



burg, with the fortified towns of Arras, Hesdin, 

 Gravelines, Landrecy, Quesnoy, ThkM)viile v Mont- 

 medy, Marienburg, Philippeville, &c. In 1815, 

 France was obliged to cede the two last named 

 fortresses to the kingdom of the Netherlands. France 

 bound herself not to support Portugal. The prince 

 of Comic and the dukes of Lorraine, Savoy, and 

 Modena, and the prince of Monaco (the two first 

 especially), were left in statu quo. In consequence 

 of this peace, Louis XIV. married Maria Theresa, 

 eldest daughter of Philip IV., who, in 1G60, re- 

 nounced all right of inheritance to the Spanish 

 throne. Louis XIV., however, afterwards made 

 pretensions to this right, from which arose the de- 

 volution war and the war of the Spanish succession. 

 See Aix-la-Chapelle, Peace of, and Utrecht, Peace of. 



PYRITES; a genus of inflammable substances, 

 composed of sulphur, which has dissolved or satu- 

 rated itself with metals. Iron pyrites according to 

 Stromier is a compound of the Protosulphtiret and 

 Bisulphuret of iron. (See Iron Magnetic Ore.) 

 Copper pyrites is a double sulphuret of iron and 

 copper, that ore from which the copper of com- 

 merce is usually obtained. 



PYRMONT, OR NEUSTADT PYRMONT; a 

 town in the principality of Waldeck, situated in a 

 pleasant valley on the Emmer, thirty-three miles 

 south-west of Hanover. It is well built, with de- 

 lightful walks, and is famous for its thermal waters, 

 which are yearly visited by 1800 strangers. The 

 waters are saline. (See Mineral Waters.} In the 

 vicinity are the ruins of the old castle of Pyrmont, 

 or Schellpyrmont, and the cave called Dunsthohle, 

 from which issues carbonic acid gas. There is also 

 here a colony of Quakers, called Friedensthal (Vale 

 of Peace.) 



PYROCHLORE ; a mineral recently detected in 

 the zircon sienite of Fredericksvaern, in Norway. It 

 occurs crystallized in regular octahedrons ; specific 

 gravity, 4.2; scratches fluor ; streak brown; frac- 

 ture conchoidal, without any trace of cleavage ; 

 lustre between vitreous and resinous. Its colour is 

 reddish brown, and on the fresh surface almost 

 black ; in thin splinters, translucent It consists of 

 titanic acid 62.75, lime 12.85, oxide of uranium 

 5.18, oxide of cerium 6.80, oxide of manganese 

 2.75, oxide of iron 2.16, oxide of zinc 0.61, water 

 4.2, fluoric acid undetermined, and magnesia a trace. 



PYROLIGNEOUS ACID. See Vinegar. 



PYROMETER; an instrument for the measure- 

 ment of temperatures above those which we are 

 able to estimate by the mercurial thermometer. 

 Mercury boils at C60, above which point it is in- 

 capable of measuring heats; although many temper- 

 atures connected with the most common processes 

 are greatly above this point, as, for example, the 

 heat of a common fire, the melting point of silver, 

 copper, and gold. The first pyrometer was that 

 invented by Mr. Wedgewood. It consisted of small 

 pieces of clay from Cornwall, moulded into cylin- 

 ders of a determinate size, and baked in a low red 

 heat. These pieces were of just such a size as to 

 enter between two square brass rods, fixed on a 

 brass plate twenty-four inches long, half an inch 

 asunder at one extremity, and 0.3 inch at the other. 

 The brass rods were divided into inches and tenths, 

 making in all 240 divisions, or degrees. When 

 pieces of clay, baked in Wedgewood's manner, are 

 exposed to heat, they shrink in their dimensions, 

 and the degree of shrinking was believed to be pro- 

 portional to the temperature. This was the foun- 

 dation of his instrument. The heat to which the 

 piece of clay was exposed was indicated, when its 

 shrinkage was measured between the brass rods. 

 If exposed to the heat at which silver melts, it ad- 



vanced between the brass roils to 22, or 8.2 inches; 

 if to the melting point of gold, to 3fc e ; and if to 

 the melting point of cast iron, to 130; and so on. 

 But this pyrometer of Wedgewood has been long 

 laid aside, in consequence of the observation, that 

 if a piece of this clay was long exposed to a low 

 temperature, it shrunk as much in its dimensions 

 as if it had been exposed for a short time to a much 

 higher temperature. In 1803, Guyton de Morveau 

 presented to the French institute a pyrometer of 

 platina, which measured high temperatures by the 

 expansion of this refractory metal. An improve- 

 ment of this instrument was brought forward by 

 Mr. Daniel in 1821, which consisted of a bar of 

 platina 10 inches long, and 0.14 inch in diameter. 

 It is placed in a tube of black lead or earthen ware, 

 and the difference between the expansion of the 

 platina bar and the earthen ware tube is indicated 

 on a circular scale. This pyrometer indicates a 

 change of about 7 of Fahrenheit; or, in other 

 words, 1 of Daniel is equal to 7 of Fahrenheit. 

 The following are some of the results obtained by 

 this instrument : 



Boil 

 Fus 



ng point of mercury, 

 ng point of tin, 



bismuth, 



lead, 



zinc, 



brass, 



silver, . . 



copper, . 



gold, 



" " cast iron, . . 



Red heat just visible in daylight, 

 Heat of a common fire, 



, 63 

 66 

 87 

 94 

 267 

 319 

 364 

 370 

 497 

 140 

 163 



644 

 441 



462 



609 



643 



1809 



2233 



2548 



2590 



3419 



980 



1141. 



A very delicate pyrometer, was invented by the 

 celebrated chronometer makers the Messrs Breguet. 

 It consists of a helix formed of three metals of un- 

 equal expansibility, one plate of gold being inclosed 

 by one of silver and another of platinum. The 

 compound plate does not exceed one hundredth part 

 of an inch in thickness, the top of the spiral being 

 fixed in a firm brass stem and the bottom carrying 

 a golden needle. When the helix expands the coil 

 moves round and turns the needle over a graduated 

 arch which indicates the degree of expansion. 

 The instrument is mounted by the Parisian makers 

 in a case the size of a thin watch, it possesses great 

 delicacy but is little known in this country. (See 

 Thermometer.) 



PYROPHORUS; an artificial product, which 

 takes fire on exposure to the air. It is prepared by 

 several methods. The oldest way of proceeding is 

 as follows : Four or five parts of burnt alum are 

 mingled with two of charcoal powder. The mix- 

 ture is introduced into a vial or matrass, with a neck 

 of about six inches long. The vial is filled about 

 two thirds full, and put into a crucible the bottom 

 of which is covered with sand. The body ot 

 the flask is also surrounded with sand, after 

 which the crucible is put into a furnace, and sur- 

 rounded with red-hot coals. The fire is gradually 

 increased until the flask becomes red hot, at which 

 temperature it is maintained for about a quarter of 

 an hour. As soon as the vessel is become cool 

 enough to be handled, the vial is taken out of the 

 sand, and the contents transferred into a dry and 

 stout glass, made warm, which must be secured 

 with a glass stopper. Whenever this mixture is 

 poured out in the air, it takes fire. A pyrophorus 

 may be prepared by mixing three parts of alum 

 with one of wheat flour, and calcining them in a 

 vial, as in the above case. Tartrate of lead, also, 

 on being heated in a glass tube until it becomes 

 converted into coaly matter, gives rise to a beauti- 

 ful pyrophorus. But the pyrophorus invented by 

 doctor Hare of Philadelphia is the most remarkable. 



