*216 



PYROMETER. 



Pyrometer.. The differences between these results are too strik- 

 ing to escape notice, and show how very imperfect is 

 our knowledge of the effects of high temperatures. 

 See the Quarterly Journal of Science, Literature, and 

 ihe Arts, vol. xi. p. 30.9 320. This instrument is 

 made by Mr. Newman, Lisle Street. 



4. Description of Dr. Ure's Pyrometer. 



Dr. Ure's This instrument, which Dr. lire does not mention 

 pyrometer. as having been actually constructed, is described in 

 his Dictionary of Chemistry, published in 1821. Art. 

 PYROMETER. 



" Since dry air," says Dr. Ure, " augments 3-8ths for 

 180, and since its progressive rate of expansion is proba- 

 bly uniform by uniform increments of heat, a pyrometer 

 might easily be constructed on this principle. Form a 

 bulb and tube of platinum, of exactly the same size as a 

 thermometer, and connect with the extremity of the 

 stem, at right angles, a glass tube of uniform calibre, 

 filled with mercury, and terminating below in a re- 

 curved bulb, like that of the Italian barometer. Gra- 

 duate the glass tube into a series of spaces equivalent to 

 3-8ths of the total volume of the capacity of the plati- 

 na bulb, with 3-4ths of its stem. The other parts 

 may be supposed to be little influenced by the source 

 of heat. On plunging the bulb and 2-3ds of the stem 

 into a furnace, the depression of the mercury will indi- 

 cate the degree of heat. As the increment of the co- 

 lumn will be very inconsiderable, it will be scarcely 

 worth while to introduce any correction, for the change 



in the initial volume by barometric variation. Care Pyrometer, 

 must be taken to let no mercury into the platina bulb." k -*"Y"'- / 



5. Description of Mill's Pyrometer. 



This instrument, proposed by Mr. Nicholas Mill, is Mill's py- 

 represented in Plate CCCCLXXI. Fig. 12. It consists rometei. 

 of a metallic bulb and stem AB of platinum, drawn out Fig. 12. 

 without any joint. The bulb is hollow, and has its ex- 

 ternal diameter about half an inch, according to the 

 size of the instrument. The bore of the bulb B, which 

 is perfectly cylindrical, is about the sixteenth of an inch 

 in diameter, and at the further end of this tube is at- 

 tached, by an air-tight joint, a glass tube C, which is 

 bent in a triangular form. At the extremity of the 

 tube is a bulb of glass D, of the same capacity as the 

 bulb of platinum B, with a funnel-shaped mouth, (for 

 the insertion of the mercury, ) which is afterwards her- 

 metically closed. The scale E is attached to the cir- 

 cular glass stem F and is graduated like a thermometer. 



When heat is applied to the platinum bulb, it ex- 

 pands the included atmospheric air, the pressure of 

 which, against the mercury, drives it up the glass tube 

 F, to which the scale is fixed ; and as the air expands 

 with an increase of heat, so the mercury rises, and in- 

 dicates on the scale the degree of temperature. In 

 order to protect the platinum bulb, a cylindrical cruci- 

 ble, made of the most refractory clay, is placed over 

 it, and the empty part between filled up with pounded 

 charcoal or sand. This instrument is made by Messrs. 

 Gilberts, and by Mr. Newman, London. See the 

 Monthly Medico-Chirurgical Review and Chemico- Phi- 

 losophical Magazine, vol. i. p. 1. Lond. 1824. 



P Y R 



Pyrope, PYROPE. See MINERALOGY, Vol. XIV. p. 551. 



Pyropho- PYROPHORUS isthe name of an artificial compound, 

 Sj which ignites by exposure to the air. It was first made 

 "~ Y "" by Thunberg in 1680, from a mixture of human excre- 

 ment and alum, but it may be prepared from alum by 

 calcination, with the addition of various inflammable 

 substances. 



Three parts of alum are mixed with from two to three 

 parts of honey, flour, or sugar, and this mixture is 

 dried on the fire in a glazed bowl, stirring it all the 

 while with an iron spatula. The mixture at first melts, 

 but gradually swells up and runs into dry lumps, 

 which are pounded and again roasted, till no moisture 

 whatever remains in them, the mass now resembling a 

 blackish powder of charcoal. The above operation may 

 be saved by directly mixing two parts of charcoal pow- 

 der with five of burnt alum. The powder is now 

 poured into a phial, with a neck about six inches long, 

 and the phial, when three quarters full, is put into a 

 crucible, which is exposed to the red heat of a furnace 

 for about a quarter of an hour, till the black smoke, 

 which at first issues from the mouth of the phial is suc- 

 ceeded by a sulphurous vapour, which commonly takes 

 fire. When the sulphurous flame ceases the phial is closed 

 with a clay stopper ; and when the fire is out, the pow- 

 der is transferred as fast as possible into a dry and strait 

 glass, made warm, and secured with a glass stopper. 



A good pyrophorus may be made by calcining a 

 mixture of three parts of alum and one of wheat- flower, 

 in a common phial, till the blue flame disappears, and 

 preserving it in the same phial with a good stopper. By* 

 the exposure of the pyrophorus to the air, the sulphuret 



5 



Pyrotar- 

 tarie. 



P Y R 



attracts its moisture, and produces a degree of heat ca- Pyrophysa. 

 pable of igniting the carbonaceous matter which is lite 

 mixed with it. 



PYROPHYSALITE. See MINERALOGY, Vol. XIV. 

 p. 544. 



PYROSMALITE. See MINERALOGY, Vol. XIV. 

 p. 570. 



PYROTARTARIC, ACID. This acid, which was 

 formerly confounded with the acetic, was discovered by 

 Mr. Rose. It is formed by filling a retort half full of 

 tartaric acid. The retort being fitted to a tubulated re- 

 ceiver, heat is applied, and gradually raised to redness. 

 Brown pyrotartaric acid is formed in the liquid produced. 

 When these products are filtered through paper pre- 

 viously wetted, and the liquid saturated with carbonate 

 of potash, it must then be evaporated to dryness, re- 

 dissolved, and filtered through clean moistened paper. 

 When the oily matter has been completely removed by 

 a repetition of this process, the dry salt must then be 

 heated in a glass retort, with dilute sulphuric acid, at 

 a moderate heat. At first acetic acid passes over into 

 the receiver, but near the end of the distillation there 

 is condensed in the vault of the retort a white and fo- 

 liated sublimate, which is the pyrotartaric acid perfect- 

 ly pure. It is sour, and reddens the tincture of turn- 

 sole. It is highly soluble in water, and is separated 

 in crystals by spontaneous evaporation. It forms py- 

 rotartarates with potash, soda, ammonia, barytes, stron- 

 tites, and lime. Dr. Thomson ascribes the discovery 

 of this acid to Gehlen, in 1806. See Dr. Ure's Dic- 

 tionary of Chemistry, Art. ACID Pyroiarlaric ; and 

 Thomson's Chemistry, edit. 1817, vol. ii- p. 150. 



