PYROLETER 



6422 



PYROMORPHITE 



of metal dies or 

 brands, while the 

 burnt designs are 

 often embellished 

 by carving and 

 painting. An 

 alternative name 

 is poker-work, 

 from the metal 

 skewers once 

 used. See Poker- 

 work: consult 

 also Pyrography 

 and Wood Roast- 

 ing, T. Bolas and 

 C. G. Lei and. 

 1900; Pyro 

 g r a p h y , M 

 Maude, 1901. 



Pyroleter (Or. 

 pyr, fire; oleier, 

 destroyer). Fire- 

 extinguishing ap- 

 paratus. It com- 

 prises a pump by 

 which solutions 

 of hydrochloric 

 acid and sodium 

 bicarbonate are 

 mixed in a cylin- 

 der, and the car- 



Pyrometer. 



Diagrams illustrating chief types of 

 instrument. See text 



tbe 



bonic acid gas generated by the re- 

 action is projected upon the fire. 

 See Fire Prevention. 



Pyroligneous Acid. Name 

 given to crude acetic acid (q.v.), ob- 

 tained by the destructive distilla- 

 tion of wood. On account of its 

 smoky taste, pyroligneous acid is 

 sometimes sold as essence of smoke, 

 and is used for the purpose of im- 

 parting to hams and bacon a 

 smoky flavour. 



Pyrolnsite (Gr. pyr, fire ; louein, 

 to wash ). In mineralogy, the name 

 given to manganese dioxide. Nearly 

 black to steel grey in colour, 

 with a metallic lustre, it is one of 

 the common ores of manganese. It 

 is used as a colouring material, and 

 in the manufacture of chlorine and 

 oxygen and many manganese 

 alloys. See Manganese. 



Pyromancy (Gr. pyr, fire ; 

 manteia, divination). Divination 

 by means of fire, practised in clas- 

 sical times and probably much 

 earlier. The movements of the 

 tlame and the forms assumed by 

 the embers were noted, and omens 

 deduced from them. See Divina- 

 tion ; Magic. 



Pyrometer (Gr. pyr, fire ; met- 

 ron, measure). Instrument for 

 measuring temperatures above 

 those within the range of mercury 

 thermometers. The first pyro- 

 meter depended upon the expan- 

 sion of metallic bars, while Wedg- 

 wood devised an instrument which 

 depended upon the contraction of 

 clay cylinders under heat. The gas 

 thermometer depends upon the 

 expansion of nitrogen. 



Expanding metal instruments 

 are still used, especially for moder- 

 ately high temperatures, such as 

 those of boiler Hues. Fig. 1 shows 

 such an instrument in which the 

 metals are a copper bar, A, and 

 an iron or steel tube, B, which is 

 exposed to the heat; both the 

 metals expand, but as the copper 

 bar lengthens more than the iron 

 tube, the effect is that the bar 

 lengthens upwards. The movement 

 is very slight, but is multipled by a 

 system of levers sufficiently to 

 move the index pointer over the 

 scale, thus indicating the tempera- 

 ture reached. Fig. 2 is a diagram- 

 matic view of an air or gas pyro- 

 meter in which is a bulb, A, of 

 porcelain, which is exposed to the 

 heat to be measured. The bulb is 

 filled with air or gas which, as it 

 expands under the influence of the 

 heat, presses upon a column of 

 quicksilver in a partially pro- 

 tected glass tube. The end of the 

 tube remote from the bulb is sealed, 

 and has a graduated scale attached. 



Instruments have been devised, 

 the principle of which depends on 

 the fact that the resistance of an 

 electrical conductor varies with 

 the temperature. 



Electric Pyrometers 



The essential features of a 

 modern instrument on this prin- 

 ciple are shown in Fig. 3, where A 

 is the electrical conductor in the 

 form of a double coil of platinum 

 wire wound on a strip of mica, B. 

 and enclosed in a porcelain con- 

 tamer, C, sealed at the lower end, 

 which is exposed to the heat. The 



coil is connected by leads through 

 the binding screws shown with an 

 electrical system, D. The electrical 

 balance of this system is disturbed 

 when the coil is heated, the degree 

 of disturbance being a measure 

 of the temperature. Compensating 

 devices (not shown hi the diagram ) 

 are introduced to neutralise the 

 effect of temperature on the plati- 

 num and copper leads. The electri- 

 cal portion of the instrument, which 

 is suitable for temperatures up to 

 1,000 and over, may be at any dis- 

 tance from the coil, and hence the 

 leads are shown interrupted at x. y. 



Electrical pyrometers are also 

 made for determining tempera- 

 tures by means of radiant heat. 

 The oldest arrangement is the 

 thermopile, which consists of a 

 number of bars, alternately of 

 antimony and bismuth, soldered 

 together in series. The junctions of 

 the metals are coated with lamp- 

 black so as to absorb radiation 

 When this absorption takes place 

 an electric current is set up which 

 can be measured by a delicate 

 galvanometer. Fig. 4 shows such 

 an instrument, A being the 

 thermopile. The rays of heat 

 enter as shown by the dotted lines, 

 a, b, . . f, and are reflected on to 

 the thermopile by the lens, B, 

 the current thus set up being com- 

 municated to the galvanometer, 

 C, through the binding screws and 

 leads shown. D is a rack and 

 pinion by which the position of the 

 lens B may be adjusted. 

 Optical Pyrometers 



Optical pyrometers depend for 

 their principle on the change of 

 colour of a heated body from red 

 to white with change of tempera- 

 ture. A change of brilliancy also 

 accompanies these phenomena, 

 and all three can be estimated 

 accurately by the employment of 

 suitable photometers, as shown 

 diagrammatically in Fig. 5, which is 

 a plan view. The rays of heat 

 enter at a, 6, and reach the eye- 

 piece, B, through suitable lenses. 

 At D are two plates of tinted 

 glass, adjustable so that their 

 united thickness may be varied. 

 A is a standard lamp, the light 

 from which is reflected into the 

 eye-piece by the mirror, C. D is 

 adjusted until an agreement in 

 colour or brilliance is reached be- 

 tween the rays from the lamp and 

 those from the furnace or other 

 source of heat, when the tempera- 

 ture is indicated by a pointer on 

 one of the adjustable plates and a 

 scale on the other. 



Pyromorphite. In mineralogy, 

 a lead phosphate and chloride. It 

 has a resinous lustre, green, yellow, 

 and shades of brown in colour, and 

 is found with lead ores. See Lead 



