FAHRENHEIT. -29 -28 -27 -26 20 -15 --14 -13 -12 -20.2 37 98.6 103 -18.4 38 100.4 104 -16.6 39 102.2 105 -14.8 40 104. 106 25 -13. 41 105.8 107 224.6 173 -24-11.2 42 107.6 108 226.4 174 23 - 9.4 43 109.4 109 228.2 175 -22 7.6 44 111.2 110 -21 -5.8 45 113. 111 231.8 177 4. 46 114.8 112 233.6 178 19 2.2 47 116.6 113 235.4 179 -18 0.4 48 118.4 114 237.2 180 -171.4 49 120.2 115 239. 181 16 3.2 50 122. 116 240.8 182 5. 51 123.8 117 242.6 183 6.8 52 125.6 118 244.4 184 8.6 53 127.4 119 10.4 54 129.2 120 217.4 169 219.2 170 221. 171 12.2 55 131. 121 249.8 187 14. 56 132.8 122 251.6 188 15.8 57 134.6 123 253.4 189 17.6 58 136.4 124 255.2 190 19.4 59 138.2 125 257. 191 21.2 60 140. 126 258.8 192 23. 61 141.8 127 260.6 193 24.8 62 143.6 128 262.4 194 26.6 63 145.4 129 264.2 195 28.4 64 147.2 130 30.2 65 149. 131 267.8 197 32. 66 150.8 132 269.6 198 33.8 67 152.6 133 271.4 199 35.6 68 154.4 134 273.2 200 37.4 69 156.2 135 275. 201 39.2 70 158. 136 276.8 202 41. 71 159.8 137 278.6 203 42.8 72 161.6 138 280.4 204 44.6 73 163.4 139 282.2 205 8 46.4 74 165.2 140 368.6 253 487.4 580 1076 1240 2264 370.4 254 489.2 590 1094 1250 2282 9 10 11 13 14 48.2 75 167. 141 285.8 207 50. 76 168.8 142 287.6 208 51.8 77 170.6 143 289.4 209 12 53.6 78 172.4 144 291.2 210 55.4 79 174.2 145 293. 211 57.2 80 176. 146 294.8 212 413.6 278 532.4 15 16 19 20 23 24 25 59. 81 177.8 147 296.6 213 60.8 82 179.6 148 298.4 214 17 62.6 83 181.4 149 300.2 215 18 64.4 84 183.2 150 302. 216 66.2 85 185. 151 303.8 217 68. 86 186.8 152 305.6 218 424.4 284 543.2 21 69.8 87 188.6 153 307.4 219 426.2 285 545. 22 71.6 88 190.4 154 309.2 220 428. 286 546.8 73.4 89 192.2 155 311. 221 429.8 287 548.6 75.2 90 194. 156 312.8 222 431.6 288 550.4 77. 91 195.8 157 314.6 223 433.4 289 552.2 CENTIGRADE. -24 -40-40. -39-39.4 27 -38 -38.9 28 -37-38.3 29 -36-37.8 30 -35-37.2 31 -34-36.7 32 -33-36.1 33 -32-35.6 34 -31-35. 35 -30-34.4 36 29-33.9 37 -28 -33.3 38 -32.8 39 -26-32.2 40 -31.7 41 -31.1 42 -25 23-30.6 43 -22 -30. 44 -21 -29.4 45 3 -20 -28.9 46 -19 -28.3 47 -18-27.8 48 -17-27.2 49 -16-26.7 50 -15 -26.1 51 -14-25.6 52 -13 -25. 53 -12 -24.4 54 -11-23.9 55 -10-23.3 56 9-22.8 57 8-22.2 58 7--21.7 59 6-21.1 60 -20.6 61 -20. 62 -19.4 63 -18.9 64 1-18.3 65 -17.8 66 + -17.2 67 -16.1 69 -15. 71 -14.4 72 -13.9 73 8 -13.3 74 9 -12.8 75 10 -12.2 76 11 -11.7 77 80 16 17 345 1.1 96 35.6 162 0.6 97 36.1 163 0. 98 36.7 164 0.6 99 37.2 165 1.1 100 37.8 166 1.7 101 38.3 167 2.2 102 38.9 168 2.8 103 39.4 169 3.3 104 40. 170 3.9 105 40.6 171 4.4 106 41.1 172 5. 107 41.7 173 5.6 108 42.2 174 6.1 109 42.8 175 6.7 110 43.3 176 7.2 111 43.9 177 7.8 112 44.4 178 8.3 113 45. 179 8.9 114 45.6 180 9.4 115 46.1 181 10. 116 46.7 182 10.6 117 47.2 183 11.1 118 47.8 184 11.7 119 48.3 185 12.2 120 48.9 12.8 121 49.4 13.3 122 50. 13.9 123 50.6 14.4 124 51.1 190 15. 125 51.7 191 15.6 126 52.2 192 16.1 127 52.8 193 16.7 128 53.3 194 17.2 129 53.9 195 17.8 130 54.4 196 18.3 131 55. 197 18.9 132 55.6 198 19.4 133 56.1 199 20. 134 56.7 200 20.6 135 57.2 201 21.1 136 57.8 202 21.7 137 58.3 203 95. 269 131.7 335 168.3 22.2 138 58.9 204 95.6 270 132.2 336 168.9 22.8 139 59.4 205 96.1 271 132.8 337 169.4 23.3 140 60. 206 96.7 272 133.3 338 170. 23.9 141 60.6 207 97.2 273 133.9 339 170.6 24.4 142 61.1 208 97.8 274 134.4 340 171.1 25. 143 61.7 209 98.3 275 135. 341 171.7 25.6 144 62.2 210 98.9 276 135.6 342 172.2 26.1 145 62.8 211 99.4 277 136.1 343 172.8 26.7 146 63.3212 100. 278 136.7 344 173.3 27.2 147 63.9 213 100.6 279 137.2 845 173.9 8.9 82 27.8 148 64.4 214 101.1 280 137.8 346 174.4 8.3 83 28.3 149 65. 215 101.7281 138.3 347 175. 187.8 84 28.9 150 65.6 216 102.2 282 138.9 348 175.6 19 7.2 85 29.4 151 66.1 217 102.8 283 139.4 349 176.1 20 6.7 86 80. 152 66.7 218 103.3 284 140. 21 6.1 87 80.6 153 67.2 219 103.9 285 140.6 5.6 88 31.1 154 67.8 220 104.4 286 141.1 5. 89 81.7 155 68.3 221 105. 287 141.7 4.4 90 32.2 156 68.9 222 105.6 3.9 91 32.8 157 69.4 223 106.1 Platinum or Copper Ball Pyrometer.-A weighed piece of platinum, copper, or iron is allowed to remain in the furnace or heated chamber till it has attained the temperature of its surroundings. It is then suddenly taken out and dropped into a vessel containing water of a known weight and temperature. The water is stirred rapidly and its maximum temperature taken. Let W weight of the water, w the weight of the ball, t = the original and T the final heat of the water, and S the specific heat of the metal; then the temperature of fire may be found from the formula The mean specific heat of platinum between 32° and 446° F. is .03333 or 1/30 that of water, and it increases with the temperature about .000305 for each 100° F. For a fuller description, by J. C. Hoadley, see Trans. A. S. M. E., vi. 702. Compare also Henry M. Howe, Trans. A. I. M. E., xviii. 728. For accuracy corrections are required for variations in the specific heat of the water and of the metal at different temperatures, for loss of heat by radiation from the metal during the transfer from the furnace to the water, and from the apparatus during the heating of the water; also for the heatabsorbing capacity of the vessel containing the water. Fire-clay or fire-brick may be used instead of the metal ball. Le Chatelier's Thermo-electric Pyrometer.-For a very full description see paper by Joseph Struthers, School of Mines Quarterly, vol. xii, 1891; also, paper read by Prof. Roberts-Austen before the Iron and Steel Institute, May 7, 1891. The principle upon which this pyrometer is constructed is the measure. ment of a current of electricity produced by heating a couple composed of two wires, one platinum and the other platinum with 10% rhodium-the current produced being measured by a galvanometer. The composition of the gas which surrounds the couple has no influence on the indications. When temperatures above 2500° F. are to be studied, the wires must have an isolating support and must be of good length, so that all parts of a furnace can be reached. For a Siemens furnace, about 11% feet is the general length. The wires are supported in an iron tube, 1⁄2 inch interior diameter and held in place by a cylinder of refractory clay having two holes bored through, in which the wires are placed. The shortness of time (five seconds) allows the temperature to be taken without deteriorating the tube. Tests made by this pyrometer in measuring furnace temperatures under a great variety of conditions show that the readings of the scale uncorrected are always within 45° F. of the correct temperature, and in the majority of industrial measurements this is sufficiently accurate. Le Chatelier's pyrometer is sold by Queen & Co., of Philadelphia. Graduation of Le Chatelier's Pyrometer.-W. C. RobertsAusten in his Researches on the Properties of Alloys, Proc. Inst. M. E. 1892, says: The electromotive force produced by heating the thermo-junction to any given temperature is measured by the movement of the spot of light on the scale graduated in millimetres. A formula for converting the divisions of the scale into thermometric degrees is given by M. Le Chatelier; but it is better to calibrate the scale by heating the thermo-junction to temperatures which have been very carefully determined by the aid of the airthermometer, and then to plot the curve from the data so obtained. Many fusion and boiling-points have been established by concurrent evidence of various kinds, and are now very generally accepted. The following table contains certain of these: The Temperatures Developed in Industrial Furnaces.M. Le Chatelier states that by means of his pyrometer he has discovered that the temperatures which occur in melting steel and in other industrial operations have been hitherto overestimated. M. Le Chatelier finds the melting heat of white cast iron 1135° (2075° F.). and that of gray cast iron 1220° (2228° F.). Mild steel melts at 1475° (2687 F.), semi-mild at 1455° (2651° F.), and hard steel at 1410° (2570° F.). The furnace for hard porcelain at the end of the baking has a heat of 1370° (2498° F.). The heat of a normal incandescent lamp is 1800° (3272° F.), but it may be pushed to beyond 2100° (3812° F.). Prof. Roberts-Austen (Recent Advances in Pyrometry, Trans. A. I. M. E., Chicago Meeting, 1893) gives an excellent description of modern forms of pyrometers. The following are some of his temperature determinations. GOLD-MELTING, ROYAL MINT. Degrees. Degrees. Centigrade. Temperature of standard alloy, pouring into moulds. 1180 1147 a previous occasion, by thermo-couple)..... Temperature of standard alloy, pouring into mould...... 980 Cupola furnace, No. 2 cast iron, pouring into ladle.. Fahr. 2156 2097 1634 1796 2993 1580. 2876 930 1706 1600 2912 The following determinations have been effected by M. Le Chatelier: A. Fuel gas near gas generator... B. Fuel gas entering into bottom of regenerator chamber Completion of conversion. 1500 2732 Molten steel. In the ladle-Commencement of casting.. 1580 In the moulds. 1520 2768 For very mild (soft) steel the temperatures are higher by 50° C. Hobson's Hot-blast Pyrometer consists of a brass chamber having three hollow arms and a handle. The hot blast enters one of the arms and induces a current of atmospheric air to flow into the second arm. The two currents mix in the chamber and flow out through the third arm, in which the temperature of the mixture is taken by a mercury thermometer. The openings in the arms are adjusted so that the proportion of hot blast to the atmospheric air remains the same. The Wiborgh Air-pyrometer. (E. Trotz, Trans. A. I. M. E. 1892.) The inventor using the expansion-coefficient of air, as determined by Gay-Lussac, Dulon, Rudberg, and Regnault, bases his construction on the following theory: If an air-volume, V, enclosed in a porcelain globe and connected through a capillary pipe with the outside air, be heated to the temperature T (which is to be determined) and thereupon the connection be discontinued, and there be then forced into the globe containing V another volume of air V' of known temperature t, which was previously under atmospheric pressure H, the additional pressure h, due to the addition of the air-volume V' to the air-volume V, can be measured by a manometer. But this pressure is of course a function of the temperature T. Before the introduction of V', we have the two separate air-volumes, Vat the temperature T and V' at the temperature t, both under the atmospheric pressure H. After the forcing in of V' into the globe, we have, on the contrary, only the volume V of the temperature T, but under the pressure H+h. The Wiborgh Air-pyrometer is adapted for use at blast-furnaces, smelting. works, hardening and tempering furnaces, etc., where determinations of temperature from 0° to 2400° F. are required. Seger's Fire-clay Pyrometer. (H. M. Howe, Eng. and Mining Jour., June 7, 1890.)-Professor Seger uses a series of slender triangular fire-clay pyramids, about 3 inches high and 5% inch wide at the base, and each a little less fusible than the next; these he calls "normal pyramids" ("normal-kegel "). When the series is placed in a furnace whose temperature is gradually raised, one after another will bend over as its range of plasticity is reached; and the temperature at which it has bent, or "wept,' so far that its apex touches the hearth of the furnace or other level surface on which it is standing, is selected as a point on Seger's scale. These points may be accurately determined by some absolute method, or they may merely serve to give comparative results. Unfortunately, these pyramids afford no indications when the temperature is stationary or falling. Mesuré and Nouel's Pyrometric Telescope. (Ibid.)-Mesuré and Nouel's pyrometric telescope gives us an immediate determination of the temperature of incandescent bodies, and is therefore much better adapted to cases where a great number of observations are to be made, and at short intervals, than Seger's. Such cases arise in the careful heating of steel. The little telescope, carried in the pocket or hung from the neck, can be used by foreman or heater at any moment. It is based on the fact that a plate of quartz, cut at right angles to the axis, rotates the plane of polarization of polarized light to a degree nearly inversely proportional to the square of the length of the waves; and, further, on the fact that while a body at dull redness merely emits red light, as the temperature rises, the orange, yellow, green, and blue waves successively appear. If, now, such a plate of quartz is placed between two Nicol prisms at right angles, "a ray of monochromatic light which passes the first, or polarizer, and is watched through the second, or analyzer, is not extinguished as it was before interposing the quartz. Part of the light passes the analyzer, and, to again extinguish it, we must turn one of the Nicols a certain angle," depending on the length of the waves of light, and hence on the temperature of the incandescent object which emits this light. Hence the angle through which we must turn the analyzer to extinguish the light is a measure of the temperature of the object observed. For illustrated descriptions of different kinds of pyrometers see circular issued by Queen & Co., Philadelphia. The Uehling and Steinbart Pyrometer. (For illustrated description see Engineering, Aug. 24, 1894.)-The action of the pyrometer is based on a principle which involves the law of the flow of gas through minute apertures in the following manner: If a closed tube or chamber be supplied with a minute inlet and a minute outlet aperture and air be caused by a constant suction to flow in through one and out through the other of these apertures, the tension in the chamber between the apertures will vary with |