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 firo-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° T.), and hard steel at 1410° (2570° F.). The furnace for hard porcelain at the end of the baking has a heat of 1870° (2498° F.). The heat of a normal incandescent lamp is 1800° (3272° F.), but it may be pushed to beyond C100° (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. Temperature of standard alloy, pouring into moulds. 1180 SILVER-MELTING, ROYAL MINT. 1147 Temperature of standard alloy, pouring into mould...... 980 Degrees. 2156 2097 1634 1796 2993 1580 2876 980 Cupola furnace, No. 2 cast iron, pouring into ladle.. 1706 1600 2912 C. Metal in ingot mould. D. Ingot in reheating furnace..................................................... OPEN-HEARTH FURNACE (Siemens). Semi-Mild Steel. A. Fuel gas near gas generator... 720 1328 B. Fuel gas entering into bottom of regenerator chamber 400 Molten steel. In the ladle-Commencement of casting.. 1580 2782 2876 1490 2714 1520 2768 For very mild (soft) steel the temperatures are higher by 50° C. SIEMENS CRUCIBLE OR POT FURNACE. 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, smeltingworks, 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.)-Mosuré 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 descripuous 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 the difference of temperature between the inflowing and outflowing air. If the inflowing air be made to vary with the temperature to be measured, and the outflowing air be kept at a certain constant temperature, then the tension in the space or chamber between the two apertures will be an exact measure of the temperature of the inflowing air, and hence of the temperature to be measured. In operation it is necessary that the air be sucked into it through the first minute aperture at the temperature to be measured, through the second aperture at a lower but constant temperature, and that the suction be of a constant tension. The first aperture is therefore located in the end of a platinum tube in the bulb of a porcelain tube over which the hot blast sweeps, or inserted into the pipe or chamber containing the gas whose temperature is to be ascertained. The second aperture is located in a coupling, surrounded by boiling water, and the suction is obtained by an aspirator aud regulated by a column of water of constant height. The tension in the chamber between the apertures is indicated by a manometer. The Air-thermometer. (Prof. R. C. Carpenter, Eng'g News, Jan. 5, 1893.)-Air is a perfect thermometric substance, and if a given mass of air be considered, the product of its pressure and volume divided by its absolute temperature is in every case constant. If the volume of air remain constant, the temperature will vary with the pressure; if the pressure remain constant the temperature will vary with the volume. As the former condition is more easily attained air-thermometers are usually constructed of constant volume, in which case the absolute temperature will vary with the pressure. If we denote pressure by p and p', the corresponding absolute temper. atures by Tand T', we should have The absolute.temperature Tis to be considered in every case 460 higher than the thermometer-reading expressed in Fahrenheit degrees. From the form of the above equation, if the pressure p corresponding to a known absolute temperature T be known, T' can be found. The quotient T/p is a constant which may be used in all determinations with the instrument. The pressure on the instrument can be expressed in inches of mercury, and is evidently the atmospheric pressure bas shown by a barometer, plus or minus an additional amount h shown by a manometer attached to the air thermometer. That is, in general, p = b ± h. The temperature of 32° F. is fixed as the point of melting ice, in which case T460+32 = 492° F. This temperature can be produced by surrounding the bulb in melting ice and leaving several minutes, so that the temperature of the confined air shall acquire that of the surrounding ice. When the air is at that temperature, note the reading of the attached manometer h, and that of a barometer; the sum will be the value of p corresponding to the absolute temperature of 492° F. The constant of the instrument, K = 492÷p, once obtained, can be used in all future determinations. High Temperatures judged by Color.-The temperature of a body can be approximately judged by the experienced eye unaided, and M. Pouillet has constructed a table, which has been generally accepted, giving the colors and their corresponding temperature as below: The results obtained, however, are unsatisfactory, as much depends on the susceptibility of the retina of the observer to light as well as the degree of illumination under which the observation is made. A bright bar of iron, slowly heated in contact with air, assumes the following tints at annexed temperatures (Claudel): The boiling points of liquids increase as the pressure increases. The boiling point of water at any given pressure is the same as the temperature of saturated steam of the same pressure. (See Steam.) MELTING-POINTS OF VARIOUS SUBSTANCES. The following figures are given by Clark (on the authority of Pouillet, Claudel, and Wilson), except those marked *, which are given by Prof. Roberts-Austen in his description of the Le Chatelier pyrometer. These latter are probably the most reliable figures. Sulphurous acid Carbonic acid. Alloy, 1 tin, 1 lead.. 370 to 466° F. 148° F. 108 442 to 446 32 45 92 Phosphorus 112 Antimony Calcium.. 810 to 1150 1157* 1200 Full red heat. Acetic acid. Cobalt, nickel, and manganese, fusible in highest heat of a forge. Tungsten and chromium, not fusible in forge, but soften and agglomerate. Platinum and iridium, fusible only before the oxyhydrogen blowpipe. QUANTITATIVE MEASUREMENT OF HEAT. Unit of Heat.-The British unit of heat, or British thermal unit (B. T. U.), is that quantity of heat which is required to raise the temperature of 1 lb. of pure water 1° Fahr., at or near 39°.1 F., the temperature of maximum density of water. The French thermal unit, or calorie, is that quantity of heat which is required to raise the temperature of 1 kilogramme of pure water 1° Cent., at or about 4° C., which is equivalent to 39°.1 F. 1 French calorie 3.968 British thermal units; 1 B. T. U. = .252 calorie. The "pound calorie " is sometimes used by English writers; it is the quan |