Volume 2

Chemistry, theoretical, practical, and analytical : as applied and relating to the arts and manufactures / by Dr. Sheridan Muspratt.

  • Muspratt, Sheridan, 1821-1871.
Date:
[1860]
    FUEL Radiation of Heat—The Thebhopile. From these results it appears that the substances employed are moro strongly heated in proportion as their thickness is greater, within certain limits. Mel- loni and Lesue arrived at a different conclusion, in consequence of having used plates of such thickness that only a small proportion of the heat absorbed could penetrate to the side which was turned towards the thermoscope ; Knoblauch, on the contrary, employed media, the thickness of which was not too great to allow each successive layer to be heated, and thus to act upon the metallic surface. The Thermopile.—Mglloni found that caloric was transmitted by many bodies which were impervious to light, and these he termed diathermous or heat-trans- mitting, in contradistinction to diaphanous or trans- parent bodies. In conducting his experiments on this subject, he employed, in connection with a very delicate galvanometer, an instrument which he termed a thermo- pile. This consisted of a number of pairs of bars of bis- muth and antimony joined together, and so enclosed in a cyliuder—see Fig. 9—that by turning one end of the latter towards the region whence the heat is radiated, it would fall upon the alter- nate points of junction of the bars of metal, and ex- cite, as is well known, a cur- rent of electricity, the intensity of which is in propor- tion to the amount of heat received. By wires con- necting both ends, x and y, of this battery with the galvanometer, the electricity was measured ; and thus was obtained a ready and delicate method of estimat- | ing the amount of heat transmitted. Fig. 10 shows this arrangement, in which the pile is introduced. Both ends of the bars are blackened with soot, in order that the absorption of the rays of heat falling on them may be the more complete. By means of screens, a and b, the pile is preserved from the effects of cur- rents of air; b has a conical shape, and is intended to concentrate the rays of heat when very feeble on the end of the pile. The pile is firmly bound, as represented at p, and fixed to a sliding stand in a perfectly horizontal position, x and y are bars in connection with the opposite ends of those of the pile, to which the wires g and h are screwed at one end, the other being in connection with the helice of coated wire that serves to act upon the galvanometer at m and n. The galvanometer is composed of a carefully selected and well magnetized pair of needles, F‘g- u- bound together with fine copper wire, as seen in Fig. 11, and freely suspended in the middle of a glass cylin- der, c, by a single fibre of silk which is attached to a ball,/, by turning which the needle may be raised or lowered at will. The helice, or multiplicator, in the 'midst of which the needles are suspended, is constructed by winding Fig. 0. Fig. 10. \ B coated copper wire round a raetul frame in forty layers, and properly isolated. Both the cylinder and multiplier are fixed to a table, so that when the needle hangs iee y from f it will rest in the centre of the closely divided circle, pointing to zero in the plane of tho mag- netic meridian. When the pile and multiplier are connected, the least change of temperature that may
    affect the ends of the compound metals deflects the needle, and the amount of this deflection may be noted on the divided circle. When working with this instrument, the first deviation of the needle must be carefully distinguished from the proper angle of deflec- tion—id est, from the angle which it makes with the magnetic meridian, when unaffected by any electrical currents. If the equilibrium of the galvanometer is disturbed by a stream of electricity, it returns from the point to which it has been deflected, with a certain de- gree of velocity, which causes it to go beyond zero: it will oscillate thus for some time before the stationary line is attained. To avoid the delay which these oscillations would occasion, Melloni ascertained by experiments the ratio between the first and final deflection—id est, he determined how large the final deflection is that cor- responds to the original one. The knowledge of this relation offers great advantages, inasmuch as each ex- periment lasts only ten or twelve seconds, whereas, if the operator had to wait till the needle became station- ary, several minutes would be required. If the principle of the apparatus comes to be con- sidered, it will be evident that the relation which exists between the difference of temperature of the solder- ing points of the pile and the deflection of the needle cannot be ascertained in an absolute manner. To give the deflection a definite value as to the amount of caloric, Melloni had to determine—after establishing the fact, that the strength of the electric stream from a pile of bismuth and antimony is proportional to the difference of temperature of the soldering points—the relation of the deviation of the needle to the strength of the stream. For this purpose, he placed at either end of the pile a constant source of heat—such as a Locatelli’s lamp—at such a distance, that when working alone at one end it caused a deflection of about 40° to the right, and, when placed at the other, the deflection marked 35° to the left side; but, when the sources of heat were permitted to operate on both ends at once, the deflection to the right marked 15°. From this behavior it was inferred that the difference between 40° and 35° corresponded with 15° counted from 0°. By operating in this way, it may easily be understood how, by changing these experiments, a table may be constructed, the first column of which expresses the observed deflection, and the second the corresponding number of degrees which would be ar- rived at if the deviation were proportional to the strength of the stream, and the action of the latter on the needle were not the weaker the more the latter is deflected. With the apparatus employed by Melloni, the numbers on both columns up to 20° were equal— that is to say, till 20° the deflection of the needle is proportioned to the strength of the stream; but with the observed deflection, 25, 30, 35, 40, and 45°, cor- respond the value 27, 35, 47, 62, and 83° of the second column. A stream, therefore, that produces a deflec- tion of 40° is 62 times stronger than another that causes only a variation of one degree. Melloni so arranged his experiments that the deflections were always less than 30°. To return to the manner of working the apparatus ; if the body emitting rays of heat be fixed in the focus of a reflector that impels the lays of heat in a horizontal line with the pile, and one of the ends of the latter be exposed to them, the effect upon the needle will, upon the principles already laid down, be indica- tive of the quantity of radiated heat. When different sources of caloric are thus presented in succession, the register of the deflection of the galvanometer will show the difference of radiation. Transmission of Heat through Thin Plates.—The bodies employed by Melloni were a Locatelli’s lamp, fixed as at A in Fig. 10; a coil of pla- tinum kept at incandescence by the flame of alcohol, as seen in Fig. 12; a blackened copper foil fixed to a stand, and heated with a spirit lamp to 752°, as repre- sented in Fig. 13; and a brass canister filled with water kept at 212°, as shown in Fig. 14. One or other Fig. 12. Fig. 13. Fig. 14. of these was placed on a movable support, as at A, behind the perforated screen, B, the rays being con- centrated when necessary by the reflector at A, and received at a certain distance from this upon the thermoscope. The sensitiveness of the latter was proved by placing a double screen of polished copper, D, between it and the source of heat, so as to intercept all the calorific rays, and observing the deflection of the needle of the galvanometer in c, when the screen was removed. The elevation of temperature produced by the direct action of the radiating body being thus known, the substance to be examined was then intro- duced in the place of the screen, as at E. By observ- ing the difference of temperature as indicated by the needle now, and comparing it with the effect pro- duced without the screen, the proportion of heat, trans- mitted by any interposed body was at once ascer- tained. By this method, Melloni found that plates of rock-salt of great transparency, and varying in thickness from one-twelfth of an inch to two or three inches, transmitted ninety-two out of every hundred rays of heat which fell upon them, no matter from what source derived. As the remainder of the rays were found to be reflected from both surfaces of the plate, it may hence be concluded that what the color- less plate of glass is to rays of light, the plate of rock- salt is to those of heat. Sometimes the calorific rays which pass through one body are intercepted by a plate of another body, or by another plate of the same. In experimenting upon this, Melloni found that the caloric which lias passed through one plate of glass, becomes less subject to absorption in passing through a second and a third plate of the same material. Thus, of one thousand rays of heat from an oil lamp,
    FUEL Specific Heat. t four hundred and fifty-one were intercepted in passing through four plates of equal thickness, and flame from an argand oil-lamp, the annexed results were obtained:— Of these the first plate intercepted “ the second “ “ the third “ “ the fourth “ 381 43 18 9 451 It was found by Delaroche that the higher the temperature of the source of heat, the greater in proportion to the whole is the quantity which passes through a plate or screen of glass. He observed that from a body heated to 182° only one-fortieth of the whole permeated, whereas when the tem- perature was 346° the one-sixteenth passed through, and when the heat was raised to 960° I ahr. as much as one-fourth of the whole amount of heat was transmitted. To show the independence of diather- macy and translucency, Melloni took a blackened ball of copper heated to 400° Fahr., and placing it midway between the blackened bulbs of two thermo- scopes so that they might receive an equal amount of heat, noted the effect; then fixing between the ball and the instruments for measuring the heat plates of rock-salt and glass of equal thickness, it was quickly observed that the temperature of the bulb behind the former was much more elevated than the other—thus showing that more heat passed through it than through the glass one, although in transparency they were equal. In liquids this inde- pendenbe is still more manifest. Thus, out of one hundred rays that fell from an argand lamp on each of four fluids equally transparent,-—namely, water, oil of turpentine, ether, and sulphuric acid—the number of rays of heat transmitted were:— Water 11 Sulphuric acid . .. 17 Ether 21 Oil of turpentine 31 The following is a tabulated statement of some of the results ascertained by Melloni on the subject of the transmission of heat through various bodies of equal thickness:— Transmission of 100 rays of heat from 'o • ■*» g as . Name of the interposed substance. 'gs .2 =* Common thickness 01U2 inch. .*2 -e -2 e.?» S.U a « a 9 - / ~ — O C N 0,00 Rock salt, transparent and colorless, 92 .. 92 .. 92 .. 92 Sicilian sulphur, yellow, 74 .. 77 .. 60 .. 54 Fluor spar, limpid, 72 .. 69 !. 42 ” 33 Rock crystal, cloudy, 65 .. 65 .. 65 .. 65 “f.O’h- 54 .. 23 .. 13 .. 0 r lint glass, 67 # Plate glass, 39 1‘. 24 " 6 0 Iceland spar 39 .. 28 .. 6 .. 0 Rock crystal, limpid, 38 .. 28 .. 6 .. 0 “ brownish, 37 .. 28 .! 6 !! 0 Tourmaline, dark green, 18 .. 6 3 0 9«tnc^id .. 2.; 0:: o Alum, g _ _ 2 0 0 Sugar candy, colorless, ’ ’ s’’ 1 0 0 flno"aPar 8 " 6." 4;; 3 lee, transparent and colorless, 6.. O.. 0 0 Similar experiments being performed with liquids contained in glass, the stratum being 0'362 inch in thickness, and the source of heat being in each case Bisulphide of carbon, 63 Bichloride of sulphur, red-brown, 63 Tcrchloride of phosphorite, 62 Essence of turpentine, 31 Colza oil, yellowish, 30 Olive oil, greenish, 30 Ether, 21 Sulphuric acid, colorless, 17 “ brown, 17 Nitric acid, 15 Alcohol, 15 Distilled water, 11 The fact that bodies which are pervious to light do not maintain the same relation to heat, is beet exemplified by sulphate of copper, which permits the passage of blue light abundantly, but absolutely inter- cepts caloric. On the contrary, the opaque glass which is used for polarizing mirrors, allows the thermal rays to pass, but quite intercepts the light; and smoked rock-salt and black mica act in a similar way. Badiated heat is not only transmitted, hut refracted in the same manner as light. This is proved by the well-known property of convex lenses or burning glasses, which concentrate not only the light, but the rays of heat, in the focus. Caloric further resembles light in appa- rently consisting of rays which possess different d< grees of refrangibility, as may be proved by subjecting a beam of light to the action of a transparent prism of rock-salt, and examining the spectrum so obtained I*y means of a delicate thermometer. In this case it will be found that the heat varies at different parts of the spectrum ; and experiment has shown that when the rays of the sun are operated upon, the most part of the rays of heat are less refrangible than even the red light; the maximum temperature being found at some distance below the extreme red. The refrangibility of the rays varies with the source of heat; the higher the temperature the greater is the refraction. For ex- ample, the rays of heat emitted from an argand lamp are refracted all over the spectrum, but the maximum intensity is about the middle; from ignited platinum the maximum falls nearer to the red; from copper heated to 750°, nearer still; and so on till the temper- ature of the source cools to 212°. when it is found to emit scarcely any of the more refrangible rays. Specific Heat.—Bodies have different capacities for heat; or, in other words, the application of the same amount of caloric will elevate the temperature of dif- ferent bodies unequally. This capacity for caloric, differing in different bodies, is termed their specific heat. If a certain weight of water, at the ordinary tem- perature of the atmosphere, be mixed with an equal quantity of this liquid raised to a higher degree, the mixture will indicate a mean between these extremes; but if another liquid, such as oil or mercury, be added, instead of the second portion of water, a great differ- ence will be observed. When a measure of water at 60° Fahr. is agitated with as much mercury at 140°, the compound, instead of marking 100° as in the pre- ceding case, will indicate only 86 6°. Again, if mer- cury at 40° be added to an equal hulk of water at 156°, the heat of the latter is reduced by 3-7°, which, being absorbed by the fluid metal, raises it to 152‘3°, so that
    No text description is available for this image
    FUEL Latent Caloric, or Heat or Fluidity. AKlturttt in foot. o To>mpernturii at thu Kquator. 80 Temperature at tin: Tolci. 0° 5000 64.4 ... — 18-5 1-0000 48-4 ... — 37-8 1•5OO0 31-4 ... — 58-8 o-noivi 12-8 — 82-1 9-^nnn 7-6 ... — 109-1 3-0000 30-7 ... — 140-3 Taking the limit of the atmosphere to be forty-five miles high, it is probable that the most subtle and per- manent gases would not only be condensed but even sohdilled by the degree of cold which would there act upon them, could the ordinary pressure on the surface of the globe be sustained. Elevation of temperature also increases the capacity of bodies for caloric, and hence it requires the applica- tion of a greater heat to raise their temperature when they have combined with a large amount of caloric than in the contrary case. The appended table shows the increasing capacity of the bodies enumerated within the limits assigned with matter, counteracted the cohesive attraction of the atoms of solids, ami thus explaining the pheno- menon of liquefaction, as that condition in which the cohesive and repellent forces are in exact equilibrium. This view of the subject appears to be well founded ; and it is believed that the condition in which matter is found, as solid, liquid, or aeriform, entirely depends on the amount of caloric in combination with it. This has been proved with reference to most substances, and there is strong ground to believe that even tire most refractory may be converted into an elastic vapor, and the most permanent of the latter class rendered solid, by the communication of heat on the one hand, and its abstraction on the other. Solids very much vary in the phenomena which at- tend their conversion to fluidity: while many of them are transmuted at once to this state, others pass through various stages of softness previous to their assuming it. The following table expresses the melting or solidi- fying point of a few bodies:— Capacity for heat be- a“me' , tween 32° and 212°. Mercury, 0-0330 Platinum, -0335 Antimony, ’0507 Silver...... ‘0557 Zincv -0927 Copper, -0949 Iron, -1098 Glass,. T770 Water ranks first of all bodies yet known in its increasing capacity for heat, at an increased tempera- ture. Between 22° and 32° Fahr. the specific heat of solidified water is O'505, assuming it to be unity in the liquid state, and if converted into steam the specific heat of the vapor increases with its state of dilatation. This property contributes in no small degree towards moderating the rapidity of the transitions from heat to cold, and vice versa, in the atmosphere, owing to the large quantity of heat which is absorbed by or emitted from the water of the ocean, when the temperature ex- ceeds or falls short of the normal range. In the determination of the specific heat of vapors, much remains to he done, to arrive at satisfactory results. Dulong and Petit endeavored to establish the re- lation of the specific heat of bodies and their atomic equivalent. This relation they expressed by a general law, that the specific heats of elementary bodies vary inversely with their atomic weights; and that an atom of any one simple substance, whether small or large, has the same capacity for caloric, and requires the same quantity of this imponderable to raise its temperature through a given number of degrees, as an atom of any other element. Kegnault, by observing that the product of the specific heat into the atomic weight is nearly a constant quantity, represented by 3'2°, ad- vanced a considerable step towards establishing tho existence of this general law; still, there aro many exceptions which have not yet been reconciled with it. Latent Caloric, or Heat of Fluidity.—Black asserted, many years ago, that fluidity was owing to the chemical combination of matter with a certain amount of heat, which could not bo detected by the thermometer. To this he applied the term heat of fluidity, or latent, heat, assuming that heat, by its chemical combination Drr. Fakr Lead melts at 612 Bismuth, 476 Tin, 442 Sulphur, 232 Wax, 142 Spermaceti, 112 Phosphorus, 108 Tallow, 92 Oil of Anise, 50 Olive oil, 36 Ice, 32 Milk, 30 Wines, 20 Oil of turpentine, 14 Mercury, —39 Licpiid ammonia, —46 Ether, —46 It must be remarked, however, with regard to the above table, that when the preceding substances in a melted state are cooled down, they do not solidify as soon as the foregoing temperatures have been attained. A further quantity of caloric must be abstracted before they assume the solid form; and, under some circum- stances, this abstraction of caloric may actually be in- dicated by a depression of the sensible temperature extending to several degrees before any change occurs. Thus, water, which, in the form of ice, always melts exactly at 32°, may be cooled down to 8°, or even to 5°, Avithout altering its state of aggregation. To produce this curious effect, it is necessary that no solid substance be introduced into the water, and that it be kept perfectly still*; for, should the least move- ment of the liquid be occasioned, it Avould immediately begin to solidify, and the mass would rise to 32°. The sudden rise of temperature is occasioned by the evolution of the caloric which was required to liquefy the mass, and, consequently, had remained in- sensible to tho instruments usually employed for its detection. This caloric is generally called latent heat-, but the same term is applied to that which is contained in solid bodies, as well as to the heat of fluidity. Much caloric is always absorbed and becomes latent by the solution of solid bodies in various menstrua, and the degree of cold which this occasions is often very great. For philosophical, and often for industrial pur- poses, the method followed to effect a reduction of the Ditto between 32° and 572°. 0-0350 •0355 •0549 •0611 •1015 •1013 •1218 ■1900