Temperature and Elastic Force of the Vapours of different Liquids—Rankine's Formula. In Regnault's formulæ the elastic force (F) of the steam is expressed in millimètres of mercury in the latitude of Paris, and at a height of sixty mètres above the level of the sea. The equivalent length of the mercurial column in English inches (i) at the level of the sea and at the equator is expressed by the formula 87 or Log. i=a,,+ba,,T+c3,,T, where a,, = a + 2.5964748382. Log. a,,= 555497 log. a; log. ß,, =555497 log. ß, and T denotes the temperature in degrees Fahrenheit. The first of the tables given in page 88, computed by these formulæ, has been taken with some abridgments from Dixon's very excellent Treatise on Heat. The second table, also based upon Regnault's experiments, was computed by Mr. Lewis Oldrick, C.E., from Mr. Clark's formula, and constitutes a portion of a table given in Molesworth's valuable pocket-book of engineering formulæ and memoranda. This table shows nearly the same results as the table given at page 445. M. Regnault extended his researches to the pressure of other vapours besides that of water. The following are the results he obtained with alcohol, ether, sulphuret of carbon, chloroform, and essence of turpentine : *555497T •555497T TEMPERATURE AND ELASTIC FORCE OF THE VAPOURS OF DIFFERENT LIQUIDS, BY M. REGNAULT. case, p = (a + b T), was first proposed by Dr. Thomas Young nearly sixty years ago. The same formula, with the index n = 5, was used by Arago and Dulong in 1829, and with the index n=6, by Tredgold about 1828.† The history of that and many other formulæ is given by M. Regnault in his Relation des Expériences, &c., vol. i. pp. 582 et seq. He gives the preference, for purposes of interpolation, to the formula proposed by Biot in 1844, log, p = a + ba2 + c ß', the five constants a, b, c, a, ß, being deduced from five experimental data for each fluid. Young's formula, it is true, contains three constants only, a, b, and n; but, as M. Regnault has shown, it is deficient in exactness. It has, in particular, two faults-that for a certain a temperature, T = ——, it makes the pressure of the fluid disappear and become negative b below that temperature, which is exceedingly improbable; and that it makes the pressure of every vapour increase without limit as the temperature rises-a result contradicted by the experiments of M. Regnault, which (as he states in vol. ii. p. 647) point to the conclusion that "the elastic force of a vapour does not increase indefinitely with the temperature, but converges towards a limit which it cannot exceed." The first of those faults, but not the second, exists in Roche's formula, besides agreeing very closely with experiment at all temperatures, gives the following results: That every substance can exist in the state of vapour at all temperatures above the absolute zero; and that the pressure of saturation of every vapour tends towards a limit as the temperature increases-the latter result being in accordance with the conclusion deduced by M. Regnault from his experiments. It may be remarked that if vapours at saturation were perfectly gaseous, it can be proved from the laws of thermo-dynamics that their pressures of saturation would be given by the formula, b cc, hyp. log. t; (c'-c) t hyp.log. pa- c'-c where c is the specific heat of the gas at constant volume, c' its specific heat at constant pressure, c' the specific heat of the liquid, b the total heat of gasefication of the fluid at the absolute zero, from which t is reckoned, and a a constant to be determined by experiments on the pressure corresponding to a given boiling-point. So far as I know, this proposition has not before been published, but its demonstration will be obvious to anyone acquainted with the principles of thermo-dynamics. When the formula is applied to steam, it gives pressures agreeing very closely with actual pressures of steam from 0° to 160° C., but above the latter temperature the effect of the deviation of the vapour from the perfectly gaseous condition becomes considerable; so that at 220° C. the pressure given by the formula for a perfect gas is about one-fiftieth part less than the actual pressure. Since the above was written I have seen the formula proposed by Mr. Edmonds in the Philosophical Magazine for March, 1865. In the notation of the present paper that formula is thus expressed : 10g. p = b{1 - (-)"}· It obviously possesses the same general character with my formula of 1849, viz. it makes the pressure a function of the reciprocal of the absolute temperature, containing three constants, vanishing at the absolute zero, and converging towards a limit when the temperature increases indefinitely; and it is satisfactory to me to see that Mr. Edmonds, by an independent investigation, has arrived at a result which thus agrees in the main with mine. 66.51 6628 321 186 22 322 188 86 188 22 323 191 53 190.88 324 19423 193 ⚫57 325 196 96 196 29 326 199 73 19905 327 202 52 201 ⚫83 328 205 34 204 64 7469 329 208 20 20749 75.96 330 211 08 210 36 77 24 331 21400 213 27 185 59 367 34205 340 88 24 237.8 1036 79 311-1 337 134 349-5 205 345·13 349.41 353 73 25 240.1 996 80 312.0 333 135 350-1 203 358 10 28 362 ⚫50 29 366 95 30 27 244.4 926 82 313.6 246.4 895 83 314-5 321 248.4 866 84 315.3 318 250.4 838 85 316.1 314 252.2 813 86 316.9 311 254.1 789 87 317.8 308 255.9 767 88 318.6 305 257.6 746 89 319.4 301 259.3 726 90 320-2 298 260.9 707 91 321.0 295 37 262.6 688 92 321.7 292 38 264.2 671 93 325 322.5 289 277.1 550 102 329.1 265 278.4 539 103 329.9 262 279-7 529 104 330'6 260 281.0 518 105 331.3 257 282.3 509 106 331.9 283.5 500 107 332.6 253 284.7 491 108 333.3 285.9 482 109 334.0 287.1 474 110 334.6 247 288-2 466 111 245 335.3 57 289.3 458 112 336.0 243 58 290.4 451 113 336.7 241 291.6 444 114 337:4 239 292.7 437 115 338.0 237 293.8 430 116 338.6 235 294.8 424 117 339.3 233 295.9 417 118 231 339.9 296.9 411 119 229 340.5 65 298'0 405 120 341·1 227 66 299.0 399 121 341.8 225 67 300.0 393 122 342.4 224 68 300.9 388 123 343.0 222 69 301.9 383 124 343.6 221 185 375-3 151 190 377-5 195 379-7 148 144 200 381-7 141 255 210 386-0 135 220 389-9 129 251 230 393 8 123 | 249 240 397.5 119. 250 401-1 114 260 404-5 110 CHAP. II. GENERAL THEORY OF THE STEAM ENGINE. THE steam engine is a machine in which the motive power of heat is utilised with a certain measure of efficiency, and the theory of its action forms a part of the general theory of the mechanical value of heat, and the mutual convertibility of heat and mechanical power. All substances exposed to two different temperatures are capable of developing power, and in the development of power there is heat consumed, of equivalent value to the power produced, and the greater the extremes of temperature, the greater will be the power generated. Since, too, all substances exposed to the same extremes of temperature will develope the same amount of power, it follows that, other things being equal, those substances are most suitable for the development of power, which can be subjected to the greatest extremes of temperature without practical inconvenience. A metal alternately expanded by heat and contracted by cold, will develope power and consume heat, with the same efficacy as a liquid or a vapour, subjected to the same extremes of temperature, and as gases may be subjected to the greatest extremes of temperature without any change of their constitution, they appear to be the substances best adapted for the production of power. In the steam engine, the extremes of temperature or the difference in the temperature of the boiler and the condenser is not very great, and air engines, therefore, in which greater extremes of temperature may be employed, are more suitable than steam engines for the production of power. Hitherto, however, certain practical difficulties have prevented the employment of air engines. When those difficulties have been surmounted, as no doubt they will be, the steam engine will be superseded by the air engine. Heat, electricity, light, and all other imponderable agents, are merely different forms of mechanical power, and in the proportion in which they create mechanical power, they themselves disappear. The cheapest source of a mechanical power that will be available in all situations, is, so far as we yet know, the combustion of coal. Electricity and galvanism have been proposed as motive powers, and may be used as such, but they are much more expensive than coal. Mr. Joule has ascertained by his experiments that a grain of zinc, consumed in a galvanic battery, will generate sufficient power to raise a weight of 145-6 lbs. through the height of one foot; whereas a grain of coal, consumed by combustion, will generate sufficient power to raise 1261-45 lbs. to the height of one foot. A grain of zinc consumed in a Daniell's battery will generate enough heat to raise the temperature of a pound of water 1°.634. Mr. Joule has very conclusively shown by his experiments that the heat required to raise a pound of water one degree in temperature by Fahrenheit's thermometer, would suffice if utilised in a perfect engine, to raise 772 lbs. through the height of one foot. This performance is, therefore, called the Mechanical Equivalent of Heat, and by the aid of it we can easily tell how far the performance of any given engine falls short of the theoretical value of the coal. If a degree of Fahrenheit will raise 772 lbs. through a height of one foot, then a degree of the centigrade thermometer, which is nearly twice greater, will raise 1390 lbs. through a height of one foot. The zero of the centigrade scale is the freezing point of water; the zero of the Fahrenheit scale is 32 Fahrenheit degrees below the freezing point of water, and the absolute zero or point of the absolute privation of heat is believed to be 274 centigrade degrees, or 494 Fahrenheit degrees below the freezing point of water. Now it has been demonstrated by Thomson and These are Mr. Joule's figures. The point of absolute zero is 'now reckoned to be -461-2° Fahrenheit, or 493-2° below the freezing point of water. others that the proportion of heat converted into mechanical effect by any perfect engine will be equal to the range of temperature between the boiler and condenser, or the heating and cooling vessels divided by the highest temperature from the absolute zero of temperature. Therefore, in a perfect steam engine, if a be the temperature of the boiler, reckoning from the point of absolute zero, and b be the temperature of the condenser, reckoning also from the point of absolute zero, the fraction of the entire heat communicated to the boiler which a-b will be converted into mechanical effect, will be Now it is • a clear if a=b, or if the temperature of the boiler and condenser are a-b the same, the value of becomes equal to 0, or there is none of a the heat utilised as power, whereas on the other hand, if a be taken larger and larger, the value of the fraction becomes continually greater, indicating that by increasing the difference of the temperatures of the boiler and condenser, a great quantity of the heat expended is converted into mechanical effect, and by taking a = ∞, or infinity, the limit to which the fraction approaches is found to be unity, showing that in such a case if it were possible of realisation, the whole of the heat would be converted into power. Now if a grain of coal produces as much heat as, if it could all be turned into mechanical effect, would raise 1261.45 pounds 1 foot high,* the power produced by any perfect engine, of which heat is the moving power, 1261.45 (a-b), will be represented by the expression a supposing that the principle of expansion is carried to the utmost extent, that the heat generated by the coal is all absorbed by the boiler, and that there is no waste of power in friction. Suppose that such an engine could be constructed, and that it were worked with steam of a pressure of 14 atmospheres. By the experiments of the French academy, the temperature of such steam will be 387° Fahrenheit; and if the condenser be kept at 80°, the temperature of the steam above the point of absolute zero will be 846° Fahrenheit, and the temperature of the condenser above the point of absolute zero will be 539° 1261-45(846-539) Fahr. The power produced by the engine will be 846 =457.76 pounds raised one foot high by one grain of coal. This duty, it will readily be perceived, much exceeds the duty of any existing steam engine. The maximum performance of the best modern engines may be taken at 120,000,000 lbs., raised 1 foot high by a bushel or 94 lbs. of coal. If we reckon 7000 grains to the pound avoirdupois, then 94 times 7000 or 658,000 will be the number of grains of coal required to raise 120,000,000 lbs. 1 foot high, or 1 grain will raise 182:37 lbs. one foot high. The duty of a perfect steam engine is, therefore, 24 times greater than the best modern performance, but in an air engine, in which greater extremes of tem perature may be used, a still better result will be obtained. This will be made apparent by the following example: - Suppose that the temperature of the air in the heating vessel is 739° 12 Fahrenheit, and that the air is expanded in the working cylinder, until at its escape it has a temperature of 219 66 Fahrenheit. Then adding to each temperature 459°, which is the number of degrees Fahrenheit that the absolute zero of temperature is below the temperature of Fahrenheit's scale, we obtain 1198° 12 as the highest temperature, and *This estimate of Mr. Joule's is too small, as will be seen by a reference to page 77. N 90 Investigation of the Relations of Heat and Power.-Performance of a perfect Engine. 1261.45 (1198 12-678.66) 1198.12 678° 66 as the lowest, and =546.92, which is the number of pounds lifted one foot high by the combustion of 1 grain of coal in an air engine having a temperature in the air boiler of 739°·12, and cutting off the air at one fourth of the stroke of the cylinder, so that it expands through three-fourths of the stroke. The performance of such an air engine will, therefore, be three times greater than that of the best modern steam engines, but various practical impediments have heretofore prevented the introduction of the air engine except in the case of very small powers. In an air engine the air must be forced into the air boiler or heating vessel by means of a pump, and this pump will in its action compress the air, and force it into a smaller volume before it acquires elasticity sufficient to overcome the pressure in the boiler. Now, if we suppose the pump to be impervious to heat, the increase of temperature which the air acquires by compression will be retained by it; and if we suppose that the air, without receiving any increase of heat in the boiler, escapes into a cylinder and urges the piston with the same measure of expansion that it had previously undergone of compression, it would issue from the cylinder at its original temperature and pressure, and the power produced by the cylinder would exactly balance that consumed by the pump. We may, therefore, discard the consideration of the pump in estimating the effective power of an air engine, since power is neither gained nor lost by it, and the available power is the effect altogether of the heat imparted by the combustible. If the temperature of the air entering the pump be 50° Fahrenheit, and if it be compressed into one-fourth of its volume, or, in other words, if three-fourths of the stroke of the pump be performed with the effect merely of compressing the air, while during the other one-fourth of the stroke it enters the boiler, then the temperature of the air k-l entering the boiler will by Poisson's formula* = (v.) be found to be 439° 59 Fahrenheit, and its pressure will be 105 92 lbs. on the square inch, t and t being the temperatures, and V and V' the corresponding volumes, while k is the ratio of the specific heat under a constant pressure to the specific heat under a constant volume. Suppose now that the volume of the cylinder is to that of the pump as 4 to 3, then the temperature must be so far increased that, when the air is expanded to the atmospheric pressure, the volume shall be greater in the proportion of 4 to 3. To accomplish this augmentation of volume the air must be heated to a temperature of 739° 12 Fahrenheit, which is the temperature already assumed. It has already been stated that air expands both of its volume at 32° for each degree Fahrenheit of additional temperature it acquires; so that when the volume at any one temperature is known, the volume at any other temperature can easily be computed. All gases and vapours follow the same law very nearly, supposing that they are not near the point of condensation; so that the expansion of steam, as well as of air by heat, becomes thus readily ascertainable. The formula given by Professor Thomson for determining the power generated by a perfect thermo-dynamic engine, is as follows: If S be the temperature of the source of heat, and T be the temperature of the refrigerator, both expressed in centigrade degrees; and if H denote the total heat in thermal units centigrade, entering the engine in a given time; and J be Joule's equivalent of 1390 lbs. raised one foot high by a centigrade degree; — then the power produced, or W the work performed, is Finally, multiply this product by 1390. The result is the number of pounds that the engine will raise a foot high in the minute. The temperatures are all taken in degrees centigrade.* Example. In a steam engine working with a pressure of 14 atmospheres, the temperature of the steam in the boiler will be 215° centigrade, and the temperature of the condenser may be taken at 44°.44 centigrade. If a grain of coal be burned per minute, the heat imparted every minute to a pound of water will, according to Mr. Joule's estimate, be 905° centigrade. Now 215-44°44-170-56 and 215 +274=489, and 170 56 divided by 489=0·35, which multiplied by 905 and by 1390=440 lbs. raised 1 foot high every minute, nearly the same result as that before obtained. There appears to be no doubt that Mr. Joule's estimate of the heating power of coal is too small. Upwards of 10 lbs. of water are evaporated by 1 lb. of the best coal consumed under a good boiler in actual practice, although in such cases a good deal of the heat escapes up the chimney. Under circumstances which prevent any loss of heat, a pound of coal will evaporate 12 lbs. of water, which is equivalent to a pound of water being raised 2 degrees Fahrenheit in temperature by the combustion of a grain of coal. Good coal will raise its own weight of water about 14,000° Fahrenheit in temperature. If we take the specific heat of air as determined by Regnault at 237, and if 250 cubic feet of air, each weighing 075 lbs., making 18·75 lbs., or say 20 lbs. of air, are required to pass through the furnace for the combustion of 1 lb. of coal, then the air employed to maintain the combustion in a furnace would, supposing its expansion were prevented, attain a temperature of 14,000÷237=60,000÷20=3,000° Fahrenheit, over and above the temperature which the air had before being subjected to heat. This is about the melting point of platinum; but, as the air expands in being heated, the temperature of the furnace will be reduced by the absorption of heat to a lower temperature than is here represented. The amount of the expansion which air undergoes by the application of heat is represented by the formula T 490, 3000 490 V=(1+0); when v is the volume of the air at 32o, T the temperature above 32° to which it is heated, and V the new volume at the temperature T. A cubic foot of air at 32° therefore, if heated to 3,000° Fahrenheit, will have a volume of +171 cubic feet. The pressure of air of the atmospheric tension, heated so that its volume is 6 times increased, will be increased 6 times; or, in other words, air of the atmospheric tension, to which 3000° Fahrenheit have been imparted, will have acquired a pressure of 90 pounds per square inch above the pressure of the atmosphere. If heat be added to a quantity of gas, which may be supposed to be contained in a vessel that is impermeable to heat, the phenomena resulting are increase of temperature, increase of elasticity, and increase of volume; and there may occur either increase of temperature and of elasticity without any change of volume, or increase of temperature with change of volume, but without any alteration of elasticity. In the first case, no motion of matter occurs; in the second, on the contrary, the effect of the heat is in part increase of temperature, and in part a motion of matter. But the effect of the heat may likewise be simply represented by a generated motion. For this purpose it is only requisite, in the cases which have been considered, to allow the gas to expand without alteration of its quantity of heat until it has again acquired the previous temperature. In this case the effect of the heat added consists wholly in the expansion it produces, and consequently the pressure under which the gas stands, is driven back through a certain space which must in all cases be regarded as equivalent in its effect to raising a weight to a height; so that in this case the effect of the heat consists solely in a mechanical action, and is measured by it. The effect of the heat added to the gas is consequently either increase of temperature combined with increase of elasticity, or a mechanical action, or a combination of the two. The first important investigation in connexion with this subject is that of S. Carnot, who, in 1824, published a work at Paris, entitled "Réflexions sur la puissance motrice du feu, et sur les machines pro For a comparative table of different thermometers, see p. 66. 1° centigrade = 1.8" Fahrenheit. Performance of a perfect Engine.-Mechanical Equivalent of Heat. pres à développer cette puissance," and which contains some remarkable researches. Carnot shows that whenever power is produced by heat, and a permanent alteration of the body in action does not at the same time take place, a certain quantity of heat passes from a warm body to a cold one. For example, the vapour which is gene rated in the boiler of a steam engine, and passes thence to the condenser, where it is precipitated by the application of cold, carries heat from the furnace to the condenser. Carnot supposed that the quantity of heat remained the same in the condenser as in the boiler; but it is now known that the whole heat which the boiler generates is not to be found in the condenser or hot-well of the engine, inasmuch as a portion of it has been transformed into the mechanical power exerted by the engine. If it were the fact that the whole heat of the boiler existed in the hot-well, then, inasmuch as mechanical power is capable of generating heat by friction or otherwise, it would follow that the heat in a boiler is capable of generating a greater amount of heat than that which already exists in it; and, in fact, any given amount of heat, however small, would be capable of generating any amount of heat, however large. Carnot's views were still further developed by Clapeyron, and subsequently by Meyer, Holtzmann, Joule, Thomson, Clausius and others; and we now know that in all cases in which power is produced by heat, a quantity of heat proportional to the work done is expended; and inversely, by the expenditure of a like quantity of power, the original amount of heat may be produced. This principle, first established by the researches of Meyer and Joule, has already, in fact, afforded a clue to the elucidation of some of the departments of physics heretofore inaccessible, or respecting which most vague ideas prevailed, and as it constitutes the basis of a theoretical knowledge of the steam engine, or of any machine which derives its moving power from heat, it is necessary that we should give it our attentive consideration. If a body in a certain state, for instance, a quantity of gas at the temperature to and volume v。, be subjected to various alterations as regards temperature and volume, and be finally brought into its original state, the sum of its sensible and latent heats must, according to the hypothesis heretofore prevailing, be the same as before. Hence, if during any part of the process heat be communicated from without, the quantity of heat thus received must, according to the old doctrine, be returned during some other part of the process before the original condition can be resumed. With every alteration of volume, however, a certain quantity of work is either produced or expended by the gas; for by its expansion, an outward pressure, either that of the atmosphere or some other, is forced back through a certain space, and on the other hand compression can only ensue from the advance of an external pressure. If therefore, alteration of volume be among the changes which the gas has undergone, power must be produced and expended. It is not, however, necessary that at the conclusion of the process, when the original condition of the gas is again established, the entire amount of power produced should be exactly equal to the amount expended. An excess of the one or the other will be present if the compression has taken place at a lower or higher temperature than the expansion. When a gas at a temperature to and with the volume v。 has to be brought to the higher temperature t,, and the larger volume the quantity of heat required to effect this change would, according to the old hypothesis, be quite independent of the manner in which it is communicated. In point of fact, however, the quantity of heat required will be different according as the gas is first heated at the volume v。 and then permitted to expand at the temperature t,, or is first expanded at the temperature to and afterwards heated to the temperature t In like manner, when a quantity of water at the temperature to has to be converted into steam of the temperature t the amount of heat required for the operation will be different, if the water be first heated to t,, and be then allowed to evaporate, to what it will be if it be suffered to evaporate at the temperature to, and the vapour be then heated to the temperature t,. The heat communicated to the water is either sensible heat or latent heat. Where power is produced, however, the latent heat disappears and is transformed into an equivalent amount of mechanical power. When steam is raised from water, the heat expended is consumed 91 in producing a two-fold effect. 1st, a certain part is expended in overcoming the cohesive attraction of the particles of the water, and in separating them to the distances which they assume in the state of vapour; and 2nd, the residue is expended in forcing back the external pressure to the extent necessary to afford room for the vapour or steam. Both of these effects are equivalent to a certain amount of work done, and Clausius designates the former as internal work and the latter as external work. The latter is alone representative of the useful power produced, and the power necessary to overcome the cohesion of the water is no more utilised than would be the heat expended in melting ice, supposing that it was to be used to feed a steam boiler instead of water. No doubt the heat expended in overcoming the cohesion of water is again surrendered when the steam is condensed; but it then only serves to heat the condenser, and thus produces an injurious effect. Of the heat imparted to water, one portion only must be regarded as sensible: the other portion goes to loosen the cohesion of the particles, as in the melting of ice is more the case. 66 MECHANICAL EQUIVALENT OF HEAT. In a paper on the heat evolved by metallic conductors of electricity, and in the cells of a battery during electrolysis, printed in the 'Philosophical Magazine" for October 1841, Mr. Joule recounts the results of a series of experiments made to determine the heating powers of different metallic wires when a current of electricity is passed through them. The wires were immerged in water, and the accession of temperature gained by the water was measured by a very sensitive thermometer. Mr. Joule ascertained that when a given quantity of voltaic electricity is passed through a metallic conductor for a given length of time, the quantity of heat evolved by it is always proportional to the resistance which it presents, whatever may be the length, thickness, shape, or kind of that metallic conductor. He also found that when a current of voltaic electricity is propagated along a metallic conductor, the heat evolved in a given time is proportional to the resistance of the conductor multiplied by the square of the electric intensity. In electrolysis it was found that the same law obtained. If a pair of plates be placed in undulated water, or a number of pairs be arranged so as to form a galvanic battery, the heat which is generated in any pair by true voltaic action, is proportional to the resistance to conduction of that pair multiplied by the square of the intensity of the current. Mr. Joule concluded from his experiments that, if the electrodes of a galvanic pair of given intensity be connected by any simply conducting body, the total heat generated by the entire circuit (provided always that no local action occurs in the pair) will, whatever may be the resistance to conduction, be proportional to the number of atoms (whether of water or of zinc) concerned in generating the current. If the resistance to conduction be diminished, the quantity of current will be increased in the same proportion; and hence, according to the law already enunciated, the quantity of heat generated in a given time will also be increased proportionally, whilst of course the number of atoms which would be electrolyzed in the pair will be increased in the same proportion. The total voltaic heat which is produced by any pair, is directly proportional to its intensity, and the number of atoms which are electrolyzed in it; and when any voltaic arrangement, whether simple or compound, passes a current of electricity through any substance, whether an electrolyte or not, the total voltaic heat which is generated in any time is proportional to the number of atoms which are electrolyzed in each cell of the circuit, multiplied by the virtual intensity of the battery. The opinion was propounded by Davy, and afterwards more specifically by Berzelius, that the light and heat produced by combustion are occasioned by the discharge of electricity between the combustible and the oxygen with which it is united in the act of combination. Mr. Joule acquiesces in this view, and is of opinion that the heat made manifest in combustion is the consequence of resistance to electrical conduction. His experiments on the heat produced by the combustion of zinc turnings in oxygen gas confirm this view, as do also the experiments made by Crawford to determine the heat produced by exploding a mixture of hydrogen and oxygen. In Crawford's experiments, one grain of hydrogen produced as much heat by its combustion as sufficed to raise the temperature of a pound of |