asphalt, or similar deposits and also in mineral resins. | The occurrence of paraffin hydrocarbons in plants is not very common, and so far as observed is confined to a few members of the group and to a few species of plants. The large deposits in the earth's crust can not, then, be attributed to the accumulation of unchanged plant residues, and a great many theories have been propounded to account for these deposits, most of them based on some transformation of organic material. In spite of the fact that these hydrocarbons are of rather rare occurrence in plants and are seldom added to soil in plant débris, the wide distribution of extensive deposits of such compounds and the occurrence also of mineral resins and shales from which hydrocarbons can be obtained in the rocks from which soils are formed might lead one to expect to find some trace of these compounds in the soil. The question is also raised by this consideration whether some of the processes by which hydrocarbons have been formed from more complex organic compounds may not take place in the soil and escape recognition because the conditions are not favourable for the accumulation of these with alcoholic potash, the alcohol removed, and the soap dried and extracted with petroleum ether. On evaporation of the petroleum ether the residue was a light coloured waxy mass, completely soluble in a relatively large volume of hot alcohol. On cooling the alcoholic solution so obtained, there was a separation of a feathery micro-crystalline body which was collected, washed, and purified by re-crystallising several times from alcohol. As thus obtained, the body was a hard waxy mass, melting at 68° C., and having a specific gravity of 0.780 at its melting-point. It was readily soluble in ether and petroleum ether, difficultly soluble in hot and very slightly soluble in cold alcohol. It was unacted on by fuming nitric acid at room temperature and did not absorb bromine. Elementary analysis gave the following figures:Calculated for C81H64. Carbon .. Found. 85.32 14.68 The method by which this body was obtained fixes it as either a hydrocarbon or a higher alcohol. Its behaviour toward nitric acid and its elementary composition prove that it can not be a higher alcohol, and its behaviour toward bromine shows that it must be a saturated compound. It being thus fixed as a saturated or paraffin hydrocarbon, its melting-point shows it to be hentri acontane. products in the soil. The production of the simplest paraffin hydrocarbon, methane, is known to take place in soil organic matter when submerged under water, as in swamps. The production here is supposed to be due to the activity of anaerobic micro-organisms, but it is not known that absolutely anaerobic conditions are essential to this production or that methane may not be formed in small quantities in ordinary soils. Methane is present in the gases in the paraffin residue of some petroleums. It has also Hentriacontane is a member of the paraffin series found from the combustion of fuel even when excess of oxygen is available, and it has been found in the combustion of been found in beeswax, together with another member of organic compounds in elementary analysis that some of the same series, heptocosane, C27H56 (Schwald, Ann. the carbon may be present in the products of combustion Chem., 1886, ccxxxv., 117). It occurs also in some plants, as methane instead of carbon dioxide, and this when the having been found in the leaves of Gymnema silvestre combustion was carried on in pure oxygen (Dunstan, Proc. (Power and Tutin, Pharm. Journ., 1904, [4], xix., 234), Chem. Soc., 1896, xii., 48). It may be, therefore, that in in tobacco leaves (Thorpe and Holmes, Journ. Chem. Soc., the decomposition of organic matter the formation of 1901, lxxix., 982), and in East India Ko-sam seeds (Brucea methane rather than carbon dioxide depends on the sumatrana) (Power and Lees, Pharm. Journ., 1993, [4], structure or constitution of a portion of the material decom-xvii., 183). With this information regarding its occurposed, and similarly more complex members of this series rence as a natural product, and in the absence of any may also be formed. In connection with this discussion of hydrocarbons in soils it should be noted that there are in nearly all soils dark coloured particles of organic matter that are very resistant to solvents and the action of either acids or alkalis. These sometimes are evidently particles of charcoal or coal that may have found their way into the soil, but a considerable portion is often made up of structureless bituminous-like material having the elementary composition so far as examined of lignites or brown coals. Whether this is formed in the soil is a matter for further investigation. Since such material often makes up a considerable portion of the organic content, its composition, constitution, and origin should be considered. One paraffin hydrocarbon has been isolated from a soil, and while in this particular case there is nothing to indicate that it may not be an unchanged plant residue, the isolation is of interest not only in accounting for a small portion of the organic matter, but also in that it opens up the question of a possible connection between the processes that go on in the soil and the processes by which paraffin hydrocarbons have been formed in nature. Hentriacontane, C31H64. A peaty soil from North Carolina containing 27 per cent organic carbon when extracted with boiling 95 per cent alcohol yields a dark coloured extract, from which on cooling a light yellow micro-crystalline body separates. This material was separated by filtration and the alcohol removed from the filtrate by evaporation, the volume being kept constant by the addition of water. There was thus formed a reddish brown precipitate which after separation and washing was in the form of a brown resinous powder. Extraction of this with boiling petroleum ether yielded a light coloured solution, which after removal of the petroleum ether left a light yellow oily residue. This was saponified information regarding the possibility of its formation from other soil organic matter, this paraffin hydrocarbon may be regarded as an unchanged plant residue. HYDROXY-FATTY ACIDS. Hydroxy acids of the fatty series are very widely distributed in the vegetable kingdom. One or more of the three hydroxy acids-malic, citric, or tartaric-is usually present in an acid plant or fruit juice, and some of the less common, such as glycollic, also occur in plants. Some members of this group can be formed by micro-organisms from more complex material-lactic acid by the lactic fermentation of sugar and citric acid by citromycetes (Mazé, Ann. Inst. Pasteur, 1909, xxiii., 830). All members of the group, however, seem to be readily broken down by other bacteria or fungi into simpler compounds with the loss of the hydroxy character. Lactic acid goes readily to butyric and others to acetic or formic acid or formaldehyde. In view of this fact, while there is no doubt that vegetable acids of this group are added to soils in large quantities and become temporarily, at least, a part of the organic matter of the soil, it does not seem likely that they would persist unchanged for any length of time. Two hydroxy acids of the fatty series have been isolated from soils, but neither are known as natural products. These are a-hydroxystearic acid and the dihydroxystearic acid previously described (Bull. 53, Bureau of Soils, U.S. Dept. Agr., 1909; Fourn. Am. Chem. Soc., 1908, xxx., 1599). Both must be looked on at present as the products of the action of micro-organisms, probably fungi, on some of the organic matter known to be of plant or animal origin. While at present little is known of the processes by which these compounds are formed in the soil, and little can be said that is not of a speculative nature, it may be of interest at this point to note the laboratory methods by } Chemical Nature of Soil Organic Matter. CHEMICAL NEWS Jan. 12, 1912 which hydroxy acids are formed. Three general methods are known by which the hydroxy acids are formed from the corresponding acid. These are:-Making a halogen substitution product and treating this with silver oxide and water; making an amido derivative and treating this with nitrous acid; and making a sulphonic-acid derivative and treating it with caustic potash. In attempting to find a parallel between these reactions and the processes likely to take place in the soil, the second method seems to be the only one that offers any foundation for a theory. It is known that amido compounds result from the decomposition of more complex nitrogenous compounds and may possibly be formed or built up by the action of ammonia which is commonly formed in soils. Nitrous acid, as the result of denitrification or as the first stage in the change of ammonia into nitrates, is formed in nearly all soils and would supply the reagent required in the second stage of the reaction." In addition to these purely chemical methods of formation, there are the biological formations by fungi or bacteria to be considered, but this would lead somewhat afield from the purposes of the present Bulletin. a-Monohydroxystearic Acid, C18H3603. When the humus extract of a soil obtained by extraction with dilute alkali is acidified, a brown or black flocculent precipitate of the so-called humus bodies is formed. If this precipitate is separated by filtration, washed, and treated while still moist with boiling 95 per cent alcohol, a portion of the precipitate goes into solution. The amount of the humus precipitate so dissolved varies with the character of the soil treated, but the alcoholic solution obtained in this way is always dark coloured. On careful evaporation of this alcoholic solution, adding water to keep the volume constant until the alcohol is removed, there is formed a brown or reddish brown precipitate, which can be separated by filtration. When so separated, washed, and dried it is in the form of resinous lumps or powder, varying in colour, melting-point, and composition with the soil from which it was obtained. 17 This composition corresponds with that of the monohydroxystearic acids, two of which are known, designated a and 8 respectively, and having the formula C18H3603. The properties of the acid isolated from the soil fix it as the a-acid. The a-acid is much less soluble in alcohol than the 3-acid, and the 3-acid, moreover, forms an anhydride on heating with hydrochloric acid, which is not the case with the a-acid nor the acid from the soil. The melting-points of the - and -acids are so nearly the same that this property can not be used to distinguish between them. The melting-point of the pure a-acid, artificially prepared, remained unchanged on mixing with the acid from the soil, and this fact, together with the composition found and sparing solubility in alcohol and failure to form an anhydride, is sufficient to establish the identity of the acid from the soil as a monohydroxystearic acid. a-Hydroxystearic acid is easily made in the manner described by Sadomsky (Ber., 1891, xxiv., 2388). When stearic acid is treated with red phosphorus and bromine, a-bromostearic acid is formed. On heating this with alcoholic potash the potassium salt of a-hydroxystearic acid is formed, and on acidifying the aqueous solution of this salt the acid is set free and can be extracted with ether. a-Hydroxystearic acid is not known to occur in any natural animal or vegetable product, and up to the present has been isolated from only one soil. The possible origin of this acid has already been discussed from a speculative point of view, and while it is not On extracting this resinous material with petroleum ether there is obtained an extract generally colourless or light coloured, which on evaporation of the petroleum ether leaves a residue which may vary from an oily semi-known as a natural product it must be remembered that solid mass to a waxy solid. This residue is generally wholly soluble in hot alcohol. From this alcoholic solution there sometimes separates on cooling a white or yellowish microcrystalline mass or powder which in the case of one soil has been identified as a-hydroxystearic acid. The soil from which this compound was obtained was a sample of Elkton silt loam, a type covering a considerable area in Maryland. This soil is almost white in colour, high in clay and silt, and contains o‘53 per cent organic carbon and 0.066 per cent nitrogen. The sample examined was one of several hundred pounds obtained from the Eastern Shore of Maryland. This soil when treated with 2 per cent sodium hydroxide solution yields an extract much darker than might be expected from a soil so light in colour. From this brown alkaline extract there is precipitated on acidifying with sulphuric acid a brown flocculent mass. On separation of this by filtration, washing, and treating with boiling 95 per cent alcohol, there is obtained an alcoholic solution nearly as dark in colour as the original alkaline extract. The precipitate formed by evaporation of the alcohol and addition of water was, after filtration, washing, and drying, a brown mass easily pulverised. Extraction of this brown powder with petroleum ether and evaporation of the solvent left an oily semisolid light yellow mass, which was completely soluble in hot 95 per cent alcohol. On cooling this alcoholic solution there separates a yellow microcrystalline powder, which after separation by filtration, washing with cold alcohol, dissolving again in hot alcohol, and repeating the separation several times, can be obtained free of colour and of constant melting-point. natural fats and oils are usually complex mixtures of gly. cerides, and that the chemistry of such glycerides as occur in these products in small amounts is very incomplete. More complete chemical knowledge of the natural fats and oils may show the presence of a-monohydroxystearic acid. The method of its laboratory preparation does not suggest any possible parallelism in the soil as was the case when the origin of dihydroxystearic acid was under discussion. In the earlier literature of the hydroxystearic acids there is some confusion of nomenclature, as well as disagreement regarding their constitution. The B-acid described by Saytzeff (Fourn. Prakt. Chem., 1887, [2], xxxv., 369) was designated as the a-acid by Geitel (Journ. Prakt. Chem,, 1888, [2], xxxvii., 53). The designations a- and 8-acid seem to have been used primarily to distinguish isomers, the constitution of which were not known. The constitution, as now accepted and established by Shukoff and Schestakoff (Journ. Prakt. Chem., 1903, [2], lxvii., 415), is not in harmony with the common meaning of a and 3 designations. In the simple hydroxy-fatty acids the term a is applied to that acid having the hydroxyl group next the carboxyl group, for example, a-hydroxypropionic acid (lactic) is represented thus CH3.CHOH.COOH; the term 8 is applied to that acid having the hydroxyl on the second carbon atom, for example, 8-hydroxypropionic (hydracrylic) is represented thus: CH2OH.CH2COOH. The constitution of the aand 3-hydroxystearic acids is represented as follows: a - acid, CH3(CH2)6CHOH(CH2), COOH ; B - acid, CH3(CH2)7CHOH(CH2)8COOH. In neither case is there a- or 3-structure. The authors in discussing these formula used the designations: I. II. for the a-acid and I. 10. IF 16 grms. of oxygen gas at o° C. are placed in contact with 2016 grms. of hydrogen gas at the same temperature, and both under atmospheric pressure, no reaction is evident. But if a negligible amount of heat be supplied to the mixture in the form of an electric spark, a violent reaction takes place, and 18.016 grms. of water are formed, and 68,511 calories of heat are given out (Mixter, Am. Journ. Sci., 1903, [4], xvi., 214). (The value given is the mean of the values obtained by Thomsen, Schüller and Wartha, Than, and Mixter, after reduction to the calorie at 15° to 16° as the unit; Mixter thinks the value correct to onetenth of 1 per cent). If the reaction took place at a different temperature, or under different conditions of pressure or volume, the amount of heat evolved would have been different, but the chemical reaction in each case would have been the same. From whence came the enormous amount of heat given out by the reaction? Why and how does the amount of heat given out vary under different conditions? Why did not the reaction take place when the hydrogen and oxygen were first mixed? It is the purpose of this paper to answer these questions and to point out certain facts concerning chemical energy, and certain possibilities regarding the relation of chemical energy to electrical and other forms of energy. (c) Dewar, Proc. Roy. Soc., A, 1905, lxxvi., 325; 1902, Ixix., 361; 1904, lxxiii., 251. He determined the specific heat of ice, -252.6 to - 188 = 0·146, -78 to 188 0 285, 78 to - 18° = 0'403. (d) Wiedemann, Pogg. Ann., 1876, clvii., 1; Phil. Mag., 1876, [5], ii., 81. = (e) Alt, Zeit. Phys. Chem., 1905, li., 252; Phys. Zeit., 1905, vi., 346; Ann. der Physik., 1904, xiii., 1010; "Dissertation," Munchen, 1903. (f) Regnault, Mem. de l'Acad., 1862, xxvi., 1. (g) Smith, Phys. Rev., 1903, xvii., 193. The total heat necesssary to raise these substances from -273° to o° C. may therefore be estimated as follows: Total heat, -273° to o° C. for I grm. Total heat, 273° to o° C. for 16 grms. Water (1 Grm.). Latent heat of fusion. The Source of the Energy given out by the Reaction. If the term "absolute zero of temperature" be used, some one will object that there may be no absolute zero of temperature, that we are not certain of the existence of Specific heat of solid, 273° to 0° molecules, and that if they do exist we certainly do not know that they cease to move at the so-called absolute Granting for the present the validity of the objection, we will not use the term absolute zero, but will speak of 273° C. No one will deny the existence of that temperature since a temperature below - 260° C. has already been reached. zero. Total heat, 273° to o° C. for I grm. Total heat, 273° to o° C. for 18.016 gims. = 39'75 123.26 The 18-016 grms of water at o° C. contain, therefore, at least 2887 calories, and since 68,511 calories of heat were given out by the reaction of the hydrogen and oxygen gases, these gases before the reaction contained at least 71,398 calories of energy. Of this total amount of energy, 2125 calories were supplied to the 2016 gims. of hydrogen, and 1972 calories were supplied to the 16 grms. of oxygen, in converting them from the solid condition at -273° C. to the gaseous condition at o° C.—a total of 4097 calories. It follows therefore that while in the solid condition at - 273° C. the oxygen and hydrogen contained at least 71,398-4097 = 67,301 calories of energy. Now, Dewar (Proc. Roy. Soc., 1904, lxxiii., 251) has shown by slight extrapolation of measurements extending to -258.9° C. that the molecular volume of oxygen at -273° C. is 21.21 cc., of hydrogen 24-18 cc., and of ice 19.21 cc. Therefore the 16 grms. cf oxygen and the 2016 grms. of hydrogen together at -273° C. occupy 34'78 cc., and when occupying this volume at that temperature they contain 67,300 calories more of energy than does the 18.016 gims. of ice which they form if united, and which occupies a volume of 19:21 cc. There is no supposition whatever connected with this fact, except the slight uncertainty due to the measurements and their extrapolation, and this uncertainty is prob ably not greater than 100 calories. A study of substances The total energy possessed by the hydrogen and oxygen at -273° C. is probably very much more than 67,300 calories, and may be many times that amount, for we have no evidence whatever as to the energy which the ice possesses at that temperature. We only know that the energy of the ice is 67,300 calories less than the amount possessed by the equivalent hydrogen and oxygen before the combination. The ice may, and in our opinion certainly does, possess a vast amount of energy. Its store of energy is perhaps comparable to that possessed by radium. In what form does the 67,300 calories of energy possessed by the 34 78 cc. of hydrogen and oxygen at -273° C. exist? The answer to the question, "What is energy?" and "What is matter?" must both be given before any sufficient answer to the first question could be made. But there is certainly no harm in stating what we do know concerning the answer to that question, and it is this:If the same mechanical laws which govern larger masses of matter and energy at higher temperatures apply to the hydrogen and oxygen at -273° C., then a stable system could not exist if all of the energy were kinetic, or if all of the energy were potential, but some portion of the energy must be potential and some portion must be kinetic (see Meyer, "Kinetic Theory of Gases," p. 344, English translation of second revised edition). There has never been the slightest evidence produced to show that these mechanical laws do cease to hold at -273° C., or with small sub-divisions of mass, and therefore we think it probable that at -273° C. the small particles-atoms if you please to call them so-of hydrogen and oxygen, are in exceedingly rapid motion, and are held together by some force which gives rise to a potential energy. The force we will call chemical affinity, and the energy we will call chemical energy. It is not out of place to point out here, for it is very suggestive, that if we have two masses of matter which attract each other inversely as the square of their distance apart, and which form a stable system, they will revolve around their common centre of gravity, and they cannot give out a greater amount of energy than they retain as kinetic energy. Just what relation would hold if we had numerous particles governed by the same laws, mathematics has not yet proved adequate to reveal. The relation may be a very simple one in spite of the mathematical complexity of the problem. The answer to our first question is therefore that 67,300 calories of the total energy possessed by the 2016 grms. of hydrogen and the 16 grms. of oxygen at o° C. existed in some form in those substances at -273° C., and 4097 calories of energy were added in raising those substances to o° C. and changing them to the gaseous condition. Energy Changes caused by a Rise in Temperature. We wish next to show why 4097 calories of energy were necessary to change the temperature and condition of the hydrogen and oxygen as described. Of this amount of energy 2125 calories were added to the hydrogen. Now the hydrogen at -273° C. originally occupied a volume of 24'18 cc., and at o° C. it occupied a volume of 22,431 cc. This expansion necessitated the expenditure of work in pushing back the atmosphere. The work so done we will call Es, and it may be cal. culated for 1 grm. from the equation (see Note)— = = 19 (NOTE. The constants used in this paper are:-Density of mercury 13'5956 at 0° referred to water at 4° C.; attraction of gravity= 980 5966 at latitude 45° and sealevel; atomic weight of oxygen 1600; density of hydrogen at latitude 45° and sea-level 0.0000898765. This is an average of the values given by Morley, ("Smithsonian Contributions to Knowledge," No. 980), and the value given by Rayleigh (Proc. Roy. Soc., liii., 147, No. 322), after reduction to latitude 45°. Rayleigh's value was an average of his own value, that of Leduc, and the value of Regnault as corrected by Crafts. The unit calorie is taken as from 15° to 16° C., and as equal to 41,880,000 ergs. This is Rowland's value as corrected by Day-Phys. Rev., 1898, vi., 194; see also Ber. Deut. Phys. Ges., v., 578). During the expansion of the hydrogen the molecules of the hydrogen were moved further apart, and a certain amount of energy was necessary to overcome the attraction between the hydrogen molecules. This amount of energy, which we will denote by Ea, may be calculated, as the author has shown in a series of papers,* from the equation3 d 3 Ea = D) calories (2) where d and D are the density in the original and final conditions respectively, and u' is a constant which may be obtained from the following equation: Here L is the heat of vaporisation, Et is the energy spent in pushing back the atmosphere during the vaporisation, and is calculated from Equation 1, d is the density of the liquid, and D the density of the saturated vapour at the temperature of vaporisation. To calculate u' for hydrogen, L = 1231 calories. The density of the liquid at its boiling-point has been determined by Dewar as o'070025, corresponding to a volume of 14 28 cc. per grm. The density of the saturated vapour may be calculated on the supposition that it obeys the gas laws, the error so introduced being negligible. The equation for this calculation is : D = 0·000016014 Pm T 3 Since T is 20:41°, D becomes o'001202, and the corresponding volume is 8319 cc. From Equation 1, Eɛ is found to be 19.78 calories, and L- Es is therefore 103.32. Dividing this by the value of 3 √d - √D, namely, 0.3059, we have for μ' the value 3377. Substituting this value in Equation 2, and using for d the density of hydrogen at -273° C. as given by Dewar, o'08272, and for Ď the value already given at o° under standard conditions, namely, 0.00008988, we have finally,— Ea=337'7X0'3909 × 2·016 = 266⋅ 1 calories. It is not necessary to pause here to defend the kinetic theory of gases. That theory represents the attempt to extend the mechanical laws which govern large masses of matter to smaller particles of the same material. Its foundation upon these mechanical laws is quite as secure as are the foundations of any system of thermodynamics yet advanced-both theories alike resting upon observed laws to which no single exception has ever been found. Moreover, it has led to important discoveries and correlated numerous facts. Making use now of the kinetic theory, it is easy to calculate the energy necessary to add to the grm. molecular *Journ Phys. Chem., 1902, vi., 209; 1904, viii., pp. 383, 593; 1905, ix., 402; 1906, x., 1; 1907, xi., pp. 132, 594. The equation has been proved to hold for liquids as they expand to the volume of the saturated vapour. The author believes that the equation, which was theoretically derived, may be applied as above, and the result appears to justify the belief. We know also from the kinetic theory of gases that whenever we increase the kinetic energy of a molecule we at the same time increase its internal energy, which we will call Er. The increase in the internal energy is proportional to the increase of the kinetic theory, and its amount may be calculated from the relation first proposed by Waterston, namely, — specific heat of gas at constant pressure EI motion.. Energy necessary for internal work oxygen will require 1802 calories. The amount actually To effect the above mentioned change for 16 grms. of added to the oxygen was found to be 1972 calories. The divergence here, amounting to about 10 calories per (6). grm., cannot, we believe, be considered as entirely due to experimental error, and we have made an extended investigation as to its cause. As a result of this investigation, the details of which it would be impossible to reproduce within the limits of this paper, we believe that besides the Ek and so-called external, attractive, kinetic, and internal energy, " T for which allowance has been made, all bodies, while in to 1:— the solid condition, require yet an additional amount of energy, the exact office of which we are unable to explain. The amount of this unaccounted for energy varies with the absolute temperature of the melting-point of the body. In the case of hydrogen because of its very low meltingpoint, 14° absolute, the amount thus unaccounted for was well within the limit of experimental error. But with oxygen this is not the case. solving for E1, we obtain finally, since T is equal EI 5/3- Ek calories = γ-Ι (7). For hydrogen y = 1'4084 from the measurements of Lummer and Pringsheim ("Smithsonian Contributions to Knowledge," No. 1126), and so we have for E, for 2016 grms. of hydrogen, 514'6 calories. As a summary, therefore, we have for the total energy necessary to change 2016 grms. of hydrogen from the solid condition at -273° C. to the gaseous condition at 0° C. under 760 mm. pressure: E& : = energy necessary to overcome external pressure ........ Energy necessary to overcome molecular attraction .. Energy necessary for translational motion Energy necessary for internal work Total.. Calories. We are led here to add that the total energy necessary to change a solid monatomic element from -273° to the liquid condition at its melting-point, appears to us to be three times the kinetic energy of translation required by the element at that temperature; or, in other words, 8.94 T calories, where T is the absolute temperature of the Prof. J. W. Richards (Trans. American melting-point. Electrochem. Soc., 1908, xiii., 447) has reached nearly the same conclusion, considering the total heat in the molten metal at its melting point to be 10 T calories. We will publish our data and conclusions upon this subject later. Unfortunately our calculations cannot be extended to water, for it is an associated substance. Except for the discrepancy of 170 calories, we have shown why and how the 4097 calories of energy added to the hydrogen and oxygen to change them from their condition at -273° C. to their condition at o° C. were expended, and have therefore, in part at least, answered the second question as to why and how the amount of heat given out by the reaction of the hydrogen and oxygen will vary under different conditions of volume, temperature, and pressure. The Chemical Changes involved in the Reaction. The answer to the third question, as to why the reaction did not take place when the hydrogen and oxygen were first mixed, and before the passage of the electric spark, has doubtless occurred to everyone. It was first necessary to loosen the union of some of the hydrogen atoms from their combination with other hydrogen atoms, and the union of some of the oxygen atoms from their combination with other oxygen atoms. Then, once free, the hydrogen atoms and the oxygen atoms unite, and in so doing give out enough heat to loosen the neighbouring hydrogen and oxygen molecules, and these in their turn unite, and thus the reaction is propagated. But it is perhaps not so clearly recognised, that the force of which we call chemical affinity is probably never directly affected by a rise in temperature. Certainly in the case under consideration we have accounted for all of the energy added to the hydrogen and the oxygen from - 273° to o° C., save 170 calories, as having been used to effect |