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Introduction to the History of Science

<h2>CHAPTER XII</h2> <h3>THE REIGN OF LAW—DALTON, JOULE</h3> In the middle of the eighteenth century, when Lambert and Kant were recognizing system and design in the heavens, little progress had been made toward discovering the constitution of matter or revealing the laws of the hidden motions of things. Boyle had, indeed, made a beginning, not only by his study of the elasticity of the air, but by his distinction of the elements and compounds and his definition of chemistry as the science of the composition of substances. How little had been accomplished, however, is evident from the fact that in 1750 the so-called elements—earth, air, fire, water—which Bacon had marked for examination in 1620, were still unanalyzed, and that no advance had been made beyond his conception of the nature of heat, the majority, indeed, of the learned world holding that heat is a substance (variously identified with sulphur, carbon, or hydrogen) rather than a mode of motion. How scientific thought succeeded in bringing order out of confusion and chaos in the subsequent one hundred years, and especially at the beginning of the nineteenth century, can well be illustrated by these very matters, the study of combustion, of heat as a form of energy, of the constituents of the atmosphere, and of the chemistry of water and of the earth. Reference has already been made to Black's discovery of carbonic acid, and of the phenomena which[Pg 156] he ascribed to latent heat. The first discovery (1754) was the result of the preparation of quicklime in the practice of medicine; the second (1761) involving experiments on the temperatures of melting ice, boiling water, and steam, stimulated Watt in his improvement of the steam engine. In 1766 Joseph Priestley began his study of airs, or gases. In the following year observation of work in a brewery roused his curiosity in reference to carbonic acid. In 1772 he experimented with nitric oxide. In the previous century Mayow had obtained nitric oxide by treating iron with nitric acid. He had then introduced this gas into ordinary air confined over water, and found that the mixture suffered a reduction of volume. Priestley applied this process to the analysis of common air, which he discovered to be complex and not simple. In 1774, by heating red oxide of mercury by means of a burning-glass, he obtained a gas which supported combustion better than common air. He inhaled it, and experienced a sense of exhilaration. "Who can tell," he writes, "but in time this pure air may become a fashionable article in luxury? Hitherto only two mice and myself have had the privilege of breathing it." The Swedish investigator Scheele had, however, discovered this same constituent of the air before 1773. He thought that the atmosphere must consist of at least two gases, and he proved that carbonic acid results from combustion and respiration. In 1772 the great French scientist Lavoisier found that sulphur, when burned, gains weight instead of losing weight, and five years later he concluded that air consists of two gases, one capable of absorption by[Pg 157] burning bodies, the other incapable of supporting combustion. He called the first "oxygen." In his Elements of Chemistry Lavoisier gave a clear exposition of his system of chemistry and of the discoveries of other European chemists. After his studies the atmosphere was no longer regarded as mysterious and chaotic. It was known to consist largely of oxygen and nitrogen, and to contain in addition aqueous vapor, carbonic acid, and ammonia which might be brought to earth by rain. Cavendish obtained nitrogen from air by using nitric oxide to remove the oxygen, and found that air consists of about seventy-nine per cent nitrogen and about twenty-one per cent oxygen. He also by use of the electric spark caused the oxygen and nitrogen of the air to unite to form nitric acid. When the nitrogen was exhausted and the redundant oxygen removed, "only a small bubble of air remained unabsorbed." Similarly Cavendish had found that water results from the combination of oxygen and hydrogen. Watt had likewise held that water is not an element, but a compound of two elementary substances. Thus the great masses,—earth, air, fire, water,—assumed as simple by many philosophers from the earliest times, were resolving into their constituent parts. At the same time other problems were demanding solution. What are the laws of chemical combination? What is the relation of heat to other forms of energy? To the answering of these questions (as of those from which these grew) the great manufacturing centers contributed, and no city more potently than Manchester through Dalton and his pupil and follower Joule. [Pg 158] John Dalton (1766-1844) was born in Cumberland, went to Kendal to teach school at the age of fifteen, and remained in the Lake District of England till 1793. In this region, where the annual rainfall exceeds forty inches, and in some localities is almost tropical, the young student's attention was early drawn to meteorology. His apparatus consisted of rude home-made rain-gauges, thermometers, and barometers. His interest in the heat, moisture, and constituents of the atmosphere continued throughout life, and Dalton made in all some 200,000 meteorological observations. We gain a clue to his motive in these studies from a letter written in his twenty-second year, in which he speaks of the advantages that might accrue to the husbandman, the mariner, and to mankind in general if we were able to predict the state of the weather with tolerable precision. In 1793 Dalton took up his permanent residence in Manchester, and in that year appeared his first book, Meteorological Observations and Essays. Here he deals, among other things, with rainfall, the formation of clouds, evaporation, and the distribution and character of atmospheric moisture. It seemed to him that aqueous vapor always exists as a distinct fluid maintaining its identity among the other fluids of the atmosphere. He thought of atmospheric moisture as consisting of minute drops of water, or globules among the globules of oxygen and nitrogen. He was a disciple of Newton's (to whom, indeed, Dalton had some personal likeness), who looked upon matter as consisting of "solid, massy, hard, impenetrable, movable particles, of such sizes and figures, and with such other properties, and in such proportion, as[Pg 159] most conduced to the end for which God formed them." Dalton was so much under the influence of the idea that the physical universe is made up of these indivisible particles, or atoms, that his biographer describes him as thinking corpuscularly. It is probable that his imagination was of the visualizing type and that he could picture to himself the arrangement of atoms in elementary and compound substances. Now Dalton's master had taught that the atoms of matter in a gas (elastic fluid) repel one another by a force increasing in proportion as their distance diminishes. How did this teaching apply to the atmosphere, which Priestley and others had proved to consist of three or more gases? Why does this mixture appear simple and homogeneous? Why does not the air form strata with the oxygen below and the nitrogen above? Cavendish had shown, and Dalton himself later proved, that common air, wherever examined, contains oxygen and nitrogen in fairly constant proportions. French chemists had sought to apply the principle of chemical affinity in explaining the apparent homogeneity of the atmosphere. They supposed that oxygen and nitrogen entered into chemical union, the one element dissolving the other. The resultant compound in turn dissolved water; hence the phenomena of evaporation. Dalton tried in vain to reconcile this supposition with his belief in the atomic nature of matter. He drew diagrams combining an atom of oxygen with an atom of nitrogen and an atom of aqueous vapor. The whole atmosphere could not consist of such groups of three because the watery particles were but a small portion of the total atmosphere.[Pg 160] He made a diagram in which one atom of oxygen was combined with one atom of nitrogen, but in this case the oxygen was insufficient to satisfy all the nitrogen of the atmosphere. If the air was made up partly of pure nitrogen, partly of a compound of nitrogen and oxygen, and partly of a compound of nitrogen, oxygen, and aqueous vapor, then the triple compound, as heaviest, would collect toward the surface of the earth, and the double compound and the simple substance would form two strata above. If to the compounds heat were added in the hope of producing an unstratified mixture, the atmosphere would acquire the specific gravity of nitrogen gas. "In short," says Dalton, "I was obliged to abandon the hypothesis of the chemical constitution of the atmosphere altogether as irreconcilable to the phenomena." He had to return to the conception of the individual particles of oxygen, nitrogen, and water, each a center of repulsion. Still he could not explain why the oxygen did not gravitate to the lowest place, the nitrogen form a stratum above, and the aqueous vapor swim upon the top. In 1801, however, Dalton hit upon the idea that gases act as vacua for one another, that it is only like particles which repel each other, atoms of oxygen repelling atoms of oxygen and atoms of nitrogen repelling atoms of nitrogen when these gases are intermingled in the atmosphere just as they would if existing in an unmixed state. "According to this, we were to suppose that atoms of one kind did not repel the atoms of another kind, but only those of their own kind." A mixed atmosphere is as free from stratifications, as though it were really homogeneous. [Pg 161] In his analyses of air Dalton made use of the old nitric oxide method. In 1802 this led to an interesting discovery. If in a tube .3 of an inch wide he mixed 100 parts of common air with 36 parts of nitric oxide, the oxygen of the air combined with the nitric oxide, and a residue of 79 parts of atmospheric nitrogen remained. And if he mixed 100 parts of common air with 72 of nitric oxide, but in a wide vessel over water (in which conditions the combination is more quickly effected), the oxygen of the air again combined with the nitric oxide and a residue of 79 parts of nitrogen again resulted. But in the last experiment, if less than 72 parts of nitric oxide be employed, there will be a residue of oxygen as well as nitrogen; and if more than 72, there will be a residue of nitric oxide in addition to the nitrogen. In the words of Dalton, "oxygen may combine with a certain portion of nitrous gas [as he called nitric oxide], or with twice that portion, but with no intermediate portion." Naturally these experimental facts were to be explained in terms of the ultimate particles of which the various gases are composed. In the following year Dalton gave graphic representation to his idea of the atomic constitution of chemical elements and compounds. <div class="figcenter"> <ANTIMG src="images/image161.jpg" width-obs="524" height-obs="112" alt="" /></div> Much against Dalton's will his method of indicating chemical elements and their combinations had to[Pg 162] yield to a method introduced by the great Swedish chemist Berzelius. In 1837 Dalton wrote: "Berzelius's symbols are horrifying: a young student in chemistry might as soon learn Hebrew as make himself acquainted with them. They appear like a chaos of atoms ... and to equally perplex the adepts of science, to discourage the learner, as well as to cloud the beauty and simplicity of the Atomic Theory." Meantime Dalton's mind had been turning to the consideration of the relative sizes and weights of the various elements entering into combination with one another. He argued that if there be not exactly the same number of atoms of oxygen in a given volume of air as of nitrogen in the same volume, then the sizes of the particles of oxygen must be different from those of nitrogen. His interest in the absorption of gases by water, in the reciprocal diffusion of gases, as well as in the phenomena of chemical combination, stimulated Dalton to determine the relative size and weight of the atoms of the various elements. Dalton said nothing of the absolute weight of the atom. But on the assumption that when only one compound of two elements is known to exist, the molecule of the compound consists of one atom of each of these elements, he proceeded to investigate the relative weights of equal numbers of the two sorts of atoms. In 1803 he pursued this investigation with remarkable success, and taking hydrogen (the lightest gas known to him) as unity, he arrived at a statement of the relative atomic weights of oxygen, nitrogen, carbon, etc. Dalton thus introduced into the study of chemical combination a very definite idea of quantitative relationship. By him[Pg 163] the atomic theory of the constitution of matter was made definite and applicable to all the phenomena known to chemistry. <div class="figcenter"> <ANTIMG src="images/facing162.jpg" width-obs="600" height-obs="275" alt="" /> Painting by Ford Madox Brown By permission of the Town Hall Committee of the Manchester Corporation JOHN DALTON COLLECTING MARSH GAS</div> During the following months he returned to the study of those cases in which the same elements combine to form more than one compound. We have seen that oxygen unites with nitric oxide to form two compounds, and that into the one compound twice as much nitric oxide (by weight) enters as into the other. A like relation was found in the weight of oxygen combining with carbon in the two compounds carbon monoxide and carbonic acid. In the summer of 1804 he investigated the composition of two compounds of hydrogen and carbon, marsh gas (methane) and olefiant gas (ethylene), and found that the first contained just twice as much hydrogen in relation to the carbon as the second compound contained. In a series of compounds of the same two elements one atom of one unites with one, two, three, or more atoms of the other; that is, a simple ratio exists between the weights in which the second element enters into combination with the first. This law of multiple proportions afforded confirmation of Dalton's atomic theory, or chemical theory of definite proportions. "Without such a theory," says Sir Henry Roscoe, "modern chemistry would be a chaos; with it, order reigns supreme, and every apparently contradictory discovery only marks out more distinctly the value and importance of Dalton's work." In 1826 Sir Humphry Davy recognized Dalton's services to science in the following terms: "Finding that in certain compounds of gaseous bodies the same elements[Pg 164] always combined in the same proportions, and that when there was more than one combination the quantity of the elements always had a constant relation,—such as 1 to 2, or 1 to 3, or 1 to 4,—he explained this fact on the Newtonian doctrine of indivisible atoms; and contended that, the relative weight of one atom to that of any other atom being known, its proportions or weight in all its combinations might be ascertained, thus making the statics of chemistry depend upon simple questions in subtraction or multiplication and enabling the student to deduce an immense number of facts from a few well-authenticated experimental results. Mr. Dalton's permanent reputation will rest upon his having discovered a simple principle universally applicable to the facts of chemistry, in fixing the proportions in which bodies combine, and thus laying the foundation for future labors respecting the sublime and transcendental parts of the science of corpuscular motion. His merits in this respect resemble those of Kepler in astronomy." In 1808 Dalton's atomic theory received striking confirmation through the investigations of the French scientist Gay-Lussac, who showed that gases, under similar circumstances of temperature and pressure, always combine in simple proportions by volume when they act on one another, and that when the result of the union is a gas, its volume also is in a simple ratio to the volumes of its components. One of Dalton's friends summed up the result of Gay-Lussac's research in this simple fashion: "His paper is on the combination of gases. He finds that all unite in equal bulks, or two bulks of one to one of another,[Pg 165] or three bulks of one to one of another." When Dalton had investigated the relative weights with which elements combine, he had found no simple arithmetical relationship between atomic weight and atomic weight. When two or more compounds of the same elements are formed, Dalton found, however, as we have seen, that the proportion of the element added to form the second or third compound is a multiple by weight of the first quantity. Gay-Lussac now showed that gases, "in whatever proportions they may combine, always give rise to compounds whose elements by volume are multiples of each other." In 1811 Avogadro, in an essay on the relative masses of atoms, succeeded in further confirming Dalton's theory and in explaining the atomic basis of Gay-Lussac's discovery of simple volume relations in the formation of chemical compounds. According to the Italian scientist the number of molecules in all gases is always the same for equal volumes, or always proportional to the volumes, it being taken for granted that the temperature and pressure are the same for each gas. Dalton had supposed that water is formed by the union of hydrogen and oxygen, atom for atom. Gay-Lussac found that two volumes of hydrogen combined with one volume of oxygen to produce two volumes of water vapor. According to Avogadro the water vapor contains twice as many atoms of hydrogen as of oxygen. One volume of hydrogen has the same number of molecules as one volume of oxygen. When the two volumes combine with one, the combination does not take place, as Dalton had supposed, atom for atom, but each half-[Pg 166]molecule of oxygen combines with one molecule of hydrogen. The symbol for water is, therefore, not HO but H2O. Enough has been said to establish Dalton's claim to be styled a great lawgiver of chemical science. His influence in further advancing definitely formulated knowledge of physical phenomena can here be indicated only in part. In 1800 he wrote a paper On the Heat and Cold produced by the Mechanical Condensation and Rarefaction of Air. This contains, according to Dalton's biographer, the first quantitative statement of the heat evolved by compression and the heat evolved by dilatation. His contribution to the theory of heat has been stated thus: The volume of a gas under constant pressure expands when raised to the boiling temperature by the same fraction of itself, whatever be the nature of the gas. In 1798 Count Rumford had reported to the Royal Society his Enquiry concerning the Source of Heat excited by Friction, the data for which had been gathered at Munich. Interested as he was in the practical problem of providing heat for the homes of the city poor, Rumford had been struck by the amount of heat developed in the boring-out of cannon at the arsenal. He concluded that anything which could be created indefinitely by a process of friction could not be a substance, such as sulphur or hydrogen, but must be a mode of motion. In the same year the youthful Davy was following independently this line of investigation by rubbing two pieces of ice together, by clock-work, in a vacuum. The friction caused the ice to melt, although the experiment was undertaken in a temperature of 29° Fahrenheit. [Pg 167] For James Prescott Joule (1818-1889), who came of a family of brewers and was early engaged himself in the brewing industry, was reserved, however, the distinction of discovering the exact relation between heat and mechanical energy. After having studied chemistry under Dalton at Manchester, he became engrossed in physical experimentation. In 1843 he prepared a paper On the Calorific Effects of Magneto-Electricity and on the Mechanical Value of Heat. In this he dealt with the relations between heat and the ordinary forms of mechanical power, and demonstrated that the mechanical energy spent "in turning a magneto-electrical machine is converted into the heat evolved by the passage of the currents of induction through its coils; and, on the other hand, that the motive power of the electro-magnetic engine is obtained at the expense of the heat due to the chemical reactions of the battery by which it is worked." In 1844 he proceeded to apply the principles maintained in his earlier study to changes of temperature as related to changes in the density of gases. He was conscious of the practical, as well as the theoretical, import of his investigation. Indeed, it was through the determination by this illustrious pupil of Dalton's of the amount of heat produced by the compression of gases that one of the greatest improvements of the steam engine was later effected. Joule felt that his investigation at the same time confirmed the dynamical theory of heat which originated with Bacon, and had at a subsequent period been so well supported by the experiments of Rumford, Davy, and others. Already, in this paper of June, 1844, Joule had[Pg 168] expressed the hope of ascertaining the mechanical equivalent of heat with the accuracy that its importance for physical science demanded. He returned to this question again and again. According to his final result the quantity of heat required to raise one pound of water in temperature by one degree Fahrenheit is equivalent to the mechanical energy required to raise 772.55 pounds through a distance of one foot. Heat was thus demonstrated to be a form of energy, the relation being constant between it and mechanical energy. Mechanical energy may be converted into heat; if heat disappears, some other form of energy, equivalent in amount to the heat lost, must replace it. The doctrine that a certain quantity of heat is always equivalent to a certain amount of mechanical energy is only a special case of the Law of the Conservation of Energy, first clearly enunciated by Joule and Helmholtz in 1847, and generally regarded as the most important scientific discovery of the nineteenth century. Roscoe, referring to the two life-sized marble statues which face each other in the Manchester Town Hall, says with pardonable pride: "Thus honor is done to Manchester's two greatest sons—to Dalton, the founder of modern Chemistry and of the Atomic Theory, and the discoverer of the laws of chemical combining proportions; to Joule, the founder of modern Physics and the discoverer of the Law of the Conservation of Energy." [Pg 169] <h3>REFERENCES</h3> <div class="hanging-indent"> Alembic Club Reprints, Foundations of the Atomic Theory. Joseph Priestley, Experiments and Observations on Different Kinds of Air. Sir William Ramsay, The Gases of the Atmosphere and the History of their Discovery. Sir Henry E. Roscoe, John Dalton. Sir E. Thorpe, Essays in Historical Chemistry. </div> <hr class="chap" /> [Pg 170] <div style="break-after:column;"></div>

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