Popular Science Monthly/Volume 5/August 1874/Editor's Table



ON the 1st of August, 1874, it will be exactly a hundred years since oxygen gas was first made known to the world. This discovery is one of the most important ever made in science, and we commemorate its centennial by doing something to make more widely known the character of the illustrious man whose name will be associated with it as long as science is cultivated or civilization continues.

A hundred years of advancing knowledge has steadily exalted the importance of Priestley's discovery. It formed a great epoch in the progress of modern chemistry, and gave a profound clew to the internal constitution of Nature. The element first revealed, examined, and described by Priestley, is the most extensive in its distribution, and the most potent in its influence, of all the material constituents of the world. We now know with some definiteness the proportions in which oxygen exists in the various parts of Nature, but the aggregates are so stupendous as utterly to baffle the imagination. It exists in the smallest proportion in the atmosphere, forming but one-fifth of its weight. As there are fifteen pounds weight of air on every square inch of the earth's surface, it follows that there are three pounds of oxygen to the same area. By a simple calculation, it therefore turns out that the amount of oxygen in the earth's atmosphere is one quintillion, one hundred and seventy-eight quadrillions, one hundred and fifty-eight trillions of tons—a quantity absolutely inconceivable by the human mind.

In the world of waters, the scale of proportions is enormously increased, as eight-ninths of the weight of this liquid consists of oxygen. The ocean is assumed to cover two-thirds of the earth's surface, and to have an average depth of two miles, which would be sufficient to cover its entire surface to the depth of one mile and one-third. This would give us twenty-seven hundred pounds of oxygen for every square inch of the earth, or an amount in the oceans equal to nine hundred atmospheres.

Chemical analysis has also shown us the proportions of oxygen in the various classes of rocks. It forms one-half the weight of silica, one-third that of alumina, and two-thirds that of lime; and, as the great bulk of the geological formations are made up of these minerals, it follows that the entire crust of the globe, so far as it has been explored, with its twenty miles thickness of stratified rocks and its underlying granites, consists of oxygen to the extent of one-half of its weight.

If we turn now to the world of life, although the absolute magnitudes are much less, the relative proportions of oxygen are very high, and the grandeur of its operations is simply amazing. Three-fourths the weight of the entire animal world, and four-fifths the weight of the whole vegetable kingdom, consist of this element alone. Moreover, the operations of life in both branches are intimately dependent upon its activity and the rapid changes of which it is the main agent; while the vegetable kingdom is a grand laboratory, worked by the power of the solar rays to liberate oxygen from its combinations, and pour it back into the atmosphere in a free and active state. The animal kingdom, on the other hand, through all its grades, depends for its existence upon the incessant withdrawal of oxygen from the air. Each adult person consumes two pounds a day of this gas, or over seven hundred pounds a year, or some twenty-five tons in the allotted period of seventy years; and the thousand million human beings upon the earth are all busy, day and night, from birth to death, in altering the constitution of the air at the same rapid rate. And what man is doing, all the multitudinous tribes of inferior life, in the sea, on the land, and in the air, are doing also. Besides this, the great operations of combustion, fermentation, and decay, upon the globe, are carried on by the insatiable affinities of the same ubiquitous agent. It has been calculated that the oxygen required daily to maintain the course of terrestrial transformations is no less than eight thousand million pounds, or seven millions one hundred forty-two thousand eight hundred and forty-seven tons.[1] And, though this is probably an extreme under-estimate, we have seen that the stock of free oxygen in the air is so vast that it would require millions of years for this rate of consumption to make a sensible impression upon it, even if the counter-changes of the vegetable kingdom, by which the balance is constantly restored, should altogether cease.

Such is the grandeur of the part played by this wonderful element of Nature which has now been known exactly a hundred years. In his beautiful lecture which forms the opening article of our present number, Dr. Draper has vividly portrayed the office of oxygen in relation to the scheme of terrestrial life, and to this nothing needs to be added. But it is fit, on the present occasion, to give emphasis to the fact that, up to the time of Priestley, mankind were as absolutely ignorant of these things as if they had been destitute of all capacity to understand them. The human race had indeed run a vast career of intellectual activity, and had exploited numberless fields of thought with great results. Forms of religion and systems of philosophy had grown and decayed; numerous arts were perfected and forgotten; literatures were cultivated, exhausted, and passed by; empires and civilizations had flourished and faded, and for many thousands of years the world's greatest minds had been speculating, questioning, and inventing, before the man appeared who first explained the constitution of the air, and who first gave a rational answer to the question, "What is the breath of life?" At a superficial glance we should infer that there had been an enormous waste of precious intellectual force in all those historic ages over futile and worthless subjects, and that, while investigating with infinite assiduity every thing that was remote and impossible, the vital and immediate matters of daily and intimate concern had been systematically shunned as objects of study. But the intellectual evolution of man has conformed to a method, and Nature seems to have been no more economical of her mental than of her material resources. There is a prodigality in her ways which a narrow philosophy cannot comprehend. Of her profusion of flowers, but few issue in fruit; of her myriads of eggs, but few are hatched; of her numerous tribes of life appearing in the remote past, multitudes are extinct; and, of the achievements of her intellect, the great mass is lost in oblivion. But, through all her seeming waste, Nature has, nevertheless, a grand economy. She gives the widest chances, under a system which favors the best; the failures are rejected and the fittest survive. Through apparently boundless waste, with infinite deliberation, she works onward and upward to a better state of things, and in the mental world no less than in the physical, through interminable defeats and failures, and a prodigious amount of empty and fruitless effort, solid and permanent results are at last arrived at. Modern science arose from the exhaustion of previous methods of thought. The earlier philosophy speculated concerning Nature, and sought after her truths in the depths of the human mind. All that high genius and varied intellectual power could do was done, but to no purpose until the searchers for truth changed their attitude to Nature, and began to inquire of her by the simple and despised methods of experimental investigation. Dr. Priestley, first of all men, approached the problem of the constitution of the air in this spirit, and was even compelled to devise the contrivances by which gaseous bodies could be manipulated. He was on the right track, he had struck the true method, and magnificently did Nature reward his sagacity and his wisdom. Of course, for the Greeks or the Romans, or the schoolmen of the middle ages, to have discovered oxygen, would have been impossible. Only with the decline of their modes of thought could new methods arise, and only through the apprenticeship of generations in the field of physical investigation were men prepared to pass to the subtler search of the inner nature of material things. The discovery of oxygen, therefore, came in its due time in the mental unfolding of humanity; and while to Dr. Priestley undoubtedly belongs the honor of having first disclosed and identified it, others would quickly have plucked the ripened fruit if he had not; and in point of fact oxygen was independently discovered shortly after by the Swedish chemist Scheele, who also discovered chlorine in 1774.

But, if the discovery of oxygen formed a great epoch in our advancing knowledge of the constitution of Nature, its influence was no less profound upon the advance of chemical science. We are accustomed to regard chemistry as a kind of knowledge that is peculiarly modern, but it is really very old, and has had a long course of development. Liebig has stated that the completion of a science implies three stages or operations. There are 1.—The ascertainment of the properties of things by observation and experiment; 2. The bringing of them into relation by principles or ideas; and, 3. The application of mathematics, or subjecting the phenomena to the test of quantitative investigation. In chemistry, the first of these stages runs back to antiquity. The ancients knew many facts and made many empirical experiments in the arts which were of a chemical nature. They knew seven metals—gold, silver, mercury, copper, iron, tin, and lead. They also knew various preparations of zinc, antimony, and arsenic, and must have had a very considerable knowledge of metallurgical processes. They had also a knowledge of glass, pottery, soap, dyes, pigments, precious stones, asphalt, alum, starch, beer, and many other substances which, if not exact, was still so positive as to guide them in the processes of manufacture. This kind of knowledge of the properties of bodies must have gradually increased, and when we come down to the time of Gheber, the Arabian, who wrote a thousand years ago, we find that this species of information had not only greatly increased, but had become more definitely chemical in character, while laboratory operations were systematically practised. Gheber, for example, knew the properties of common salt, potash, soda, saltpetre, ammonia, copperas, borax, corrosive sublimate, oxide of copper, metallic arsenic, compounds of sulphur with the metals, and the methods of preparing sulphuric and nitric acids, aqua-regia, litharge, and the operations of distillation, sublimation, smelting, and a great number of chemical processes, as they were practised down to the end of the eighteenth century. By the alchemists these facts were immensely multiplied, forming a vast body of knowledge concerning the chemical properties of substances which form the foundation of the science, and constitute Liebig's first stage in its progress.

Although the second stage—the formation of general ideas or theories—is a sequence of the first, and implies accumulated observations to be explained, yet it was begun early. The doctrine of the four primitive elements, fire, air, earth, and water, was the first chemical theory, and sufficed for many centuries. To these four elements of Aristotle, which were regarded as the four fundamental causes of the physical properties of matter, were added three new elements—mercury, sulphur, and salt—which also stood for certain properties and causes of change, rather than concrete bodies. Mercury represented volatility, and was supposed to give this property to matter; sulphur was connected with changeableness by fire, or combustibility, and salt represented fixity, like the salts found in ashes. On this view, alcohol, or aqua vitæ, was regarded as "sulphurous vegetable mercury," which only meant that it was inflammable and volatile. Hence Basil Valentine says: "When a rectified aqua vitæ is kindled, its mercury and sulphur separate; the sulphur burns quite vividly, for it is pure fire, and the delicate mercury flies into the air and returns to its original chaos."

Such rude ideas answered to begin the work of chemical theorizing, but the increase of facts at length showed that they were contradictory and absurd. About a hundred years before the time of Priestley, Beccher, a German chemist, in undertaking to correct the doctrine of salt, sulphur and mercury, struck a new conception which soon grew into a comprehensive and important chemical theory. In working with sulphur, he sagaciously detected the analogy between the formation of sulphuric acid from sulphur and the reduction of metals to an earthy form (calx). The metal was supposed to consist of an earth, and something which, in the process of combustion, was separated from it; in like manner sulphur was supposed to consist of an acid and something that was separated from it, by burning, and to this something Stahl afterward gave the name of phlogiston—Greek for combustible. So intimately and extensively were fire and combustion involved with chemical changes, that a theory of combustion was regarded as the same thing as a theory of chemistry. It was assumed that all combustible bodies are compounds. One of the constituents was supposed to be dissipated during the process, while the other remained behind. The part dissipated, phlogiston, was held to be the same in all combustible bodies whatever, and hence the differences among them depended upon the residues. On this view, the property of combustibility is always owing to the presence of phlogiston, and fire, or inflammation, to its escape. Phlogiston was communicable from body to body. When phosphorus is burned it loses its phlogiston, and an acid remains. But if now the acid is heated in a retort with charcoal-powder, sugar, or resin, these combustibles are deprived of their phlogiston, which, passing over to the acid, reproduces phosphorus. Bodies saturated with phlogiston were said to be phlogisticated, and, when deprived of it, were dephlogisticated, processes which might be as partial or complete as the variations of combustive phenomena. These ideas were founded upon experiments so decisive that, when the existence of the principle itself was once admitted, the explanation was entirely satisfactory. "There are ideas," says Liebig, "so great and vast that, even when entirely perforated, as it were, in all directions, they leave enough of matter to occupy the powers of thought of mankind for a century. Such a vast idea was that of phlogiston. The question as to its material existence was void of all significance, so long as the idea was fruitful in the classification of known facts, and prepared the way for new generalizations."

Chemistry had made rapid advances under the phlogistic theory for a century, but the idea was now to be brought to the test of quantitative examination. The introduction of the balance threw a new light upon the subject, and, under its application, the assumptions of the phlogistic system of chemistry proved to be entirely erroneous. The effect of careful weighing was to show that metals and other combustible bodies, in burning, grew heavier; that there was no subtraction or loss of any thing, but always an addition; and that the compounds produced were, in every case, equal in weight to the combining elements.

Dr. Priestley was a firm believer in phlogiston, and named the new element of the atmosphere which he had discovered, dephlogisticated air. He made but little use of weighing in his researches, and was not qualified by his training to go on and reap the full scientific advantages to which his great discovery opened the way. These were secured by the French chemist Lavoisier, who named the new element oxygen, and, having by his experiments overthrown the old view, he had the largest share in establishing the oxygen theory of chemistry which took its place. As Dr. Whewell observes; "Few revolutions in science have immediately excited so much general notice as the introduction of the theory of oxygen. The simplicity and symmetry of the modes of combination which it assumed, and, above all, the construction and universal adoption of a nomenclature which applied to all substances, and which seemed to reveal their inmost constitution by their name, naturally gave it an almost irresistible sway over men's minds."

But, while the theory of oxygen has guided the development of chemistry for the past hundred years, it is now following the fate of its predecessor: the facts have outgrown it, and a "New Chemistry "has arisen in its place. Yet, whatever may be the vicissitudes of theory, oxygen is still in the field—still the object of wonderful interest, and no possible changes in the future can ever dim the lustre of its discovery.


Several of the most distinguished chemists of the country have united in a call to all interested to convene at Northumberland, Pa., on the 1st of August, where Dr. Priestley lies entombed, to celebrate the one hundredth anniversary of his discovery of oxygen gas. Such a tribute will be most proper and befitting to his memory, and will suggest interesting phases of thought that cannot fail to make the occasion profitable to all who participate in it. In the circular of invitation it is said: "The fact that this illustrious man spent the last years of his fruitful life in this country, renders the recognition of his work by American chemists peculiarly appropriate;" and it may be added that the circumstances which brought him here, and which pertain both to his own character and the condition of his native country, are matters especially suitable for consideration at such a time. For Dr. Priestley was more than an eminent scientific discoverer—he was a sincere, courageous, high-minded man, and stood forth as the unflinching champion of liberal opinion when his country was given over to the narrow spirit of fanatical bigotry. Dr. Priestley's career exhibits the sublime moral spectacle of a man against a nation, and that, too, on a vital question of constitutional rights; and such was the conduct of the two parties, as, in the language of Dr. Thomson, to "fix an indelible disgrace upon the country," while Dr. Priestley's course will be honored as long as freedom of opinion and independence of character elicit the admiration of men.

Dr. Priestley's intellectual greatness is the more remarkable as he led what may be called a divided life. He was a discoverer in science, and a pioneer in theology. His extensions of our knowledge of Nature will suffice for his immortality, while the extent and power of his theological work made him famous among his contemporaries. Nevertheless it is only by concentration that the highest results can be achieved. We have shown in the preceding article where Dr. Priestley fell short as a man of science. His scientific education was insufficient. He began these studies late, and pursued them at great disadvantage, for scientific pursuits are expensive. He says: "I applied myself with great assiduity to my studies, which were classical, mathematical, and theological. These required but few books. As to experimental philosophy, I had always cultivated an acquaintance with it, but I had not the means of prosecuting it." His great rival, Lavoisier, was more fortunate. His father was rich, and spared no expense on his education; and, having an early taste for the physical sciences, he was trained to experimental research, which he pursued so successfully that, at twenty-one, he received a gold medal for a memoir on the best and most economical method of lighting the streets of a large city. Could Priestley have had similar early advantages, there is little doubt that he would have devoted himself entirely to science, and, with his remarkable genius for investigation, would have impressed himself far more profoundly upon the chemistry of his period.

Of the truth or error of Dr. Priestley's religions opinions, it is no place here to speak; but, that he sought the truth in all earnestness, and maintained what he believed to be the truth with steadfast determination, does not now admit of question. That he led a life of the highest purity was never doubted, even by his enemies, and that he was ever animated by a high religious aspiration his works bear abundant witness. A portion of each day was given to prayer and private devotional exercises, and he kept up the practice of Sunday preaching, whether officially engaged or not; while the uniform testimony of all his parishioners showed that his ministrations were conducted in a loving, Christian spirit. Shall we question that the religious experience of such a man was not profound and genuine? And yet he was a speculative materialist; that is, he did not believe in "the immateriality of the sentient principle in man." No one, however, had a firmer belief in immortality and the future life than Dr. Priestley. This transcendent article of his faith he did not ask at the hands of Science nor hold as dependent upon her investigations. His repose in the prospect of immortality was grounded on the Christian doctrine of a resurrection; no results of science could reach or disturb it, and in this he was far in advance, not only of his own age, but of ours. As an illustration of his independence of character, and his scorn of all temporizing, it may be stated that he promulgated these views while living under the patronage of Lord Shelburne, and beset with solicitations to accept high favors from the Church and the state. Undoubtedly, as Dr. Draper remarks, it is upon his discoveries that his future fame will rest, while his theological works are already forgotten; yet the world owes him a debt for his manly maintenance of independent inquiry in a cowardly age and among a craven people, which will command respect as long as the nobler virtues of character continue to be appreciated.


The attention of those desiring to procure physical-science apparatus is called to the advertisement of Professor W. C. Richards, Ph.D., who, having retired from the public lecture-field, offers for sale his extensive collection of instruments. The stock includes duplicates of important pieces, such as coils, batteries, spectroscopes, vacuum-tubes; and it offers an excellent chance for colleges, high-schools, and private students, to supply themselves from this collection. Those who are in want of such instruments should send to Professor Richards for his catalogue.

  1. The foregoing data are taken from Faraday's "Lectures on the Non-metallic Elements." London: Longmans, 1858.