Stillman: The Dawn of Modern Chemistry.

Popular Science, heinäkuu 1915

By Professor John Maxson Stillman
Stanford University

The period of the history of chemistry which i have chosen to designate as the dawn of modern chemistry begins practically in the early sixteenth century and extends well toward the latter part of the eighteenth century. Not that the chemistry of that period shows any very clear relation to the present state of chemical science, but because at about the middle of the sixteenth century there was inaugurated an era of activity in chemical thought and experimentation, which has continued with steadily increasing velocity and productiveness to the present time. The period referred to does not by any means mark the beginnings of chemical arts or theories, for the beginnings of the technical arts of chemistry may be tracked back as far as recorded history. The earliest records of Egyptian or Babylonian origin show that the arts of metallurhy, the making of bronzes and other alloys, have been practised, and uninterruptedly so, since at least some 3,500 years before the Christian era. So also the manufacture of glass and pottery, the coloring of glass and pottery, the manufacture of colors for dyeing and painting, are of great antiquity. it is worthy of note also that these technical arts of chemistry possessed since very ancient times a kind of literature of their own in the form of recipes and directions for the various processes of the special art. Such manuscripts were doubtless not meant for public information, but for the use of the artisan alone, and were transmitted from the master to the apprentice or successor for his own use. The earliest original manuscript of this character known to exist is a manuscript on papyrus written in the Greek language which was discovered in an Egyptian tomb at Thebes, and is now preserved at Leyden. it dates from the third century of our era, and was doubtless a manuscript which escaped the wholesale destruction of alchemical and magical works in A.D. 290 by order of the Emperor Diocletian, issued, as believed, to prevent the danger of the possible making of gold by the alchemists and its resulting influence upon the currency system of the Empire. This work consists of recipes for the testing of metals, their purification, their alloying, making of bronzes and brasses, the coloring of metallic objects by superficial alloying, imitations of gold, writing in gold letters, preparation of purple colors, etc. Some hundred recipes in all are contained in this manuscript. it is evidently based upon earlier works of similar character, and indeed earlier works whose contents have been preserved to us through the mediation of copies or abstracts by later writers evidence that the ideas and methods were doubtless mostly centuries old when this papyrus manuscript of Leyden was written. The researches of scholars, notably of Berthelot, have shown how very similar, in many cases identical, recipes to those of the papyrus of Leyden have been transmitted through Roman, Arabic and later languages in manuscript form, probably uninterruptedly in Europe down to the beginning of the printing of books.

It is believed that the Greeks originally derived their knowledge of the chemical arts largely from Egypt, but that the ancient Greek philosophers were the first to divorce the philosophy of chemistry from the religious ideas and magical notions of the Egyptian priesthood which with them obscured the logical reasoning from cause to effect, or from effect to cause. However that may be, the Greeks were the first sources of natural philosophy for European thought. And such names as Thales, Democritus, Pythagoras, Plato and Aristotle are names that characterize the period of the height of clarity of Greek philosophy somewhere from about 600 to 300 B.C.

At about the time when this papyrus of Leyden was written the so-called Alexandrian Schoold of Greek philosophers was dominant. This later period of Greek phisophy was marked by much brilliancy and genius, but was also characterized by a distinct influence from Egyptian sources of oriental mysticism and occult philosophy.

The Romans were the natural inheritors of Greek thought, and the Roman conquest of the civilized and much of the uncivilized world again operated to spread the useful arts of chemistry as known to the ancients, though Roman influence did not contribute greatly to generalizing thought.

In A.D. 489 the Alexandrian Academy was destroyed by the Emperor Zeno and its Greek scholars scattered. A body of these, mainly Syrians, established themselves in Persia, where they continued the study and teaching of the science of the Alexandrian school.

Barbaric invasion resulted in almost complete extinction of the remains of Greek civilization in Europe. The Syrians in Persia were the principal conservators of ancient science, and they continued to preserve and reproduce the works of the ancient Greek writers.

In the seventh century occurred the gread Mohammedan conquest of the Mediterranean countries. The conquering Moslems overran Persia and Syria. Fortunately they were impressed by the Syrian scholarship, and Syrian scholars were given place in the courts of the Caliphs, and such works of the science of the ancient Greeks as were in their possession were translated into Syriac and Arabic, and thus such authors as Euclid, Archimedes, Ptolemy, Hippocrates, Galen, Zosimus and Aristotle became accessible to Arabian scholars and served as the foundation to the science of the Arabians.

In the eleventh and twelfth centuries these Syrian schools were in their turn suppressed by Mohammedan fanatics and the Arabians themselves became the principal guardians of ancient science. Arabian translations of Greek authorities and the works of Arabian commentators, often translated into Latin, became the authoritative sources of medieval science. So completely indeed had the original Greek works disappeared from Europe that later centuries assumed that the Arabians were the originators of much that they merely acquired and transmitted from the ancient Greeks and Egyptian through Syrian and Arabian translations. Arabian physicians, astronomers, mathematicians, and aclhemists bevame the teachers of science to the Europe of the middle ages.

The original literature of the ancient world having practically disappeared from Europe during the early middle ages, science and philosophy had reached a low ebb. The medieval Christian Church was also discouraging in its attitude toward scientific discovery and philosophic readoning. Clerical authorities and the scholastic learning became more and more intolerant of dissenting opinions or any kind of free thought. Stagnation in science was the consequence, especially in the natural sciences. in medicine, for example, experiment and independent observation hardly existed. The works of Avicenna, Averroes, Mesue and other Arabian interpreters of the Greek authors Galen and Hippocrates were the recognized authorities, and even in the universities of the fourteenth and fifteenth centuries, the teaching of medicine consisted in reading and expounding the works of these authors. The works of Galen and Hippocrates themselves were indeed hardly known in their original purity, but as elaborated with infusions of Arabian mysticism and superstitions, symbolism and astrology.

Other sciences exhibited similar tendencies. Astronomy had degenerated from the rationality of Pythagoras or of Ptolemy into a stereotyped Ptolemaism mixed with astrology. The doctrines were the accepted natural philosophy. The condition of chemistry was similar. While mining, metallurgy and other ancient arts of chemistry maintained their continuity in spite of barbarian invasions or Mohammedan conquests, and gradually added to their store of useful facts, the generalizations or theories which have always been essential to great advances in science had deteriorated to a condition which might be called rudimentary even as compared with the earlier chemical philosophy of Thales, Democritus or Aristotle. The early Greeks had at least reasoned logically from the limited knowledge in their possession. That their generalizations were often more metaphysical than scientific resulted from the fact that their deductions were not based so much on experiment as upon the observation of the more obvious natural phenomena. And, however valuable metaphysical reasoning may be for intellectual discipline, or as a tool in the critical analysis of observed phenomena and their relations, it can not go beyond the facts involved in its premises and can not materially advance the development of experimental sciences. Thus it is safe to say that up to the fourteenth or fifteenth centuries the natural and physical sciences presented few advances and much retrogression from the best days of ancient Greek science.

Arabian scholarship, however it may have contributed to mathematics, astronomy and certain fields of physics, had brought to chemistry little new of value and much of confusion of mysticism and superstition. This statement is largely justified by the results of modern critical investigation whic hhave shopwn that the works of chemical character attributed to the authorship of Gheber, Avicenna and other Arabian authors are quite generally fabrications of the twelfth to fifteenth centuries, publiches under those names either to obtain a wider circulation or to avoid the unpleasant consequences that might visit the real authors for dabbling in a suspected or forbidden art. Just as the medical science of the early renaissance was a medley of Greek Galenism, oriental mysticism and medieval superstition, so the chemical philosophy of the time was a medley of Aristotelian philosophy, with similar infusions of oriental occultism. Many chemical substances were known which to Greeks or Egyptians were unknown - but in so far as any valuable body of theory is concerned, hardly an advance had been made. The chemical theory of the time was mainly of Greek and Egyptian origin filetered, as we have seen, through the Syrian and Arabian sources and for centuries nearly without material progress.

Let me attempt to present the main fundamental concepts of the nature of matter and its changes which constituted the generally accepted chemical theory at the beginning of the sixteenth century, whence we date the revival of chemistry.

The ancient Greeks entertained a very persistent notion of the essential unity of matter. They differed at various times and in different schools of natural philosophy as to the formulation of this theory. Thus some considered that water was the primal element from which all others had been developed, others considered the air as the primal element, others fire. Aristotle finally formulated the notion of the constitution of matter which became the most generally accepted theory in later centuries. This was the theory of the five elements - fire, air, water, earth, and ether or essence. it seems very probable that this theory was derived originally from ancient Hindoo philosophy, because in ancient Hindoo classics it is more completely elaborated than by Aristotle. The four elements - ari, fire, water, earth - were not considered as distinct elementary substances, according to our modern definition of an element, but rather as determining qualities.

Thus fire combined the qualities of warmth and dryness; air - warmth and moistness; water-cold and moistness; earth - cold and dryness. All substances were considered as combinations of these elementary qualities, or in some sense as composed of these elements. The fifth element, ether or "essence," was more subtle and less clearly defined. it was supposed to be capable of taking all forms, and finally came to be identified with the "materia prima," or primal matter, out of which all other forms of matter were supposed to be born.

The Aristotelian notion of the four elements also implied the possibility of the change of one element to another. Thus when water evaporated by heat it became air; that is, by the addition of warmth, it changed from cold and moist to warm and moist, the properties of air. This idea mong later alchemists served to justify the notion oft he transmutability of the elements, that will-o'-the-wisp of chemist for many centuries. But this idea of the possibility of transmuting one element into another as of the baser metals into gold and silver received greater vitality from the observations and experienes of the metallurgists upon the occurrence, preparation and alloys of the metals.

The metals known to the ancients were seven in number, gold, silver, lead, mercury, iron, copper and tin, though they were not considered as elements. Other metals indeed entered into their alloys, but they were not recognized by them as separate or distinct from those already named. Arsenic was known, though not considered as a metal. Bismuth and zinc and antimony began to be recognized as distinct substances about the beginning of the sixteenth century. As methods of analysis were rudimentary even at this later date, and as there was no realization of the concept of an element of unvarying composition and properties, and as the metals were obtained in varying degrees of purity or admixture, it can be understood how the changes in appearance and properties of the metals, as obtained from their ores, was believed to be due to a partial transmutation in the Aristotelian sense.

In the alloying of various metals, the character of the alloys was changed in ways that easily suggested actual changes in the character of the metals themselves. Thus we know that the Egyptian considered certain alloys of gold and silver as a distinct metal "electrum." The frequent occurence of some gold in silver as obtained from its ores also easily suggested the idea that this gold had in some way been produced from the silver.

Hence, if by alloying certain metals they obtained a metal resembling gold in color, this was perhaps really an approach to making gold, and, if it had been possible to make such an alloy by any combination of materials as should answer all their known tests for gold, from their standpoint it might well be real gold.

We can comprehend that if we considered an element only as a combination of certain qualities and not as a specific simple substance - there would be no a priori improbability in such an hypothesis.

Thus the experience of the chemists with the metals was the real motive force in vitalizing and modifying the ideas of the Greek philosophers with respect to the nature of matter and its changes. The attempt to imitate precious stones was another line of work which helped to confirm these theories, thought it may well be doubted wheter in all cases the alchemists were self-deceived as to their success in producing the real articles even when they succeeded in passing them off as genuine.

Nevertheless the accepted theory of the essential unity of matter and of the possibility of transmuting one element or substance into another was the working hypothesis that kept the alchemists, for so many centuries, at their vain labors. As the study of the metals and their uses formed so large a part of chemical activity, there also grew up in time special theories as to the origin and changes of metals. One of the oldest of these can also be traced to the Egyptians and to Plato - the notion that mercury bears a peculiar relation to the origin of metals. Among the Egyptians lead occupied a similar position, but the substitution of mercury in this rôle took place as early as Plato.

The very peculiar properties of mercury - argentum vivum, the liquid living silver, quick-silver - and the strange manner in which it lost its identity in combination and in alloys with other metals gave rise to a theory that it was the source of the other metals. And again, as with other metals, it might not always be the same in composition and properties, the idea developed that not the ordinary mercury, but a mystical purified mercury - the so-called "mercury of the philosophers" was a constituting element in all the metals.

So also sulphur bore a prominent relation to the occurrence and to the furnace reactions of metallic ores. its combustibility, its frequent presence in metallic ores, the combinations with metals and the colors of these combinations - the red or black of its mercury combinations - the black copper compound - the yellow or red of arsenic compounds - etc., endowed it also with a mysterious relation to the metals, and it also became considered as a constituting element of the metals. Arsenic, which acts very similarly to sulphur in many such compounds, was sometimes associated with it in that rôle. And here again was assumed not ordinary sulphur, but a fancied perfect sulphur - the "sulphur of the philosophers."

Again the seven metals were associated with the seven planets of the ancients - hold with the sun, silver with the moon, copper with Venus, lead with Saturn, iron with Mars, mercury with Mercury, tin with Jupiter, and these planets were supposed to exert influences upon the generation and development of perfection of the metals in the earth. The base metals were often supposed to exert influences upon the generation and development or perfection of the metals in the earth. The base metals were often supposed to be undergoing a gradual development toward perfection. This development toward perfection, that is, toward silver and gold, might be influenced by many factors, such as the relative quantities of their sulphurs or their mercuries or sulphurs, the time and local conditions of their position in the earth and the influences of their planets. it was not considered improbable that chemists might by experiment devise means to hasten this natural growth.

These notions I believe fairly summarize the quite generally entertained theories which make up the representative chemical theory at the beginning of the sixteenth century. But this beginnig of the sixteenth century is the period of the full flower of the Renaissance. The first impulse to this period of remarkable activity in all domains of human thought originated in italy, and at least as early as the thirteenth century. it began with a renewed interest in ancient Greek and Roman literature and art, naturally also a fresh interest in philosophy. it was fostered by the Florentine Academy under the protections of the Medici, though its influence soon spread to other parts of Europe. A new spirit of criticism was awakened, and even the church was invaded by a long-forgotten stimulus to freedom of though and discussion. As the movement spread, the aroused interest of men in all domains of human activity gave the rise to many great movements. in the thirteenth century were founded the universities of Padua, Bologna, Salerno, Salamanca, Paris, Montpelier, Oxford and Cambridge. Some of these trace their foundation to clerical schools of even earlier date - but grew to importance and influence under the new impulse.

In the fourteenth century the German universities of Vienna, Prague and Heidelberg were founded, and the fifteenth century was marked by a rapid increase in the number of German and French universities and in their influence. An influence of similar importance to that of the universities of the time - and perhaps even surpassing that influence - arose from the invention of printing from moveable metal types which occurred about the middle of the fifteenth century. The revival of interest in ancient literature as well as the promulgation of new ideas was vastly stimulated by the possibility of making written works accessible to a vastly increased constituency, and the interchange of information and ideas thus made possible contributed enormously to the great intellectual development which we call the renaissance. The civilized world became stimulated to new thoughts and to and to new enterprises, one might almost say it became intoxicated with great ideas and great ventures.

Natural science was the last field of thought to feel the new impulse, and in chemistry there was little evidence of progress until the sixteenth century. The representative chemical authors known to the fifteenth century were Arnalf of Villanova, the unknown writers who wrote under the name of Raimundus Lullus (or Lully) and unknown writers who wrote chemistry under the name of Gheber, or of Albertus Magnus. All these writings were obscure in style and contributed little to the knowledge of chemistry or to clear thinking. the chemists of the period might be classified into two groups - artisansa who were not generally of university education, working by traditional methods in their respective arts and not addicted to writing or philosophizing; and the learned class, usually physicians, sometimes clericals. Some interest in chemistry existed but was mainly confined to the efforts to discover the transmutation of metals or the elixir of life. Chemical facts were at times developed by their efforts, but disappointments and disillusions had brought the chemical theories of the ancients and alchemists into general stagnation and disrepute. Cornelius Agrippa, writing about 1530, quotes a proverb of the time - "An alchymist is either a physician or a soap boiler."

Four men notably mark the beginning of a new era in chemical activity, Theophrastus von Hohenheim (called Paracelsus), Georg Bauer (called Agricola), Vannuccio Biringuccio and Bernard Palissy.

Paracelsus was born in Switzerland in 1493; Agricola in Saxony in 1494; Biringuccio of Siena, Italy, probably about the same time; while Palissy was born in France and his birth year is variously given as 1499 and 1510.

We can better appreciate the stimulating intellectual atmosphere of the period in which these men lived if we recall that the span of their lives touched the life times of Michelangelo, Macchiavelli, Leonardo da Vinci, Ariosto, Rafael, Rabelais, Copernicus, Vesalius, Thomas More, Columbus, Cortez, Cardanus, Martin Luther, Erasmus and Savonarola.

Three of the four chemists mentioned - Agricola, Biringuccio and Palissy - may be said, each in his own line and country, to have laid the foundations of modern chemical technology. Each of them wrote an almost epoch-making work in a particular field of applied chemistry and exerted a powerful impetus toward raising the profession of technical chemist above the rank of Agrippa's "soap-boiler."

Biringguccio's work was published in 1540 in Italian under the title of "Pirotechnia." It treats of the metals, the semi-metals, their ores and minerals, and of some salts; of the alloys of the metals, their manufacture and uses. It contains also recipes for the use of the goldsmiths, the potters and other artisans. It is important as an attempt to give a sober, sensible and intelligent description of the technical chemistry within his knowledge. It is interesting also because it preceded the greater work of Agricola by about sixteen years and is mentioned by the latter as having been in his hands, though it contained little that was of use to him.

While Biringuccio is known only through his one book, the works of Agricola are more numerous. They are chiefly upon minerology, mining or geology. He began publishing about 1530, but his great work, "De re Metallic," appeared in 1556. Agricola was a man of university training, and a scholar of fine type. He has studied in Italy and was a physician by profession. He was city physician at Joachimsthal in Bohemia, and later at Chemnitz in Saxony. His location in these mining centers gave him ample opportunity to become interested in mining and mineralogy and in the chemical operations used in metallurgy and assaying. The great work above referred to is for the time a very remarkably clear description of the operations of mining, smelting and assaying, with very complete description of the chemistry of these arts as known to the miners of the time and region. He does not claim apparently to have contributed original work to these arts, but the work of Agricola may justly be considered as the first really great work in the line of the scientific presentation of a chemical industry, a worthy pioneer to the many great technical works which have since appeared in so many lines of chemical industry. Its influence in its own field was immediate, as shown by the later editions called for and even still more by the number of similar though less important treatises which followed its appearence.

Bernard Palissy was a man of much less scholarship than Agricola. What he lacked in that respect he compensated for in an unconquerable enthusiasm in experimentation in the field which most interested him - the making of pottery and its glazes and enamels. He was a real investigator in his field, and his published works describe his experiments and discuss them clearly with neither the digmatism not the mystical jargon that most chemical writings of the previous centuries, or even of the subsequent century, exhibit. His works published between 1557 and 1580 may be said to have done much the same for the arts of the potter that the work of Agricol did for mining and the chemistry of metallurgy, with the difference that Palissy's work was rather a presentation of the result of his own labors than a complete compendium of existing knowledge and practise as was the "De re Metallica."

It can not be claimed either for Agricola or for Palissy that they were free from the prevalent superstitions or mystical ideas that were almost universally entertained in their century - but it can be asserted that they kept their constructive labor and thought free from obstruction from such notions. Both repudiated the transmutation ideas of the alchemists as vain and profitless, and both endeavored to make their knowledge and their ideas as comprehensible as possible for their successors or contemporaries. THeirs was the spirit of service and that is also the spirit of moder science.

The work of these three chemists, however scientific its spirit and method, was not such as to affect immediately the thought of the time in lines outside of the industries they represented, nor to influence the chemical notions of the university faculties - mainly interested in philosophy and medicine.

The fundamental basis of chemical theory of the middle ages - the rudimentary chemical philosophy of the Greek-Arabian philosophers and alchemists - was not seriously affected by the work of these pioneers.

It is to Paracelsus that we are indebted for the impetus that was to inaugurate a broader and livelier interest in chemical activity and in chemical theories. Paracelsus was a man of very different type from his three colleagues already mentioned. A physician by training and profession, as his father was before him, he had traveled much and far - from Sweden to Italy, and from France to Bohemia - as an army surgeon, student or itinerant doctor. Brought up in childhood and in early manhood in mining countries, he had early become interested in the chemistry of the metals and had himself worked in the laboratories of the mines. He was a man of original power, restless activity, great energy and a natural-born revolutionary.

The early influence of philosophers of the fantastic neo-platonic natural philosophy of the Florentine Academy and its followers, had shaken his faith in the accepted Aristotelian and Galenic philosophy which was the basis of medical theory and medical teaching of the time. This revolt from the traditional dogmas, combined with manifestly acute powers of observation and an open mind for such medical or chemical practises or ideas as he met with in the course of his extensive experiences among all classes of people in many lands, resulted apparently in enabling him to surpass the conventionally restricted medical practise of his time in the successful treatment of many diseases. His reputation as a brilliant and able physician attracted early the notice of some of the noted scholars at Basel - and Paracelsus was called to that city as city physician and professor in the university. In his teaching he at once began opposing the conventional dogmas and the antiquated practise of medicine. The history of medicine and the testimony of learned critics of the period such as Erasmus, Agrippa, and Peter Ramus give ample evidence that the time was ripe for a reform in medicine. For centuries all initiative had been discouraged by the accepted infallibility of the traditional Greek and Arab authorities. The medical practise was based on analogical reasonings, and astrology, charms, incantations and exorcisms played an important part. To question the foundations of the medical theory or to introduce innovations in medical practise was unpardonable heresy to the guild of physicians.

Paracelsus must be credited with the ability to appreciate the failings of the profession and with courage and ability with which he adressed himself to the task of breaking fown the wall of inertia and tradition behind which the medical profession had entrenched itself. In this task he found but scat assistance from within the fold. On the contrary, he soon aroused the liveliest animosity and the most bitter opposition on the part of medical faculties. But opposition did not discourage him. His was the spirit of the propagandist and the fanatic, and antagonism and persecution but intensified the earnestness and the energy with which he labored for the spread of his revolutionary doctrines. That he might appeal to a wider constituency than the hostile academically trained profession, he followed the example of Martin Luther in discarding the use of the Latin language in lectures and writings, and wrote and spoke in his native German. This was also a flagrant offence against professional etiquette and helped to widen the breach between the medical schools and Paracelsus and his pupils and followers.

Irritated by the attacks of his colleagues, he retorted by publicly burning the Canon of Avicenna, as Luther had burned the papal bull, and similarly to show his contempt for the assumed infallibility of the ancient authorities of medicine.

The lines of attack of Paracelsus upon the medical doctrines of his time were mainly three: First: Not the authority of the ancient authors, but observation and experiment must serve as the basis of medical diagnosis and treatment. Second: The substances of the human body are chemically constituted, the processes of the body are chemical processes and hence chemistry must form one of the foundations of rational medicine. Third: The use of the complex mass of decoctions of rare and costly herbs which served as the basis of the Galenic physicians' practise was not founded on reason, but on superstition. In his view every medicinal plant or mineral has an essential principle or spirit and to find and purify these and to apply them to the cure of diseases in a worthy and important aim of chemistry.

Many interesting and valuable improvements in medical practise are attributed to Paracelsus, but it is not the early history of medicine that interests us here except as it is involved with the development of chemistry.

The works of Paracelsus were apparently written between 1526 and his death in 1541, and therefore were written before the publication of the work of the three chemists above mentioned. They are, as collected, a columinous mass and of heterogeneous character, medical, surgical, philosophical, chemical and theological.

In harmony with his notions of the value of chemically prepared medicines he introduced into the practise many remedies not authorized nor sanctioned by the medical schools. Preparations of antimony, iron, mercury and opium were prominent among these, and apparently were employed with success in his own practise. To the chemists he especially appealed to abandon the vain search for the making of gold and silver - "the threshing of empty straw" - and to devote their energy and skill to the preparation of new remedies, and to their application to medicine.

But few of the works of Paracelsus were printed during his lifetime. In several cases the reason for this can be directly traced to the opposition of the medical faculties and their influence upon the public censors or publishers. But he did not cease writing on that account, and some twenty years after his death there began the active publication of his manuscripts. Some of these were autograph manuscripts - others more or less complete copies, or lecture notes edited or expanded by forrmer pupils - some of doubtful authenticity, and others known to be fabrications published by anonymous writers. It is still difficult in many cases to be certain as to the authenticity of some of the many treatises attributed to him. Their populatiry and influence during the succeeding century was very great, as is evidenced by the fact that the Paracelsus bibliography by Sudhoff enumerates no less than 390 titles of pritned publications up to 1658, when the last and best known Latin edition of his collected works made its appearance. Among these were four editions of his collected works in German and two in Latin.

Through the mass of writing of Paracelsus are scattered, rather than systematically gatheres, the chemical facts and theories which comprise his contribution to chemical literature. Together they form a considerable body of chemical knowledge, descriptions of chemical processes and substances known in his time with much of speculative theory. There is no evidence that he added in any important way to the chemical knowledge of his time. Though the first announcement of some chemical facts appear in his writings, he makes no assumption of originality in their announcement, any more than do Agricola and Biringuccio in their works. It was rather by his evident faminiarity with the chemistry of his time, and the novel and radical application of chemical preparations in the practise of medicine, that he challenged the attention of the chemists of his time. Here his influence was epochmaking. In the field of chemical theory he shows greater originality, and while much of his speculations are fantastic in the fashion of the philosophy of the time, yet in other directions he exerted important influence.

One very influential contribution to chemical theory, however, is to be attributed to Paracelsus. This was the theory of the three principles - the "tria prima". It will be remembered that the early alchemists had recognized the peculiar relation of sulphur to the occurence and changes of the metals - the sulphur of the philosophers - and similarly with respect to arsenic and mercury. Upon these vague and variously formulated hypotheses Paracelsus founded his more consistent theory.

All matter was, according to Paracelsus, constituted of three principles, sulphur, mercury and salt. Sulphur, he explains, is that which burns - the principle which renders bodies in any degree combustible and yielding heat. Mercury was that principle of bodies which renders them liquid and volatile, which enables them to melt on heating or to pass off as a vapor by distillation or volatilization. salt was the principle which resists the action of heat - the ash or the non-combustible and non-volatile constituents of matter. It will be observed that this is a generalization of the properties of substances based upon the observation of their behavior towards the various degrees of heat to which they were subjected in the customary processes of roasting, distillation, ignition or reduction (this word also we first find in Paracelsus).

The doctrine of the three principles of Paracelsus possessed that advantage over the Aristotelian elements - fire, water, earth, air - in that it was more closely related to experiment and experience and not so purely metaphysical. It could serve as a kind of working hypothesis to help understand the results of chemical experiment. The tria prima received early recognition in chemistry. The very celebrated work called the "Triumphal Chariot of Antimony," written about 1600 and passed off on the public as a translation of an early manuscript by an alleged Benedictine monk, Basil Valentine, adopted and helped to give a wider circulation to this theory. It became almost universally accepted by the chemists of the seventeenth century, and such popular text-books as those of the French chemists, Christopher Glaser and Nicholas Lemery, placed it at the foundation of chemical theory (the latter as late as 1713).

In the latter part of the seventeenth century, Becher introduced a variation of this theory, by placing, instead of sulphur, a terra pinhuis, as the combustible constituent, fat or oil having, in so far as its combustibility is concerned, a similar behavior to sulphur - for mercury and salt he substituted a terra mercurialis (mercurial earth) and a terra lapidis (or stony earth).

This in itself was no advance, but Becher's pupil, Stahl,and his followers elaborated this sulphur of Paracelsus or terra pinguis of Becher into the idea of a more abstract heat substance, phlogiston, while the less useful hypotheses of the mercury and salt gradually disappeared.

In the eighteenth century under the influence of such able chemists as Scheele, Black, Cavendish and Priestley the phlogiston theory became the most inspiring theory to stimulate the observation and researches of chemists. Only at the close of the eighteenth century when the phlogiston theory was no longer adequate to explain all known facts were the facts it attempted to explain re-interpreted by the genius of Lavoisier in terms of the modern theory of oxidation and reduction.

In considering the value and influence of all these now abandoned theories, we should keep in mind that the value of a theory in science at a particular epoch depends not so much upon its absolute truth or reality as upon the extent that it assists in classifying and accounting for observed facts and in stimulating to new observations or experiments.

It will be seen how the above theories are linked together and how each served for its own century and prepared the way for its successor. Nevertheless, the greatest service which Paracelsus contributed to the development of chemistry was in the influence which his teaching and his example and his widely published works exerted in battering down the wail of infallible dogma that for centuries had protected the doctrines of medicine from any important development from the side of its relation to chemistry. His unceasing criticism of the defects of the theory and practise of the ancient authorities, his trenchant arguments for a broader experimental basis for the science, his severe arraignments of the ignorance and venality of the physicians of his time; his ridicule and defiance of their sacred authorities, togerher with the constant reiterations of the knowledge of chemistry as essential to understanding the life processes in health and disease, exerted a powerful influence not indeed so much upon the university faculties or the physicians schooled in their doctrines as upon the younger and more progressive generation of students. Also his appeal to the chemists as such to find in the future of medicine a field of endeavor more promising of success than the as yet unrewarded efforts for the transmutation of the base metals into gold, found much following among those who were interested in the study of chemistry. If we recall that most of the scholarly trained chemists were also physicians, we can understand how this combination of medical and chemical aims advocated by Paracelsus found fertile soil among young physicians and medical students as among chemists of less conventional training.

That this is true is shown, not only by the tremendous vogue of his printed works, but also by the fierce contest which for a century split the medical profession of Europe into hostile and embittered factions of Paracelsists and anti-Paracelsists - adherents of the new chemical medicines and advocates of the older Galenic remedies.

While the greatest service of Paracelsus was to shatter confidence in dogmas revered for the sake of their authors' great names, the new doctrines which he set up to replace the dogmas he combated were, in many respects as fantaastic and unscientific as the earlier ones. Nevertheless, the shattering of the blind faith in traditional techings, which gave to Paracelsus his popularity and following, necessarily operated also to prevent his new doctrines from becoming considered as sacred or fallible. Free criticism and independent thought once aroused could not again be contented with blind adhesion to any unchanging system of doctrines.

Very naturally the perios of chemical activity following the shattering of long-accepted dogmas was characterized by many wild and fantastic notions. Many of the most extravagant claims of alchemy and of marvelous medical norstrums are found in the literature of the latter part of the sixteenth and of the first half of the seventeenth century. But much was done, on the other hand, in developing chemical facts. Men like Van Helmont and Glauber, while retaining much of the mysticism and obscurity of Paracelsus and earlier chemists, yet contributed in no unimportant way to the constructive work of adding to established chemical facts as the result of their experiments, though indeed contributing little of permanent value to chemical theory or generalization. Chemists were generally either adherents of the Aristotelian elements, or of the three elements of Paracelsus, according as they belonged to the conservative or radical parties. Nevertheless, there was much independent speculation and theorizing, though rarely on a scientific bassis. The new freedom found expression in extravagances of ignorance and superstition, in charlatanry and imposture, as well as in much earnest and valuable labor. But at all events, chemistry was now, at last, very much alive, and the mission of chemistry was at last recognized as of importance and dignity. Werner Rolfink, professor of anatomy, surgery, botany, medicine and chemistry at Marburg, is said to have been the first officially recognized professor of chemistry in Germany - A.D. 1629. A chair of chemistry was espablished early in the same century at the University of Paris, and a Scotch physician, William Davisson, was the first incumbent. In 1635 he published a text-book on chemistry for the use of his tudents, a work which passed through many editions.

The University of Leyden is credited with the first chemical laboratory at a European university, and the distinguished De la Boe Sylvius was the professor of the theory and practise of chemistry as well as of medicine. He was a strong adherent of the chemical medicines. Other early university laboratories were at Altorf, 1663, Stockholm, 1683.

Thus was beginning to be realized the ideal so confidently maintained though vaguely realized by Paracelsus, of exalting the study of chemistry and recognizing its importance in the development of medical science. How important the interrelation of these two sciences was to be in our day revealed, not even the imagination of Paracelsus could have dreamed.

As Paracelsus in the sixteenth century gave the first important impulse to the development of modern chemistry, so, in the middle of the seventeenth century. Sir Robert Boyle may be said to have inaugurated a new epoch in chemistry by his remarkably sane and sound criticisms of the chemical thought and theories of the time. Boyle was a broadly and thoroughly trained scholar of the time, and prominent in many lines of activity. He was one of the founders iof the Royal Society of England and at one time its president. he was also a man of wealth, but his main interest was in experiment in chemistry and physics, and many notable observations stand to his credit. Every student of chemistry of physics knows of Boyle's law of gases.

It is not, however, by his experimental work - valuable as it was - that he exertedthe greatest influence, but rather by his extended and frequent careful and scientific criticisms of the prevalent chemical theories, both the Aristotelian and Paracelsan theories, of the nature of substances and matter. Particularly by his work published in 1661 entitled "The Sceptical Chymist," in which, rather verbosely, but with great throughness and yet with great tolerance and patience, he submits the theories of the time to really constructive criticism. By a wealth of facts and experimental illustrations he demonstrates the purely metaphysical characeter of both the prevalent theories, and gradually develops the only consistent concetp of an element which was possible for his time - namely, any substace which no experimetnal evidence could show to be reducible to simpler subtances. He makes indeed, no attempt to say that any particular known substance is indeed an element in the sense of his characterization, though one might infer from his discussion that gold and silver were as well deserving of the title as any substances known to him, as he has never been able to obtain anything else from them or to know of any reliable experiments with such results. Unlike Paracelsus, or Glauber, or Van Helmont, or their imitators, Boyle was no dogmatist, being slow to assert and yet open-minded to any facts and very respectful to the opinions of others though not in the least dominated by them.

The "Spectical Chymist" of Boyle, as well as othes of his writings, had a very wide circulation throughout the continent as well as in Great Britain, and his sane and persuasive reasoning, free from mysticism, and based on legitimate inferences from observed facts, made a great impression upon scientific men. While he offered no theory to replace the discredited Aristotelian and Paracelsan theories of the constitution of matter, he transferred the emphasis of chemical thought from a priori speculation to rational deductions from observed phenomena, and, though these might often be imperfect or mistaken, yet chemical reasoning was launced upon a course which could only lead to clearer understanding and to more soundly established theories.

The century following Boyle may be well characterized as the phlogistic period, because the representative chemists of that period were largely occupied in systematizing chemical actions with reference to that theory.

The fundamental notion of this theory was, as we have mentioned, a development from the combustible and heat-giving sulphur of Paracelsus to the notion of a heat substance, phlogiston, which constituted a part of all combustible or, as we should say, oxidizable substances. The phenomena of combustion or oxidation were in terms of this theory dye to a loss of phlogiston - the phenomena of reduction to a gain of phlogiston. It is just to say of this theory that it proved a fertile and valuable hypothesis to the science of chemistry in developing a vast amount of excellent experimetnal work and of comprehensive genralizations. We have only to recall the names of Scheele, Priestley, Marggraf, Black and Cavendish to realize the class of chemists whose labors were influenced and stimulated by the adoption of this theory.

Two serious obstacles to continuous progress were, however, inherent in this theory. The supposed phlogiston could not be separated or isolated and weighed. It could not be known whether it had a positive weight in combination, or whether it could affect in any definite or determinable way the weight of other substances. It might even have the effect of buoyancy or of diminishing the weight of substances with which it was combined, and so long as such ideas were held the weights as given by the balance could not be depended upon to give the real quantative relations of chemical reactions.

The second obstacle this theory offered to chemical development lay in the fact that so long as this theory was mainained n oidentification of substances as elements was possible. Boyle had given us a proper definition of an element, but so long as such oxidizable substances as phosphorus, sulphur, iron, zinc or carbon were considered as combinations of phlogiston with other substances (viz., their oxides) and so long as the products of combustion, such as we now know, as the oxides of phosphorus, sulphur, iron, etc., were considered as products of the loss of phlogiston, and therefore to that extent simpler or more nearly elementary than the combustibles from which they were produced, it is manifest that the elementary character of most of the known elements could not have been recognized. It required the insight of Lavoisier to discern the real nature of combustion and reducation, and to banish at last the element phlogiston from the weighable factors of chemical reactions.

But with this period of chemistry, the dawn of modern chemistry was past and the sun was shining brightly above the horizon.