Chapter VIII (2)

The first papers of his which were inserted in the Memoirs of the Academy were geometrical: he gave a general method of finding an infinity of curves, described by the extremity of a straight line, the other extremity of which, passing along the surface of a given curve, is always obliged to pass through the same point. Next year he gave a geometrical work on Developes; but this was the last of his mathematical tracts. He was charged by the academy with the task of giving a description of the arts, and his taste for natural history began to draw to that study the greatest part of his attention. His first work as a naturalist was his observations on the formation of shells. It was unknown whether shells increase by intussusception, like animal bodies, or by the exterior and successive addition of new parts. By a set of delicate observations he showed that shells are formed by the addition of new parts, and that this was the cause of the variety of colour, shape, and size which they usually affect. His observations on snails, with a view to the way in which their shells are formed, led him to the discovery of a singular insect, which not only lives on snails, but in the inside of their bodies, from which it never stirs till driven out by the snail.

During the same year, he wrote his curious paper on the silk of spiders. The experiments of M. Bohn had shown that spiders could spin a silk that might be usefully employed. But it remained to be seen whether these creatures could be fed with profit, and in sufficiently great numbers to produce a sufficient quantity of silk to be of use. Reaumur undertook this disagreeable task, and showed that spiders could not be fed together without attacking and destroying one another.

The next research which he undertook, was to discover in what way certain sea-animals are capable of attaching themselves to fixed bodies, and again disengaging themselves at pleasure. He discovered the various threads and pinnæ which some of them possess for this purpose, and the prodigious number of limbs by which the sea-star is enabled to attach itself to solid bodies. Other animals employ a kind of cement to glue themselves to those substances to which they are attached, while some fix themselves by forming a vacuum in the interval between themselves and the solid substances to which they are attached.

It was at this period that he found great quantities of the buccinum, which yielded the purple dye of the ancients, upon the coast of Poitou. He observed, also, that the stones and little sandy ridges round which the shellfish had collected were covered with a kind of oval grains, some of which were white, and others of a yellowish colour, and having collected and squeezed some of these upon the sleeve of his shirt, so as to wet it with the liquid which they contained, he was agreeably surprised in about half an hour to find the wetted spot assume a beautiful purple colour, which was not discharged by washing. He collected a number of these grains, and carrying them to his apartment, bruised and squeezed different parcels of them upon bits of linen; but to his great surprise, after two or three hours, no colour appeared on the wetted part; but, at the same time, two or three spots of the plaster at the window, on which drops of the liquid had fallen, had become purple; though the day was cloudy. On carrying the pieces of linen to the window, and leaving them there, they also acquired a purple colour. It was the action of light, then, on the liquor, that caused it to tinge the linen. He found, likewise, that when the colouring matter was put into a phial, which filled it completely, it remained unchanged; but when the phial was not full, and was badly corked, it acquired colour. From these facts it is evident, that the purple colour is owing to the joint action of the light and the oxygen of the atmosphere upon the liquor of the shellfish.

About this time, likewise, he made experiments upon a subject which attracted the attention of mechanicians--to determine whether the strength of a cord was greater, or less, or equal to the joint strength of all the fibres which compose it. The result of Reaumur’s experiments was, that the strength of the cord is less than that of all the fibres of which it is composed. Hence it follows, that the less that a cord differs from an assemblage of straight fibres, the stronger it is. This, at that time considered as a singular mechanical paradox, was afterwards elucidated by M. Duhamel.

It was a popular opinion of all the inhabitants of the sea-shore, that when the claws of crabs, lobsters, &c., are lost by any means, they are gradually replaced by others, and the animal in a short time becomes as perfect as at first. This opinion was ridiculed by men of science as inconsistent with all our notions of true philosophy. Reaumur subjected it to the test of experiment, by removing the claws of these animals, and keeping them alone for the requisite time in sea-water: new claws soon sprang out, and perfectly replaced those that had been removed. Thus the common opinion was verified,and the contemptuous smile of the half-learned man of science was shown to be the result of ignorance, not of knowledge.

Reaumur was not so fortunate in his attempts to explain the nature of the shock given by the torpedo; which we now know to be an electric shock produced by a peculiar apparatus within the animal. Reaumur endeavoured to prove, from dissection, that the shock was owing to the prodigious rapidity of the blow given by the animal in consequence of a peculiar structure of its muscles.

The turquoise was at that time, as it still is, considerably admired in consequence of the beauty of its colour. Persia was the country from which this precious stone came, and it was at that time considered as the only country in the universe where it occurred. Reaumur made a set of experiments on the subject and showed that the fossil bones found in Languedoc, when exposed to a certain heat, assume the same beautiful green colour, and become turquoises equally beautiful with the Persian. It is now known, that the true Persian turquoise, the _calamite_ of mineralogists, is quite different from fossil bones coloured with copper. So far, therefore, Reaumur deceived himself by these experiments; but at that time chemical knowledge was too imperfect to enable him to subject Persian turquoise to an analysis, and determine its constitution.

About the same period, he undertook an investigation of the nature of imitation pearls, which resemble the true pearls so closely, that it is very difficult, from appearances, to distinguish the true from the false. He showed that the substance which gave the false pearls their colour and lustre, was taken from a small fish called by the French _able_, or _ablette_. He likewise undertook an investigation of the origin of true pearls, and showed that they were indebted for their production to a disease of the animal. It is now known, that the introduction of any solid body, as a grain of sand, within the shell of the living pearl-shellfish, gives occasion to the formation of pearl. Linnæus boasted that he knew a method of forming artificial pearls; and doubtless his process was merely introducing some solid particle of matter into the living shell. Pearls consist of alternate layers of carbonate of lime and animal membrane; and the colour and lustre to which they owe their value depends upon the thinness of the alternate coats.

The next paper of Reaumur was an account of the rivers in France whose sand yielded gold-dust, and the method employed to extract the gold. This paper will well repay the labour of a perusal; it owes its interest in a great measure to the way in which the facts are laid before the reader.

His paper on the prodigious bank of fossil shells at Touraine, from which the inhabitants draw manure in such quantities for their fields, deserves attention in a geological point of view. But his paper on flints and stones is not so valuable; it consists in speculations, which, from the infant state of chemical analysis when he wrote, could not be expected to lead to correct conclusions.

I pass over many of the papers of this most indefatigable man, because they are not connected with chemistry; but his history of insects constitutes a charming book, and contains a prodigious number of facts of the most curious and important nature. This book alone, supposing Reaumur had done nothing else, would have been sufficient to have immortalized the author.

In the year 1722 he published his work on the _art of converting iron into steel, and of softening cast-iron_. At that time no steel whatever was made in France; the nation was supplied with that indispensable article from foreign countries, chiefly from Germany. The object of Reaumur’s book was to teach his countrymen the art of making steel, and, if possible, to explain the nature of the process by which iron is changed into steel. Reaumur concluded from his experiments, that steel is iron impregnated with _sulphureous_ and _saline_ matters. The word _sulphureous_, as at that time used, was nearly synonymous with our present term _combustible_. The process which he found to answer, and which he recommends to be followed, was to mix together

4 parts of soot
2 parts of charcoal-powder
2 parts of wood-ashes
1½ parts of common salt.

The iron bars to be converted into steel were surrounded with this mixture, and kept red-hot till converted into steel. Reaumur’s notion of the difference between iron and steel was an approximation to the truth. The saline matters which he added do not enter into the composition of steel; and if they did, so far from improving, they would injure its qualities. But the charcoal and soot, which consist chiefly of carbon, really produce the desired effect; for steel is a combination of _iron_ and _carbon_.

In consequence of these experiments of Reaumur, it came to be an opinion entertained by chemists, that steel differed from iron merely by containing a greater proportion of phlogiston; for the charcoal and soot with which the iron bars were surrounded was considered as consisting almost entirely of phlogiston; and the only useful purpose which they could serve, was supposed to be to furnish phlogiston. This opinion continued prevalent till it was overturned towards the end of the last century, first by the experiments of Bergmann, and afterwards by those of Berthollet, Vandermond, and Monge, published in the Memoirs of the French Academy for 1786 (page 132). In this elaborate memoir the authors take a view of all the different processes followed in bringing iron from the ore to the state of steel: they then give an account of the researches of Reaumur and of Bergmann; and lastly relate their own experiments, from which they finally draw, as a conclusion, that steel is a compound of iron and carbon.

The regent Orleans, who at that time administered the affairs of France, thought that this work of Reaumur was deserving a reward, and accordingly offered him a pension of 12,000 livres. Reaumur requested of the regent that this pension should be given in the name of the academy, and that after his death it should continue, and be devoted to defray the necessary expenses towards bringing the arts into a state of perfection. The request was granted, and the letters patent made out on the 22d of December, 1722.

At that time tin-plate, as well as steel, was not made in France; but all the tin-plates wanted were brought from Germany, where the processes followed were kept profoundly secret. Reaumur undertook to discover a method of tinning iron sufficiently cheap to admit the article to be manufactured in France--and he succeeded. The difficulty consisted in removing the scales with which the iron plates, as prepared, were always covered. These scales consist of a vitrified oxide of iron, to which the tin will not unite. Reaumur found, that when these plates are steeped in water acidulated by means of bran, and then allowed to rust in stoves, the scales become loose, and are easily detached by rubbing the plates with sand. If after being thus cleansed they are plunged into melted tin, covered with a little tallow to prevent oxidizement, they are easily tinned. In consequence of this explanation of the process by Reaumur, tin-plate manufactories were speedily established in different parts of France. It was about the same time, or only a little before it, that tin-plate manufactories were first started in England. The English tin-plate was much more beautiful than the German, and therefore immediately preferred to it; because in Germany the iron was converted into plates by hammering, whereas in England it was rolled out. This made it much smoother, and consequently more beautiful.

Another art, at that time unknown in France, and indeed in every part of Europe except Saxony, was the art of making porcelain, a name given to the beautiful translucent stoneware which is brought from China and Japan. Reaumur undertook to discover the process employed in making it. He procured specimens of porcelain from China and Japan, and also of the imitations of those vessels at that time made in various parts of France and other European countries. The true porcelain remained unaltered, though exposed to the most violent heat which he was capable of producing; but the imitations, in a furnace heated by no means violently, melted into a perfect glass. Hence he concluded, that the imitation-porcelains were merely glass, not heated sufficiently to be brought into fusion; but true porcelain he conceived to be composed of two different ingredients, one of which is capable of resisting the most violent heat which can be raised, but the other, when heated sufficiently, melts into a glass. It is this last ingredient that gives porcelain its translucency, while the other makes it refractory in the fire. This opinion of Reaumur was soon after confirmed by Father d’Entrecolles, a French missionary in China, who sent some time after a memoir to the academy, describing the mode followed by the Chinese in the manufactory of their porcelain. Two substances are employed by them, the one called _kaolin_ and the other _petunse_. It is now known that _kaolin_ is what we call porcelain-clay, and that _petunse_ is a fine white felspar. Felspar is fusible in a violent heat, but porcelain-clay is refractory in the highest temperatures that we have it in our power to produce in furnaces.

Reaumur made another curious observation on glass, which has been, since his time, employed very successfully to explain the appearances of many of our trap-rocks. If a glass vessel, properly secured in sand, be raised to a red heat, and then allowed to cool very slowly, it puts off the appearance of glass and assumes that of stoneware, or porcelain. Vessels thus altered have received the name of _Reaumur’s porcelain_. They are much more refractory than glass, and therefore may be exposed to a pretty strong red heat without any danger of softening or losing their shape. This change is occasioned by the glass being kept long in a soft state: the various substances of which it is composed are at liberty to exercise their affinities and to crystallize. This makes the vessel lose its glassy structure altogether. In like manner it was found by Sir James Hall and Mr. Gregory Watt, that when common greenstone was heated sufficiently, and then rapidly cooled, it melted and concreted into a glass; but if after having been melted it was allowed to cool exceedingly slowly, the constituents again crystallized and arranged themselves as at first--so that a true greenstone was again formed. In the same way lavas from a volcano either assume the appearance of slag or of stone, according as they have cooled rapidly or slowly. Many of the lavas from Vesuvius cannot be distinguished from our _greenstones_.

Reaumur’s labours upon the thermometer must not be omitted here; because he gave his name to a thermometer, which was long used in France and in other parts of Europe. The first person that brought thermometers into a state capable of being compared with each other was Sir Isaac Newton, in a paper published in the Philosophical Transactions for 1701. Fahrenheit, of Amsterdam, was the first person that put Newton’s method in practice, by fixing two points on his scale, the freezing-water point and the boiling-water point, and dividing the interval between them into one hundred and eighty degrees.

But no fixed point existed in the thermometers employed in France, every one graduating them according to his fancy; so that no two thermometers could be compared together. Reaumur graduated his thermometers by plunging them into freezing water or a mixture of snow and water. This point was marked zero, and was called the freezing-water point. The liquid used in his thermometers was spirit of wine: he took care that it should be always of the same strength, and the interval between the point of freezing and boiling water was divided into eighty degrees. Deluc afterwards rectified this thermometer, by substituting mercury for spirit of wine. This not only enabled the thermometer to be used to measure higher temperatures, but corrected an obvious error which existed in all the thermometers constructed upon Reaumur’s principle: for spirit of wine cannot bear a temperature of eighty degrees Reaumur without being dissipated into vapour--absolute alcohol boiling at a hundred and sixty-two degrees two-thirds. It is obvious from this, that the boiling point in Reaumur’s thermometer could not be accurate, and that it would vary, according to the quantity of empty space left above the alcohol.

Finally, he contrived a method of hatching chickens by means of artificial heat, as is practised in Egypt.

We are indebted to him also for a set of important observations on the organs of digestion in birds. He showed, that in birds of prey, which live wholly upon animal food, digestion is performed by solvents in the stomach, as is the case with digestion in man: while those birds that live upon vegetable food have a very powerful stomach or gizzard, capable of triturating the seeds which they swallow. To facilitate this triturating process, these fowls are in the habit of swallowing small pebbles.

The moral qualities of M. Reaumur seem not to have been inferior to the extent and variety of his acquirements. He was kind and benevolent, and remarkably disinterested. He performed the duties of intendant of the order of St. Louis from the year 1735 till his death, without accepting any of the emoluments of the office, all of which were most religiously given to the person to whom they belonged, had she been capable of performing the duties of the place. M. Reaumur died on the 17th of October, 1756, after having lived very nearly seventy-five years.

John Hellot was born in Paris in the year 1685, on the 20th of November. His father, Michael Hellot, was of a respectable family, and the early part of his son’s education was at home: it seems to have been excellent, as young Hellot acquired the difficult art of writing on all manner of subjects in a precise, clear, and elegant style. His father intended him for the church; but his own taste led him decidedly to the study of chemistry. He had an uncle a physician, some of whose papers on chemical subjects fell into his hands. This circumstance kindled his natural taste into a flame: he formed an acquaintance with M. Geoffroy, whose reputation as a chemist was at that time high, and this friendship was afterwards cemented by Geoffroy marrying the niece of M. Hellot.

His circumstances being easy, he went over to England, to form a personal acquaintance with the many eminent philosophers who at that time adorned that country. His fortune was considerably deranged by Law’s celebrated scheme during the regency of the Duke of Orleans. This obliged him to look out for some resource: he became editor of the Gazette de France, and continued in this employment from 1718 to 1732. During these fourteen years, however, he did not neglect chemistry, though his progress was not so rapid as it would have been, could he have devoted to that science his undivided attention. In 1732 he was put forward by his friends as a candidate for a place in the Academy of Sciences; and in the year 1735 he was chosen adjunct chemist, vacant by the promotion of M. de la Condamine to the place of associate. Three years after he was declared a supernumerary pensioner, without passing through the step of associate. His reputation as a chemist was already considerable, and after he became a member of the academy, he devoted himself to the investigations connected with his favourite science.

His first labours were on zinc; in two successive papers he endeavoured to decompose this metal, and to ascertain the nature of its constituents. Though his labour was unsuccessful, yet he pointed out many new properties of this metal, and various new compounds into which it enters. Neither was he more successful in his attempt to account for the origin of the red vapours which are exhaled from nitre in certain circumstances. He ascribed them to the presence of ferruginous matters in the nitre; whereas they are owing to the expulsion and partial decomposition of the nitric acid of the nitre, in consequence of the action of some more powerful acid.

His paper on sympathetic ink is of more importance. A German chemist had shown him a saline solution of a red colour which became blue when heated: this led him to form a sympathetic ink, which was pale red, while the paper was moist, but became blue upon drying it by holding it to the fire. This sympathetic ink was a solution of cobalt in muriatic acid. It does not appear from Hellot’s paper that he was exactly aware of the chemical constitution of the liquid which constituted his sympathetic ink; though it is clear he knew that cobalt constitutes an essential part of it.

Kunkel’s phosphorus, though it had been originally discovered in Germany, could not be prepared by any of the processes which had been given to the public. Boyle had taught his operator, Godfrey Hankwitz, the method of making it. This man had, after Boyle’s death, opened a chemist’s shop in London, and it was he that supplied all Europe with this curious article: on that account it was usually distinguished by the name of _English phosphorus_. But in the year 1737 a stranger appeared in Paris, who offered for a stipulated reward to communicate the method of manufacturing this substance to the Academy of Sciences. The offer was accepted by the French government, and a committee of the academy, at the head of which was Hellot, was appointed to witness the process, and ascertain all its steps. The process was repeated with success; and Hellot drew up a minute detail of the whole, which was inserted in the Memoirs of the Academy, for the year 1737. The publication of this paper constitutes an era in the preparation of phosphorus: it was henceforward in the power of every chemist to prepare it for himself. A few years after the process was much improved by Margraaf; and, within little more than twenty years after, the very convenient process still in use was suggested by Scheele. Hellot’s experiments on the comparative merits of the salts of Peyrac, and of Pecais were of importance, because they decided a dispute--they may also perhaps be considered as curiosities in an historical point of view; because we see from them the methods which Hellot had recourse to at that early period in order to determine the purity of common salt. They are not entitled, however, to a more particular notice here.

In the year 1740 M. Hellot was charged with the general inspection of dyeing; a situation which M. du Foy had held till the time of his death in 1739. It was this appointment, doubtless, which turned his attention to the theory of dyeing, which he tried to explain in two memoirs read to the academy in 1740 and 1741. The subject was afterwards prosecuted by him in subsequent memoirs which were published by the academy.

In 1745 he was named to go to Lyons in order to examine with care the processes followed for refining gold and silver. Before his return he took care to give to these processes the requisite precision and exactness. Immediately after his return to Paris he was appointed to examine the different mines and assay the different ores in France; this appointment led him to turn his thoughts to the subject. The result of this was the publication of an excellent work on assaying and metallurgy, entitled “De la Fonte des Mines, des Fonderies, &c. Traduit de l’Allemand de Christophe-André Schlutter.” The first volume of this book appeared in 1750, and the second in 1753. Though this book is called by Hellot a translation, it contains in fact a great deal of original matter; the arrangement is quite altered; many processes not noticed by Schlutter are given, and many essential articles are introduced, which had been totally omitted in the original work. He begins with an introduction, in which he gives a short sketch of all the mines existing in every part of France, together with some notice of the present state of each. The first volume treats entirely of docimasy, or the art of assaying the different metallic ores. Though this art has been much improved since Hellot’s time, yet the processes given in this volume are not without their value. The second volume treats of the various metallurgic processes followed in order to extract metals from their ores. This volume is furnished with no fewer than fifty-five plates, in which all the various furnaces, &c. used in these processes are exhibited to the eye.

While occupied in preparing this work for the press he was chosen to endeavour to bring the porcelain manufactory at Sevre to a greater state of perfection than it had yet reached. In this he was successful. He even discovered various new colours proper for painting upon porcelain; which contributed to give to this manufactory the celebrity which it acquired.

In the year 1763 a phenomenon at that time quite new to France took place in the coal-mine of Briançon. A quantity of carburetted hydrogen gas had collected in the bottom of the mine, and being kindled by the lights employed by the miners, it exploded with great violence, and killed or wounded every person in the mine. This destructive gas, distinguished in this country by the name of _fire-damp_, had been long known in Great Britain and in the Low Countries, though it had not before been known in France. The Duke de Choiseul, informed of this event, had recourse to the academy for assistance, who appointed Messrs. de Montigny, Duhamel, and Hellot, a committee to endeavour to discover the remedies proper to prevent any such accident from happening for the future. The report of these gentlemen was published in the Memoirs of the Academy;[182] they give an account both of the fire-damp, and _choke-damp_, or _carbonic acid gas_, which sometimes also makes its appearance in coal-mines. They very justly observe that the proper way to obviate the inconveniency of these gases is to ventilate the mine properly; and they give various methods by which this ventilation may be promoted by means of fires lighted at the bottom of the shaft, &c.

[182] 1763, p. 235.

In 1763 M. Hellot was appointed, conjointly with M. Tillet, to examine the process followed for assaying gold and silver. They showed that the cupels always retained a small portion of the silver assayed, and that this loss, ascribed to the presence of a foreign metal, made the purity of the silver be always reckoned under the truth, which occasioned a loss to the proprietor.

His health continued tolerably good till he reached his eightieth year: he was then struck with palsy, but partially recovered from the first attack; but a second attack, on the 13th of February, 1765, refused to yield to every medical treatment, and he died on the 15th of that month, at an age a little beyond eighty.

Henry Louis Duhamel du Monceau was born at Paris in the year 1700. He was descended from Loth Duhamel, a Dutch gentleman, who came to France in the suite of the infamous Duke of Burgundy, about the year 1400. Young Duhamel was educated in the College of Harcourt; but the course of study did not suit his taste. He left it with only one fact engraven on his memory--that men, by observing nature, had created a science called _physics_; and he resolved to profit by his freedom from restraint and turn the whole of his attention to that subject. He lodged near the Jardin du Roi, where alone, at that time, physics were attended to in Paris. Dufoy, Geoffroy, Lemery, Jussieu, and Vaillant, were the friends with whom he associated on coming to Paris. His industry was stimulated solely by a love of study, and by the pleasure which he derived from the increase of knowledge; love of fame does not appear to have entered into his account.

In the year 1718 saffron, which is much cultivated in that part of France formerly distinguished by the name of Gâtinois, where Duhamel’s property lay, was attacked by a malady which appeared contagious. Healthy bulbs, when placed in the neighbourhood of those that were diseased, soon became affected with the same malady. Government consulted the academy on the subject; and this learned body thought they could not do better than request M. Duhamel to investigate the cause of the disease; though he was only eighteen years of age, and not even a member of the academy. He ascertained that the malady was owing to a parasitical plant, which attached itself to the bulb of the saffron, and drew nourishment from it. This plant extended under the earth, from one bulb to another, and thus infected the whole saffron plantations.

M. Duhamel formed the resolution at the commencement of his scientific career to devote himself to public utility, and to prosecute those subjects which were likely to contribute most effectually to the comfort of the lower ranks of men. Much of his time was spent in endeavouring to promote the culture of vegetables, and in rendering that culture more useful to society. This naturally led to a careful study of the physiology of trees. The fruit of this study he gave to the world in the year 1758, when his Physique des Arbres was published. This constitutes one of the most important works on the subject which has ever appeared. It contains a great number of new and original facts; and contributed very much indeed to advance this difficult, but most important branch of science: nor is it less remarkable for modesty than for value. The facts gathered from other sources, even those which make against his own opinions, are most carefully and accurately stated: the experiments that preceded his are repeated and verified with much care; and the reader is left to discover the new facts and new views of the author, without any attempt on his part to claim them as his own.

M. Duhamel had been attached to the department of the marine by M. de Maurepas, who had given him the title of _inspector-general_. This led him to turn his attention to naval science in general. The construction of vessels, the weaving of sailcloths, the construction of ropes and cables, the method of preserving the wood, occupied his attention successively, and gave birth to several treatises, which, like all his works, contain immense collections of facts and experiments. He endeavours always to discover which is the best practice, to reduce it to fixed rules, and to support it by philosophical principles; but abstains from all theory when it can be supported only by hypothesis.

From the year 1740, when he became an academician, till his death in 1781, he made a regular set of meteorological observations at Pithiviers, with details relative to the direction of the needle, to agriculture, to the medical constitution of the year, and to the time of nest-building, and of the passage of birds.

Above sixty memoirs of his were published in the Transactions of the French Academy of Sciences. They are so multifarious in their nature, and embrace such a variety of subjects, that I shall not attempt even to give their titles, but satisfy myself with stating such only as bear more immediately upon the science of chemistry.

It will be proper in conducting this review to notice the result of his labours connected with the ossification of bones; because, though not strictly chemical, they throw light upon some branches of the animal economy, more closely connected with chemistry than with any other of the sciences. He examined, in the first place, whether the ossification of bones, and their formation and reparation, did not follow the same law that he had assigned to the increments of trees, and he established, by a set of experiments, that bones increase by the ossification of layers of the periosteum, as trees do by the hardening of their cortical layers. Bones in a soft state increase in every direction, like the young branches of plants; but after their induration they increase only like trees, by successive additions of successive layers. This organization was incompatible with the opinion of those who thought that bones increased by the addition of an earthy matter deposited in the meshes of the organized network which forms the texture of bones. M. Duhamel combated this opinion by an ingenious experiment. He had been informed by Sir Hans Sloane that the bones of young animals fed upon madder were tinged red. He conceived the plan of feeding them alternately with food mingled with madder, and with ordinary food. The bones of animals thus treated were found to present alternate concentric layers of red and white, corresponding to the different periods in which the animal had been fed with food containing or not containing madder. When these bones are sawn longitudinally we see the thickness of the coloured layers, greater or less, according to the number of plates of the periosteum that have ossified. As for the portions still soft, or susceptible of extending themselves in every direction, such as the plates in the neighbourhood of the marrow, the reservoir of which increases during a part of the time that the animal continues to grow, the red colour marks equally the progress of their ossification by coloured points more or less extended.

This opinion was attacked by Haller, and defended by M. Fougeroux, nephew of M. Duhamel; but it is not our business here to inquire how far correct.

One of the most important of M. Duhamel’s papers, which will secure his name a proud station in the annals of chemistry, is that which was inserted in the Memoirs of the Academy for 1737, in which he shows that the base of common salt is a true fixed alkali, different in some respects from the alkali extracted from land plants, and known by the name of _potash_, but similar to that obtained by the incineration of marine plants. We are surprised that a fact so simple and elementary was disputed by the French chemists, and rather indicated than proved by Stahl and his followers. The conclusions of Duhamel were disputed by Pott; but finally confirmed by Margraaf. M. Duhamel carried his researches further, he wished to know if the difference between potash and soda depends on the plants that produce them, or on the nature of the soil in which they grow. He sowed kali at Denainvilliers, and continued his experiments during a great number of years. M. Cadet, at his request, examined the salts contained in the ashes of the kali of Denainvilliers. He found that during the first year soda predominated in these ashes. During the successive years the potash increased rapidly, and at last the soda almost entirely disappeared. It was obvious from this, that the alkalies in plants are drawn at least chiefly from the soil in which they vegetate.

The memoirs of M. Duhamel on ether, at that time almost unknown, on soluble tartars, and on lime, contain many facts both curious and accurately stated; though our present knowledge of these bodies is so much greater than his--the new facts ascertained respecting them are so numerous and important, that the contributions of this early experimenter, which probably had a considerable share in the success of subsequent investigations, are now almost forgotten. Nor would many readers bear patiently with an attempt to enumerate them.

There is a curious paper of his in the Memoirs of the Academy for 1757. In this he gives the details of a spontaneous combustion of large pieces of cloth soaked in oil and strongly pressed. Cloth thus prepared had often produced similar accidents. Those who were fortunate enough to prevent them, took care to conceal the facts, partly from ignorance of the real cause of the combustion, and partly from a fear that if they were to state what they saw, their testimony would not gain credit. If the combustion had not been prevented, then the public voice would have charged those who had the care of the cloths with culpable negligence, or even with criminal conduct. The observation of M. Duhamel, therefore, was useful, in order to prevent such unjust suspicions from hindering those concerned from taking the requisite precautions. Yet, twenty years after the publication of his paper, two accidental spontaneous combustions, in Russia, were ascribed to treason. The empress Catharine II. alone suspected that the combustion was spontaneous, and experiments made by her orders fully confirmed the evidence previously advanced by the French philosopher.

One man alone would have been insufficient for all the labours undertaken by M. Duhamel; but he had a brother who lived upon his estate at Denainvilliers (the name of which he bore), and divided his time between the performance of benevolent actions and studying the operations of nature. M. Denainvilliers prosecuted in his retreat the observations and experiments intrusted by his brother to his charge. Thus in fact the memoirs of Duhamel exhibit the assiduous labours of two individuals, one of whom contentedly remained unknown to the world, satisfied with the good which he did, and the favours which he conferred upon his country and the human race.

The works of M. Duhamel are very voluminous, and are all written with the utmost plainness. Every thing is elementary, no previous knowledge is taken for granted. His writings are not addressed to philosophers, but to all those who are in quest of practical knowledge. He has been accused of diffuseness of style, and of want of correctness; but his style is simple and clear; and as his object was to inform, not philosophers, but the common people, greater conciseness would have been highly injudicious.

Neither he nor his brother ever married, but thought it better to devote their undivided attention to study. Both were assiduous in no ordinary degree, but the ardour of Duhamel himself continued nearly undiminished till within a year of his death; when, though he still attended the meetings of the academy, he no longer took the same interest in its proceedings. On the 22d of July, 1781, just after leaving the academy, he was struck with apoplexy, and died after lingering twenty-two days in a state of coma.

He was without doubt one of the most eminent men of the age in which he lived; but his merits as a chemist will chiefly be remembered in consequence of his being the first person who demonstrated by satisfactory evidence the peculiar nature of soda, which had been previously confounded with potash. His merits as a vegetable physiologist and agriculturist were of a very high order.

Peter Joseph Macquer was born at Paris, in 1718. His father, Joseph Macquer, was descended from a noble Scottish family, which had sacrificed its property and its country, out of attachment to the family of the Stuarts.[183] Young Macquer made choice of medicine as a profession, and devoted himself chiefly to chemistry, for which he showed early a decided taste. He was admitted a member of the Academy of Sciences in the year 1745, when he was twenty-seven years of age. Original researches in chemistry, the composition of chemical elementary works, and the study of the arts connected with chemistry, occupied the whole remainder of his life.

[183] I do not know what the true name was of which Macquer is a corruption. Ker is a Scottish name belonging to two noble families, the Duke of Roxburgh and the Marquis of Lothian; but I am not aware of M’Ker being a Scottish name: besides, neither of these families was attached to the house of Stuart.

His first paper treated of the effect produced by heating a mixture of saltpetre and white arsenic. It was previously known, that when such a mixture is distilled nitric acid comes over tinged with a blue colour; but nobody had thought of examining the residue of this distillation. Macquer found it soluble in water and capable of crystallizing into a neutral salt composed of potash (the base of saltpetre), and an acid into which the arsenic was changed by the nitric acid communicating oxygen to it.

Macquer found that a similar salt might be obtained with soda or ammonia for its base. Thus he was the first person who pointed out the existence of arsenic acid, and ascertained the properties of some of the salts which it forms. But he made no attempt to obtain arsenic acid in a separate state, or to determine its properties. That very important step was reserved for Scheele, for Macquer seems to have had no suspicion of the true nature of the salt which he had formed.

His next set of experiments was on Prussian blue. He made the first step towards the discovery of the nature of the principle to which that pigment owes its colour. Prussian blue had been accidentally discovered by Diesbach, an operative chemist of Berlin, in 1710, but the mode of producing it was kept secret till it was published in 1724, by Dr. Woodward in the Philosophical Transactions. It consisted in mixing potash and blood together, and heating the mixture in a covered crucible, having a small hole in the lid, till it ceased to give out smoke. The solution of this mixture in water, when mixed with a solution of sulphate of iron, threw down a green powder, which became blue when treated with muriatic acid: this blue matter was _Prussian blue_. Macquer ascertained that when Prussian blue is exposed to a red heat its blue colour disappears, and it is converted into common peroxide of iron. Hence he concluded that Prussian blue is a compound of oxide of iron, and of something which is destroyed or driven off by a red heat. He showed that this something possessed the characters of an acid; for when Prussian blue is boiled with caustic potash it loses its blue colour, and if the potash be boiled with successive portions of Prussian blue, as long as it is capable of discolouring them, it loses the characters of an acid and assumes those of a neutral salt, and at the same time acquires the property of precipitating iron from the solutions of the sulphate at once of a blue colour. Macquer ascribed the green colour thrown down, by mixing the blood-lie and sulphate of iron to the potash in the blood-lie, not being saturated with the colouring matter of Prussian blue. Hence a portion of the iron is thrown down in the state of Prussian blue, and another portion in that of yellow oxide of iron: these two being mixed form a green. The muriatic acid dissolves the yellow oxide and leaves the Prussian blue untouched. Macquer, however, did not succeed in determining the nature of the colouring matter; a task reserved for Scheele, whose lot it was to take up the half-finished investigations of Macquer, and throw upon them a new and brilliant light. Macquer thought that this colouring matter was _phlogiston_. On that account the potash saturated with it, which was employed by chemists to detect the presence of iron by forming with it Prussian blue, was called _phlogisticated alkali_.

Macquer, conjointly with Baumé, subjected the grains of crude platinum, to which the attention of chemists had been newly drawn, to experiment. Their principle object was to examine its fusibility and ductility. They succeeded in fusing it imperfectly, by means of a burning mirror, and found that the grains thus treated were not destitute of ductility. But upon the whole the experiments of these chemists threw but little light upon the subject. Many years elapsed before chemists were able to work this refractory metal, and to make it into vessels fitted for the uses of the laboratory. For this important improvement, which constitutes an era in chemistry, the chemical world was chiefly indebted to Dr. Wollaston.

In the year 1750 M. Macquer was charged with a commission by the court. There existed at that time in Brittany a man, the Count de la Garaie, who, yielding to a passion for benevolence, had for forty years devoted himself to the service of suffering humanity. He had built an hospital by the side of a chemical laboratory: he took care of the patients in the hospital himself; and treated them with medicines prepared in his laboratory. Some of these were new, and, in his opinion, excellent medicines; and he offered to sell them to government for the service of his hospital. Macquer was charged by government with the examination of these medicines. The project of the Count de la Garaie was to extract the salutary parts of minerals, by a long maceration with neutral salts. Among other things he had prepared a mercurial tincture, by a process which lasted several months: but this tincture was merely a solution of corrosive sublimate in spirit of wine. Such is the history of most of those boasted secrets; sometimes they are chimerical, and sometimes known to all the world, except to those who purchase them.

M. Macquer had the fortune to live at a time when chemistry began to be freed from the reveries of alchymists; but methodical arrangement was a merit still unknown to the elementary chemical books, especially in France, where a residue of Cartesianism added to the natural obscurity of the science, by surcharging it with pretended mechanical explanations. Macquer was the first French chemist who gave to an elementary treatise the same clearness, simplicity, and method, which is to be found in the other branches of science. This was no small merit, and undoubtedly contributed considerably to the rapid improvement of the science which so speedily followed. His elements of chemistry were translated into different languages, especially into English; and long constituted the textbook employed in the different European universities. Dr. Black recommended it for many years in the University of Edinburgh. Indeed, it was only superseded in consequence of the new views introduced into chemistry by Lavoisier, which, requiring a new language to render them intelligible, naturally superseded all the elementary chemical books which had preceded the introduction of that language.

Macquer, during a number of years, delivered regular courses of chemical lectures, conjointly with Baumé. In these courses he preferred that arrangement which appeared to him to require the least preliminary knowledge of chemistry. He described the experiments, stated the facts with clearness and precision, and explained them in the way which appeared to him most plausible, according to the opinions generally received; but without placing much confidence in the accuracy of these explanations. He thought it necessary to theorize a little, to enable his pupils the better to connect the facts and to remember them; and to put an end to that painful state of uncertainty which always results from a collection of facts without any theoretical links to bind them together. When the discoveries of Lavoisier began to shake the foundation of the Stahlian theory, Macquer was old; and it appears from a letter of his, published by Delametherie in the Journal de Physique, that he was alarmed at the prophetic announcements of Lavoisier in the academy that the reign of Phlogiston was drawing towards an end. M. Condorcet assures us that his attachment to theory, by which he means phlogiston, was by no means strong;[184] but his own letter to Delametherie rather shows that this statement was not quite correct. How, indeed, could he fail to experience an attachment to opinions which it had been the business of his whole life to inculcate?

[184] Hist. de l’Acad. R. des Sciences, 1784, p. 24.

Macquer also published a dictionary of chemistry, which was very successful, and which was translated into most of the European languages. This mode of treating chemistry was well suited to a science still in its infancy, and which did not yet constitute a complete whole. It enabled him to discuss the different topics in succession, and independent of each other: and thus to introduce much important matter which could not easily have been introduced into a systematic work on chemistry. The second edition of this dictionary was published just at the time when the gases began to attract the attention of scientific men; when facts began to multiply with prodigious rapidity, and to shake the confidence of chemists in all received theories. He acquitted himself of the difficult task of collecting and stating these new facts with considerable success; and doubtless communicated much new information to his countrymen: for the discoveries connected with the gases originated, and were chiefly made, in England, from which, on account of the revolutionary American war, there was some difficulty of obtaining early information.

M. Hellot, who was commissioner of the counsel for dyeing, and chemist to the porcelain manufacture, requested to have M. Macquer for an associate. This request did much honour to Hellot, as he was conscious that the reputation of Macquer as a chemist was superior to his own. Macquer endeavoured, in the first place, to lay down the true principles of the art of dyeing, as the best method of dissipating the obscurity which still hung over it. A great part of his treatise on the art of dyeing silk, published in the collection of the Academy of Sciences, has these principles for its object. He gave processes also for dyeing silk with Prussian blue, and for giving to silk, by means of cochineal, as brilliant a scarlet colour as can be given to woollen cloth by the same dye-stuff. He published nothing on the porcelain manufacture, though he attended particularly to the processes, and introduced several ameliorations. The beautiful porcelain earth at present used at Sevre, was discovered in consequence of a premium which he offered to any person who could point out a clay in every respect proper for making porcelain.

Macquer passed a great part of his life with a brother, whom he affectionately loved: after his death he devoted himself entirely to his wife and two children, whose education he superintended. He was rather averse to society, but conducted himself while in it with much sweetness and affability. He was fond of tranquillity and independence. Though his health had been injured a good many years before his death, the calmness and serenity of his temper prevented strangers from being aware that he was afflicted with any malady. He himself was sensible that his strength was gradually sinking; he predicted his approaching end to his wife, whom he thanked for the happiness which she had spread over his life. He left orders that his body should be opened after his decease, that the cause of his death might be discovered. He died on the 15th of February, 1784. An ossification of the aorta, and several calculous concretions found in the cavities of the heart, had been the cause of the disease under which he had suffered for several years before his death.

These four chemists, of whose lives a sketch has just been given, were the most eminent that France ever produced belonging to the Stahlian school of chemistry. Baron, Malouin, Rouelle senior, Tillet, Cadet, Baumé, Sage, and several others whose names I purposely omit, likewise cultivated chemistry, during that period, with assiduity and success; and were each of them the authors of papers which deserve attention, but which it would be impossible to particularize without swelling this work into a size greatly beyond its proper limits.