December, 1923
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Robert Brown and the Discovery of the Brownian Movement’ By Lyman C. Newel1 BOSTONUNIVEZSITY, BOSTON,MASS.
R
by their thoroughness and conscientious accuracy, and display ODERT BROWN, the eminent botanist and discoverer of the Brownian movement, was born December 31, 1773, powers of both minute detail and broad generalization. Between 1825 and 1834 his publications (up to 1834) were cola t Montrose, Scotland, the son of an Episcopal clergyman. In 1787 he entered Marischal College, Aberdeen, but two years lected and issued in four divisions by Nees von Esenbeck, in German, under the title of “Vermischte Botanische Schriften” later weat to Edinburgh University, where he studied medicine, (Leipzig and Nuremberg). In 1866 the and received his degree of M.D. While a t Ray Society reprinted, under the editorship Edinburgh he also studied botany, and his interest in botany attracted the attention of of J. J. Bennet, his friend and successor in the keepership of the Batanical DepartJohn Walker (1731-1803), prpfessor of natment of the British Museum, his complete ural history in the university. He obtained a commission, in 1795, as “ensign and aswritings, the “Prodromus” alone excepted, bearing the title “iMiscellaneous Botanical sistant surgeon,” in a Scottish regiment, and served in the north of Ireland. Works” (2 volumes with atlas of plates, In 1798 he made the acquaintance of Sir 1866-1868). Joseph Ranks. Deciding t o devote himself The portrait of Brown shown herewith is a reproduction of an engraving dated to botany, he resigned his army commission May 24, 1837. The engraving was made in 1800, :and in 1801, on the recommendaby Charles Fox from a painting by H. W. tion of Sir Joseph Banks, he was engaged Pickersgill, R.A., which has recently been as naturalist of an expedition sent out to presented to the Linnean Society by some explore and survey the coasts of Australia, of Brown’s friends. which a t that time were almost unknown. The expedition returned t o England in THEBROWNIAN MOVEMGNT 1805, and Brown brought back nearly four The continuous movements observed by thousand species of Australian plants, the microscope among minute particles susmany of which were new t o science. He pended in a liquid were first noticed by was immediately appointed librarian of the Brown in 1827, and these movements were Linnean Society. I n this position, though later called “The Brownian movement” in not one of great emolument, he had abunROBERTBROWN honor of the discoverer. The discovery was dant opportunities for research and writmade during ininz. - a physiological-botanical - . - In 1810 he published the first volume of his great work, the “Prodromus Florae Novae Hollandiae et vestigation. The investigation is recounted in two magazine Insulae Van Dieman,” which did much to further the general articles published in 1828 and 1829. The first article was pubadoption of de Jussieu’s natural system of plant classification. lished in the Edinburgh New Philosophical Journal, Vol. 5, April The merits of this book were immediately recognized by scien- to September, 1828, pp. 358-371. This article is dated July 30, tists, and it gave the author an international reputation among 1828, and bears the title, “A Brief Account of Microscopical Observations Made in the Months of June, July, and August, botanists. It is rare in the original edition, the author having 1827, on the Particles Contained in the Pollen of Plants; and on suppressc:d it, because the Edinburgh Review severely criticized its Latin. With the exception of a Supplement published in the General Existence of Active Molecules in Organic and Inorganic Bodies.” The second article was published in the Edin1830, no more of the “Prodromus” appeared. In 1810 Brown became also librarian to Sir Joseph Banks. burgh Journal of Science, Vol. 1, April to October, 1829, new series, pp. 314-319. It is dated July 28, 1829, and has the On the death of Sir Joseph in 1820, Brown was given the use of his libraiy and collections for life. In 1827 the library and col- brief title, “Additional Remarks on Active Molecules.” The lections were transferred to the British Museum, with Brown’s first article is the more important. In giving an account of Brown’s investigation which includes consent and in accordance with the will of the donor. Brown was appointed keeper of the Botanical Department of the British his famous discovery, his own words will be used as far as possible. Museum, and he held this position until his death in 1858. Soon The word “particles” will be substituted for “molecules,” and botanical parts reafter the death of Sir Joseph Banks, Brown resigned as librarian since we are chemists-not botanists-the of the Linnean Society, though from 1849 to 1853 he served as its lating t o shape and change of shape of the particles will be expresident. He was elected a Fellow of the Royal Society in 1811, cluded in favor of the chemical parts dealing with the moveand in 1839 was awarded the Copley medal for his “discoveries ments of particles. His apparatus was very simple. He possessed a double on the subject of vegetable impregnation.” Oxford conferred the degree of D.C.I,, on him in 1832, Edinburgh gave him an convex lens and also a pocket microscope with two lenses having L.L.D., and in 1838 he was elected one of the five foreign as- a delicate adjustment. Nevertheless, he says: sociates of the Institute of France. He died June 10, 1858, in The observations have all been made with a simple microscope, the house in Soh0 Square, London, bequeathed to him by Sir and indeed with one and the same lens, the focal length of which Joseph Banks. His works, which embrace not only systematic is about l/32 of an inch. botany, but also plant anatomy and physiology, are distinguished In his introduction he states his thesis thus: 1 Presented before the Section of History of Chemistry a t the 66th Meeting of t h e American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923.
The examination of the unimpregnated vegetable ovulum, an account of which was published early in 1826, led me to attend
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INDUSTRIAL A N D ENGINEEEING CHEMISTRY
more minutely than I had done before to the structure of the pollen, and to inquire into its mode of action. Like most of us, he did not get a quick start, for he states: It was not until late in the autumn of 1826 that I could attend to this subject; and the season was too far advanced to enable me to pursue the investigation. Finding, however, in one of the few plants then examined, the figure of the particles contained in the grains of pollen clearly discernible, and that figure not spherical but oblong, I expected, with some confidence, to meet with plants in other respects more favorable t o the inquiry, in which those particles, from peculiarity of form, might be traced through their whole course. His delay was not long, however, and he continues: My inquiry on the point was commenced in June, 1827. The first plant examined was Clarckia pdchella, of which the grains of pollen, taken from antherae full grown, but before bursting, were filled with particles or granules of unusually large size, varying from nearly ‘/.aoooth t? abqut l/sooOth of an inch inlength, and of a figure between cylindrical and oblong, perhaps slightly flattened, and having rounded and equal extremities. His next observation reveals the skilled investigator, and for
us is intensely interesting. While examining the form of these particles immersed in water, I observed many of them very evidently in motion; their motion consisting not only of a change of place in the fluid, manifested by alteration in their respective positions, but also not unfrequently of a change of form in the particle itself. * * * These motions were such as to satisfy me, after frequently repeated observation, that they arose neither from currents in the fluid nor from its gradual evaporation, but belonged to the particle itself. In these simple words Brown stated the discovery that has subsequently taken such an overwhelmingly important place in chemistry. Realizing the significance of this observation, he continues along the same line: I n extending my observations t o many other plants of the same natural family, similar motions of particles were ascertained to exist. I found also in their grains of pollen taken from certain plants immediately after bursting an increase in the number of particles. This great increase in the number of the particles before the grain of pollen could possibly have come in contact with the stigma was a perplexing circumstance in this stage of the inquiry, and I accordingly examined numerous species of many of the more important and remarkable families of the two great primary divisions OF phaenogamous plants. I n a great proportion of these plants I remarked the increase of the number of particles after the bursting of the antherae; the particles, of apparently uniform size and form, being then always present; and in some cases, indeed, no other particles were observed, either in this or in any early stage of the secreting organ. I n many plants belonging to several different families the membrane of the grain of pollen is so transparent that the motion of the larger particles within the entire grain was distinctly visible; and it was manifest also a t the more transparent angles, and in some cases even in the body of the grain. The successful outcome with living plants led him to broaden the field. He goes on to say: Having found motion in the particles of the pollen of all the living plants which I had examined, I was led next t o inquire whether this property continued after the death of the plant, and for what length of time it was retained. I n plants, either dried or immersed in spirit for a few days only, the particles of pollen of both kinds were found in motion equally evident with that observed in the living plant; specimens of several plants some of which had been dried and preserved in an herbarium for upwards of twenty years, and others not less than a century, still exhibited the smaller particles in considerable numbers, and in evident motion, along with a few of the larger particles, whose motions were much less manifest, and in some cases not observable. He next extends his field still further: I n this stage of the investigation, having found, as I believed, a peculiar character in the motions of the particles of pollen in water, it occurred to me to appeal t o this peculiarity as a test in certain families of Cryptogamous plants, namely, Mosses, and the genus Equisetum, in which the existence of sexual organs had not been universally admitted.
Vol. 15, No. 12
I n the supposed stamina of both these families, Mosses and Equiseta, I found minute spherical particles having equally vivid motion on immersion in water; and this motion was still observable in specimens both of Mosses and of Equiseta, which had been dried upwards of one hundred years. This time he was astonished, but continues: The very unexpected fact of seeming vitality retained by these minute particles so long after the death of the plant, would not perhaps have materially lessened my confidence in the supposed peculiarity. But I a t the same time observed that on bruising the ovula or seeds of Equiseta, which at first happened accidentally, I so greatly increased the number of moving particles, that the source of the added quantity could not be doubted. I found also, that on bruising the first floral leaves of Mosses, and then all other parts of those plants, I readily obtained similar particles, not in equal quantity indeed, but equally in motion. Many investigators would have stopped at this point. Not was seeking the whole truth. Like other famous discoverers he reflected, and then acted. Reflecting on all the facts with which I had now become acquainted, I expected to find these particles in all organic bodies; and, accordingly, on examining the various animal and vegetable tissues, whether living or dead, they [the particles] were always found to exist; and merely by bruising these substances in water, I never failed to disengage the particles in sufficient numbers t o ascertain their apparent identity, in size, form, and motion, with the smaller particles of the grains of pollen, I examined also various products of organic bodies, particularly the gum resins, and substances of vegetable origin, extending my inquiry even to pit-coal; and in all these bodies particles were found in abundance. I remark here, also, partly as a caution to those who may hereafter engage in the same inquiry that the dust or soot. deposited on all bodies in such quantity, especially in London, is entirely composed of these particles. One of the substances examined was a specimen of fossil wood, found in Wiltshire oolite, in a state t o burn with flame; and as I found these particles abundantly, and in motion in this specimen, I supposed that their existence, though in smaller quantity, might be ascertained in mineralized vegetable remains. With this in view a minute portion of silicified wood, which exhibited the structure of Coniferae, was bruised, and particles in all respects like those so frequently mentioned, were readily obtained from it. Hence I inferred that these particles were not limited to organic bodies nor even to their products.
so Brown-he
The discovery of moving particles in substances on the borderline between organic and inorganic matter led him to test the hypothesis just made. So he says: To establish the correctness of the inference, and to ascertain t o what extent the particles existed in mineral bodies, became the next object of inquiry. The first substance examined was a minute fragment of window glass, from which, when merely bruised, I readily and copiously obtained particles agreeing in size, form, and motion with those which I had already seen. I then proceeded to examine, and with similar results, such minerals as I either had a t hand or could readily obtain, including several of the simple earths and metals, with many of their combinations. Rocks of all ages, including those in which organic remains have never been found, yielded the particles in abundance. Their existence was ascertained in each of the constituent minerals of granite; a fragment of the Sphinx being one of the specimens examined. Convinced of the truth of his discovery, he says: To mention all the mineral substances in which I have found these particles, would be tedious; and I shall confine myself in this summary to an enumeration of a few of the most remarkable. These were both of aqueous and igneous origin, as travertine, stalactites, lava, obsidian, pumice, volcanic ashes, and meteorites from various localities. (I have since found the particles in the sandtubes, formed by lightning, from Drig in Cumberland.) Of metals I may mention manganese, nickel, plumbago, bismuth, antimony, and arsenic. I n a word, in every mineral which I could reduce to a powder sufficiently fine to be temporarily suspended in water, I found these particles more or less copiously. The second article adds little of fundamental value to the discovery described in the f i s t article. However, a few portions of the second article are significant.
December, 1923
INDUSTRIAL AND ENGINEERING CHEMISTRY
About twelve months ago I printed an account of Microscopical Observations made in the summer of 1827, on the Particles contained in the Pollen of Plants; and on the general Existence of active Molecules in Organic and Inorganic Bodies. I have remarked that certain substances, namely, sulfur, resin, and wax, did not yield active particles, which, however, proceeded merely from defective manipulation; for I have since readily obtained them from all these bodies; at the same time I ought to notice that their existence in sulfur was previously mentioned to me by my friend, Mr. Lister. He adds this information about his lenses: In proEecuting the inquiry subsequent to the publication of my Observations, I have chiefly employed the simple microscope mentioned in the Pamphlet, as having been made for me by Mr. Dollond, and of which the three lenses that I have generally used, are of a 40th, 60th, and 70th of an inch focus. Many of the observations have been repeated and confirmed with other simple microscopes having lenses of similar powers, and also with the best achromatic compound micrgscopes, either in my own possession or belonging t o my friends. His sunimary is quoted in full: The results of the inquiry a t present essentially agree with that which may be collected from my printed account, and may here be briefly stated in the following terms, namely: That extremely minute particles of solid matter, whether obtained from organic or inorganic substances, when suspended
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in pure water, or in some other aqueous fluids, exhibit motions for which I am unable to account, and which from their irregularity and seeming independence resemble in a remarkable degree the less rapid motions of some of the simplest animalcules of infusions. That the smallest moving particles observed, and which I have termed Active Molecules, appear to be spherical, or nearly so, and to be between l/zo,oooth and l/ao,oooth of an inch in diameter; and that other particles of considerably greater and various size, and either of similar or of very different figure, also present analogous motions in like circumstances. I have formerly stated my belief that these motions of the particles neither arose from currents in the fluid containing them, nor depended on that [internal] motion which may be supposed to accompany its evaporation.
In Jean Perrin’s little book entitled “The Brownian Movement and Molecular Reality,” the famous French chemist says: They [the particles] go and come, stop, start again, mount, descend, remount again, without the least tending toward immobility. This is the Brownian movement, so named in memory of the naturalist Brown who discovered it in 1827 (very shortly after the discovery of the achromatic objective), then proved that the movement was not due t o living animalculac, and recognized that the particles in suspension are agitated the more briskly the smaller they are. If we believe with Perrin and others in the reality of molecules and their continuous movements, then the name of Robert Brown will be immortal.
T h e Testing of Chemicals in t h e Bureau of Chemistry from 1920 to 1923’ By G. C. Spencer BUREAU OF
CAIMISTRY,
T
HE practice of testing all chemicals purchased a t the
Bureau of Chemistry has been systematically followed for over twenty years, with results that have demonstrated the sound economy of this policy. As an illustration of the necessity for watchfulness on the part of Government purchasing officers, instances have been noted where chemicals that had been rejected hy the Bureau of Chemistry were hauled away by the dealer and delivered directly to one of the neighboring bureaus, which accepted these supplies without examination. It is the purpose of this paper t o discuss some of the cases that have arisen in the bureau during the past three years with a view to showing: 1-The nature of the objections that may be raised by the purchasers. 2-In vvhat respects the manufacturers may be to blame. 3-A few suggestions that might possibly lead t o better uatderstandings between dealers and customers. The following examples of chemicals rejected by the bureau will help to illustrate in some measure the buyer’s point of view: Calcium oxide, discolored by iron and contained about 36 per cent of magnesium oxide Hydrochloric acid, 40 parts per million of arsenic. A replacement order contained 5 parts per million Fuming sulfuric acid, 50 per cent; not over 25 per cent free SO8 found, and was liquid a t room temperature Lead carbonate, 5.37 per cent water-soluble matter Absolute methanol, 5.5 mg. residue per 100 cc. Sodiunt hydroxide, high in sulfates and chlorides / Sulfuric acid, 10 parts per million of arsenic Ammonium thiocyanate, iron enough t o give it a pink color Calcium chloride, 8.9 per cent alkalinity as CaO 1 Presented before the Division of Industrial and Engineering Cheniistry at the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 to 14, 1923.
WASRINGTON, D . C.
Potassium carbonate, 8 per cent foreign matter. The second and third replacement orders showed no improvement Absolute ether from two different dealers; both reacted strongly with sodium and contained aldehydes Benzene, put up in wet bottles Acetic acid 99.9 per cent; only 99.6 per cent was found. The manufacturer had depended upon the titration method of assay while the bureau used the cryoscopic method. As soon as the manufacturer adopted the latter method, he had no further trouble in supplying the desired acid strength Chlorinated lime; two samples contained not over 22 per cent available chlorine Ethyl acetate, 16 mg. residue from 100 cc.; brown color with sulfuric acid Carbon disulfide, 6 mg. residue from 100 cc. Amyl acetate, packed in dusty bottles as seen by suspended matter. Two replacement orders were rejected before a satisfactory lot was received. The last of these had a residue of 8 8 mg. from 100 cc. Magnesium oxide, iron and sulfates present Here also may be included the chemical samples that are just on the line of acceptability, not quite bad enough to send back but applicable only for certain kinds of work. Such samples cause more annoyance and take more time than any others. For example, the specifications of the General Supply Committee require a hydrochloric acid strength of 36 per cent and a sulfuric acid strength of 95 per cent. It has happened a number of times that the acid strengths found would run from 2 to 4 per cent below the required amounts. On a t least one occasion the dealer in question offered to adjust the price to conform t o the lower strength found. Summarizing the objectionable features in the list just enumerated, it is found that the manufacturers are a t fault in permitting dirty or wet bottles t o be used for purified chemicals. This statement is justified by the number of cases, already cited in this paper, of distilled organic liquids which should be free from
