To render the precipitated silver perfectly pure, it is only necessary to wash it in ammoniacal water.-Archiv. der Pharm., cvi. 27.

PHYSICAL SCIENCE.

On Spectrum Analysis, by W. A. MILLER, M.D., LL.D., V.P.R.S., Professor of Chemistry, King's College, London.

THE subject which I propose to bring before you on the present occasion is one which, from the striking character of its results, the precision of the observations, and the extension of views to which it has given rise, has attracted a large share of the attention, not only of the scientific community, but also of that of educated persons in general.

It must not, however, be supposed that the subject is a new one, or that it has reached its present development by the exertions of any single individual. It may not, therefore, be uninteresting to trace the principal steps of discovery, from the time of Newton, who first examined the solar spectrum, to the present day.

Newton, by admitting a beam of solar light through a small circular aperture into a darkened room, and allowing it to fall upon a triangular prism of glass, obtained the magnificent coloured image known as the solar spectrum, which shades off, by insensible gradations, from the least refracted red into the most refracted or violet portion of the light. But it does not appear that any one, from Wollaston's time, a century later, examined the effect of admitting the light through a narrow slit, with sides parallel to those of the prism (Phil. Trans., 1802, 378). Wollaston found that the spectrum so obtained was not, as it appeared to be by Newton's mode of examination, a continuous stripe of light, but that it was crossed at right angles to its length by dark bands.

It was not, however, till 1815 that these dark bands were carefully examined, when the celebrated German optician, Fraunhofer, published a minute description of them, accompanied by a careful map, in which he figured more than six hundred of these lines, which have ever since borne the name of Fraunhofer's lines. The more important of these lines he distinguished by the letters of the alphabet, and in the uppermost spectrum shown in the figure, a few of them are given as points of comparison with other spectra.

As Fraunhofer's mode of observing the spectrum is essentially that adopted by all subsequent inquirers, it will be necessary to point out the leading features of the method which he employed. The sun's light having been admitted through a narrow vertical slit into a darkened room, was allowed to fall upon a prism with its axis parallel to the slit, and at a distance of about twenty-four feet from it. The prism was fixed before the object-glass of a telescope, of low power, in such a manner that the angle formed by the incident light with the first face of the prism, was equal to that formed by the refracted beam with the second face. Under these circumstances, he observed numberless vertical lines. varying in breadth and in strength in different parts of the spectrum. These bands were always visible, whatever was the solid or liquid medium used in the construction of the prism, and whether its refracting angle were great or small; and, under all circumstances, they pre

A Lecture delivered before the Members of the Pharmaceutical Society of Great Britain; from the Pharmaceutical Journal.

201

served the same relative position in the respective coloured spaces in which they occur.

When, however, the source of the light was varied, as if the flame of a candle, the light of the fixed stars,† or the spark from the electrical machine was made use of, a different set of lines was in each case observed to occur. Beyond this fact, viz., the dependence of the position Fraunhofer was unable to ascertain anything connected of the lines upon the source of the light employed, with their cause.

The inquiry thus launched by Fraunhofer has been followed in four principal branches of research, which may be described as relating to,

1. Cosmical lines, or the black lines produced in the light of the sun, the planetary bodies, and the fixed stars. 2. Black lines produced by absorption, a class of phenomena discovered by Sir D. Brewster, in his observations upon the red vapours of nitrous acid.

4. Bright lines produced by the electric spark when taken between different conductors.

4. Bright lines produced by coloured flames, or by the introduction of different substances into flame. The following chronological table contains the names of those who have made the principal steps in these different subjects:

1. The Cosmical Lines admit only of partial illustration in the lecture-room by means of photographs, by Most of which they may be projected upon the screen. these lines shown by the photograph are, however, invisible to the eye, as they occur in that part of the spectrum which is more refrangible than even the violet rays. Edmund Becquerelt was the first who received the impression of the spectrum with suitable precautions upon a daguerreotype plate, and he made the important and interesting discovery that the inactive spaces in the portion of the chemical spectrum produced by visible rays, correspond accurately with the dark lines of Fraunhofer,--a discovery immediately afterwards corroborated by the independent observations of Dr. Draper, of New York, and subsequently confirmed in a remarkable manner for the invisible rays, by Stokes, who (Phil. Trans., 1852) succeeded in rendering the lines in the

The Moon and Venus exhibit lines corresponding with those of the Sun. Sirius shows different lines, and Castor others somewhat similar. Amongst the lines of Procyon, Fraunhofer recognised the solar line D, and in those of Capella and Betalgeus, he described both D and b.-Brewster's Edinburgh Journal of Science, 1828, vol viii. p. 7. ↑ Bibliothèque Universelle de Genève, August, 1842, No. 80 ; or Taylor's "Scientific Memoirs," ii. 537.

most refrangible and extra-violet portions apparent to the eye, by his discovery that the fluorescent power of the spectrum was interrupted by inactive spaces, the position of which corresponded accurately with the lines observed by Becquerel.

2. The Absorption Bands, produced by coloured gases, were first indicated in 1832 by Sir David Brewster (Phil. Mag., May, 1836, viii. 384), who found that the brownish-red vapours of nitrous acid have the remarkable power of absorbing the sun's rays in such a manner as to produce a series of dark bands in the light when transmitted through it. Professors W. H. Miller and Daniell subsequently showed that the same effect is produced, whatever be the source of light employed. In the course of this investigation, an important observation was made by Brewster, who noticed distinct lines and bands in the red and green spaces, which at other times wholly disappeared. This he found to be due to an absorptive action of the earth's atmosphere; for these bands were only visible when the sun approached the horizon. A few years later, I had an opportunity myself, whilst examining the spectrum of diffused daylight in the afternoon, during a violent thunder-shower, to observe the sudden appearance of a group of lines in the brightest part of the spectrum, between D and E, increasing in distinctness with the violence of the shower, and fading and disappearing as the rain passed away. These observations, therefore, prove that certain of the fixed lines in the solar spectrum are dependent, in part at least, upon the absorptive action exerted by the earth's atmosphere. But the larger portion, it is supposed, are due to another cause, first suggested by Kirchhoff. Professor Miller, of Cambridge, in conjunction with Professor Daniell, followed up these experiments, and showed that other coloured vapours, viz., those of bromine, iodine, and euchlorine possess this property (Phil. Mag., 1833, ii. 381).

Twelve years afterwards, I myself made a numerous series of experiments upon the same subject (Phil. Mag., xxvii. 81). The result of these experiments showed that mere existence of colour in a vapour does not indicate of necessity the existence of bands in its spectrum. The red vapours of chloride of tungsten give no lines, while bromine, which has to the eye the same colour, gives a remarkable series.

"The probable position of the lines cannot be inferred from the colour of the gas; with the green perchloride of manganese, the lines are most abundant in the green, whilst with the red vapours of nitrous acid they increase in number and density as they advance towards the blue end of the spectrum. Simple bodies, as well as compounds, may produce lines; and two simple bodies, which singly do not produce them, may in their compounds occasion them abundantly; e.g., neither oxygen, nitrogen, nor chlorine, when uncombined, occasions lines, but some of the oxides, both of nitrogen and of chlorine, exhibit the phenomena in the most striking manner. There are, however, oxides, both of nitrogen and chlorine (some of them coloured), which do not occasion the appearance of lines. We find also that lines may exist in the vapour of simple substances, as in iodine, which disappear in their compounds. This is exemplified in the case of hydriodic acid. Sometimes the same lines are produced by different degrees of oxidation of the same substances, a remarkable instance of which is furnished in the oxides of chlorine." Coloured lithographs of several spectra accompany the paper, including those of bromine, iodine, peroxide of nitrogen, perchloride of manganese, and peroxide of chlorine.

3. On the Spectra of the Electric Spark.Wollaston (Phil. Trans., 1862) observed that the spectrum of the electric spark is not continuous, and that it differs from that of ordinary sunlight, as well as from that furnished by the light of a candle. Fraunhofer also has a similar observation, but the first person who called attention to the important fact that the nature of the metals employed modifies the resulting spectrum, was Professor Wheatstone, who, at the Dublin meeting of the British Association for 1835, read a paper "On the Prismatic Decomposition of the Electric, Voltaic, and Electro-Magnetic Sparks." In the abstract published in the Report of the Proceedings of the Association for that year, the author states that,-1. "The spectrum of the electro-magnetic spark taken from mercury consists of seven definite rays only, separated by dark intervals from each other. These visible rays are, two orange lines close together, a bright green line, two bluish-green lines near each other, a very bright purple line, and, lastly, a violet line." 2. "The spark taken in the same manner, from zinc, cadmium, tin, bismuth, and lead in the melted state, gives similar results; but the number, position, and colours of the lines vary in each case. The appearances are so different that by this mode of examination the metals may be readily distinguished from each other." A table accompanied the paper, showing the position and colour of the lines in the various metals used.

3. "Where the spark of a voltaic pile was taken from the same metals, still in the melted state, precisely the same appearances are presented. 4. The voltaic spark from mercury was taken successively in the ordinary vacuum of the air-pump, and the Torricellian vacuum, in carbonic acid gas, &c., the same results were obtained as when the experiment was performed in air, or in oxygen gas. The light, therefore, does not arise from the combustion of the metal. Professor Wheatstone also examined by the prism the light which accompanies the combustion of the metals, in oxygen gas, and by other means, and found the appearances totally dissimilar to the above. 5. When the (electric) spark is taken between balls of dissimilar metals, the lines appertaining to both are simultaneously seen."

The next point of importance relating to the subject of the spectrum produced by ignition in the voltaic arc, is due to M. Foucault, who in 1849 published in the Journal de l'Institut, February 7, a note on the light of the electric arc, reprinted in the Ann. de Chimie et de Physique, III. lviii. 476. In this paper he says:— Icaused a solar image, formed by a converging lens, to fall upon the arc itself, an arrangement by which I was able to observe simultaneously the superposed solar and electric spectra, and I observed myself in this manner that the double brilliant line of the arc coincided exactly with the double black line of the solar light,

"This method of investigation enabled me to make some unexpected observations. In the first place, it proved to me the extreme transparency of the electric arc, which only casts a slight shadow upon the solar light. It has shown me that this arc, placed in the track of a beam of solar light, absorbs the rays D, so that the said line 1) of the solar light is considerably strengthened when the two spectra are exactly superposed. When, on the contrary, they only partially overlap each other, the line D appears darker than usual in the solar light, and stands out brightly in the electric spectrum, so that it is easy to judge of their perfect coincidence. Thus, the arc offers us a medium which itself emits the rays D, and which, at the same time, absorbs them when they come from another luminous source. In order to make

with the crystallisation of an ordinary salt. There is nothing of the kind, however.

Take another portion of the same crystals, and examine them one by one. You will find that one-half has the form, a model of which I here present, characterised by a non-superposable hemihedrity; that the other half has the inverse form identical with the first in all its respective parts, and yet cannot be superposed on it. Then let the two kinds of crystals be isolated to be dissolved separately, and we observe that one of the two solutions deviates the polarised light to the left, and the other to the right, and both equally.

If we extract, by the ordinary chemical processes, the acids from these two kinds of crystals, we perceive that one of them is identical with common tartaric acid, and that the other is in all points similar, except that it cannot be superposed on it. They bear to each other the relations of the two salts from which they were separated. They resemble each other as much as the right hand resembles the left, or as two irregular symmetric tetrahedrons resemble each other, and these analogies and these differences are found in all these derivatives. What can be done with one may be repeated with the other under the same conditions, and the resulting products constantly manifest the same properties, with this single difference, that in some the deviation of the plane of polarisation is to the right, and in others to the left, and that the forms of corresponding species, although identical in all their details, cannot be superposed.

All these facts, so clear, so demonstrative, oblige us to refer the general exterior characters of these acids and their combinations to their individual chemical molecules. Not to do it would be to ignore the rules of the most common logic. It is thus we arrive at the following conclusions:

1st. The molecule of tartaric acid, whatever it may be otherwise, is dissymmetric, and of a dissymmetry with an image non-superposable. 2nd. The molecule of the left tartaric acid is formed precisely by the group of inverse atoms. And by what characters shall we recognise the existence of molecular dissymmetry? In the one case by non-superposable hemihedrity; in the other, and especially, by the rotary optical property when the body is in solution. These principles being stated, let us examine all bodies, whether from Nature or the laboratory, and we shall find easily that among them a great number possess both this kind of hemihedrity and the molecular rotary property, and that all others possess neither the one nor the other of these characters.

I was right, then, in saying,-The legitimate and forced consequence of our first Lecture may be thus

expressed ::

All bodies (I use this expression chemically) are divided into two great classes: bodies with a superposable image, and bodies with a non-superposable image; bodies constructed of dissymmetric atoms, and

those formed of homohedric atoms.

(To be continued.)

PROCEEDINGS OF SOCIETIES.

PHARMACEUTICAL SOCIETY.
Wednesday, April z, 1862.

Mr. P. SQUIRE, President, in the Chair. PROFESSOR BENTLEY, in continuation of his papers on the new American remedies, made some remarks on the hydrastis canadensis. This plant, he said, had long been

NEWS

An old

in use among the Indians as a dye and as a medicine, and had recently been introduced by the eclectic practitioners of America as a tonic. It was also supposed to have an especial action on the mucous membranes. However that might be, the substance was now in common demand, and it was well that pharmaceutists should be made acquainted with its characters and properties. The effects concerned physicians alone, and he should express no positive opinions about them. The root or rhizome of the hydrastis canadensis was variously known as yellow root and turmeric root; and the plant was sometimes called groundraspberry, in consequence of the fruit somewhat resembling a raspberry. The plant belonged to the order Ranunculaceae, and was found only in North America. It had no interest except as a medicine. As the flower was not beautiful, it had never attracted the attention of floriculturists. The part of the plant used in medicine was the rhizome. This had an irregular, twisted appearance, and was surrounded with numerous rootlets. It was rough, and had a yellowish appearance when fresh, but became brown by keeping. It had a marked odour like opium, and a strong, opiate, and bitter taste. specimen smelt like liquorice. It contained tannic and gallic acids, starch, resin, a yellow colouring matter, and, substance, which was called hydrastine. This principle according to Durant, a peculiar, nitrogenised crystallisable was said to be separated by making an aqueous extract, adding magnesia, then extracting by boiling alcohol, filtering hot, and evaporating the filtrate. The hydrastine was thus obtained in four-sided crystals. Two other hy drastines are found among the eclectic remedies, one a resinoid, the other a neutral principle. The yellow translucent crystals of the first body when treated with strong nitric acid evolve nitrous vapours, and yield a deep red solution. Strong sulphuric acid produces an olive brown solution, which on the addition of potash becomes turbid and deposits a resin. Dr. Malha has recently discovered that the substance sold in America as hydrastine is really impure berberine, a remarkable fact, as the first discovery of that body in a ranunculaceous plant. Berberine is now known to exist in four natural orders of plants. Hydrastine, the Professor said, was prescribed as a tonic in affections of the mucous membranes and in other cases. There are substances in the market,hydrastin, hydrastine, and hydrastina. Perhaps the best preparation would be an alcoholic extract, which would contain all the active principles of the plant. More experience was necessary before any conclusions respecting the remedial value of the plant could be drawn. The Professor concluded by apologising for the somewhat discursive nature of his remarks.

The next paper was "On Hydrastine," by Mr. J. D. PERRIN. The author commenced by remarking that the hydrastis canadensis was an excellent source of berberine, and that the hydrastine of commerce had been found to be an impure berberine. Berberine, however, is difficultly insoluble in alkalies. To a solution of the two in nitric soluble in dilute nitric acid, while true hydrastine is acid, ammonia is added until a precipitate just begins to appear; the liquid is then filtered, and more ammonia is added. The precipitate so produced is collected and washed with water. Hydrastine so obtained is seen under the microscope to consist of spherical granules, which, when pressed between tiles, seem to assume a crystalline appearance. To purify the substance, it is dissolved in hot proof spirit, the solution filtered while hot, and set aside to crystallise. By dissolving these crystals a second time and treating with animal charcoal, the substance may be obtained quite pure in four-sided prisms, which lose their transparency after drying, not, however, in consequence of the loss of water. One and a half per cent. of hydrastine may be obtained from the dry root of the hydrastis. The author has not yet determined the exact composition of hydrastine, but had found

CHEMICAL NEWS, April 12, 1862.

that it contained nitrogen. It is a powerful base, and forms double salts with mercury, gold, and platinum. It is soluble in alcohol, ether, and benzole, in which berberine is not soluble. The salts of hydrastine are soluble in water, except the carbazotate. The solutions of the salts have a bitter taste, followed by a sense of numbness. Hydrastine is not a poison; five grains administered to a rabbit only made it uncomfortable for a short time. The crystals touched with sulphuric acid and peroxide of lead, give a colour very much resembling that produced by mere traces of strychnia when treated in the same way. Chlorine water with hydrastine gives a blue fluorescence very like a solution of quinine. In conclusion, the author said he had found that the xanthoriza apinfolia, another ranunculaceous plant, also contained berberine. It was, besides, a perfect bitter and a good tonic.

"On the Preparation of Iodide of Potassium and Iodides in general." By W. S. SQUIRE, Ph. D. After alluding to the difficulties in the way of the easy manufacture of iodide of potassium, and the numerous processes employed for the purpose (a manufacturer was said to have tried 700 processes, and then gave it up in disgust), Dr. Squire mentioned the well known methods of obtaining the salt by the double decomposition of the iodide of iron, or zinc and carbonate of potash, and also by decomposing the iodide of barium with sulphate of potash. In the two first processes pearlashes are generally used, and the impurities of these usually find their way into the iodide; the third method also has its objections. The author then proceeded to describe the process proposed by Liebig, namely, by acting on iodine with phosphorus, and so forming phosphoric and hydriodic acids, the solution of which is treated with milk of lime. Phosphate of lime is precipitated, and iodide of calcium remains in solution. The filtered solution of iodide of calcium is then decomposed with sulphate of potash, and any sulphate of lime is carefully removed by carbonate of potash. The solution of iodide of potassium may then be crystallised. A satisfactory result, however, the author said, was not to be obtained unless the salt was subjected to fusion. The iodide would not crystallise in the usual way, and the crystals would have a pinkish colour. Both of these objections were removed by the fusion. When making iodide of ammonium, the author recommended that the iodide of barium should be fused before the carbonate of ammonia was added. In this way the pink colour the crystals would otherwise have was obviated. A caution was then given against fusing iodide of lithium in a platinum crucible, lithium attacking platinum very strongly. The above process, although perhaps not applicable on a large scale, was not expensive. The atomic proportion of phosphorus being low and of iodine high, the quantity of phosphorus it was necessary to use in producing one pound of iodide of potassium would only cost a penny. Dr. Squire then alluded to the so-called periodide of iron, formed when the iodide of iron was kept a long time, and showed that the red solution formed when iodine was dissolved in the iodide of iron, readily yielded up the excess of iodine together, leaving the solution of the iodide. Iodide of mercury, he then said, was directed by the Pharmacopoeia to be prepared by rubbing together equivalent weights of mercury and iodine; in this way an olive brown compound was obtained. But people objected to the appearance of this salt, and preferred a yellow iodide, which was made by precipitating the protonitrate of mercury with iodide of potassium. By this means some biniodide of mercury was formed, which gave the lighter colour to the compound. As the biniodide of mercury is a much more active medicine than the iodide, this process was highly objectionable. To prove that the biniodide was present in a specimen of the yellow salt, Dr. Squire boiled some with aniline and produced a red liquid; the olive brown iodide did not produce a red solution.

205

Mr. PERRIN asked if there was any evidence of alkalinity in the iodide of potassium prepared by Liebig's process?" Mr. SQUIRE said not necessarily; if more carbonate of potash was added than was sufficient to precipitate the sulphate of lime, the salt would, of course, be alkaline. A MEMBER described a process he had employed for making iodide of potassium from iodide of lead and sulphate of potash. Dr. SQUIRE said that process was a very expensive one, sulphate of lead always carried down with it a large proportion of sulphate of potash, which was lost.

The PRESIDENT then called attention to some bottles intended for external applications, which had been exhibited at a previous meeting. They are shaped something like a shoe, and must lie flat on the sole.

A MEMBER remarked that at a distance they looked very much like feeding-bottles.

The meeting (the last of the season) then adjourned.

SOCIETY OF ARTS.

Wednesday, February 5.

Dr. A. W. MILLER, F. R. S., Professor of Chemistry at King's College, in the Chair.

(Concluded from page 191.)

Dr. CALVERT concluded his account of the coal-tar colours with a brief notice of M. Roussin's so-called artificial alizarine, with which our readers are already acquainted, and then passed on to the consideration of the more mechanical improvements in the process of calico< printing, commencing with the engraving of cylinders, which point we will quote in full.

"This branch of calico-printing has made great progress. Not only have the engravings acquired sharper outlines and finer details, but the methods of engraving have greatly multiplied. I may cite as instances the application of the principle of the pentagraph, by Messrs. Smith, so as to trace patterns on the surface of rollers. Also, calico printers have extensively availed themselves of Mr. Locket's improvements for producing the groundwork of prints, or as they are termed 'covers,' by applying 'eccentric engraving,' or etching, which produces with facility most complicated patterns on a varnished roller, by means of a diamond point guarded by machinery. Another improvement, highly interesting in a scientific point of view, is the application of galvanism to the diamond tracer. By combining the galvanic action with an eccentric motion, most beautiful and delicate engravings may be produced. This is done by tracing the pattern with varnish on a zinc cylinder, which is so placed in the engraving machine that as a needle passes over its surface and comes into contact with the zinc, the galvanic current is established, and by simple machinery causes the diamond to trace the corresponding pattern on the copper roller. The communication is so rapid and precise that a great saving of time is effected. But if mechanical art has greatly assisted the engraver, chemistry has rendered him equally important services, by enabling him to abandon costly and cumbrous modes of impressing by force the designs on the cylinder, substituting for them a great number of etching processes. By some of these processes, as by every other addition to the resources of the engraver, an entirely new and beautiful class of engraving is produced, unattainable by any other known means. For instance, owing to various improvements, rollers of 43 inches in circumference and 44 inches long have been introduced, enabling the calico printer to produce cheaply large furniture patterns."

Mercer's process for increasing the strength and beauty of cotton fabrics by passing the cloths into a strong solution of caustic alkali, and then through dilute sulphurie acid, with subsequent washing, was next commented on; while Thom's improvements in "singeing" and "sulphur