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RADCLIFFE LIBRARA

10 JAN 76 THE CHEMICAL NEWS.

VOLUMLUFRAX111.

EDITED BY WILLIAM CROOKES, F.R.S., &c.

No. 841.- JANUARY 7, 1876.
ON SOME FORMS OF SELENIUM,

because little, if anything, has been added to that knowAND ON THE

ledge for nearly twenty years, and because the statements INFLUENCE OF LIGHT ON THE ELECTRICAL sufficient, but often discordant with the results obtained

in some of the acknowledged text-books are not only inCONDUCTIVITY OF THIS ELEMENT.* by the savants to whom we owe all that up to this time

has been done in relation to the subject. By HARRY N. DRAPER, F.C.S., and RICHARD J. MOSS, F.C.S.

As we would desire to avoid matter which is supplied by

handbooks of chemistry, or details not directly bearing In a paper read before the Society of Telegraph En. upon our investigation, it must be understood that we gineerst on February 12th, 1873. Mr. Willoughby Smith note here only those hitherto observed and not widely announced the remarkable fact, that a bar of crystalline known characters of selenium which seem to us to be in selenium, through which a current of electricity passes, ntimate relation to the phenomena we have made the has its conducivity increased 15 to 100 per cent when iobjects of experiment. the bar is exposed to light. The light from an ordinary Selenium, discovered by Berzelius in 1817, was carefully gas-burner placed at a distance of several feet increased studied by that chemist, and it is through his researches, the conductivity 15 to 20 per cent. Mr. Smith satisfied ; and those of Regnauit, Mitscherlich, and Hittorf, that we himself that alterations in temperature in no way affected have almost all our knowledge of the physical characters this result, by placing the selenium in water, in such a of this element. It is upon their authority that the fol. manner that the light from burning magnesium ribbon lowing statements are made. held some inches above the bar passed through about an Selenium may exist in several different forms:inch of water before falling upon the selenium. Under

1. As a vitreous mass, with conchoidal fracture. these circumstances, the conductivity of the bar was found to increase more than two-thirds, returning to the enious acid or selenites by the action of reducing

2. As a red amorphous powder precipitated from senormal conductivity when the light was withdrawn.

agents. Lieutenant Sale, in a communication made to the Royal

3. In the form of minute crystals deposited from its Society, I describes a series of experiments undertaken solution in bisulphide of carbon. with the object of ascertaining the relative effect upon the ele&ric resistance of selenium of the light in different selenides exposed to the air.

4. In crystals deposited from solutions of the alkaline parts of the spectrum. He found that in the solar spectrum the conductivity is least in the violet, and increases metallic cobalt or cast-iron, and obtained by the heating

5. As a granular body resembling, almost completely, as the red is approached, attaining its maximum in a

and slow cooling of either of the three first mentioned position just on the outside edge of the red rays at the red

forms. side. The conductivity in this position is greater than in diffuse daylight, but very considerably less than when the

The first three modifications, it should be mentioned, selenium is exposed to full sunlight. Mr. Sale observeå resemble one another in their physical and chemical rela: that the effect of light is apparently instantaneous, but tions, and must be regarded as different conditions of the that the return in darkness to the normal resistance is not

same allotropic form of selenium. so rapid. He corroborates the statement of Mr. Wil.

It is here only necessary to speak of vitreous selenium loughby Smith, already cited, that the varying resistance and of its heat-produced allotropic modification, the is in no way due to alteration of temperature of the se

granular variety, or as it has been felicitously called by lenium.

Regnault, metallic selenium. Soon after the publication of Mr. Smith's observations,

Vitreous selenium has no definite point of fusion. At we undertook a series of experiments with the object of, temperatures exceeding 60° C. it softens, becoming graduif possible, determining the precise' molecular state of ally softer with increased heat, and being perfectly fluid selenium, which exhibited this phenomenon of diminished

at 250°. When rapidly cooled from this temperature, it ele&rical resistance under the action of light, and the returns to its original condition. At normal temperatures conditions necessary for its production.

it may be kept without change of state for many years, It would here appear necessary to give a brief resumé and is probably under these conditions perfectly stable: of the state of our knowledge of the physical properties It is, though very sparingly, soluble in bisulphide of car: and relations of selenium. This is of the more importance bon. In thin films, it appears by transmitted light of a

beautiful ruby-red colour. Its specific gravity is, accordFrom the Proceedings of the Royal Irish Academy, vol. i., Ser. II. ing to Schafigottsch, 4'276. (Sci.).

When this vitreous selenium is maintained for some time + Nature, vol. vii., p. 203. Proceedings of the Royal Society of London, vol. xxi., p. 283. at any temperature between 94o and 200° C., and is then $ No experiments are adduced in support of this statement. slowly cooled, it is sound to have assumed a metallic ap

2

Pyrology, or Analysis and Synthesis by the Blowpipe. (CHEMICAL NEWS, pearance, and to have a grey granular fracture. It is the extreme range of the mercurial thermometer, but so now, we ourselves find, perfectly opaque to light, even in much beyond that it is still diminishing when, owing to the thinnest films. Its specific gravity has increased to the rapid volatilisation of the selenium, it has been found 4:796. When heated it does not soften, but at 217° fuses necessary to terminate the experiment. without taking any intermediate pasty condition. At 250° It has hitherto been assumed that there is but one it is perfectly fluid, even when the mass is considerable; granular form of selenium, and that this is a conductor and when rapidly cooled returns, without any tendency of electricity. We have, however, obtained a granular to crystallise, to the vitreous, non-metallic modification form in no way optically differing from granular selenium All that has up to the present been made known as to of comparatively low resistance, through a rod of which, the electrical relations of selenium may be very shortly 16 m.m. long and 3 m.m. diameter, the current of ten told.

Leclanché cells does not in the least deflect the needle Solid vitreous selenium cannot, according to Berzelius,* of our highly sensitive galvanometer. Nor does light, so be rendered electrical by friction, but, on the contrary, far as our experiments have yet gone, diminish the resistBondsdorfft states that when rubbed in very dry air it ance of this modification. We have, on the other hand, has this property. Knox found that fused selenium con succeeded in obtaining bars of granular selenium through ducted the current of a battery of sixty pairs. Hittorf which the current of one Leclanché cell causes a very found that granular selenium at normal temperatures con. considerable deflection of the needle. This foron is, we ducted sufficient of the current of one Grove's element to find, in its electric resistance alrnost unaffected by light. deflect the astatic needle of a galvanometer having 200 Between these two forms of granular selenium-the apconvolutions 17°, and that when the selenium was heated parently non-conducting and the comparatively highly to 210° in a small crucible the eedle marked 80°. But conducting-there is another of intermediate resistance. when the temperature reached 217° (the point of fusion of This modification is highly sensitive to light; its congranular selenium), the needle went back suddenly to 20°. ductivity when is the form of flat bars increasing in direct

The action of light as probably effecting some change sunlight 75 to 100 per cent, and in artificial light in ratios in the allotropy of selenium was not wholly unsuspected ranging from 10 to 50 per cent. prior to Mr. Smith's observations. Gmelin mentions ex One form of granular selenium, as Hittorf first showed, posure to sunlight as a favourable condition for the pre- has its resistance considerably diminished by heat: indeed, cipitation of selenium from dilute solutions of selenious he says that could it be heated red hot its conductivity acid by sulphurous acid; and Hiltorf, while noting the would not be inferior to that of the metals. Our own exlikelihood of such an influence, was unable to detect it, periments confirm the diminution of conductivity by heat, and was obliged to attribute the observed change of amor. but we have found, in at least one modification which phous into crystalline selenium, while drying in sunlight, we have produced, a body which so far conforms to the entirely to the effect of heat. In pursuing the line of re metallic type as to have its resistance strikingly increased search we have marked out for ourselves, we have been by heat. We have made bars of selenium which when obliged to repeat much already published work, which placed in the circuit of a battery and galvanometer, have with improved means of experiment has lost somewhat of shown a deflection of 48°, while upon completing the cirits significance. We have thus encountered several ap. cuit of a nitric acid battery, the current of which heated parently contradictory statements, some of which our ex a spiral platinum wire surrounding the bar of selenium, perience has either failed to verify, or has placed in a new the needle gradually fell to 15°, as the temperature of the light; and we have been convinced that the properties of bar became greater. this remarkable substance are but imperfectly understood, For the present we refrain from comment upon these and still present a wide field for investigation. Vitreous results; and although we have been engaged during many selenium is, we should say at the outset, apparently an months in this investigation, we deser details of our exabsolute non-conductor of electricity. We have been un periments, and especially of the conditions under which able to obtain any deflection of the very sensitive astatic the different electrically resisting and light-sensitive forms needle of a high resistance galvanometer, when the thin- of selenium are obtained, until with larger experience we nest films of selenium, of the continuity of which we may hope to bring before the Academy results tending could assure ourselves, are interposed in the circuit of more closely to the solution of the questions we have proten Leclanché elements. The difficulty of producing posed to ourselves. very thin films of absolute continuity disposes us nevertheless to state our belief as to the complete non-conductivity of vitreous selenium with some reservation.

As might be expected from this character, selenium in ON PYROLOGY, OR ANALYSIS AND SYNTHESIS the vitreous form becomes electric by friction. So easily

BY MEANS OF THE BLOWPIPE.* indeed have we invariably obtained this result that we find it difficult to understand the contrary conclusion of

By W. A. ROSS. Berzelius.

(Continued from vol. xxxii., p. 252.) Hittorf, as has been stated, sound that when vitreous selenium is converted into the granular form its electrical resistance diminishes directly with its temperature, but (7). It seems incredible, and yet is undoubtedly a fact, that that when 217° is attained the resistance is suddenly and

there are English chemists-accomplished ones too-and largely augmented. In repeating this experiment we have

even public analysts almost entirely ignorant of the obtained results concordant with those of Hittorf, who analytical use of the blowpipe. To foreigners, especially appears, however, not to have exceeded the temperature Germans, it seems strange that we have riot in England of 217°: Going beyond this point, we find that the resist any systematic training, by means of lectures and practical ance diminishes up to the point of complete fusion of teaching, in blowpipe analysis, on the pattern of the the selenium, being at its maximum at 250°: We have be instituted by a rich Government like ours without

famous Freiberg University. Such a course might surely obtained also the remarkable result that when the vitreous selenium resulting from the rapid cooling of the com

much difficulty, in Jermyn Street, under the direction of pletely fused granular form is quickly heated, it begins

one of the old Freiberg students, as, for instance, Her to conduct the current at a temperature between 165 and Majesty's Inspector of Mines, within whose superinten. 175°, and that its resistance diminishes, not only up to

dence the students might make periodical visits to the

most characteristic crines, which that gentleman knows * Gmelin, “ Handbook," 11., 5. 236

so well: so that this reproach may be taken from us. It + Gmelin, 1.c. : Gmelin, 1.c.

* The termi "pyrological" ("pyrologischen Versuche") has been $ Poggendorf, Annalen der Physik und Chemie, Bd. Ixxxiv., p. 214. adopted by Professor Richter, of Freiberg, in a letter to the writer.

ON THE

CHEMICAL News,
Jan. 7, 1876.;
-}
Development of the Chemical Arts.

3 is not a sufficient reply to say that “there is a course of be correct, to what may be termed the metaphysical blowpipe instruction in almost every English chemical chemistry of modern times, it seems insufficient when class or college.” Every chemist who has been to Freiberg, absolutely and completely substituted for practical knowor even to the American colleges, knows how inefficiently ledge, and reasoning in mere English,* and, indeed, it is the blowpipe is taught, or rather, how effectually it is obvious that, in England at least, there is a tendency neglected in our otherwise excellent schools of chemistry. among our best writers, even on chemical metaphysics, to If this point be controverted, it will not be difficult to express their thoughts, not only in English, but in the take one of our most generally received analytical text very plainest English which has ever been in the possesbooks, and show what extraordinary and incorrect state sion of Her Majesty or her predecessors. There is no art ments are there made with regard to blowpipe so difficult of attainment as simplicity, and we may safely analysis, nor does an inspection of some of the English regard the value of an invention (or the description of pyrological instruments and apparatus at all reassure us. one) in the inverse ratio to its complication. Whoever I have lately, incredible as it will seem, been shown an takes the trouble to compare the amazing hieroglyphical instrument as the only kind of blowpipe in use in a public work of the communistical chemist Nacquet, translated Jaboratory in London, having an aperture at the jet, at into English the other day, with the luminous essays least a quarter of an inch in diameter; and, to make of the marvellous apothecary Scheele ;t or Axiom V., Book matters worse, filled both with the blast and with aërated I. of Newton's Optics, on the ratio between the sines of coal gas ! I saw a youth blowing through such a machine incidence and refraction in a ray of light, with the ordinary as this by means of a mouthpiece cleverly extemporised scientific account of the same simple law given in our with a glass funnel, and warned him that he would thus modern mathematical or physical works, will soon see probably injure his lungs, a misfortune which would of that the advantage in every essential particular remains course be attributed to "the blowpipe," instead of to the with the adopters of expression by means of language. personal use of such a tuyere as this.

Besides, no one, not even the most eminent philosopher, (8). It may be as well to mention here that blowpipes can afford to discard the very great advantage of address. like that devised by Von Frick, having the operator's ing himself to thousands-perhaps millions-of his fellow breath, or blast from any other source, and the gas for creatures, instead of to a few transcendentalists who ignition conveyed by the same tube, are utterly useless for cannot spread his opinions beyond their own clique. these purposes; that Bunsen burners are useless for these purposes; that Fletcher's most ingenious, and no doubt otherwise invaluable “ hot blast blowpipe” is almost useless for these purposes, which are most erro

REPORT neously supposed to be always best effected by the greatest heat. Let any student who really wishes to learn this science produce a blue pyrocone from a candle by a hand

DEVELOPMENT OF THE CHEMICAL ARTS blower, and then with a mouth blowpipe held in the other

DURING THE LAST TEN YEARS.I hand, direct a blast across this blue pyrocone, so as to

By Dr. A. W. HOFMANN. dissect it; he finds it to be a solid mass of blue flame. If he now perform the same operation on the pyrocone from

(Continued from vol. xxxii., p. 286.) a gas jet, the pyrocone is found to be slightly hollow, while the pyrocone from a Bunsen burner has only the THENARD, on bringing peroxide of hydrogen into contact merest thin shell of circumscribing ignited gaseous

with his tongue, in order to ascertain its taste, found that matter. It is obvious, therefore, that the effect of holding it was whitened. The cuticle was also blackened, and at the fragment or paste of a mineral or other essay, in the the same time a violent itching was excited. Litmus paper middle of these three pyrocones, must be different in each

without any previous reddening was at once de colourised, case ; yet how seldom in England do we see a candle or

as was also turmeric paper. oil lamp used for important results which can be obtained In 1863 Chevreul, undertook comparative experiments solely by its use?

on the bleaching power of hydrogen peroxide. Its con(9). It is obvious that in order to properly systematise centrated solution speedily turned syrup of violets green, the science of blowpipe analysis, we ought to reduce it to

oxygen being set at liberty. For the following experias close analogy as may be with the procedure in ordinary ments dilute colour-solutions were used---namely, syrup chemical analysis, which has been found to answer so

of violets, tincture of litmus, extract of peach-wood, and well. I have, therefore, in my method discarded the extract of logwood. The results were as follows :preliminary use of the salts borax and microcosmic sal',

Peach-wood. Logwood. and commenced attacking substances with the pyracids 10 mins. Imperceptible. Slight Change to “Boric and phosphoric anhydride." Boric acid, indeed,

bleaching. contrary to the account found in most of our chemical

24 hrs... Complete Almost complete Turns, works, dissolves before the blowpipe no oxide whatever

bleaching.

bleaching yellow: completely, except those of the alkaline metals, and that

80 hrs... Complete bleaching of all the solutions. of silver a little, but its reactions thus are a thousand times more valuable than if it really (as we are told) dis

Decolorisation is therefore effected less rapidly by persolved all those, while, by adding pyrologically a very

oxide of hydrogen than by chlorine. Tessié du Motay small proportion of alkali (not quite 5 per cent) we obtain and Maréchals mention it as one of the agents which they a still acid menstruum which is itself extremely soluble in propose for bleaching tissues, which, after treatment with water. Phosphoric acid, on the other hand, is, before the permanganate of potash, they recommend to be steeped blowpipe, the most powerful unmixed solvent in the in a solution of peroxide of hydrogen. But it had been world, dissolving gold leaf to a bluish violet glass quite much earlier applied as a bleaching-agent by Thénard rapidly. In either case we can further, if we like, obtain himself for a particular purpose--namely, for restoring old an acidulated water solution, in which precipitates can be produced by alkalies, &c., just as in "the wet way,” but

* The controversy at present proceeding between Dr. Frankland and

Mr. Wanklyn in the CHEMICAL News, with reference to this process requires to be worked out, and shall not analysis, may be cited as an illustration of this point. therefore be further alluded to here.

+ Schel: sems to have been a German, noi a Swede, settled as a (10). It is necessary, however, to lightly tuch upon

common apothecary, at Köping, in Sveden

* " Berichte über die Entwickelung der (h:mischen In: ustr : one part of the subject, not invidiously but conscientiously, Während des Letzten Jahrzehends." before proceeding to details. However invaluable the il Chevreul, Comptes Rendus, lv., 735. application of the symbolical and algebraical process o.

& Bull. Soc. d'Encouragement, 1867, 472.

Dingler, Pulst, Journal

cxxc(?)iv., 526. ratiocination may be, assuming its groundwork of facts to f Pélouze and Frémy, Traité de Chimie, 1861,

Time.

Violets.

Litmus.

rose.

wat:r

2

CHEMICAL NEWS, Pyrology, or Analysis and Synthesis by the Blowpipe.

Jan. 7, 1876. pearance, and to have a grey granular fracture. It is the extreme range of the mercurial thermometer, but so now, we ourselves find, perfectly opaque to light, even in much beyond that it is still diminishing when, owing to the thinnest films. Its specific gravity has increased to the rapid volatilisation of the selenium, it has been found 4796. When heated it does not soften, but at 217° fuses necessary to terminate the experiment. without taking any intermediate pasty condition. At 250° It has hitherto been assumed that there is but one it is perfectly fluid, even when the mass is considerable ; granular form of selenium, and that this is a conductor and when rapidly cooled returns, without any tendency of electricity. We have, however, obtained a granular to crystallise, to the vitreous, non-metallic modification form in no way optically differing from granular selenium All that has up to the present been made known as to of comparatively low resistance, through a rod of which, the electrical relations of selenium may be very shortly 16 m.m. long and 3 m.m. diameter, the current of ten told.

Leclanché cells does not in the least deflect the needle Solid vitreous selenium cannot, according to Berzelius,* of our highly sensitive galvanometer. Nor does light, so be rendered electrical by friction, but, on the contrary, far as our experiments have yet gone, diminish the resist. Bondsdorfft states that when rubbed in very dry air it ance of this modification. We have, on the other hand, has this property. I Knox found that fused selenium con succeeded in obtaining bars of granular selenium through ducted the current of a battery of sixty pairs. Hittorf g which the current of one Leclanché cell causes a very found that granular selenium at normal temperatures con considerable deflection of the needle. This forin is, we ducted sufficient of the current of one Grove's element to find, in its electric resistance almost unaffected by light. deflect the astatic needle of a galvanometer having 200 Between these two forms of granular selenium-the apconvolutions 17°, and that when the selenium was heated parently non-conducting and the comparatively highly to 210° in a small crucible the needle marked 80°. But conducting—there is another of intermediate resistance. when the temperature reached 217° (the point of fusion of This modification is highly sensitive to light; its congranular selenium), the needle went back suddenly to 20°. | ductivity when i: the form of flat bars increasing in direct

The action of light as probably effecting some change sunlight 75 to 100 per cent, and in artificial light in ratios in the allotropy of selenium was not wholly unsuspected ranging from 10 to 50 per cent. prior to Mr. Smith's observations. Gmelin mentions ex. One form of granular selenium, as Hittorf first showed, posure to sunlight as a favourable condition for the pre- has its resistance considerably diminished by heat: indeed, cipitation of selenium from dilute solutions of selenious he says that could it be heated red hot its conductivity acid by sulphurous acid; and Hittorf, while noting the would not be inferior to that of the metals. Our own exlikelihood of such an influence, was unable to detect it, periments confirm the diminution of conductivity by heat, and was obliged to attribute the observed change of amor but we have found, in at least one modification which phous into crystalline selenium, while drying in sunlight, we have produced, a body which so far conforms to the entirely to the effect of heat. In pursuing the line of re metallic type as to have its resistance strikingly increased search we have marked out for ourselves, we have been by heat. We have made bars of selenium which when obliged to repeat much already published work, which placed in the circuit of a battery and galvanometer, have with improved means of experiment has lost somewhat of shown a deflection of 48°, while upon completing the cirits significance. We have thus encountered several ap- cuit of a nitric acid battery, the current of which heated parently contradictory statements, some of which our ex a spiral platinum wire surrounding the bar of selenium, perience has either failed to verify, or has placed in a new the needle gradually fell to 15°, as the temperature of the light; and we have been convinced that the properties of bar became greater. this remarkable substance are but imperfectly understood, For the present we refrain from comment upon these and still present a wide field for investigation. Vitreous results; and although we have been engaged during many selenium is, we should say at the outset, apparently an months in this investigation, we deser details of our exabsolute non-conductor of electricity. We have been unseriments, and especially of the conditions under which able to obtain any deflection of the very sensitive astatic | the different electrically resisting and light-sensitive forms needle of a high resistance galvanometer, when the thin. of selenium are obtained, until with larger experience we nest films of selenium, of the continuity of which we may hope to bring before the Academy results tending could assure ourselves, are interposed in the circuit of more closely to the solution of the questions we have pro. ten Leclanché elements. The difficulty of producing posed to ourselves. very thin films of absolute continuity disposes us nevertheless to state our belief as to the complete non-conductivity of vitreous selenium with some reservation.

As might be expected from this character, selenium in ON PYROLOGY, OR ANALYSIS AND SYNTHESIS the vitreous form becomes electric by friction. So easily

BY MEANS OF THE BLOWPIPE.* indeed have we invariably obtained this result that we find it difficult to understand the contrary conclusion of

By W. A. KOSS. Berzelius.

(Continued from vol. xxxii., p. 252.) Hittorf, as has been stated, sound that when vitreous selenium is converted into the granular form its ele&rical (7). It seems incredible, and yet is undoubtedly a fact, that resistance diminishes directly with its temperature, but that when 217° is attained the resistance is suddenly and

there are English chemists-accomplished ones too-and largely augmented. In repeating this experiment we have analytical use of the blowpipe. To foreigners, especially

even public analysts almost entirely ignorant of the obtained results concordant with those of Hitlorf, who appears, however, not to have exceeded the temperature Germans, it seems strange that we have not in England of 217'. Going beyond this point, we find that the resist.

any systematic training, by means of lectures and practical ance diminishes up to the point of complete fusion of teaching, in blowpipe analysis, on the pattern of the the selenium, being at its maximum at 250°. We have be instituted by a rich Government like ours without

famous Freiberg University. Such a course might surely obtained also the remarkable result that when the vitreous much difficulty, in Jermyn Street, under the direction of selenium resulting from the rapid cooling of the completely fused granular form is quickly heated, it begins

one of the old Freiberg students, as, for instance, Her to conduct the current at a temperature between 165. and Majesty's Inspector of Mines, within whose superinten175°, and that its resistance diminishes, not only up to

dence the students might make periodical visits to the

most characteristic mines, which that gentleman knows * Gmelin, “ Handbook,"11., s. 236

so well: so that this reproach may be taken from us. It + Gmelin, 1.c. * Gmelin, 1.c.

* The term “ pyrological" ("pyrologischen Versuche") has been $ Poggendorf, Annalen der Physik und Chemie, Bd. lxxxiv., p. 214.

adopted by Professor Richter, of i'reibeig, in a lctior to the writer.

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