THE CHEMICAL NEWS. VOLUME XXXIII. EDITED BY WILLIAM CROOKES, F.R.S., &c. No. 841.-JANUARY 7, 1876. ON SOME FORMS OF SELENIUM, AND ON THE INFLUENCE OF LIGHT ON THE ELECTRICAL By HARRY N. DRAPER, F.C.S., and RICHARD J. MOSS, F.C.S. IN a paper read before the Society of Telegraph Engineers+ on February 12th, 1873, Mr. Willoughby Smith announced the remarkable fact, that a bar of crystalline selenium, through which a current of electricity passes, has its conductivity increased 15 to 100 per cent when the bar is exposed to light. The light from an ordinary gas-burner placed at a distance of several feet increased the conductivity 15 to 20 per cent. Mr. Smith satisfied himself that alterations in temperature in no way affected this result, by placing the selenium in water, in such a manner that the light from burning magnesium ribbon held some inches above the bar passed through about an inch of water before falling upon the selenium. Under these circumstances, the conductivity of the bar was found to increase more than two-thirds, returning to the normal conductivity when the light was withdrawn. Lieutenant Sale, in a communication made to the Royal Society, describes a series of experiments undertaken with the object of ascertaining the relative effect upon the electric resistance of selenium of the light in different parts of the spectrum. He found that in the solar spectrum the conductivity is least in the violet, and increases as the red is approached, attaining its maximum in a position just on the outside edge of the red rays at the red side. The conductivity in this position is greater than in diffuse daylight, but very considerably less than when the selenium is exposed to full sunlight. Mr. Sale observed that the effect of light is apparently instantaneous, but that the return in darkness to the normal resistance is not so rapid. He corroborates the statement of Mr. Willoughby Smith, already cited, that the varying resistance is in no way due to alteration of temperature of the selenium.§ Soon after the publication of Mr. Smith's observations, we undertook a series of experiments with the object of, if possible, determining the precise molecular state of selenium, which exhibited this phenomenon of diminished electrical resistance under the action of light, and the conditions necessary for its production. It would here appear necessary to give a brief resumé of the state of our knowledge of the physical properties and relations of selenium. This is of the more importance From the Proceedings of the Royal Irish Academy, vol. i., Ser. II. (Sci.). + Nature, vol. vii., p. 203. Proceedings of the Royal Society of London, vol. xxi., p. 283. § No experiments are adduced in support of this statement. because little, if anything, has been added to that knowledge for nearly twenty years, and because the statements sufficient, but often discordant with the results obtained in some of the acknowledged text-books are not only inby the savants to whom we owe all that up to this time has been done in relation to the subject. As we would desire to avoid matter which is supplied by handbooks of chemistry, or details not directly bearing upon our investigation, it must be understood that we note here only those hitherto observed and not widely known characters of selenium which seem to us to be in ntimate relation to the phenomena we have made the iobjects of experiment. Selenium, discovered by Berzelius in 1817, was carefully studied by that chemist, and it is through his researches, and those of Regnault, Mitscherlich, and Hittorf, that we have almost all our knowledge of the physical characters of this element. lowing statements are made. It is upon their authority that the fol Selenium may exist in several different forms:1. As a vitreous mass, with conchoidal fracture. enious acid or selenites by the action of reducing 2. As a red amorphous powder precipitated from se agents. 3. In the form of minute crystals deposited from its solution in bisulphide of carbon. 4. In crystals deposited from solutions of the alkaline selenides exposed to the air. 5. As a granular body resembling, almost completely, metallic cobalt or cast-iron, and obtained by the heating and slow cooling of either of the three first-mentioned forms. The first three modifications, it should be mentioned, resemble one another in their physical and chemical relations, and must be regarded as different conditions of the same allotropic form of selenium. It is here only necessary to speak of vitreous selenium and of its heat-produced allotropic modification, the granular variety, or as it has been felicitously called by Regnault, metallic selenium. Vitreous selenium has no definite point of fusion. At temperatures exceeding 60° C. it softens, becoming gradually softer with increased heat, and being perfectly fluid at 250°. When rapidly cooled from this temperature, it returns to its original condition. At normal temperatures it may be kept without change of state for many years, and is probably under these conditions perfectly stable. It is, though very sparingly, soluble in bisulphide of carbeautiful ruby-red colour. bon. In thin films, it appears by transmitted light of a ing to Schaffgottsch, 4.276. Its specific gravity is, accord When this vitreous selenium is maintained for some time at any temperature between 94° and 200° C., and is then slowly cooled, it is found to have assumed a metallic ap 2 Pyrology, or Analysis and Synthesis by the Blowpipe. pearance, and to have a grey granular fracture. It is now, we ourselves find, perfectly opaque to light, even in the thinnest films. Its specific gravity has increased to 4'796. When heated it does not soften, but at 217° fuses without taking any intermediate pasty condition. At 250° it is perfectly fluid, even when the mass is considerable; and when rapidly cooled returns, without any tendency to crystallise, to the vitreous, non-metallic modification. All that has up to the present been made known as to the electrical relations of selenium may be very shortly told. Solid vitreous selenium cannot, according to Berzelius,* be rendered electrical by friction, but, on the contrary, Bondsdorfft states that when rubbed in very dry air it has this property. Knox found that fused selenium conducted the current of a battery of sixty pairs. Hittorf§ found that granular selenium at normal temperatures con. ducted sufficient of the current of one Grove's element to deflect the astatic needle of a galvanometer having 200 convolutions 17°, and that when the selenium was heated to 210° in a small crucible the needle marked 80°. But when the temperature reached 217° (the point of fusion of granular selenium), the needle went back suddenly to 20°. The action of light as probably effecting some change in the allotropy of selenium was not wholly unsuspected prior to Mr. Smith's observations. Gmelin mentions exposure to sunlight as a favourable condition for the precipitation of selenium from dilute solutions of selenious acid by sulphurous acid; and Hittorf, while noting the likelihood of such an influence, was unable to detect it, and was obliged to attribute the observed change of amorphous into crystalline selenium, while drying in sunlight, entirely to the effect of heat. In pursuing the line of research we have marked out for ourselves, we have been obliged to repeat much already published work, which with improved means of experiment has lost somewhat of its significance. We have thus encountered several apparently contradictory statements, some of which our experience has either failed to verify, or has placed in a new light; and we have been convinced that the properties of this remarkable substance are but imperfectly understood, and still present a wide field for investigation. Vitreous selenium is, we should say at the outset, apparently an absolute non-conductor of electricity. We have been unable to obtain any deflection of the very sensitive astatic needle of a high resistance galvanometer, when the thinnest films of selenium, of the continuity of which we could assure ourselves, are interposed in the circuit of ten Leclanché elements. The difficulty of producing 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. CHEMICAL NEWS, the extreme range of the mercurial thermometer, but so One form of granular selenium, as Hittorf first showed, has its resistance considerably diminished by heat: indeed, he says that could it be heated red hot its conductivity would not be inferior to that of the metals. Our own.experiments confirm the diminution of conductivity by heat, but we have found, in at least one modification which we have produced, a body which so far conforms to the metallic type as to have its resistance strikingly increased by heat. We have made bars of selenium which when placed in the circuit of a battery and galvanometer, have shown a deflection of 48°, while upon completing the circuit of a nitric acid battery, the current of which heated a spiral platinum wire surrounding the bar of selenium, the needle gradually fell to 15°, as the temperature of the bar became greater. For the present we refrain from comment upon these results; and although we have been engaged during many months in this investigation, we defer details of our experiments, and especially of the conditions under which the different electrically resisting and light-sensitive forms of selenium are obtained, until with larger experience we may hope to bring before the Academy results tending more closely to the solution of the questions we have proposed to ourselves. BY MEANS OF THE BLOWPIPE.* As might be expected from this character, selenium in ON PYROLOGY, OR ANALYSIS AND SYNTHESIS the vitreous form becomes electric by friction. So easily indeed have we invariably obtained this result that we find it difficult to understand the contrary conclusion of Berzelius. Hittorf, as has been stated, found that when vitreous selenium is converted into the granular form its electrical resistance diminishes directly with its temperature, but that when 217° is attained the resistance is suddenly and largely augmented. In repeating this experiment we have obtained results concordant with those of Hittorf, who appears, however, not to have exceeded the temperature of 217. Going beyond this point, we find that the resistance diminishes up to the point of complete fusion of the selenium, being at its maximum at 250°. We have obtained also the remarkable result that when the vitreous selenium resulting from the rapid cooling of the completely fused granular form is quickly heated, it begins to conduct the current at a temperature between 165 and 175°, and that its resistance diminishes, not only up to By W. A. ROSS. (Continued from vol. xxxii., p. 252.) there are English chemists-accomplished ones too-and The term "pyrological" (" pyrologischen Versuche ") has been adopted by Professor Richter, of Freiberg, in a letter to the writer. * 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 laboratory 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 ;+ 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 ofthat 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, can afford to discard the very great advantage of address. ing himself to thousands-perhaps millions-of his fellow creatures, instead of to a few transcendentalists who cannot spread his opinions beyond their own clique. is (8). It may be as well to mention here that blowpipes like that devised by Von Frick, having the operator's breath, or blast from any other source, and the gas for ignition conveyed by the same tube, are utterly useless for these purposes; that Bunsen burners are useless for these purposes; that Fletcher's most ingenious, and no doubt otherwise invaluable "hot blast blowpipe almost useless for these purposes, which are most erroneously 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 blower, and then with a mouth blowpipe held in the other hand, direct a blast across this blue pyrocone, so as to dissect it; he finds it to be a solid mass of blue flame. If he now perform the same operation on the pyrocone from a gas jet, the pyrocone is found to be slightly hollow, while the pyrocone from a Bunsen burner has only the merest thin shell of circumscribing ignited gaseous matter. It is obvious, therefore, that the effect of holding the fragment or paste of a mineral or other essay, in the middle of these three pyrocones, must be different in each case; yet how seldom in England do we see a candle or oil lamp used for important results which can be obtained solely by its use? (9). It is obvious that in order to properly systematise the science of blowpipe analysis, we ought to reduce it to as close analogy as may be with the procedure in ordinary chemical analysis, which has been found to answer so well. I have, therefore, in my method discarded the preliminary use of the salts borax and microcosmic sal', and commenced attacking substances with the pyracids "Boric and phosphoric anhydride." Boric acid, indeed, contrary to the account found in most of our chemical works, dissolves before the blowpipe no oxide whatever completely, except those of the alkaline metals, and that of silver a little, but its reactions thus are a thousand times more valuable than if it really (as we are told) dissolved all those, while, by adding pyrologically a very small proportion of alkali (not quite 5 per cent) we obtain a still acid menstium which is itself extremely soluble in water. Phosphoric acid, on the other hand, is, before the blowpipe, the most powerful unmixed solvent in the world, dissolving gold leaf to a bluish violet glass quite rapidly. In either case we can further, if we like, obtain an acidulated water solution, in which precipitates can be produced by alkalies, &c., just as in "the wet way," but this process requires to be worked out, and shall not therefore be further alluded to here. (10). It is necessary, however, to lightly touch upon one part of the subject, not invidiously but conscientiously, before proceeding to detals. However invaluable the application of the symbolical and algebraical process o ratiocination may be, assuming its groundwork of facts to REPORT DEVELOPMENT OF THE CHEMICAL ARTS By Dr. A. W. HOFMANN. THENARD, on bringing peroxide of hydrogen into contact with his tongue, in order to ascertain its taste, found that it was whitened. The cuticle was also blackened, and at the same time a violent itching was excited. Litmus paper without any previous reddening was at once decolourised, as was also turmeric paper. In 1863 Chevreul undertook comparative experiments on the bleaching power of hydrogen peroxide. Its concentrated solution speedily turned syrup of violets green, oxygen being set at liberty. For the following experiments dilute colour-solutions were used-namely, syrup of violets, tincture of litmus, extract of peach-wood, and extract of logwood. The results were as follows: Time. 10 mins. 24 hrs... 80 hrs... Violets. Imperceptible. Complete Litmus. Peach-wood. Logwood. bleaching. rose. Almost complete Turns, bleaching. yellow! Complete bleaching of all the solutions. Decolorisation is therefore effected less rapidly by peroxide of hydrogen than by chlorine. Tessié du Motay and Maréchal mention it as one of the agents which they propose for bleaching tissues, which, after treatment with permanganate of potash, they recommend to be steeped in a solution of peroxide of hydrogen. But it had been much earlier applied as a bleaching-agent by Thénard himself for a particular purpose-namely, for restoring old The controversy at present proceeding between Dr. Frankland and Mr. Wanklyn in the CHEMICAL NEWS, wi h reference to water analysis, may be cited as an illustration of this point. + Sche:1: sems to have been a German, not a Swede, settled as a common apothecary, at Köping, in Sweden. Berichte über die Entwickelung der Chemischen Industr e Während des Letzten Jahrzehends." Chevreul, Comptes Rendus, v., 735. § Bull. Soc. d'Encouragement, 1867, 472. cxxc(?)iv., 526. Dingler, Polyt. Journ il Pélouze and Frémy, Traité de Chimie, 1861. Instrument for Measuring the Direct Heat of the Sun. oil-paintings and drawings. White-lead in old paintings, which has become blackened by the gradual action of sulphuretted hydrogen, is converted into sulphate of lead by dilute solutions of peroxide of hydrogen, and thus restored to its primitive colour. A fine drawing by Raffaelle, with superimposed white which had become spotted with black, was completely cleansed by a solution which contained at most five or six times its volume of available oxygen, and the paper did not suffer. A peculiar, hitherto secret, application of this bleaching agent has been recently made public by A. v. Schrötter.* During the last few years bottles labelled "Eau de Fontaine de Jouvence, golden," and containing about 140 c.c. of a colourless liquid, have been sold by perfumers in great cities. The price demanded is about 20 francs, and to them, as it appears, is due that offensive blonde shade of hair which holds an intermediate place between ash-grey and bright yellow, and attracts the attention of the spectators and the curiosity of observers by its piquante unnaturalness. According to Schrötter this secret nostrum is merely a solution of hydrogen peroxide made stable by copious dilution, and by addition of a small quantity of acid, apparently nitric acid. According to Schrötter's careful examination it contained 6 volumes of available oxygen: 1000 grms. of the liquid would therefore contain 86 of available oxygen, or 18'3 of peroxide of hydrogen. As may be imagined, however, in case of an easily decomposable body, the bottles do not all contain solutions of equal strength. An examination conducted in the laboratory of the University of Berlin showed, in 1 volume of the solution, 94 to 98 vois. of available oxygen, corresponding to 13'6 grms. O, or 28'9 grms. H2O2, per litre. A bottle costing 20 francs yields the purchaser 2.5 to 4 grms. of this substance in solution, and effects its purpose completely, though slowly, within four to six days, thus strikingly illustrating the great efficacy of peroxide of hydrogen. The name of the perfumer who understands how to speculate so successfully upon the purses of his fair contemporaries, and who deserves to be known to posterity, is E. H. Thiellay, of London. CHEMICAL NEWS, It many individual cases it may be far from being true. would therefore seem to be desirable to get rid of this uncertainty by constructing an instrument in which we are sure that the causes of variability are not allowed to operate. These causes of variability I have attempted to get rid of in the following manner. With the help of Mr Jordan, mechanician at Owens College, the following instrument has been constructed. It consists of a large mercurial thermometer with its bulb in the middle of a cubical castiron chamber, this chamber being of such massive material that its temperature will remain sensibly constant for some time. The chamber with its thermometer bas a motion in azimuth round a vertical axis, A, and also a motion in altitude round a horizontal axis, B. A three inch lens, C, of 12 inches focal length is attached by means of a rod to the cubical chamber so as to move with it. The nature of this attachment will be seen in the figure. Thus the whole instrument may be easily moved into such a position that the lens as well as the upper side of the chamber which is parallel to the plane of the lens may face the sun, and an image of the sun be thrown through a hole, D, in the side of the chamber upon the thermometer bulb, E. ON AN INSTRUMENT FOR MEASURING THE By Prof. BALFOUR STEWART, LL.D., F.R.S. THE instrument generally employed for giving the radiant energy of the sun's rays acts upon the following principle. In the first place the instrument is sheltered from the sun but exposed to the clear sky, say for five minutes; let the heat so lost be termed r. Secondly, the instrument is turned to the sun for five minutes; let the heat so gained be termed R. Thirdly, the instrument being now hotter than it was in the first operation, is turned once more so as to be exposed to the clear sky for five minutes while it is shielded from the sun; let the heat so lost be termed r'. It thus appears that r denotes the heat lost by convection and radiation united when the instrument, before being heated by the sun, is exposed for five minutes to the clear sky, while r' denotes the heat lost by these same two operations by a similar exposure after the instrument has been heated by the sun; and it is assumed that the heat lost from these two causes during the time when the instrument is being heated by the sun will be a mean between r and r', and hence that the whole effect of the sun's rays will be in reality R+ 2 Now although this assumption may in the average of a great number of experiments represent the truth, yet in *Berl. Chem. Ces., 1874, 980. The stem of the thermometer protrudes from the chamber as in the figure. A screw, S, somewhat larger in diameter than the bulb of the thermometer is made use of to attach the thermometer to its enclosure, and a smaller the thermometer to be properly adjusted and kept tight screw, S', pressing home upon india-rubber washers enables when in adjustment. In the present instrument the internal diameter of the chamber is 2 inches, while the bulb of the thermometer is about 1 inches in diameter. The scale of the thermometer is very open, more than an inch going to one degree. I have generally allowed the image of the sun given by the lens to heat the thermometer bulb for one minute, during which time an increase has been produced. of temperature, not exceeding in any case two degrees, As far as principle is concerned there appears to be no objection to the present instrument, nevertheless it is open to a very serious practical objection. The scale being so very open, the stem comprehends only a few degrees; frequently, therefore, the temperature is such that the extremity of the mercurial column is either below or above the stem. Now the thermometer has a small +A Paper read before the Manchester Literary and Philosophical upper chamber, and by means of a method of manipulaSociety. tion well known to those who work with thermometers, it |