CHEMICAL NEWS," Feb. 8, 1862, that of the salts being On the Production of New Colouring Matters. C20II (NO) O.MO. 73 substance, as far as could be determined from the very scanty amount obtained for examination1, were as follows: It is evident that it differs from its generator, nitro-As caught on the filter, it constituted nearly black naphthaline, CH, (NO) only by one equivalent of oxygen and one of water. The tinctorial power of this acid is considerable; it may be made very useful for dyeing purposes. Oxynaphthylamine.-This, as I have stated above, is the new product formed by the action of reducing agents ou nitroxynaphthalic acid. Oxynaphthylamine is a feeble base, which cannot remain in a free state without rapidly becoming coloured; a greenish-black colour is instantly produced by contact with excess of alkalies. It combines with energetic acids, the salts of which, often crystalline, become rapidly coloured; heated with excess of potash it disengages ammonia whilst dissolving, and yielding an intensely green liquid similar to that of manganate of potass; acids precipitate from it a violet-red acid. Alkaline nitrites occasion an abundant disengagement of nitrogen in the neutral hydrochloric solution, and at the same time colourless crystals are separated, which have not yet been analysed. The estimation of the elements of the crystallised hydrochlorate assign to oxynaphthylamine the formula CHIONO2, that of the hydrochlorate being C20H10NO2CH. The equivalent has been corroborated by the analysis of the platinum salt, which, on account of its instability, is with difficulty obtained pure. The electropositive action of oxynaphthylamine, which may be considered as the amide of its generator nitroxynaphthalic acid, adds yet another support to M. Cahour's recent researches in this class of bodies.-ComptesRendus. On the Production of New Colouring Matters by Decomposition of Nitronaphthaline and Dinitronaphthaline, by M. CAREY LEA, Philadelphia. 1. In the process for preparing naphthylamine by the action of acetic acid and iron on nitronaphthaline, the nitronaphthaline is placed in a retort with iron filings and acetic acid, and after the first action has passed off, the contents are heated, a receiver attached, and hot lye is added to disengage the naphthylamine. But if a well cooled receiver be attached at the outset of the operation, and if heat be applied for some time before the addition of the caustic alkali, a liquid passes over which exhibits the following reactions : It has a pale reddish colour, and exhales the disgusting odour of naphthylamine. The pale reddish colour becomes pale violet by addition of mineral acids. If it is placed in an open capsule and heated on the sand bath, with addition of dilute sulphuric acid, the pale violet colour gradually deepens in intensity to rich blue purple. After a time a black crystalline precipitate falls, which must be separated. The brown filtrate by further heating again becomes rich purple, and deposits a further quantity of precipitate. But eventually the liquid becomes muddy brown (A), and yields no more of the precipitate. This latter is produced at best in extremely small quantity, and sometimes scarcely appears at all. A grain or two is all that can be obtained from 50 or more grammes of nitronaphthaline. The properties of this very interesting and beautiful needles with a most brilliant golden green glitter. After being dissolved in alcohol, it was obtained as a dark red powder, which when placed on glass and a platinum spatula drawn a few times over it, gave a bright green, with the red powder around it. almost metallic reflecting surface, contrasting strongly It dissolved somewhat readily in alcohol, colouring it small quantity of sulphuric or nitric acid brought this an intensely deep blood red. The addition of a very through a succession of shades as the quantity of acid finally blue purple, all of the richest shades, and so increased, first ruby, then crimson, then rich purple, and intense as to require great dilution to render the solution at all transparent. The substance exhibits considerable resistance to acids. The alcoholic solution acidulated with sulphuric acid may be boiled without destroying boiling becomes pale straw colour, possibly an effect of the colour. If nitric acid be substituted, the solution by the reaction of the nitric acid on the alcohol present. The production of a red colour by alkalies and a blue by acids is becoming characteristic of a large number of organic colouring matters. Amongst these are, the colouring matter obtained by Church and Perkins from tincture of madder; by the resinous body obtained by Schiff in the spontaneous decomposition of naphthylurea; by the body obtained by Church and Perkins from nitrosonaphthaline; by carotin, as observed by Dr. Husemann3; by a blue colouring matter obtained from picric acid described by myself. The frequency of this reaction is constantly increasing as we become better acquainted with organic colouring matters. The substance which I have here described would doubtless be valuable as a dye if it could be obtained in sufficient quantity, for the richness of its colours leaves nothing to be desired, but it is only a secondary product obtained in sufficient quantity to admit of its constituin the reaction which produces it. Until it can be tion being determined, I propose to call it Ionnaphthine, from ov, a violet. 2. If the muddy brown liquid mentioned at (A) in the second paragraph be treated with liquid ammonia, brown flakes separate. If these be treated with dilute sulphuric acid and bichromate of potash they become black. They then do not dissolve in water or alcohol, but dissolve in dilute nitric acid to a deep violet solution, greatly inferior, however, in colour to the solution of ionnaphthine. This substance may possibly be identical with that described by M. Du Wildes1 and obtained by him by oxydating naphthylamine by means of nitrate of mercury. 3. If the solution of dinitronaphthaline in alcoholic ammonia be heated with solution of sulphite of ammonia, the red solution assumes a rich deep rose colour, far richer and more brilliant than the original solution. I have not as yet been able to isolate this substance. Dinitronaphthaline is as fruitful in coloured derivatives as aniline. Treated in solution in alcoholic ammonia with stannous chloride, it yields a fine blue. Roussin's 1 Much to the author's regret, he was obliged to discontinue this examination in consequence of an unexplained injurious effect upon his health by manipulating with naphthylamine. 2 Jahresbericht, 1857, p. 390. 3 Chem. Centralb., May, 1861, p. 347. * Rep de Chimre appliquee, Mai, 1861, p. 172, M. Du Wildes is in error in supposing that a reaction which he has obtained is the first instance of a reproduction of an original body from a nitro-substitution compound. "artificial alizarine" affords fine shades of purple; the reaction is obtained with great facility. Hofmann and Wood's ninaphthylamine, as I have obtained it, varies from copper to sealing wax red, but does not seem to me likely to be valuable as a dye. Roussin's alizarine will no doubt be very much so.-American Journal of Science, No. 95. On Stibiconise, a Natural Oxide of Antimony from Borneo, by T. L. PHIPSON, Phil. Nat. Doct. Bruxelles University, Member of the Chemical Society of Paris, &.c. WE get from Borneo a compact mineral, somewhat resembling certain varieties of Leptynite feldspar, and which is found more or less abundantly among the Stibine (sulphide of antimony) which the Island of Borneo launches into European commerce. It was at first looked upon as a portion of the rock which enveloped the native sulphide of antimony, and I believe many smelters have thrown it aside as such. It results from the examination to which I have submitted this mineral, that it is an oxide of antimony often very pure, and constitutes an ore sometimes superior in value to Stibine itself. The mineral in question presents itself in form of a compact matter with a crystalline structure, yellowishwhite or reddish, always giving a yellowish-white powder, and showing here and there crystals about half an-inch in length, of a peculiarly pearly lustre, and having numerous horizontal stripes; these striped crystals are straight rhomboidal prisms, terminating with two facettes (biseau), and modified upon two of the perpendicular edges. This substance is not volatile in a tube closed at one end (by which character it is distinguished from oxide of antimony Sb O); before the blow-pipe, the purer samples are entirely volatilized in the flame of reduction, but are not volatile in the outer or oxidating flame. It cannot be melted before the blow-pipe (by which it is distinguished from exitelite, or antimonic acid Sb 05, which is fusible); with carbonate of soda upon charcoal it gives a button of metallic antimony. 59 These characters prove the substance in question to be Sb O-the stibiconise of mineralogists, the antimoniate of antimony of some chemists. The samples which I have examined contain, as impurities, sulphur, stibine, oxide of iron, etc., but they were sometimes so pure that one of them gave me 65 per cent. of metallic antimony, whilst stibine seldom yields more than 45 per cent. Mineralogists are not agreed upon the quantity of combined water contained in stibiconise, but the analyses I have made of the Borneo mineral appear to leave no doubt as to that question. The following record of one of the best analyses will show in what ratio the water stands to the antimonious acid :Stibiconise from Borneo. Antimonious acid, Sb 0,65.00 Oxide of Iron } Alumina Sulphur, silica, etc. • 10'00 • 21.25 100'00 mineral gave me densities varying from 464 to 4·68, whence I concluded they would probably contain silver. However, I could not find in them sufficient silver to account for this increase of specific gravity. Neither does the Borneo stibiconise show more than a trace of arsenic. As the stibiconise (antimonious acid) of which I speak, accompanies stibine (sulphide of antimony) in Nature, and affects the same crystalline form as the latter, it is very probable that the oxide in question has been formed in Nature at the expense of the sulphide, by means of water or steam heated under pressure, as we see it act in the beautiful experiments recenly made by my friend, M. Daubrée, where Wollastonite and some other minerals were artificially formed in perfect crystals by the mere action of superheated steam upon glass in closed tubes. The chemical reaction which Nature appears to have used in forming stibiconise from stibine is as follows: = Sb S+ 3 HO Sulph. hyd.; and Sb O, combining with one proportion of oxygen from the air gives Sb 04 antimonious acid or stibiconise. If we suppose, for a moment, that the transformation in question was effected by air (oxygen) instead of water, we find that it would require nine equivalents of oxygen to produce the same effects as three equivalents of water:Sb £3 +90 Sb O3 + 3 S O2. Stibiconise has been regarded as a somewhat rare mineral in Europe, but Borneo seems to possess large quantities of it. Another argument in favour of its formation from stibine is, that it always accompanies the latter in Nature. = = + The stibiconise of Borneo is readily dissolved in a warm mixture of hydrochloric acid and tartaric acid. To transform it into metallic antimony, I succeeded best by fluxing the pulverised mineral with a mixture of charcoal, bitartrate of potash, and carbonate of soda. It occurred to me that by mixing equivalent proportions of stibiconise and stibine, and applying heat, I should get metallic antimony thus:2 Sb S3 + 3 Sb O 5 Sb 6 S02 Stibine. Stibiconise. Antimony. Sulphurous acid. But such is not the case: if the air has free access into the crucibles, the sulphide is converted in Sb O, which volatilises; and if the crucibles are nearly closed, the whole meets and forms a mobile liquid, which in cooling forms a bluish, metallic, crystalline mase, giving a brown powder when pulverised. The compound thus formed I ascertained to be an oxy-sulphide of antimony, analogous to what is called mineral kermes. The Borneo stibiconise has lately been employed as an oil paint, for which purpose, as recommended by Dr. Stenhouse, it is calcined and pulverised. It is said to possess certain peculiar advantages for house-painting, &c. According to what I have said above, the purer portions of the mineral constitute an ore of antimony of greater value than the sulphide which is generally used as such.-Technologist. Royal Institution.—The following lectures will be delivered in the ensuing week :-Tuesday, February 11, at three o'clock, John Marshall, Esq., "On the Physiology of the Senses." Thursday, February 13, at three o'clock, From this we may, therefore, deduce as the formula Professor Tyndall "On Heat." Friday, February 14, at of stibiconise: Sb O, HI O. The specific gravity of stibiconise, according to several authors, is 3.80; but all the samples of the Borneo eight o'clock, Dr. W. Odling, F.R.S., "On Mr. Graham's Researches in Dialysis." Saturday, February 15, at three o'clock, the Rev. Álex. A. J. D'Orsey, "On the English Language." CHEMICAL NEWS, Feb. 8, 1862. Arsenical Pigments in Common Life. PHARMACY, TOXICOLOGY, &c. Arsenical Pigments in Common Life, by Dr. A. W. THE following letter has been addressed by Professor 75 children's toys, &c., has attracted the attention of the sanitary authorities on the Continent for many years past. In several of the German States, more particularly in Bavaria, the very country of arsenic colours (which are manufactured on a very large scale in Schweinfurt), a town in Franconia), the application of these colours to papering or painting rooms has been repeatedly proceeded against. I have before me an edict of the In accordance with your wishes, I have examined Bavarian Government of July 21, 1845, expressly procarefully the green colouring matter of the artificial hibiting the manufacture and sale of arsenic-green leaves from a lady's head-dress which you have sent me. paper-hangings. This general prohibition, it is true, It is well known that such leaves generally contain was repealed by an Act of January 23, 1848, "for arsenic, and often in considerable quantities. An expe- industrial considerations," and the use of Schweinfurt rienced eye readily recognises the presence of an arsenic green permitted as before for house papering and paintcolour (Schweinfurt green) by its brilliancy, the intensity ing, provided the colours were permanently fixed by of which is as yet unrivalled by any other green. How- appropriate means. The relaxation of the measures against ever, should there remain the slightest doubt, an experi- Schweinfurt green appears, however, to have given but ment of the simplest kind would establish the fact. In little satisfaction. In several papers laid both by most cases it would be sufficient to burn such a leaf in chemists and physicians before the Academy of Munich, order at once to perceive the garlic odour which charac-in its sitting of June 9, 1860, undoubted cases of chronic terises the presence of arsenic. poisoning produced by arsenic papers, even when glazed, were brought forward, and the Academy was called upon to represent to the Government the necessity of strictly enforcing the former regulations against arsenic colours, and of removing all Schweinfurt-green wall-colouring from public buildings, schools, hospitals, &c. In a dozen of the leaves sent to me analysis has pointed out on an average the presence of ten grains of white arsenic. I learn from some lady friends that a ballwreath usually contains about fifty of these leaves. Thus, a lady wears in her hair more than forty grains of white arsenic, a quantity which, if taken in appropriate doses, would be sufficient to poison twenty persons. This is no exaggeration, for the leaves which you have sent me were, some of them at least, only partly coloured, others only variegated. In consequence of your inquiries, I have been led lately to pay more than usual attention to the head-dresses of ladies, and I observe that the green leaves are often much larger and more deeply coloured than those which I received. The question how far arsenic-dyed wreaths may be prejudicial to health is intimately connected with the discussion, so frequently raised of late years, as to the influence which arsenic-coloured paper-hangings exert upon the human system. This influence has been doubted on various grounds, both by the chemist and the physician. The alleged effect has been attributed to the development of arseniuretted hydrogen, or some other volatile arsenic compound, to which the white arsenic, by the action of the damp on the wall, or of the organic constituents of the paper and the paste, might possibly have given rise. Accurate experiments, how ever often repeated and often varied, have proved the inadmissibility of the assumption of gaseous arsenic exhalations, and, as it so often happens, the injury was denied simply because it could not be explained. Nevertheless, the deleterious effect of arsenic green paperhangings is at present pretty generally acknowledged. Indeed, it does not require any high-flown hypothesis to explain the transfer of the arsenic from the wall to the system. The arsenic dust, bodily separated from the wall and dispersed over the room is quite sufficient for this purpose. The investigations of the last few years have clearly shown the presence of arsenic in the dust of rooms hung with arsenic-green paper, even when this dust had been collected at the greatest possible distance from the walls. Moreover, the chronic poisoning by arsenic of persons living in such rooms has been proved experimentally, inasmuch as the presence of arsenic may be demonstrated in their secretions, more especially if the elimination of the poison be accelerated by the administration of iodide of potassium. The employment of arsenic green in the manufacture of paper-hangings, in staining paper, in painting The immense consumption of arsenic colours, and their reckless use under various conditions prejudicial to health, certainly claim the especial notice and the consideration of the public. Not satisfied with poisoning the wreaths which adorn the heads of our women, modern trade introduces arsenic without scruple even into their dresses. The green tarlatanes so much of late in vogue for ball dresses, according to an analysis made by Professor Erdmann, of Leipsic, contains as much as half their weight of Schweinfurt-green. The colour is loosely laid on with starch, and comes off by the slightest friction in clouds of dust. I am told that a ball dress requires about twenty yards of material-an estimate probably below the mark, considering the present fashion. According to the above analysis, these twenty yards would contain about 900 grains of white arsenic. A Berlin physician has satisfied himself that from a dress of this kind no less than 60 grains powdered off in the course of a single evening. It will, I think, be admitted that the arsenic-crowned queen of the ball, whirling along in an arsenic cloud, presents under no circumstances a very attractive object of contemplation; but the spectacle, does it not become truly melancholy when our thoughts turn to the poor poisoned artiste who wove the gay wreath, in the endeavour to prolong a sickly and miserable existence already undermined by this destructive occupation! Ladies cannot, I think, have the remotest idea of the presence of arsenic in their ornaments. If aware of their true nature, they would be satisfied with less brilliant colours, and reject, I have no doubt, these showy green articles, which have not even the merit of being, as far as colouring is concerned, a truthful imitation of Nature. There being no longer a demand for them, the manufacture of poisonous wreaths and poisonous dresses would rapidly cease as a matter of course. Composition of Rhodizonic Acid.-H. Will has studied (Annalen der Chem. und Pharm., Bd. cxviii. s. 187) the origin and composition of rhodizonic acid, which he says has most probably the formula C1HO12, and is tribasic. The paper contains a description of several of the salts of this acid. PROCEEDINGS OF SOCIETIES. ROYAL INSTITUTION OF GREAT BRITAIN. A Course of Six Lectures on Light' (adapted to a Juvenile LECTURE V. (Jan. 4, 1862.) NOTES TO THE LECTURE : Two colours which, when blended together, produce white are called complementary colours-The spectrum extends in both directions further than we can see it-The eye often receives the impression of colour where no colour really exists-The eyes of many people are blind to certain colours-The invisible rays of the violet end of the spectrum may be rendered visible-In passing through a simple lens, the violet being more refracted than the red, both colours do not come to the same focus. This is called the chromatic aberration of the lens. The colours which we see most commonly are colours of absorption, -that is to say, they are due to the fact that a portion of the spectrum is absorbed within the body, while a second portion is allowed to pass through the body-But colour is produced in a variety of ways without absorption. The spectrum itself is an example, its colours are those of refraction; so are the colours of the rainbow, which is, in fact, a solar spectrum-The splendid colours of a thin soap bubble are not colours of absorption-The iridescence on the neck of the dove, the hues of a peacock's tail, and the colours of the wings of certain insects are not colours of absorption-Most gorgeous colours are produced when colourless spirit of turpentine is poured on colourless waterThe gold, straw-colour, or blue of tempered steel is not a colour of absorption. Such colours are produced by a thin transparent film of gas, or liquid, or solid, which itself has no colour. They may indeed be produced by an exceedingly thin fissure which is perfectly empty -For example, I have often produced fissures in the interior of a mass of ice, which showed splendid colours, though no air could possibly reach the fissure. Colours are also produced by reflection from scratched surfacesThey glisten on the fine threads of the field spider-Thin clouds, especially in Alpine regions, are often flooded with the most splendid iridescences, even when the light which falls upon them is whiteThese colours are to be distinguished from those of the morning and evening clouds, which show simply the colour of the light that falls upon them-A dust, whose particles are all of the same size, when shaken in the air produces colours when a light is viewed through itThe colours here referred to have received various names in conformity with their modes of production. Some are called the colours of thin plates, others the colours of striated surfaces, others the colours of diffraction. They all depend on the great principle of interference. This may be a difficult point to explain, but it may be rendered intelligible thus:-All the laws referred to in the Notes of the preceding Lectures, would follow if we supposed light to be produced by waves or undulations-In waves, the angle of incidence is equal to the angle of reflection; the law of refraction is also true of wave motion-Sound is transmitted on waves through the air; the aerial waves striking on the ear produce the impression of sound-In like manner it is believed that light is transmitted in waves to the eye; the waves not being those of air, but of a substance called ether, which penetrates all things and fills celestial space. When a stone is cast into still water, circular waves are propagated These waves conround the point where the stone strikes the water. sist in a succession of ridges separated from each other by hollowsSuppose two stones a little apart to be cast into still water, the waves issuing from one stone will cross those issuing from the other-At the places where one ridge crosses another, the water is lifted higher by the combined action of both stones-At the places where one hollow cuts another, the water is more deeply depressed by the combined action-But at the point where a ridge cuts a hollow, one neutralises the other, and the water does not quit its original level-Thus, the wave of one stone can be caused to destroy the wave of another-This is true of both sound and light; we may cause one sound wave to destroy another, so that silence results from their unison; we may also cause one light wave to destroy another, so that darkness shall result from their union-This action of waves upon each other is called Interference. The waves which produce red light are the longest, those which produce violet light are the shortest; the waves which produce the other colours are intermediate in length between these two-All the colours above referred to as not belonging to the class of absorption colours are produced by the extinction of a portion of the white light by interference, the colour complementary to that which is destroyed being then revealed, In our last Lecture I took a slice of white light; and by passing it through a prism, I tore it asunder-unravelled it-disentangled it, and showed you of what that white light was composed. You saw it consisted of a variety of 1 Reported verbatim by special permission. colours, the red being the least refrangible and the violet I then took light being the most refrangible of all. a brilliant A great and those very colours which you saw so splendidly spread out with light. If strong red light falls upon the eye it colours. In fact we are all, to a certain extent, blind; and this is an experiment which, in passing, I may refer to. There is a spot on each of our eyes which is quite blind. Many of us do not know it, but it is a fact, and we may all find out this spot in this way. Take two wafers, or make two black spots upon a piece of white paper; place these two black spots at about two and a-half inches apart; then close one eye and look with the other. Say close the right eye, as I am doing, and look with the left perpendicularly down upon the right hand wafer. The light from the left wafer CHEMICAL NEWS, Feb. 8, 1862. Royal Institution of Great Britain. is now going into my eye and falling upon my blind spot, and the consequence is that I do not see one of the wafers at all. In this way I can quench the image of many boys present, and the image of the bright moon is not too large to fill up the blind spot. The consequence is that by allowing the image of the bright moon to fall upon this blind spot you have no sensation whatever of light produced, you do not see the moon at all. I am now going to make one experiment in order to show you the theory of these colours. Some people often see colours where they do not exist. This green colour that I spoke of as being under the wafer does not really exist, still you see it. I want to make one experiment which I think will give you some idea of what I mean. Here we have the light from our électric lamp, and if I interpose this piece of blue glass, you will have blue light upon the screen, together with the comparatively_faint light from the gas lamps, and I venture to say that if Mr. Anderson places his arm across you will see the shadow of it is yellow. At the present time, there is no yellow light there at all, but it is simply because you are blind to the blue that the yellow, the complementary colour to the blue, comes cut over that portion of the screen. We have learned that this white light is composed of rays of different degrees of refrangibility. We also know that when light goes through a lens it is refracted, the rays are converged and brought to a focus when they pass through a convex lens such as I hold in my hand. Now the beauty of our science, my friends, is that all these beautiful effects that you see are merely facts popping out and appearing in beauty from an under current of philosophy from an under current of reasoning. The mind goes along underneath, as it were, these visible experiments, and knowing the law can actually predict the result of the experiment before it is even seen. And this is the beauty of natural philosophy; it is not looking at pretty experiments, fine though they may be, and pleasant as they seem to us, these experiments are, so to say, the outgrowth and the blossom of thought. It is not merely our senses that we exert, but the eyes of our minds are at work as well as the eyes of our bodies. Well now, let us reason upon this light-if we send a beam of white light through that lens that beam is converged, refracted, but the blue rays of that beam will be more refracted than the red rays, and the consequence is if the blue comes to a focus there (at b) the red will not come to a focus until here (at r). These two foci are different, and this distance between the focus of the blue and the focus of the red is called the chromatic aberration of the lens. The rays of different colours do not, therefore, come to the same focus; conceive a beam of light passing through that lens, and suppose that (b) to be the focus of the blue rays and this (r) the focus of the red rays. Now just picture to yourselves the kind of light coming through here. You see that up to this point [6] we have a blue cone within a red one; and if you place a screen there we shall find an image with a red rim, because the blue cone is surrounded by the red; but as we pass this focus of the blue rays we shall have instead of a blue object surrounded by a red rim, a red object surrounded by a blue rim. Let me, however, make the experiment, that is the best way of illustrating anything. I take the lens and place it in front of the lamp, and there on the screen we have an image with a blue rim. I daresay most of you can see the focus in the dust of the room. 77 If I place my screen in the centre portion, you will see an image of the coke points. If I put it nearer the lens you have a beautiful image with a red rim, because, as I have already said, between the lens and the focus the blue cone is surrounded by the red one, the red being the least refracted. Now, let me pass beyond the focal point and see what takes place. You have now the blue rim, and this you see is the result of what we have called the chromatic aberration of the lens. I have now to direct your attention a little farther to this splendid image which we obtained in our last lecture the coloured spectrum, as it is called, produced by what may be called the unravelling of the thread of white light. Here I will place the slit in front of the lamp, for the purpose of obtaining the spectrum, and will cause the beam to pass horizontally; here we have the prism, and now I have produced that splendid coloured image which I have shown you many times. I have cast the beam in this case only through one prism; in the last lecture I passed it through two for the purpose of making the dispersion greater of throwing the colours wider apart. You will also notice that the image produced by the glass prism is less than the image produced by the bisulphide of carbon. I make use of glass in this experiment for special reasons which I found out while preparing for the present lecture. I have been talking about colour blindness, but I have now to refer to a very particular kind of blindness with which we are all afflicted. At least, I would not say it is an affliction; but at all events it is a fact. You see red light there, no doubt, but you see no light where I strike the screen [beyond the apparent red end of the spectrum], and yet at the present time there are millions of rays falling upon that dark place. These rays are not competent to produce light, but are competent to produce heat, and if these were lectures upon heat, I should be able to show you the existence of these rays here, but these being Lectures upon Light, I shall, therefore, beg to direct your attention to the other end of the spectrum. I say that there, also, you have a perfect shower of rays that are invisible to the eye-that are too shrill, I was going to say-for there are notes too shrill to be heard by the human ear, and these colours are, as it were, too shrill to be seen by the human eye. But they can be made visible. I take this pad of blotting-paper, and here I have a solution of sulphate of quinine in tartaric acid, a perfectly clear solution without any colour. [The Lecturer now directed the assistant, who had charge of the electric lamp, to cause the two poles to remain as far apart as possible during the ensuing experiment.] I want to explain to you the reason of that direction; it is not with the luminous portion of the coal points that I want to experiment; but it is with those particular rays in the space between the two carbon points—really a comparatively non-luminous portion. It is this particular place that is most wealthy in these rays that I am now going to render visible. [The Lecturer placed the blotting-paper in the dark space beyond the violet-end of the visible spectrum, and moistened it with the solution of sulphate of quinine, when it immediately glowed with a pale blue light.] This, then, is the conversion of that dark space into a luminous one, the bringing out of the invisible rays of the spectrum-the rendering of these invisible rays visible. that thus enables you to see that stripe of light upon the paper. I will now show you this in another way. I will cut away from the beam issuing from that lamp those rays that I do not need-those rays of an intensely illuminating power, but which have not the power of being rendered visible-they are not those invisible rays I am now speaking of. I interpose a dark violet glass, such as you see here. I will move the dark glass for a minute, and hold this paper in the bright light; you see nothing; but if I |