in others there is simply an alteration of the intensity o NEWS. the transmitted light. Houston, and Thompson,|| in a paper wherein no reference is made to prior workers, clearly enunciate the order of change given above. METACHROMATISM, OR COLOUR CHANGE. By W. ACKROYD, Mem. Phys. Soc. MANY inorganic bodies change colour, when they are heated, without suffering any alteration of chemical composition. These changes embrace a class of phenomena quite as important in their way as those of phosphorescence and fluorescence, with which, in fact, they are intimately connected. We venture, therefore, to propose for the phenomenon the name of Metachromatism, from the Greek pera, change, and xpwpa, colour, and it will be convenient to call colour-changing bodies metachromes. Metachromatism has received a fair share of attention from scientific men in time past. Their labours, however, are not even referred to in our text-books of chemistry and physics, perhaps from the importance of the subject being under-rated, and its bearings not being clearly seen. Hence when, at an early stage in its study, we saw that nearly all metachromatic changes take place in a definite order, the order of the spectrum colours, we were under the impression, even after much reading, that the subject was quite unworked. Stahl and followers made note of the chameleon-like behaviour of certain metallic oxides, and Schönbein,* who studied the subject, inferred from his observations that heat imparts a darker colour to metachromes, and generally red or brown. Sir David Brewstert called attention to the change in the absorption-bands of nitric peroxide when that body is subjected to heat, and twenty years later (1857) Gladstone made observations on the change of colour in salt solutions upon elevation of temperature. He observes that whilst some really exhibit colour change, Hartleys has made observations on the action of heat on the absorption spectra and chemical constitution of saline solutions. In the substances he has studied he regards colour-change as evidence of alteration of hydration. I. Metachromes, their Deportment and Classification. A large series of spectroscopic observations were made of metachromatic solutions, at low and high temperatures, for purposes of comparison. The change in most cases is very small, and may readily be confused with sources of observational error. Our main object being to arrive approximately at the cause of the phenomenon, solutions were discarded, and stable anhydrous bodies experimented with in their stead. The advantages accruing from this course are many, and such a course is moreover necessary for (1) the elimination of chemical action, and (2) a more decided change in colour, from the greater range of temperature it is possible to employ. The table below contains a list of a few anhydrous metachromes, with their changes, in addition to many of those given by Schönbein, Gladstone, and Houston and Thompson. The changes were observed on white porcelain in preference to sheet copper, as used by Messrs. Houston and Thompson. This metal at the temperatures employed is soon covered with a film of suboxide, and the play of colours on its surface, unavoidably produced by variation of temperature, can scarcely fail to give a wrong impression of the change in the metachrome under observation. The behaviour of mercuric oxide calls for a few remarks, since here decomposition was observed at a comparatively low temperature. Resolution commenced at 230° to 232° C., 760 m.m. bar., metallic mercury being deposited in the cooler parts of the containing tube as a scarcely perceptible fiim, in which globules could only be made out with the aid of a lens. of lead.. Chromate of barium Plumbic iodide phosphate Orange Yellowish white Potassic dichromate .. Gmelin's "Chemistry," vol. i., p. 238. (In N, air, and CO2.) (In N, air, and CO2.) (In sealed tube.) Dark red. (In sealed tube.) (In hydrogen.) Change. Orange, red, and brown. Yellow and orange. Dark scarlet and puce (240° C.). Orange and red. (The same change under paraffin.) Greenish yellow. Orange and red. Yellow, and when cooling just after the glow' of a bluish cast. Perceptibly greener. Nearly black. Orange-yellow, changes suddenly to orange-red. *Point of maximum density (Rodwell). + Proceedings of the Royal Society, vol. cxxvii., p. 247. Phil. Mag., vol. xiv., p. 423. Journal of the Franklin Institute, October, 1871, and CHEMICAL NEWS, vol. xxiv., pp. 177 and 188. § Proceedings of the Royal Society, No. 161, 1875. 76 Metachromatism, or Colour Change. To ascertain the more intimate nature of the change in these anhydrous bodies was a work of some difficulty until the following simple expedient was devised:-Crystalline metachromes were used. The finely-powdered body was placed upon the concave side of a watch-glass, and pressed into a thin layer by the convex side of a second glass. The spectrum of the transmitted light being obtained at the normal temperature, the temperature was now raised, and a second spectrum obtained for comparison. Such a comparison for potassic dichromate we have in the following figure: It will be observed that upon elevation of temperature the absorption-bands at the ends of the spectrum widen out, and the more refrangible increment of absorption is nearly double that of the less refrangible. From the last observation the spectral order of change characteristic of metachromatism follows as a natural consequence, the less refrangible constituents of a body's reflected light being, so to speak, more persistent than the more refrangible during elevation of temperature. In a certain class of bodies, like ZnO, the spectrum order of change is not so evident, from the fact that white has strictly no place in the spectrum. To this class belongs such bodies as TiO2, Ta2O5, MoO3, Sb2O3, Sb204, SnO2, white porcelain, lead glass, colourless solution of ferric nitrate, and nitric peroxide at low temperatures, which, being white or colourless, become yellow upon elevation of temperature. In another and larger class, of which borate of copper and plumbic oxide may be taken as examples, the spectrum order is very evident. Both classes alike owe their change to increased absorption of light, with elevation of temperature; and a white body, if the temperature be raised high enough, may be made to pass not only from white to yellow, but also from yellow to orange, and thus the line of demarcation between the two classes is broken down. Reflecting upon these facts, we see that it is possible to arrange the colours in order: this we have done as follows: August 25, 1876. The position of all the members, save the lowest three, is determined by experiment. That white has the position we give it seems probable because-(1) by experiment with the ZnO class of metachromes it plainly occupies a position at the opposite end of the scale to orange and red; (2) the behaviour of blue and green metachromes precludes its being placed between these two colours; and (3) it is the direct opposite of black. Violet and indigo are only placed in the scale provisionally to make up the spectrum colours, as there are no experiments to warrant their being so placed. The metachromatic scale may be looked upon as showing the colour effects of expansion on the one hand, or of contraction on the other. And were it possible to reach the absolute zero of temperature we should probably have there colours of the white end of the scale. II. Theories of Metachromatism. Stahl and followers connected colour-change with the varying amounts of phlogiston a body was supposed to Schönbein supposed the contain when being heated. metachromes underwent what he termed an incipient decomposition,-i.e., one of the elements was supposed to be held in a peculiar state of combination whilst hot, and to regain its normal position upon cooling. Mercuric oxide, for example, was thought to assume the brownblack colour of the suboxide from losing a part of its oxygen, which was retained in a peculiar manner in the mass. Now mercuric oxide, from being an exception to a law which we shall presently state, appears to favour Schönbein's hypothesis. When we think, however, over the fact that this oxide is partially decomposed at 232° C., whilst it is in the deep orange state, we see that no suboxide is really formed. It is difficult to see how the hypothesis can apply in the case of borates, phosphates, and silicates. That it does not hold with binary compounds will be evident after a consideration of the following law, which we discovered during our study of this subject:—In a series of anhydrous binary compounds of the same two elements, those which have the highest amount of the basylous element have the most refrangible colours, and, vice versâ, those which have the least amount of the basylous element have the least refrangible colours. The table below illustrates this, and it will be found to hold good in many more anhydrous series than are given here. From the table it is evident that decomposition (incipient or complete) of any particular compound would give us more refrangible colours instead of the less refrangible, which is the result of elevation of temperature, -e.g., incipient decomposition of the brown PtC1, would give us the more refrangible green PtCl2. It is not our intention here to enter minutely into Messrs. Houston and Thompson's theory: the reader is therefore referred to their paper in the CHEMICAL NEWS (vol. xxiv., pp. 177 and 188). We note that (1) no men Table II.-SHOWING COLOUR RELATIONS OF ANHYDROUS BINARY COMPOUNDS. tion is made of the part absorption takes in this pheno menon, probably arising from their not having studied the subject spectroscopically; and (2) that they speak of metachromes as if generating light after the manner of incandescent bodies. That absorption plays an allimportant part will be evident from what we have said in Section I., and that vibratory motion has little, if anything, to do with metachromatism we hope to make clear in the sequel. Our experiments demonstrate that metachromatism does not depend upon the surrounding medium, for bodies exhibit the change alike in nitrogen, air, carbonic anhydride, and hydrogen. It has been suggested that the phenomenon might in some way be due to volatilisation. A volatile body, however, exhibits the change under a liquid medium. Hence we conclude that it is due in some manner to the action of heat on the internal structure of the metachrome. Metachromatism is seen in solids, amorphous and crystalline,-in liquids, and in gases near their liquefying points (N2O4 and Br2*). These forms of matter have molecular structure in common; hence we attribute metachromatism to molecular alteration. What the nature of this alteration may be we think will be manifest after a close consideration of certain physical facts. Absorbed heat performs two kinds of work : i. Kinetic, sensible to the thermometer, and— ii. Potential. a. The overcoming of cohesion, molecular recession, or molar expansion, as, e.g., the conversion of ice into water, and water into steam. This kind of work is accompanied by a change of density. 3. The overcoming of chemical attraction, atomic recession, or molecular expansion, which finally ends in decomposition, as, e. g., the resolution of PtC14 in PtCl2 and Cl2. I. It is a fact well known to mineralogists that many anhydrous silicates, after being subjected to a high temperature, have upon cooling permanently changed colours. This is shown in the following tablef in each example save that of olivine. It will be noted that where colour and density are both permanently altered, as in 3 and 4, the warm-coloured variety is less dense than the same mineral with a cold colour,-i.e., the densities are in the order of the metachromatic scale, a fact we anticipated in our study of this matter. This is also strikingly evident among allotropes, the notable exception being here, as elsewhere, that of phosphorus. Red amorphous phosphorus is denser than the yellow this very fact, however, will no doubt tend to throw light on some of its other anomalies. What we more especially call attention to here is, that bodies of identical chemical composition, without even a change of density in some cases (as in 2 and 5), may at the same temperature have different colours,-i.e., may absorb light in different degrees. From this we conclude that change of colour is not due to alteration of sensible heat. Perhaps we get a better illustration of the same fact in the behaviour of mercuric iodide. Examined spectroscopically at say 16° C., a band of red light is transmitted, extending from B to D. This narrows as the temperature rises; in other words, there is an increase of absorption up to about 140° C. The band of transmitted light now suddenly widens, and extends to a little beyond b. As the temperature is on the rise there is still a gradual in crease of absorption, but at 220° C. there is not so much light absorbed as there was at 16° C. From this we again infer that absorption of light at comparatively low temperatures is not dependent upon sensible heat or vibratory motion. II. Expansion by heat-i.e., decrease of density—is an all but universal law so far as we at present know. There are several exceptions, however, and many of these are among the silicates. Their anomalous behaviour is, as a rule, pointed out by the colour-change, as in the case of the zircon. This is not always the case, for there may be change of colour, as in the beryl, without alteration of density-i.e., without appreciable molecular approach or recession. On the other hand, we have in olivine an example of change of density, molecular recession, without a corresponding alteration of colour. More facts of the same nature might readily be adduced, from which we infer that molar expansion or contraction is not a necessary concomitant of metachromatism. We have, so far, excluded from our list of possible concomitants i. and ii. a: hence we are driven to the conclusion, backed by facts which space will not allow us at present to detail here, that the only necessary concomitant is ii. ß,-i. e., atomic approach or atomic recession; in other words, alteration of atomic potentiality. From the foregoing observations we learn(1). That metachromatism arises from increased absorption of light with elevation of temperature, the more refrangible increment increasing at a greater rate than the less refrangible. (2). That the only necessary concomitant is alteration of atomic potentiality; a change from the white towards the black end of the metachromatic scale signifying atomic recession, and a change from the black towards the white end atomic approach. (3). That where this change of potentiality goes far enough to affect chemical attraction sufficient to induce chemical action, then, for bodies obeying the law of colour sequence, a change of colour from the white towards the black end of the scale indicates combination, and the opposite order resolution into a lower compound. For much help received in this study of metachromatism our thanks are due to Dr. Frankland and Mr. Wm. Valentin. ON THE ESTIMATION OF COLOUR IN WATER. By CHARLES A. CAMERON. IN "Nesslerising" water it has been proposed to use solutions of caramel instead of standard solutions of ammonia for the purpose of comparison. I have, as well as other chemists, found that the standard solution of caramel, even when it contains much alcohol, becomes, after a time, turbid and useless, and also that it soon changes its hue. I do not think that the use of any coloured solution is so reliable as that of the standard solutions of ammonia; but to those who prefer the former I would recommend the use of coloured discs to be employed as follows:-Fill a Nessler tube with distilled water and place it over a disc so coloured that on looking down through the column of water it may, by the reflected light from the disc, have the colour of a solution of say o'005 gr. of ammonia per gallon of water mixed with the usual 5 per cent of Nessler's solution. A dozen discs would be sufficient; but in using them, Nessler's solution should be always of exactly the same composition. I would suggest that Mr. Sutton, who is so valuable an ally of the chemists who have not time or inclination to prepare their solutions, &c., might make a set of cylinders, discs, and solutions, in harmony with the above sugges tion. 78 Development of the Chemical Arts. ON SOME CHEMICAL RESEARCHES ON THE By SERGIUS KERN, St. Petersburg. {CHEMICAL NEWS, August 25, 1876. copper and of soda. The entire furnace is surrounded with an air jacket and this again with a screen of masonry traversed by flues, which has the object of keeping back a part of the heat which would otherwise be lost by radiation. Another portion is supplied by the heat generated in the process by the combustion of the hydrochloric acid. The above-mentioned vertical drain-pipes serve to prevent the apparatus from being choked up with oxide or chloride of iron. It has been observed that when iron apparatus is employed for generating and conducting the hydrochloric acid gas this conveys along a certain quantity of ferric chloride, from which it cannot be freed before entering the decomposing furnace. Here the iron is has already begun, i.e., as soon as watery vapour is mixed with the gases, as pulverulent oxide of iron upon the copper sulphate. This iron dust falls from the vertical drain-pipes through the grating into the space below, whence it is easily removed. It may here, however, be remarked that Deacon, according to private communications, has latterly omitted the partition walls from the decomposition furnace, by which he effects a more ready movement of the gaseous current without any disadvantage. In a Deacon's apparatus, which the author has seen at work in the establishment of Kunheim, at Berlin, the partition walls and the vertical drain-pipes had both been omitted without any detriment being observed in the course of several months' working. It is well known that wrought-iron containing some tenths of per cent of copper is red-short; meanwhile in some of the best irons from Siberia was found from o'or to 0'03 per cent of copper. In some specimens of steel I found 0'2 per cent of copper; this steel was not brittle, and had been used with success for manufacturing steel axles. The presence of copper was found in several specimens of cast-iron coming from blast-furnaces of the South Oural mountains. These specimens, when ex-deposited either as chloride, or, if the formation of chlorine amined and analysed, showed that the presence of copper in cast-iron may amount to a higher percentage than in steel or iron without altering the quality of the metal. Unfortunately it is not so with wrought-iron or steel. The specimen examined was much used for castings; it filled up the moulds beautifully, and had a very handsome appearance; fresh cut it had a dark grey colour. Under the microscope small grains of copper were easily remarked in the mass of the metal. This peculiar sample of cast-iron was carefully analysed, and the analysis gave the following average composition : After the mixture has passed through the decomposing furnace it consists of chlorine, water, nitrogen, superfluous oxygen, and unconsumed hydrochloric acid. The latter is condensed in an ordinary condensation apparatus, charged with dilute hydrochloric acid, or water, the temperature of the gases having been previously reduced by air-coolers. The gas is next freed from the accompanying water by passage through a tower filled with chloride of calcium, or, better, through a coke-tower, down which sulphuric acid flows. The gaseous mixture is then fit for absorption in the chloride of lime chambers. As a matter of course a drying apparatus is superfluous if a watery liquid is to be saturated with chlorine, as in the preparation of potassic chlorate. (To be continued) While analysing some iron samples for copper I often used, in case only traces of copper could be detected, the following method:-The specimen is dissolved in hydrochloric acid, and the copper and iron are precipitated by an excess of ammonia; the mixture is boiled and filtered; the blue liquor is evaporated nearly to dryness, and the resulting residue is dissolved in sulphuric acid. Into this solution a piece of magnesium ribbon is placed, which, in case of traces of copper, is quickly covered with a layer of this metal; that is easily observed under the ON SOME AMERICAN VANADIUM MINERALS. microscope. REPORT DEVELOPMENT OF THE CHEMICAL ARTS By Dr. A. W. HOFMANN. (Continued from p. 67.) Chlorine, Bromine, Iodine, and Fluorine. By Dr. E. MYLIUS, of Ludwigshafen. AFTER the mixture of hydrochloric acid and air has left the regulator, by its basis, it arrives in the decomposing furnace. This consists of a cast-iron box in which are nine chambers arranged in a horizontal plane, each of them provided with a grate or false bottom at its lower part. Upon this grating stand, in the first, and also in the second chamber, vertically arranged drain-pipes which have been plunged into a hot concentrated solution of 2 mols. copper sulphate and 3 mols. sodium sulphate, and then dried. The remaining chambers are filled with fragments of bricks or balls of clay (1.5 centimetres) which have been treated in the same manner with sulphates of "Berichte über die Entwickelung der Chemischen Industrie Während des Letzten Jahrzenends." By F. A. GENTH. I. Roscoelite. I AM indebted to Dr. James Blake of San Francisco, California, for a small quantity of the very interesting mineral, which he called " 'Roscoelite," in honour of Professor Roscoe, whose important investigations have put vanadium in its proper place among theelements. Roscoelite occurs in small seams, varying in thickness from 1-20th to 1-10th of an inch in a decomposed yellowish, brownish, or greenish rock. These seams are made up of small micaceous scales, sometimes of an inch in length, mostly smaller and frequently arranged in stellate cleavage; soft; the sp. gr. of the purest scales (showing or fan-shaped groups. They show an eminent basal less than 1 per cent of impurities) was found to be 2.938; another specimen of less purity gave 2.921; lustre pearly, inclining to submetallic; colour, dark clove-brown to greenish brown, sometimes dark brownish green. Before the blowpipe it fuses easily to a black glass, colouring the flame slightly pink. With salt of phosphorus gives a skeleton of silicic acid, a dark yellow bead in the oxidising flame, and and emeral green bead in the reducing flame. Only slightly acted upon by acids, even by boiling concentrated sulphuric acid; but readily decomposed by dilute sulphuric acid, when heated in a sealed tube at a temperature of about 180° C, leaving the silicic acid in the form of white pearly scales, and yielding a deep bluish green solution. With sodic carbonate it fuses to a white mass. The roscoelite which I received for investigation was so much mixed with other substances, such as gold, quartz, a felspathic mineral, a dark mineral, and very minute quantities of one of orange colour, that it was impossible to select for analysis material of perfect purity. For this reason I have delayed the publication of my results, which were obtained over one year ago, in the hope of being able to repeat my analyses with better and purer specimens; but I now give the results of my analyses because there is no prospect of getting any more of this mineral, as will be seen from a letter of Dr. Blake, dated San Francisco, April 5th, 1876, in which he says, that the mine in which it occurs cannot be worked any farther until a tunnel has been run, and that it is quite uncertain when this will be done. Although by no means perfect, my results approach the truth and give a fair idea of the composition of the mineral, even if the evident admixture of other minerals, varying in the different samples analysed, from about I to perhaps over 12 per cent, does not permit one to calculate the atomic ratio of the constituents and establish the constitution of this species. There is especially an uncertainty with reference to the quantities of silicic acid, alumina, and potassa which belong to the roscoelite, or which may have been introduced by admixtures of felspathic and other minerals, as will appear from the results given below, which show that the mineral, when decomposed with sulphuric or dilute hydrofluoric acid generally gives only about 6 per cent of potassa, while fusion with calcic carbonate and ammonic chloride yields from 8 to 9 per cent. Some of these uncertainties could have been removed, if a larger quantity of the mineral had been at my disposal. Particular attention was paid to the correct determination of the vanadium and the form in which it exists in the roscoelite. The separation of vanadium is attended with great difficulties, and I have not found any of the methods of separation to give fully reliable results. This is in part owing to the incomplete precipitation of the vanadic acid, and in part to the impossibility of washing the precipitates completely without loss of vanadium. It was therefore always determined by the only method which I found to give fully reliable results-by titration with potassic permanganate. After the separation from the other elements, the vanadic acid was reduced by hydrosulphuric acid into V204, which, after the excess of hydrosulphuric acid had been expelled by continued boiling, was re-oxidised into V205 by the permanganate. I have satisfied myself by numerous experiments that no matter whether only a very minute quantity of sulphuric acid is present, or a very large excess, the V2O4 is completely oxidised into V205 by this process. For the determination of the state of oxidation of the vanadium in the roscoelite, a quantity of the mineral was dissolved in dilute sulphuric acid in a sealed tube at a temperature of about 180° C., and was titered after cooling; the liquid was then reduced by hydrosulphuric acid, and after boiling off the excess of the latter it was again titered. From the quantity of oxygen required for oxidation in both cases it was found that vanadium in the mineral is present as V6O11=2V2O3, V205. The determinations of the other elements were made by the usual methods. The finely-powdered mineral was dried (unless otherwise stated) for two days over sulphuric acid, and the different samples gave the following results: (a.) Purest Scales.-The analysis was made by dissolving one portion in sulphuric acid and determining in this the quantity and state of oxidation of the vanadium, the silicic acid, and insoluble impurities. The latter were left behind in dissolving the silicic acid in sodic carbonate and gave 0.85 per cent; a second portion was decomposed by sodic carbonate and nitrate, and a third for the determination of the alkalies by J. L. Smith's method. The V6О11 given below is the mean of the two determinations. (b.) Another sample, not quite as pure as a, was analysed by fusion. (c.) Still more contaminated with impurities, was analysed by dissolving in dilute sulphuric acid in a sealed tube, &c., ca is the result of this analysis, cẞ after deducting 11:45 per cent of the impurities. (d.) Another sample was decomposed by dilute hydrofluoric acid; the analysis was unfortunately lost except the determinations given below; the material for this analysis had not been dried over sulphuric acid. (e.) This sample was dried over sulphuric acid for several weeks; a portion, which was decomposed by sulphuric acid, gave 5'37 per cent insoluble silicates, o'23 per cent of gold, and 43'24 per cent of silicic acid; the V6011 was determined by difference. The results given below were obtained by decomposing the mineral by fusion :— II. Psittacinite, a New Hydrous Vanadate of Lead and Copper. In a paper on "American Tellurium and Bismuth Minerals," read before the American Philosophical Society at the meeting of August 21, 1874 (Proc. Am. Phil. Soc., xiv., 223-231), I mention, on the authority of Mr. P. Knabe, a siskin green pulverulent mineral from the "Iron Rod Mine," Silver Star District, Montana, as a new "Tellurate of lead and copper." I had at that time no opportunity to examine into the merits of this mineral, having mislaid the small sample which he had sent me. On receiving a copy of my paper Mr. Knabe furnished me with several specimens, which gave me a sufficient quantity of fair material for an analysis. A qualitative examination proved it to be a hydrous vanadate of lead and copper and not a tellurate. When I communicated this result to Mr. Knabe he gave me an interesting account of how he fell into his error. At the Uncle Sam's Lode, in Highland District, occurs with the tetradymite a siskin green mineral, which has not yet been analysed, but which appears to be a tellurate. It looks exactly like the pulverulent variety of the psittacinite from the Iron Rod Mine. When Mr. Knabe dissolved the latter in hydrochloric acid, the evolution of chlorine indicated the presence of a higher oxide; the solution precipitated with an excess of ammonic sulphide gave sulphides of lead and copper and a filtrate, which, on addition of an acid, gave a black pre |