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Chemical Notices from Foreign Sources.

the physiological action of magenta free from arsenic, and finds that, though not a violent poison, it produces some morbid phenomena. In a state of chemical purity he considers that its use would not occasion any great in-mittee of Chemical Arts on the Pneumatic Malting

convenience.

Circumstances of Production of the Two Varieties of Sulphur, the Prismatic and the Octahedral.-M. D. Gernez.-An account of the precautions to be taken in order to obtain sulphur in the two states mentioned. Critical Researches on Certain Methods Employed for the Determination of Vapour-Densities, and on the Conclusions to be Deduced.-L. Troost and P. Hautefeuille.-Not adapted for abstraction.

Action of Hydracids upon Selenious Acid.-M. A. Ditte. The author states that the compound SeO2,2HBr is capable of taking up more bromine, and forming the compound 2SeO2,5HBг. He has also examined the behaviour of selenious acid with the hydriodic, hydrocyanic, hydro-fluoric, hydro-sulphuric, and hydro-selenic

acid.

Observations on Iodine as a Reagent for Starch. -M. E. Puchot.-The author finds that the sensibility of iodine as a reagent for starch is affected by certain nitrogenous organic matters, such as albumen. If albumen is poured upon iodide of starch suspended in water the colour disappears. If albumen is added to a solution of starch saturated iodine water produces no colouration.

Rhodeine, a New Reaction of Aniline.-M. E. Jacquemin. The author having mentioned that the hypochlorites of lime and soda cease to indicate the presence of aniline in solutions containing less than 1 centigrm. in 500 c.c. of water, shows that if after adding the test solution of hypochlorite to these dilute solutions there be further added a few drops of dilute sulphide of ammonium (1 part to 30 of water) a splendid rose colouration appears. In this manner I part of aniline may be detected in 250,000 of water. He gives the name rhodeine to the colouring matter thus generated. No other oxidising agent can be substituted for the hypochlorites, and no colour is obtained if a sulphite or hyposulphite is used instead of a sulphide. Diphenylamin and toluydin simiarly treated produce no such reaction.

Action of Water upon the Glycols.-MM. Nevolé. -Not adapted for abstraction.

Existence in Spain of a Bed of Nickel Ores Analogous to those of New Caledonia.-M. Meissonier.-The ore in question is found in the province of Malaga, and is a silicate of nickel free from cobalt, and, it is intimated, from arsenic and antimony. The amount of nickel is about 9 per cent.

Microzymas of the Bladder as the Cause of the Ammoniacal Fermentation of Urine.-M. A. Béchamp. -A controversial paper, with reference to the papers of Pasteur, Joubert, and Berthelot (Comptes Rendus, lxxxi., page 5.)

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August 18, 1876. Bulletin de la Société d'Encouragement pour l'Industrie Nationale, No. 32, August, 1876. Report of M. J. A. Barral on behalf of the ComProcess of M. Galland, Introduced at the Brewery of Maxiville, near Nancy. The principle of the invention consists in forcing air always at the same temperature and always saturated with moisture through the layer of barley with a speed exactly sufficient to remove the excess of carbonic acid. The barley may be spread to the depth of 30 to 50 c.m. The results are stated to be very satisfactory. From a statistical table given it appears that the average consumption of beer in Bavaria reaches the enormous amount of 219 litres per head, that of England being 118.

Report of M. Lamy on behalf of the Committee of Chemical Arts on the Manufacture of French Yeast and of Corn Spirit of Sprenger and Co., of Maisons Alfort (Seine).—Not adapted for abstraction.

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M. Reimann's Farber Zeitung.
No. 25, 1876.

This issue contains a long leader on the condition o the dyeing trade in Berlin. According to the figures given a dyer loses on the average 53 pfennige (about 41d.) on every kilo. of woollen yarn that passes through his hands. It is now nothing uncommon to dye living animals. Some time ago a lady of the demimonde drove four greys dyed a splendid magenta in the Bois de Boulogne. White lap-dogs are often seen with light blue, green, and rose tails. (We have often seen ducks dyed magenta.) The manufacture of eosin has been commenced by A. Poirrier, of Paris.

No. 26, 1876.

This issue contains a notice that the method of producing pittakall, a blue colouring matter obtained more than thirty years ago from beech-wood tar by Reichenbach, has been re-discovered by Grätzel, of Hanover. It has the peculiarity of being coloured blue by alkalies and orange by acids. The shades produced with it are as fast as those yielded by indigo.

No. 27, 1876.

According to the process of Saroz and Chognard (French patent) the lichens are macerated for a quarter of an hour in water, to which a little hydrate of lime has been added, and are then heated in a closed vessel to 100° to 120° by the introduction of steam at a tension of several atmospheres. The duration of the heating as well as the temperature are modified according to the kind of lichens made use of. The purpose of this heating is the rapid and complete conversion of the lichen acids into orcin. The clear liquid is then separated from the undissolved woody matter by a filter, a hydro-extractor, or a press, and concentrated by evaporation. It is then mixed with ammonia, and put in a tightly-fitting vessel of iron or wood, into which oxygen is conducted. The formation of orcein is thus more rapid than on the common procedure, in which the extract is left to the action of the atmosphere. The oxygen prepared by the process of Tessié du Motay enters at the bottom of the vessel by means of a perforated tube: the portion not absorbed is conducted away by a second pipe passing through the lid, and may be reserved

Manufacture of Orchil Extract and Paste.

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for a second operation. The evaporating ammonia escapes through the same pipe, and is absorbed in water with a view to its being re-utilised. When the oxidation is complete, and the liquid contains an excess of ammonia, it is driven off by exposure to the air or by a gentle heat. To prepare orchil paste, the above-described extract, after concentration and mixture with ammonia, is thickened with a quantity of extracted lichens, and treated with oxygen. The closed vessel is provided with a mechanical agitator. When the oxidation is complete the paste is allowed to stand for some days exposed to the air, with occasional agitation.

No. 28, 1876.

This issue contains a paper on the depressed state of the tinctorial trades, and an announcement that Dr. Ferd. Springmühl is undergoing a prosecution for having insulted Prince Bismark and the Emperor ("Ego et rex meus").

An establishment has been opened in Belgium for extracting the wool from grease by means of alcohol and ether. The yield, according to preliminary experiments, is understood to be large. Similar attempts with other liquids, e.g., bisulphide of carbon and fusel oil (Richter's process), have failed owing to the escape of the solvents.

No. 29, 1876.

This issue, again, contains complaints on the depressed state of the dyeing trade in Berlin and the unremunerative scale of prices.

Consumers of vanadium salts are cautioned against tasting any mixtures in which such are present, or bringing them in contact with any part which has been deprived of the cuticle, as they are intensely poisonous. Prussiate of potash and tannin are proposed as antidotes.

MISCELLANEOUS.

University of London.-Several important changes have been made in the regulations for the degrees of Bachelor and Doctor in Science, conferred by the UniverIsity of London. In the Matriculation examination German may now be substituted for Greek. In place of the superficial acquaintance with both Zoology and Botany, formerly required at the first B.Sc. examination, there will be a single examination (written and practical) in General Biology, in which a more thorough knowledge will be required of the simplest forms and elementary phenomena of Animal and Vegetable Life, such as is now made the basis of the teaching of some of the most distinguished professors in each department. Thus the student who may be intending to devote himself specially to Physical or Chemical Science, will be brought to apprehend the general conceptions common to the two great Organic Kingdoms, without being required to master the specialities of either. And the student who intends to present himself at the second B.Sc. examination in either Physiology, Zoology, or Botany, or all combined, will have laid the best foundation for those special studies in the study of General Biology. The regulations for the second B.Sc. examination are framed with the view of allowing the candidate to bring up any three of the following nine subjects:

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It is intended that the examinations in these several subjects should be, as nearly as may be, on the same grade, as to the amount of attainment they require. The experience of the Examiners in Mathematics justifies them in stating that any candidate who has thoroughly mastered the Mathematics of the first B.Sc. examination, and who has such an aptitude for the study as would lead him to select Pure Mathematics as one of his subjects at the second, would find no difficulty in mastering the requirements of its programme, by such an amount of study, carried on through an eight months' Academical Session, as would leave him free to bestow the same amount of time and attention on two or even three other

subjects. It is understood the amount of proficiency expected in each of the three subjects chosen will be that which the candidate might attain by the steady devotion to it of about one-third of the sessional work of a diligent student. In regard to the Doctor's degree a change has been made in favour of candidates who prolong the interval between their first and second examinations for the degree of Bachelor from one year to two or more; as such will be allowed to come up for the degree of Doctor of Science within a year of their attaining the degree of Bachelor. We shall refer at greater length to the new regulations in our Student's Number, which will be published on September 15.

Analysis of the Weissenburg Water. - The springs of Weissenburg, in the Bernese Oberland, enjoy a considerable reputation as useful in the treatment of pulmonary affections. Cavities in the lungs are said to become cicatrised by its use. Its chemical composition can scarcely be said to throw much light upon its medicinal efficacy. The two main ingredients, according to Dr. Stierlin's minute and evidently careful examination, are sulphates of lime and magnesia. Lithium is present as chloride and iodide, the latter only in very minute quantity. There is an organic compound having the odour of blackberries, and also cæsium and rubidium in traces too small for quantitative determination.

PATENTS.

ABRIDGMENTS OF PROVISIONAL AND COMPLETE SPECIFICATIONS.

employed therein. L. Brumleu, Newcastle-on-Tyne. April 20, 1875. Improvements in the production of white lead and in the apparotus No. 1437. The essential features of this invention consists in first effecting the division of the lead to be converted into white lead, and the action of either acetic acid or of acetate of lead, or of mixtures of then subjecting the same contained in a suitably arranged chamber to the same, and also to the action of air and of carbonic acid; the chamber or chambers being so constructed that a rocking motion may be given to them in order that the white lead formed upon the surface therein, and a fresh surface be thereby exposed. of the lead may be removed by the action of the solution contained

Improvements in the treatment and preparation of certain chemical compounds for the purpose of rendering their carriage, sale, use, and application more convenient and economical. T. Hyatt, Gloucester Gardens, Hyde Park, London, Middlesex. April 21, 1875.-No. 1451. My invention relates to the consolidation of chemical substances, such as sal-soda, alum, and other compounds containing water of crystallisation, for the purpose of lessening their bulk, and thus diminishing the cost of packing, handling, and carriage, and also for the purpose of preventing the waste which arises when such substances are in powder or in crystal form; also to make their employment in domestic use, and in the arts and manufactures, more precise, convenient, and economical. My invention also relates to the consolidation of materials other than the above, when such materials are joined, mixed, combined, connected, or united to them in the production of new and useful manufactures, such as soda and seidlitz powders in medicines, and such as fireproof compositions, or compounds in the manufacture of fireproof safes, and in the protection of buildings or other constructions against fire.

Improvements in the manufacture of manure from certain mineral phosphates. P. Spence, Newton Heath, Manchester, Lancaster. April 21, 1875.-No. 1455. This invention relates to a method of treating phosphates of alumina, or phosphates of alumina and iron, whereby valuable manure is obtained. The substance chiefly used is that called Rodonda phosphate, and the treatment thereof is an improvement upon that method for which a Patent was granted to the present inventor, dated June 9, 1870, No. 1676.

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Improvements in the manufacture of artificial fuels. C. Kingsford, Fulham, Middlesex. April 21, 1875.-No. 1458. This invention mainly consists in consolidating small coal or slack, or similar substances, by addition thereto of a composition made of a solution of silicate of soda or potash, to which a small quantity of pitch or other suitable substance is added, and to enable the pitch to combine with the solution the silicate is heated with a small quantity of flour or suitable paste-making materials to convert it into a paste, and while hot the pitch is added. For consolidating the substances the composition while hot is submitted to pressure. The coal may be ground, and, if desired, mixed with clay and lime, which react upon the silicates, and hasten the solidification of the fuel.

Improvements in the manufacture of manure, and in the apparatus employed therein, J. H. Johnson, Lincoln's Inn Fields, Middlesex. (A communication from H. O. P. Lissagaray, Pantin, France.) April 22, 1875.-No. 1484. This invention relates to the manufacture of soluble and putrescible manure from new products obtained by the special treatment of nitrogenous substances, such, for example, as leather, wool, and horn, which in their natural condition are insoluble and imputrescible, and also to apparatus to be employed in operating upon the before-mentioned substances.

Improvements in the manufacture of glucose or grape-sugar from rice or other grain. E. E. Pearse, Oberstein Road, New Wandsworth, Surrey. April 23, 1875.-No. 1489. This invention has reference to Letters Patent, No. 1044, 1873, and relates to the use of a small jet of water or other suitable liquid to flow in with the grain as it passes into the saccharifier through the feed-trough to prevent any tendency to choking. By these means the operation on broken and refuse grain, as well as the operation on grain that has previously been reduced to small particles or powder, is facilitated.

Improvements in the manufacture of perforated blocks of chloride of sodium or chloride of potassium for use in the manufacture of sulphate of soda and sulphate of potash. J. Brock, Widnes, Lancashire. April 23, 1875.-No. 1502. This invention consists in making perforated blocks of the salts named by placing the crystals wet from the boiling pans in frames filled with taper pegs, and then draining, turning them out of the frame, and stoving them.

Improvements in the method of and apparatus for purifying carbu retted hydrogen gas. H. W. Cook, Thurloe Square, Middlesex. April 23, 1875.-No. 1505. The objects of this invention are to economise the chemical ingredients employed for the purification of gas. To this end the puritying materials (say lime, for instance) are presented to the gas in such a manner that they will act energetically on the gaseous impurities, and will offer continually fresh absorbing

surfaces.

Improvements in the manufacture of sugar from sugar-canes, and in apparatus to be employed therein, which apparatus is also applicable to other like purposes. B. Hunt, Serle Street, Lincoln's Inn, Middlesex. (A communication from A. F. C. Reynoso, Paris.) April 28, 1875.No. 1558. This improved process is essentially different from all those which are now employed, and consists in the complete extraction of the juice from the sugar-cane or sorghum. For this purpose, instead of rolling the canes or sorghum in a mill, the inventor commences by cutting them in pieces by means of cutters or knives suitably arranged; these pieces are then reduced into a pulp by means of rasps, millstones, revolving cylinders, or plates, or other mechanism or apparatus adapted to lacerate the cellules in order to obtain by the complete crushing thereof a homogeneous paste. The pulp thus obtained is submitted to the action of the ordinary presses, or hydraulic or other presses, or any other process employed to separate the juice therefrom. This apparatus may also be employed for the extraction of starch from tapioca and other roots, and for the reduction to pulp of cocoa-nuts and other fruits, or for the treatment of sorghum or maize, either for the extraction of sugar or the preparation of food for animals.

Improvements in apparatus or appliances employed in the manufacture of sulphates of soda and potassa. J. Hargreaves and T. Robinson, both of Widnes, Lancaster. April 29, 1875.-No. 1576. This invention relates to our direct-action process for the production of sulphates of soda and potassa, and consists-(1) In the employment of an overhead steam or other crane for charging the chambers. (2) In using the said crane in combination with a weighted or other tool for loosening the sulphate in the chambers. (3) In employing a revolving shaft provided with expanding cutters to loosen the sulphate. (4) In employing troughs or endless travelling bands to carry away to the desired place the finished sulphate. (5) In lengthening the filling necks, and filling the intervening spaces with non-conducting material to form a working floor and prevent radiation. (6) In forming the hydrochloric gas flues of iron to prevent leakage.

Improvements in dyeing or printing. C. A. Martius, Berlin, Prussia. April 29, 1875.-No. 1584. This invention relates to improvements in dyeing or printing with aniline and other coal-tar colours without the use of mordants now necessary when those colours are employed, by the employment of the fatty salts of the bases of the aniline colours, or the other basic coal-tar colours dissolved in alcohols or in the hydrocarbons of the benzol and petroleum series, the above-mentioned salts being insoluble in water.

Improvements in treating slag from blast-furnaces to produce a new article of manufacture. E. T. Hughes, Chancery Lane, London. (A communication from M. E. Bergius, Mannheim, Baden.) April 30, 1875. No. 1595. This consists in treating slag with a blast of steam so as to transform it into a cotton-like state, which is called silicate

cotton.

An improved process for the manufacture of red sulphide of mercury. A. M. Clark, Chancery Lane, Middlesex. (A communication from W. J. S. Grawitz, Paris.) April 30. 1875.-No. 1604. The invention consists in manufacturing red sulphide of mercury by dissolving without the aid of heat, and whilst protected from the action of light, either the binoxides of mercury or the salts of the binoxide of mercury

CHEMICAL NEWS, Augnst 18, 1876.

in a soluble hyposulphite, the precipitate obtained being gradually raised in temperature in order to deposit the sulphide of mercury. Improvements in the production of aniline-black for printing and other purposes, and in dyeing aniline-black. A. M. Clark, Chancery Lane, Middlesex. (A communication from W. J. S. Grawitz, Paris.) May 1, 1875.-No. 1620. This invention relates to the production of aniline-black, first, in the form of a paste or powder for printing purposes, and for the manufacture of colours, varnishes, and inks of all kinds; and, secondly, the fibres of textile fabrics, by the concurrent reaction on aniline oil of certain metallic salts, and certain chromates or bichromates.

An improved method of and apparatus for filtering and deodorisiug sewage so as to prevent rivers being polluted thereby. T. Pape, Great Alfred Street, Nottingham. May 3, 1875.-No. 1625. The chief features of the invention consist in a machine being placed horizontally on a shaft driven by steam-power, and when once set in motion the apparatus is self acting, and never need stop except for repairs. Improvements in the manufacture of chlorine. H. Deacon, Appleton House, Widnes, Lancaster. May 3, 1875.-No. 1632. The essential feature of this invention consists in the employment in what is known as Deacon's chlorine process of the residue of burnt or calcined pyrites or sulphurets of iron, such residues being either impregnated with a salt of copper, or the copper contained therein, being rendered soluble and active either by means of water or by means of an acidulated solution.

Improvements in the manufacture of sulphuric anhydride. E. Sonstadt, Highgate Road, Middlesex. May 3, 1875.-No. 1638. This invention consists, first, in substituting anhydrous sulphate of magnesium for the ordinary ferric sulphate or other like substance nsually employed in manufacturing or obtaining sulphuric anhydride. At about the melting-point of cast-iron, the anhydride is completely driven off, and may be condensed in the usual manner. This invention consists, secondly, in using ordinary magnesium sulphate for the same purpose. The water of crystallisation is first completely driven off at a temperature below a red heat, then the heat is raised, and the process is continued as in the first part of the invention.

Improvements in the method of treating grease for the purification thereof, to be used in the manufacture of soap and for other purposes. J. Hopkinson, Southfield Square, Bradford, York. May 5, 1875.-No. 1667. Of the grease to be purified I make a lime or insoluble soap, and dissolve out the impure fat with a suitable solvent: I prefer bisulphide of carbon applied under pressure or otherwise. The same is run into a still, and the bisulphide of carbon is distilled off, leaving the impure fat in the still. The fatty acids distilled are decomposed by means of an acid; I prefer hydrochloric, which liberates the fatty acids from the lime base.

Improvements in the manufacture of artificial fuel. J. Deere, Brighton, Sussex. May 5, 1875.-No. 1680. The fuel is composed of coal, lime, clay, gypsum, or copperas, mixed with a gelatincus solution.

Improvements in the purification of gas. J. Whitley, Roundhay, York. May 6, 1875.-No. 1694. This invention describes a means of purifying gas by filtering it through layers of cotton-wool or other fibrous material.

Improvements in apparatus for utilising inflammable fluids for illuminating and heating purposes. H. Browne, Raymond's Buildings, Gray's Inn, Middlesex, May 7, 1875.-No. 1701. This invention has for its objects the improvement of the means of employing inflammable fluids, such as petroleum, naphtha, and the like, for illuminating and heating purposes, and also the rendering the employment for such purposes of such inflammable fluids less dangerous, and consists of an arrangement of reservoirs, pipes, and cocks for supplying the fluid to the lamps or other apparatus automatically.

Improvements in the treatment of substances containing alumina and iron for the purpose of obtaining certain useful substances therefrom. P. and F. M. Spence, Newton Heath, Manchester. May 7, 1875.No. 1704. This invention relates to the production of a cake of sulphate of alumina and iron from minerals known under the name of

bauxite.

A new or improved process for oxidising anthracen, and improvements in the colouring matter produced therefrom. C. Heinzerling and G. McGowan, Glasgow, Lanark, N.B. May 8, 1875.-No. 1712. The features of novelty which constitute this invention are the treatment of anthracen with bleaching-powder, and dilute or non-dilute hydrochloric or equivalent acid, and treating alizarin with cyanide or sulphocyanide of potassium.

Improvements in the manufacture of soda. J. Mactear, Glasgow, Lanark, N.B. May 8, 1875.-No. 1714. This invention relates to an improved combination of processes, whereby in the manufacture of soda a part of the operations hitherto required may be dispensed with, whilst soda sulphate is more completely separated from the products and profitably unlised.

Improvements in the manufacture of sugar. A. Manbré, Cleveland Villas, Penge, Surrey. May 8, 1875.-No. 1724. My invention has for its object improvements in the manufacture of glucose-sugar for brewing purposes. I have found that by mixing a portion of canesugar with a portion of glucose-sugar, and by subjecting the mixture to the action of heat and in a vacuum, I am able to produce a new kind of sugar, which I call a "specialite sugar," for making beer, possessing all the properties required for producing bitter, India, and other pale ales, common beer, stout, and porter of the finest and purest quality, possessing great fullness and great delicacy of flavour.

Improvements in the production of compounds containing xyloidine, and in the application of the same. D. Spill, High Street, Homerton, Middlesex. May 11, 1875.-No. 1739. This invention relates to im provements in the production and application of xyloidine, and of those compounds which consist essentially of what is known as soluble guncotton, specially applicable to the manufacture of fusees, fusee tubes and imitation tortoise-shell or turtle-shell.

CHEMICAL NEWS, August 25, 1876.

Metachromatism, or Colour Change.

THE CHEMICAL

VOL. XXXIV. No. 874.

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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 μera, 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,

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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.

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Plumbic iodide

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Potassic dichromate

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* Gmelin's "Chemistry," vol. i., p. 238.

Change.

Orange, red, and brown. Yellow and orange. Dark scarlet and puce (240° C.).

(In N, air, and CO2.)
(In N, air, and CO2.)
(In sealed tube.)
Dark red.
(In sealed tube.)

(In hydrogen.)

(In air and CO2.)

Orange and red.

(The same change under paraffin.)

Greenish yellow.

Orange and red.

Yellow, and when cooling just after the 'glow' of a

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*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.

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Metachromatism, or Colour Change.

CHEMICAL NEWS, August 25, 1876.

To ascertain the more intimate nature of the change in The position of all the members, save the lowest three, these anhydrous bodies was a work of some difficulty is determined by experiment. That white has the position until the following simple expedient was devised:-Crys- we give it seems probable because-(1) by experiment talline metachromes were used. The finely-powdered with the ZnO class of metachromes it plainly occupies a body was placed upon the concave side of a watch-glass, position at the opposite end of the scale to orange and and pressed into a thin layer by the convex side of a red; (2) the behaviour of blue and green metachromes second glass. The spectrum of the transmitted light precludes its being placed between these two colours; being obtained at the normal temperature, the temperature and (3) it is the direct opposite of black. Violet and was now raised, and a second spectrum obtained for com- indigo are only placed in the scale provisionally to make parison. Such a comparison for potassic dichromate we up the spectrum colours, as there are no experiments to have in the following figure:warrant their being so placed.

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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, Ta205, M0O3, Sb2O3, Sb2O4, 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:

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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 whilst it is in the deep orange state, we see that no subthe fact that this oxide is partially decomposed at 232° C., oxide 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 PtCl 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.

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PtCl

Red

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Orange

Yellow

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In405

MnO

NiO Au2O Cd2O

Hg2l2 CoO Cr2O3

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