Par M. DUMAS. THIS treatise composes the seventh volume of the Fifth Series of the Annales de Chimie et de Physique, and embodies the labours of the special commission issued to investigate this minute but formidable enemy of the vineyards. The following are the conclusions arrived at:As regards the phylloxera of the roots it is found that the sulpho-carbonate of potassium, of which more than 20,000 kilos. have been already used, is a rapid insecticide, the only one which certainly destroys the phylloxeras fixed upon the roots, and which affords at the same time an efficient nourishment to the vine. The sulpho-carbonate of sodium offers similar advantages as an insecticide only. The sulpho-carbonate of barium being an anhydrous salt, and sparingly soluble is recommended by its resistance to the action of oxygen and to that of carbonic acid, which renders it a poison less rapid, but of an effect more durable. ments were tried, and it was found that if the secondary | Etudes sur le Phylloxera et sur les Sulpho-Carbonates• current from an induction coil be used instead of a current direct from the battery the effects are much more marked. When the induced spark was thus diverted, either wholly or partially, into a short coil which was insulated very perfectly from the core inside, a spark about half an inch in length, which has a decided effect on the nerves, could be drawn off from the core, and this was sufficient to illuminate a small vacuum tube; the spark, however, does not exhibit the usual signs of polarity. It was shown by observing the illumination thus produced with a rotating mirror, that the discharge is in reality a reciprocating one, each spark returning on its path after a minute interval of time. Under certain conditions it is also possible to charge an electroscope either positively or negatively by means of the spark, and Mr. Thompson has shown that the spark ignites a jet of gas, but fails to deflagrate metallic wire or ignite gunpowder. From the above and other experiments, which will be exhibited on a future occasion, the author concludes that the cause of the phenomena is obvious, and that the hypothesis of a new force is unnecessary. Prof. MCLEOD referred to a paper on the same subject, which appeared in the CHEMICAL NEWS (vol. xxxiii., p. 173), by Professors Houston and Thomson. Mr. DAVID Ross, B.A., enquired the tension of the Leyden jar arrangement used in the experiments, but Mr. Thompson pointed out that it would be very difficult of determination on account of the rapid change of the spark from positive to negative. As to the winter-eggs the heavy oil of gas-tar, and especially the so-called oil of anthracen, seems to be the most suitable agent for anointing the branches and for destroying the winter-eggs. The application of gas-tar to the branches and of sulpho-carbonates to the roots is best performed in the months of February and March. That the investigation has been carried out on truly scientific principles the name of M. Dumas is a sufficient guarantee, and the signal success which has been attained is a fresh instance of the practical value of seemingly abstract research, and of the efficiency of scientific method. NOTICES OF BOOKS. The Journal of the Iron and Steel Institute. No. 2, 1875 THIS issue contains an account of proceedings at the Of the papers read one only seems to come fairly within our cognizance, namely, an essay by Mr. I. L. Bell, F.R.S., on the use of caustic lime in the blast-furnace. The author shows that of the total heat generated 22 per cent was absorbed by the expulsion of carbonic acid from the limestone, and the decomposition of this compound of oxygen and carbon. Of this loss 16 per cent is due to the use of limestone. Hence he argues that :-“ An expenditure of 16 per cent of the heating power of the fuel, which is rendered necessary by the presence of one of the constituent parts of our flux affords, prima facie, a strong reason why we should seek to relieve the furnace of a duty represented by about 4 cwts. of coke, particularly as half this weight of inexpensive small coal sufficed for the purposes of the lime-kiln." In certain experiments undertaken with furnaces 48 feet high he failed to find any tangible economy in fuel effected by the substitution of burnt lime for the raw limestone. In the same furnaces, however, he found an advantage in the increased make and superior quality of the iron when burnt lime was employed. With furnaces 80 feet in height this improvement was no longer to be traced. In the experiments undertaken with these furnaces the composition of the cinder in each case was found almost absolutely identical, and no change in the removal of silicon or sulphur from the metal was effected by the use of burnt lime. CORRESPONdence. ON A NEW REACTION OF TARTARIC ACID. I HAVE lately noticed the following reaction, which, I have tried the same experiment, using citric, succinic, malic, oxalic, or acetic acids, or sugar, in place of tartaric acid, but without getting a similar result. If a ferric salt be used instead of a ferrous salt, the colour is not obtained. The violet compound formed appears to be potassic or sodic ferrate. It is destroyed at once by sulphurous acid, and is slowly discharged by boiling. I I have tried to obtain the higher oxides of manganese and chromium in the same way, but without success. intend to follow up the investigation more fully.— am, &c., H. J. H. FENTON. I Christ's College, Cambridge, April 25, 1876. ORGANISATION AMONG CHEMISTS. To the Editor of the Chemical News. SIR,-I am glad to find that chemists seem to be waking Hence he concluded that in what he called an "imper-up to the fact that they ought to have a position as memfect furnace," i.e., a furnace less than 80 feet high, there was certainly an advantage in using limestone in a calcined state. But in complete and perfect furnaces, where the economy of coke is carried as far as the chemical nature of the operation permits, there is nothing to be gained by a change. bers of an honourable profession. There is no doubt that it is a splendid science, and I regret much at the low tone that is taken by some of your correspondents. Connected as chemistry is so closely with physics, medicine, sanitary matters, not to speak of the arts and manufactures, it seems to me a pity that anyone should suggest that it is sufficient qualification to pass in inorganic chemistry alone: this can be learnt in a year, and I am quite sure that no one can learn chemistry in that time so as to be any credit either to himself or the profession. There is no doubt that at present chemists are held in very low estimation, and there can be no wonder that in this great commercial country some are found to grumble at the very poor remuneration that is attached to it. This, however, is perfectly intelligible, as so few men study and qualify for it properly. I must beg to differ from one of your correspondents, who says that it is "those who have a sufficient private income who degrade the profession by the acceptance of wretchedly low fees." It seems to me that very few men with a "sufficient private income " take up chemistry as a profession, and I wish there were more. With regard to "organisation," I think this might be more properly referred to the highest authorities in our profession, and I am glad to say I have good reason to believe that the Council of the Chemical Society is taking some steps towards distinguishing between those who are properly qualified and those who are not.—I am, &c., May 2, 1876. CHEMICAL NOTICES FROM THETA. in this liquefied stratum; the spots are produced by masses of gas and electrified vapours proceeding from the interior of the orb, penetrating the liquid layer, and giving to the edges of the cavities forms which characterise the passage of positive electricity. The faculæ seem to be a brilliant phase in the evolution of the gaseous masses when they approach the surface before their eruption. The protuberances are formed by the gases themselves issuing from the interior of the sun at a higher temperature, and consequently more luminous than those which form the atmosphere of his surface. Influence of the Asparagin contained in Saccharine Juices (Canes and Beet-roots) upon the Saccharimetric Assay: Destruction of the Rotatory Power of Asparagin, and Method for its Determination. MM. P. Champion and H. Pellet.-The presence of asparagin in saccharine juices makes the percentage of sugar apparently too high, the error amounting in certain cases to 0.7 per cent. An addition of acetic acid destroys this disturbing influence. tical paper, not suited for abstraction. Use of the Magneto-Electric Machines of M. NOTE.-All degrees of temperature are Centigrade, unless otherwise expressed. Comptes Rendus Hebdomadaires des Seances, de l'Academie des Sciences. No. 15, April 10, 1876. Experimental Criticism on the Formation of Sugar in the Blood, and on the Function of Physiological Glycemia.-M. Claude Bernard. The author maintains that the experiments, on the faith of which earlier authors have thought themselves entitled to deny or to affirm the presence of sugar in the blood of diabetic patients, have really no scientific value. The experiments of Tiedemann, Gmelin, and Magendie are exact as crude facts, but the interpretation which connects them with an amylaceous or saccharine diet is erroneous. Analytical Solution of the Problem of Distribution in a Magnet.-M. J. Jamin.-A strictly mathematical paper, unfit for abstraction. Vegetation of Maize begun in an Atmosphere free from Carbonic Acid.-M. Boussingault.-The author's experiment shows that a seed placed in a barren soil supporting a barren atmosphere forms at first, on germinating, a fertile atmosphere, that is to say, an atmosphere containing carbon, in which, under the influence of light, the leaves develop chlorophyll, and subsequently amylaceous and saccharine matters. Verbal Observations on the foregoing Communication.-M. Pasteur.-We may comprehend that special cellules, animal or vegetable, other than those of chlorophyll may behave towards electricity as the cells of green matter behave with the solar radiations, and that the carbonic acid is decomposed and is carbon assimilated, because the electric vibrations are transformed into chemical force. Seventeenth Note on the Electric Conductibility of Bodies Moderately Conductive.-M. Th. du Moncel. -Not suitable for abstraction. Solar Spots, and on the Physical Constitution of the Sun.-M. G. Planté.-M. Planté concludes from his experiments that the sun may be considered as a hollow electrified globe, full of gases and vapours, and covered with a liquid covering of molten incandescent matter; the wrinkles, or luculi of his surface, result from undulation Simple Apparatus for the Analysis of Gaseous Mixtures by means of Absorbent Liquids.-M. F. M. Raoult. This paper requires the accompanying illustrations. Exchanges of Ammonia between Natural Waters and the Atmosphere.-M. Th. Schlosing.-The quantity of ammonia condensed in each gramme of water increases as the temperature falla, in spite of the gradual impoverishment of the air. Products of the Reduction of Anethol, and on the Probable Constitution of this Latter Body.-M. F. Landolph.-The author holds that the formula of anethol ought to be doubled. PATENTS. ABRIDGMENTS OF PROVISIONAL AND COMPLETE Improvements in the manufacture of manures. Major-General H Y. D. Scott, C.B., Ealing, Middlesex. February 1, 1875.-No. 373 The object of this invention is the production from fœcal matters of manures sufficiently concentrated to command a ready market without the creation of a nuisance in the process. Instead of employing deodorants of a bulky and (as respects fertilising properties) inert nature, I make use in some of the closets of coal soot which contains considerable quantities of ammoniacal salts, and in others I apply as a deodorant lime, which is subsequently neutralised with phosphoric acid in a soluble form combined or uncombined with a base. The combined matters are afterwards stirred in a pug-mill, and then dried and reduced to a powder. Improvements in the treatment of farinaceous substances for the Johnson, Lincoln's Inn Fields, Middlesex. (A communication from manufacture of starch and fermented and distilled liquors. J. H. W. Adamson, Philadelphia, Pennsylvania, U.S.A.) February 2, 1875. -No. 381. The essential features of this invention consist in preparing farinaceous substances for conversion into starch, beer, or alcohol by subjecting them to the action of heated hydrocarbons or hydrocarbon vapour under heat and pressure. Improvements in the process of and apparatus for treating and purifying sewage and polluted waters, which improvements are applicable for collecting the soap, grease, and oils for the manufacture of gas, and for removing incrustation in steam-boilers. G. Rydill, Quality Court, Chancery Lane, Middlesex. February 3, 1875.-No. 399. This inven tion of improvements is for the purification of sewage and polluted waters, preventing the pollution of rivers and streams, which improvements are applicable for collecting the soap, grease, and oils, which prevents insoluble soaps and slimy scum from mixing with the Marot, Paris.) February 3, 1875.-No. 408. The essential feature of this invention consists in raising the saccharine solutions to a boiling temperature, and then adding thereto or bringing the same in admixture in another vessel with a solution of lime or baryta, and then adding an alkali, either soda, potash, or ammonia, the same being by preference free from carbonates. Improvements in furnaces used in the manufacture of glass. J. Sheffield, Glasgow, Lanark, North Britain. February 4, 1875.-No. 411. The features of novelty which constitute this invention are(1) The water tank at the sides of and below the fire-bars. (2) The employment of air, and heating it by tortuous passages in the sides of the "cupola." (3) Constructing tank-furnaces with an air space passing up through the" cave," so as to divide the tank, thus enabling two kinds of glass to be simultaneously treated in the same furnace. A new and useful process in the manufacture of imitation braids, trimmings, leather, wood, and other articles. H. Loewenberg, Charlotteburg, near Berlin, Germany. February 4, 1875.-No. 420. This invention relates to the production of flexible or elastic casts in imitation of leather, straw, or woven goods, wood, ornaments, &c. A mould is first made of the object to be imitated by pouring over the same a compound, consisting by preference of a solution of glue with glycerin, which is removed after it has solidified. Into this mould is then poured a liquid compound, consisting of a solution of glue with glycerin, oil, or soap, and any desired colouring matter. Before this solidifies the greater portion is poured out again, leaving a thin layer in the mould, which is removed after it has solidified. The surface of the mould is treated with chromic acid or acetate of iron to prevent the compound adhering to it. Ch Physical, 3. Chemical Technology, or Chemistry in its Applications to the Arts and Manufactures. BY THOMAS RICHARDSON and HENRY WATTS. Second Edition, illustrated with numerous Wood Engravings. Vol. I., Parts 1 and 2, price 36s., with more than 400 Illustrations. Nature and Properties of Fuel: Secondary Products obtained from Fuel: Production of Light: Secondary Products of the Gas Manufacture. Vol. I., Part 3, price 338., with more than 300 Illustrations. Sulphur and its Compounds: Acidimetry: Chlorine and its Bleaching Compounds: Soda, Potash: Aikalimetry: Grease. Vol. I., Part 4, price 21s., 300 Illustrations. Aluminium and Sodium: Stannates, Tungstates, Chromates, and Silicates of Potash and Soda: Phosphorus, Borax: Nitre: GunPowder: Gun Cotton. Vol. I., Part 5, price 368. Prussiate of Potash: Oxalic, Tartaric, and Citric Acids, and Appendices containing the latest information, and specifications relating to the materials described in Parts 3 and 4. BAILLIERE AND Co., 20, King William Street, Strand. For or Sale, cheap, suitable for a Metallurgic Chemist, a Hot-Blast Gas- Furnace, with bellows, crucibles, &c., complete; large Gas-Bag, with iron frame and pressure-board; Iron Oxygen-Retort and Furnace, and sundry other apparatus.-For particulars apply to P. H., care of Mr. Woods, 1, Great Queen Street, Westminster. GLASGOW CORPORATION GAS. ESIDUAL PRODUCT WORKS TO LET, RES AND RESIDUAL PRODUCTS FOR SALE. The Glasgow Corporation Gas Commissioners are prepared to receive OFFERS for a LEASE of their RESIDUAL_PRODUCT WORKS, at Dawsholm, near Maryhill, and also for the PURCHASE of the TAR and AMMONIACAL LIQUOR produced at their GASWorks there. The Lease to be for such Term of Years from 1st July next as may be agreed on. Offerers must offer a Fixed Rent of £1400 per Annum, and also a further Sum in respect of each Ton of Coal Carbonised at the Dawsholm Gas-Work. On application at the Gas Office (Manager's Department), 42, Virginia Street, intending Offerers will receive Orders for inspecting the Works. Conditions of Let may be seen in the hands of the Subscriber, from whom also Forms of Offer may be obtained, which will be received by him up till 1st June next. The Commissioners do not undertake to accept the highest or any Offer. CHEMICAL WORKS AT WHITECROOK, DALMUIR, NEAR GLASGOW. To be Sold (under the Direction of the High Court of Justice) by Public Roup, within the Faculty Hall, Saint George's Place, Glasgow, on Wednesday, May 10, 1876, at 2 o'clock in the afternoon. The Whitecrook Chemical Works of the British Seaweed Company (Limited), situated upon the Forth and Clyde Canal, with the ground connected therewith, and whole Engines, Machinery, Boilers, Retorts, Pans, Vitriol Chambers, Chimneys, and whole other Movable Plant, and Buildings on the ground, including Apparatus of the most approved construction for the manufacture on a large scale of Sulphuric Acid, Carbonate, Chlorate, Muriate, and Sulphate of Potash, Caustic Soda, Refined Brimstone, Iodine, Bromine, Iodide and Bromide of Potassium, &c. The Works have unusual facilities for water carriage, and are near to the Dalmuir Station of the North British Railway Company, by which there is direct communication to all parts of the United Kingdom. The ground connected with the Works extends to 8 acres and 10 and 7-10th poles (more or less) subject to a feu duty of £149 13s. Entry immediately. For further particulars apply to H. J. C. F. Woodhouse, Public Accountant, 14, Warwick Court, Holborn, London; to J. N. Cuthbertson, Chemical Broker, 29, Bath Street, Glasgow, Official Liquidators of the British Seaweed Company (Limited); to Bannatynes, Kirkwood, and McJannel, Writers, 145, West George Street, Glasgow; to William A. Crump and Son, Solicitors, 10, Philpot Lane, London, E.C.; to Chauntrell, Pollock, and Mason, Solicitors, 63, Lincoln's Inn Fields, London, W.C.; or to Balfour and Paterson, Writers, 138, Hope Street, Glasgow, the latter of whom will exhibit the Titles and Articles of Roup. M essrs. Mawson and Swan require the services of a Gentleman accustomed to the Chemical and Philosophical Apparatus Business.-11 and 13, Mosley Street, Newcastleon Tyne. ANALYTICAL CHEMIST OR MANAGER. Wanted, appointment as above. Ten years manufacturing experience. England or abroad. Good linguist. -Address, R. J. A., 56, Bevington Road, Westbourne Park, W. Wanted, a Chemist thoroughly understanding Tar Products-State salary, with references, to 321, CHEMICAL NEWS Office, Boy Court, Ludgate Hill, London, E.C. THE CHEMICAL NEWS. VOL. XXXII. No. 859. NEW RESEARCHES ON GALLIUM. I HAVE just reduced to the metallic state about 10 centigrms. of gallium, which I believe is very sensibly pure. As I have stated, the first specimen of gallium presented to the Academy owed its solidity to the presence of a small quantity of foreign metals. Pure gallium melts at about 29'5°, and is therefore liquefied when held in the fingers; it remains very readily in super-fusion, which explains how a globule remained in the liquid state at temperatures falling at times as low as zero. Gallium obtained by the electrolysis of an ammoniacal solution is identical with that prepared by means of a potassic solution. When once solidified the metal is hard and resistant, even at temperatures little below its meltingpoint. Nevertheless, it is sectile, and possesses a certain degree of malleability. Melted gallium adheres readily to glass, on which it forms a fine mirror, whiter than that produced by mercury. If heated to bright redness in presence of air gallium is only oxidised very superficially, and is not volatilised. In the cold it is not sensibly attacked by nitric acid, but with the aid of heat it dissolves with the evolution of red fumes. The specific gravity of the metal, determined approximately on a specimen weighing 64 milligrms., is 4'7 at 15° C., with respect to water at the same temperature. The mean sp. gr. of aluminium and indium is 48 at 0°. The specific gravity agrees, therefore, with theoretical prevision, but its extreme fusibility is a fact totally unexpected. For the other properties of gallium I must refer to my sealed packet, dated March 6, and to my former communications. With the permission of the Academy I will shortly describe certain new reactions of the compounds of gallium, and point out the method to be followed for its extraction from ores." M. Wurtz laid before the Academy three specimens of gallium, one of them in a state of super-fusion, and demanded, in the name of M. Lecoq de Boisbaudran, that the sealed packet in question should be opened. This having been accordingly done by the Perpetual Secretary, it was found to contain the following paper: "The specimen of gallium which I had the honour of presenting to the Academy had been obtained by the electrolysis of an ammoniacal solution of sulphate of gallium. The metal thus prepared was solid, and even rather hard. Its solution in hydrochloric acid gave the rays of gallium with brilliance, and those of zinc much more feebly. The metal, therefore, was gallium containing, according to the indications of the spectrum, small quantities of zinc and insignificant traces of other metals. "The solubility of oxide of gallium in ammonia not being great, I sought for some other solvent which might enable me to obtain concentrated solutions suitable for electrolysis. Caustic potassa dissolves a large quantity of oxide of gallium: this solution readily undergoes electrolysis, but the metal obtained by this process is liquid, and not solid like that obtained from an ammoniacal solution. "The following observations have been made on about I milligrm, of liquid gallium : (1.) A very small globule, exposed to the open air for more than three weeks, lost neither its liquidity nor its metallic lustre. (2.) The metal is deposited upon a negative electrode of platinum as a dead, whitish grey coating formed of numerous minute globules, It dissolves in the cold in dilute hydrochloric acid with brisk disengagement of hydrogen. (3.) The hydrochloric solution of the metal yields a (5. Liquid gallium, deposited by electrolysis upon a "At the time of those experiments I still had a portion of the gallium which I had presented to the Academy, and which had been returned to me. I made use of it to satisfy myself anew of the hardness of this gallium, and of the nature of its spectrum, which I found as before was composed of brilliant gallium rays, feeble zinc rays, and insignificant traces of other metals. by the electrolysis of a potassic solution to the presence "We cannot ascribe the liquidity of the gallium obtained of a small quantity of potassium reduced by the voltaic current, since the alkaline metal would have been quickly oxidised, both during the washings and by contact with moist air. I think, therefore, that pure gallium is really liquid, and if I obtained it at first in the solid state it was probably by reason of its being alloyed with small quantities of other metals, especially zinc. Solid gallium is, in fact, less pure than liquid gallium. The solidity of gallium seems to be caused by relatively inconsiderable quantities of foreign metals. "We may still suppose that by the electrolysis of an ammoniacal solution there is deposited, not pure gallium, but a compound of the metal with the elements of ammonia-a hydride, amidide, or nitride. I eagerly await the time--I hope not far distant-when, having at my disposal several centigrms. of purified gallium, I shall be able to determine its physical properties, which promise to be interesting."-Comptes Rendus. REPORT DEVELOPMENT OF THE CHEMICAL ARTS Progress in the Artificial Production of Cold and Ice. (Continued from p. 188.) IN 1869 the design and description of an ice machine constructed by F. Windhausen, of Brunswick,† were made public. It has only one cylinder, with a piston of the diameter of the height of the stroke. On one side of the piston there occurs compression and on the other expansion. The compressed air is forced through a cooler with a large surface, which serves at the same time as a * "Berichte über die Entwickelung der Chemischen Industrie Während des Letzten Jahrzenends." + Windhausen, Mech. Mag., 1869, 387. Dingl. Pol. Journ., cxcv., 115. Wagner, Jahresberichte, 1870, 542. reservoir for the compressed air. Whilst on one side of the piston the air is compressed it expands on the other. On the return of the piston the cold air is forced into the ice-chest, from which, when deprived of its cold, it is immediately drawn on the other side of the piston. That side of the long cylinder in which condensation takes place is surrounded with water as a cooling agent, whilst the other end is packed with a bad conductor of heat. The broad piston renders it impossible for an equalisation of temperature to take place within the cylinder. For this purpose there requires an especial external arrangement for the admission and for the cutting off of the air which enters the expansion end. If the object is not to make ice but to cool spaces, the expanded cold air is forced directly into these, whilst the fresh external air is drawn into the compression end of the piston. As regards the performance of the machine nothing has transpired. In the summer of 1871 the author saw at Berlin a powerful ice machine destined for New Orleans, constructed and experimentally set up by Windhausen. The construction was different from that above described, the compression and expansion cylinders being distinct, according to the scheme which we considered as most correct in principle, and took for the foundation of our preliminary investigation. It yielded air at -40°C, compression cylinder constantly drew in fresh air, hygroscopic water was deposited in the cooler, where on account of the contracted space it could no longer remain in the state of vapour. From there the air, saturated with water, passed into the expansion-cylinder, and in consequence of the cold produced by the expansion the greater part of the existing vapour was necessarily deposited as This circumstance very much interfered with the working of the machine, as the friction of the piston was considerably increased by the snow, which also choked up the escape-pipes. The latent heat set at liberty acted also in opposition to the fall of the temperature even though the sum total of the negative heat units was not lessened. The piston was appropriately lubricated with glycerin. The author could ascertain nothing as to the experimental measurements made to determine the actual which was filled with abundant snow-flakes. As the snow. effect of this machine. Since the beginning of 1873 Nehrlich and Co., of Frankfort-on-the-Main, make the Windhausen machine with two cylinders of one size only, with especial regard to the demand in breweries. It requires a 40-horse power engine, and is guaranteed to yield hourly 2500 cubic metres of air at temperatures of from -30° to -50°. If we assume that these temperatures refer to initial temperatures of from 10° to 30° the total reduction of temperature amounts to 60°, whence the amount of the negative heat units may be calculated as 50,000, corresponding at most to 400 kilos. of ice. If the production of ice were the object in view the same quantity of air might be made to circulate. A steam-engine of 40-horse power consumes hourly 80 kilos. of coal; consequently 1. kilo. of coal would give 5 kilos. of ice-a very favourable result. Such a machine, including the engine, cost in 1873 66,000 marks (£3300). L. Mignot, of Paris, in 1870, constructed also an air ice machine with distinct compression and expansion cylinders. It is distinguished from that of Windhausen by the arrangement that a small pump injects water into the compression-cylinder, and that the air in the condenser sweeps over open water. This arrangement is, without doubt, advantageous. The labour of compression is much reduced when the temperature of the air is kept low. The water cannot have an injurious effect in the air since the cooled and compressed air is in any case saturated with moisture. It may therefore be expected that the compression of the air will be effected at a less cost, and its complete refrigeration will require a smaller condenser. L. Mignot, Mech. Mag., Dec., 1870, 404. cxcix., 362. Wagner, Jahresbericht, 1871, 696. Dingl. Pol. Journ., | Particulars concerning this machine have not transpired. The more recent Windhausen machines are also provided with an injection apparatus. (To be continued) THE DETECTION OF ADULTERATIONS IN COFFEE. By Prof. G. C. WITTSTEIN. BEFORE Coffee is brought to us as a beverage it is not unfrequently subjected to different adulterations, one of which is even carried so far that of the original bean nothing but the mere name remains. H. Ludwig, for instance, relates that in commerce coffee-beans are found which are made of dough moulded after the true bean in the most perfect and deceptive manner. Such beans, however, unlike the genuine, always possess sharp edges, and may be very easily ground to a grayish yellow powder. On boiling with water they are converted into a pasty mass, which on addition of iodine assumes a deep blue colour. The detection of this imitation is therefore never attended with difficulty, and it may only escape notice if the proportions in which the artificial product is mingled with the natural bean are comparatively small. The attempts, however, of imparting to the poorer classes of coffee the colour and general appearance of the more excellent varieties, are far more frequent. The methods of arriving at this end, whether through colouring matters or otherwise, are quite various. (See Polyt. Journ., 1874, No. 213, 172.) I am informed, from sources of unquestionable authority, that one of these methods consists in placing the coffee together with a sufficient quantity of shot or lead granules in an empty barrel, rolling the latter about for some time until enough lead has been rubbed on the beans to give them the glossy appearance usually considered characteristic of the better qualities of coffee. This adulteration is not easily detected by the naked eye; usually a good lens will suffice. When absolute certainty, however, is desired, it will be found convenient to adopt the following process:-Digest the suspected beans with dilute nitric acid (110 sp. gr.); decant the liquid after one hour, dilute with three times its volume of water, and then precipitate the lead with sulphuretted hydrogen as usual. Another substance for colouring coffee is a greenish powder, one hundred parts of which, according to the analysis of Lohr, are composed of 15 parts Prussian blue, 35 parts chromate of lead, 35 parts of a mixture of clay and gypsum, 15 parts water. Use is, therefore, here made of a mixture similar to that which the Chinese have for some time employed for the colouration of green tea, except that in the latter mixture turmeric is substituted as the yellow constituent in place of the harmful plumbic chromate. The different ingredients of the coloured mixture-Prussian blue often replaced by indigo (Warington), turmeric, and gypsum-may be quite distinctly seen adhering to the tea-leaves under the lower powers of the microscope, or even by a good lens, as I have often had occasion to convince myself. The microscope alone, therefore, is frequently sufficient to discover whether a similar mixture adheres to the coffee beans or not. For more accurate examination, however, it is better to put a considerable quantity of the beans in a suitable vessel, and to pour distilled water upon them. After two hours or so the beans are removed, and the turbid liquid allowed to settle. In presence of gypsum the supernatant clear liquid will become densely turbid on addition of baric chloride and ammonic oxalate. Prussian blue may be detected in the sediment by giving rise to a brown colouration on addition of KHO. If this change of colour should not occur, the mixture will not * Dingler's Polyt. Journ, No. 215, 84 (translated for American Chemist by Carl Barus). |