페이지 이미지
PDF
ePub

The quantitative question, in reference to the amounts of silver and gold necessarily expended in the operation of photographic printing, has received some further elucidation, by experiments lately made in this direction by Mr. John Spiller, assistant chemist to the War Department, at Greenwich. The practical conclusions established by this gentleman's analytical results are to the effect, that upwards of eighty per cent. of the silver originally employed in the process of sensitizing the paper may be recovered in the state of precipitated chloride and sulphide, by judiciously collecting the various washings and waste solutions, and treating them with common salt; or, in the case of the fixing baths, and other solutions containing hyposulphides, with crude sulphide of potassium. These products being separately reduced to metal, are stated to yield in the aggregate the large amount of silver indicated, from which the pure nitrate may be again prepared, and, at the same time, a certain proportion of gold rescued for further employment in the toning process. By adopting the suggestions of the author, it appears that of the fifty grains of nitrate of silver ordinarily taken up by the full-sized sheet of albumenized paper, at least forty grains are recoverable, and that, at the rate of four shillings per ounce trov, one pennyworth of silver need only be actually expended in the production of a single proof of the largest possible size (seventeen by twenty-two inches).

The most striking improvement in construction which we feel called upon to notice is one referring to the camera. In the ordinary form of the double-bodied instrument, it has hitherto been customary to make the hinder portion slide within the front case, to meet the adjustment for focus; but, by reversing this arrangement (which is now becoming a general practice), the lens and smaller front part of the camera are made to travel forwards by the action of an endless screw in the base board, the ground glass remaining stationary, by which means the operation of focusing is more readily accomplished than when, on the old plan, the image is constantly approaching or receding from the eye. Another advantage gained by this arrangement is, the increased accommodation provided for the reception of the plate-holder at the back of the camera, and the possibility of taking therein pictures of somewhat larger dimensions, on account of the interior form of the instrument humouring, instead of being opposed to, the direction taken by the rays of light diverging from the lens. The large camera, made on this principle by Mr. Dallmeyer, and shown in the nave of the International Exhibition, is one among many illustrations of this novelty in construction.

PHYSICS: LIGHT, HEAT, AND ELECTRICITY.

PAPER, by A. J. Angström, has been communicated to the Editor A of the Philosophical Magazine, “ On the Fraunhofer's-lines visible in the Solar Spectrum.” He repeats the statement, “ that a body in a state of glowing heat emits just the same kinds of light and heat which it absorbs under the same circumstances ;” and considers that “the electric spectrum must be vieweil as the superposition of two spectra

the one belonging to the metal or conductor of which the electrodes are made; and the other, to the gas through which the spark passes.” The object of his present investigation was to make a new examination and accurate drawings of the solar spectrum ; to determine the wave-lengths of many of its lines, and also of the lines in the spectra of different metals. He has confirmed the statement of Kirchoff-that the atmosphere of the sun contains iron, magnesium, nickel, and chromium ; the lines due to iron" are the most characteristic in the whole spectrum.” He adds, as a result of this last research, that calcium, aluminium, and manganese exist in the sun ; and also, in all probability, strontium and bariuin; and concludes by some remarks on “Fluorescence.”

Mr. J. Attfield has examined, by the aid of prismatic analysis, various flames containing carbon, and has found that ignited oxy-carbons, hydrocarbons, sulpho-carbons, and nitro-carbons emit certain rays of light in common; and concludes that these rays emanate from ignited carbon vapour. When observed by the unassisted eye, the prevailing colour of ignited carbon is light blue. By special manipulation, he has obtained the carbon spectrum with carbonic oxide, olefiant gas, bi-sulphide of carbon, and cyanogen.

M. Jaunsen, in a note communicated to the French Academy of Sciences, affirms that he has recently been able to determine the presence in the solar spectrum of permanent rays which ought undoubtedly to be attributed to the action of the terrestrial atmosphere, and has constructed a spectroscope by which he has been enabled to examine these rays or bands, moment by moment, from sunrise to sunset, and has found them to vary in intensity with the height or thickness of the atmosphere through which the sun's light has to pass.

Some time ago, Gladstone examined the nature of light which had passed through dilute solutions of nitrate of didymium, and discovered two dark lines in it by spectrum analysis; and Professor Rood, of America, has lately repeated the experiments with a strong solution of considerable thickness of the same substance. He has found that when sunlight or lamplight is transmitted through a thickness of twelve inches of this strong solution, and analyzed by Kirchoff's spectroscope, the spectrum is seen crossed by twelve distinct lines, some of which are very broad and others very fine. D, or the sodium line, is just cut off by one of these, and from this results the singular phenomenon that a sodium flame is invisible through a foot thickness of this liquid, although the liquid is nearly colourless and scarcely at all alters the tint of ordinary white objects viewed through it.

In our last number, we stated that a French commission had examined and commended M. Serrin's newly-invented regulator for electric lights ; since then, M. Serrin has exhibited his electric lamp at the Polytechnic Institution, London, and all agree in stating that the light emitted was perfectly steady and uniform in intensity—a result which has never heretofore been perfectly obtained with an electric lamp, and which was in the highest degree desirable. The following are some particulars of the structure and action of the lamp from a published description of it by M. Serrin ; and those who are acquainted with the mechanism of such

VOL. 11.—NO. V.

lamps will at once perceive that it does not differ from them in many respects. The two carbon electrodes are vertical, the upper or positive one being fixed; the lower one is attached to the armature of an electro-magnet, and is capable of moving up and down vertically within a space of about one-tenth or one-eighth of an inch ; it is supported at the required height by two springs, which are capable of adjustment by means of a screw, and is drawn downwards by the attractive force of the magnet upon the armature when it approaches too near the upper electrode; it requires a weight varying from 150 to 460 grains to depress the armature, according to the degree of tension imparted by the screw to the second spring. The apparatus is very solid and durable.

The development of the marvellous power of the electric induction coil is still progressing, and it is impossible at present to say how much further it will proceed. It began but a few years ago to excite attention, when sparks half an inch in length were obtained by Rhumkorff, in his admirable apparatus, by means of superior insulation and greater length of wire; from that time many investigators have been engaged in extending its power : Mr. Hearder, of Plymouth ; Dr. Callan, of Maynooth ; Messrs. Bentley and Ladd, of London, and others, gradually increased its power of giving sparks to a distance of about five or six inches; and Mr. Ritchie, of Boston, United States, in a large coil which he made for Mr. Gassiott, of London, by winding the enormous quantity of fifty miles of fine wire on his coil in a peculiar manner, obtained sparks about twelve or fourteen inches long; and even this length of spark has been considerably exceeded by Rhumkorff, who has obtained sparks nineteen inches long. Recently, however, at the last conversazione of the Royal Society of London, a very remarkable coil was exhibited by Mr. Siemens, and excited great admiration, which has altogether surpassed previous attainments in this direction. First, we will take the effects said to have been obtained by it, and then briefly describe its construction and peculiarities. On the evening in question, with two elements or cells of Bunsen's battery connected with the primary coil, the two wires of the primary coil being connected parallel, sparks were obtained twelve inches in length, and, with six elements, they were thirteen inchies and a half long; but, by connecting the two primary wires as one continuous wire, the sparks were increased in length to nineteen inches; the electricity then escaped in brilliant flashes of light through the air from many parts of the coil. On the above occasion, the coil was not worked to its full power, in consequence of the batteries being hurriedly prepared, and therefore did not give the masimum length of sparks. On a previous occasion, the following effects were stated to have been obtained :-A single Bunsen's element gave sparks 8:4 inches long; two elements, 15:6 inches; three ditto, 19 inches; four ditto, 20:4 inches ; five ditto, 22 inches; and six ditto, 23.2 inches.

In all cases with this coil, the mechanism for making and breaking contact is worked by a separate battery consisting of Daniell's elements, and the contact at the break is made by a platinum point, dipping into a vessel containing mercury amalgam covered with spirits of wine. The plates of the Bunsen's battery for exciting the coil were about ten inches wide. The iron core of the coil is 37•4 inches long, and 2:36 inches diameter, and consists of varnished straight iron wires 0.05 inch diameter. The outer diameter of the coil is about 8 inches. The primary coil consists of two parallel insulated copper wires 0.1 inch thick, and may be connected either as one wire of the total length, or as a double wire of half the length. The primary coil is surrounded by a cylinder of ebonite, which is thicker at its ends than at its middle, to resist the greater tension of the electricity at those parts. The secondary coil consists of 11,762 yards, or 6-88 statute miles, of insulated copper wire, of 0:006 inch diameter, and is wound upon the ebonite cylinder in 299,198 turns; its total weight is 64 pounds. The great power of the coil depends largely upon the arrangement of the secondary wire, which is as follows :—The space outside the ebonite cylinder is divided into 150 narrow and deep grooves, by means of thin, flat, annular discs of ebonite, which fit closely upon the cylinder; the fine wire was wound into each of these adjacent spaces alternately in opposite directions, until they were all filled, connecting each section of wire at the bottom of the groove with its neighbouring section on one side, and at the top of the groove with its other neighbouring section on the other side, and so on throughout the entire series, so as to form one continuous wire. This separation of the secondary coil into numerous sections by a powerfully insulating material greatly increases the resisting power of the insulation ; the plan also of winding each alternate section in opposite directions is also of great value in a similar aspect. The condenser consists of several discs of paper glued together, and covered with tin-foil, the surface of the two tin-foil coatings being equal to sixteen square feet each ; the condenser of this apparatus does not much affect the length of the spark, but is important to prevent the mercury of the break contact from being violently thrown about. Owing to the peculiar construction of this coil, greater effects are obtained with seven miles of secondary wire than had been previously obtained, in some other coils, with fifty miles; the leading principle of its construction appears to have been, to proportion the amount of resistance to the amount of tension in all its parts.

Mr. Siemens also exhibited a new telegraphic instrument remarkable for rapid transmission of messages through long circuits : it is worked by means of magneto-electric currents, and each signal requires two currents, one positive and one negative, to produce it; the code of signals is that known as “ Morse's alphabet.” Eighty words per minute were transmitted through a resistance equal to 3,000 statute miles of underground wire. It is said that a speed of 400 letters per minute may be accomplished, day and night continuously, by means of this instrument.

M. Becquerell has exhibited to the French Academy of Sciences specimens of metals obtained by electrolysis, accompanied by a memoir describing the methods he adopted to obtain fine specimens of cobalt, nickel, silver, gold, and platinum. The plan he adopts is to decompose concentrated solutions of the respective metals by currents of very feeble intensity, thus avoiding tumultuous deposits, and enabling the molecules to group themselves regularly and firmly ; the intensity of the currents he employs varies with the density of the respective solutions,

Mr. Gore has described, in the Proceedings of the Royal Society, “ two additional kinds of electro-deposited antimony possessing the property of evolving heat : one of them is obtained from a solution of bromide, and the other from a solution of iodide of antimony," and has given “additional information respecting the peculiar heating-antimony obtained from the aqueous terchloride.” The manifestation of heat is greatest with the one from the chloride solution, and least with that from the iodide. An explanation is also suggested of the mode of formation and action of these singular heat-giving substances.

Dr. Frankland has made various experiments on the“ Igniting Point of Coal-gas," and has found that coal-gas cannot, even under the most favourable circumstances, be inflamed at a temperature below that necessary to render iron very perceptibly red-hot by daylight in a well-lighted room, but this is considerably below a red-heat visible in the open air on a dull day; and this high temperature necessary is chiefly due to the presence of olefiant gas and other hydro-carbons in the coal-gas. Explosive mixtures of coal-gas and air may be inflamed by sparks from metal and stone, as from the tools of a workman excavating the ground, &c. Explosive mixtures of the gas of coal-mines and air require a far higher temperature for ignition than similar mixtures of coal-gas and air ; and, therefore, the use of the safety-lamp is far more effectual in the former case than it would be in the latter.

The last ascent of Mr. Glaisher in a balloon, at Wolverhampton, is full of interest : he ascended to the unprecedented height of upwards of six miles, the reading of the barometer being at that height about eight inches; the temperature of the air was exceedingly low, at least thirty-seven degrees below the freezing-point of water ; the readings of the instruments at the very highest point were rendered impossible by Mr. Glaisher having become quite unconscious, and Mr. Coxwell, the aëronaut, nearly so, indicating that an altitude of between five and six miles is nearly the limit of human existence.

Professor Chadbourne, of America, has shown that, if a spoonful of dry powdered ice or granular snow be thrown into a smooth glass vessel nearly filled with water slowly boiling, strong ebullition is produced, the particles of ice or snow acting like particles of iron or sand would under similar circumstances.

A discourse was recently delivered, at the Royal Institution, by Mr. Faraday, “ On Gas Furnaces," and was chiefly devoted to an explanation of the construction and action of the “ Regenerative Gas Furnace" of Mr. W. C. Siemens, of London. This arrangement of heat-generator is rapidly becoming employed for all great furnaces where a very high degree of heat is required, such as in iron puddling, iron-tube welding, glass-making, &c., chiefly in consequence of its economy in enabling the very commonest kind of coal (called “slack”) to be employed instead of a better quality, and with the production of a very much greater degree of heat, --so great, indeed, that on several occasions, when its management has been neglected, the most refractory clay-vessels have been softened and destroyed.

« 이전계속 »