Class X.]
145
Ross and. Thomson*, of Edinburgh (299, p. 839), arefairly entitled to attentive consideration from their suc-cessful use of the albumenized glass, which they prepareby a process different to that adopted by M. Niepce, itsoriginator, applying the albumen so as to ensure its evendistribution, upon which evenness the success of thepicture is mainly dependent. The pictures in their collec-tion combine, with exceeding delicacy of execution, arichness of colour equal to that of Martens, but surpasshim in the diversity of tints; the collection, besides em-bracing a long range of sepia tints and Vandyke browns,includes a small picture the colour of which is blue , andas this is a hitherto unprecedented result, we are led togive it weight, and will, in another place, describe theprocess by which it is produced. Some details connectedwith the methods adopted by Messrs. Ross and Thomson,and kindly furnished by them, are subjoined.
The process for producing negative Talbotypes , onglass, is as follows:—The whites of two eggs, being aquantity sufficient for coating a plate of glass 12 inchessquare, are placed in a bowl, and cleared from all opaqueparticles; ten drops of a saturated solution of iodide ofpotassium are added for each egg, and two-thirds of awine-glass of water for both,—the whole being thenbeaten up to a light froth and carefully covered up andleft to regain its liquid state. The glass to be coated iswell cleaned with a solution of pure water and soda, orpotass, and rubbed quite dry with a silk rag. The mix-ture is then poured on as evenly as possible, and fasteninga piece of wire to the opposite corners, the excess of albu-men is poured off by turning the plate gently upsidedown ; it is afterwards made to revolve before a clear fire,by a thread of worsted tied to the suspending wire; whenthe albumen begins to crack, the plate should be removedto a greater distance, and there suffered to remain untilequally cracked all over. To render the plate so preparedfit for the camera, it is breathed upon, to give it a degreeof softness and to cause it to absorb as much silver aspossible; it is then dipped (the prepared side undermost)very gently in a bath of nitrate of silver, prepared in theproportion of GO or 70 grains to an ounce of water, theplate being prevented from touching the bottom of thevessel by a piece of bent glass, or metal covered with wax.It is then washed in a large dish of clean water, by re-peated dippings, care being taken to keep the waterrunning in the same direction. The plate is then placedin the camera, and if the picture when taken, is tobe immediately developed, a quantity of acetic acid isadded.
The mode of developing the image is as follows:—aquantity of saturated gallic acid is poured on the plate,and spread evenly with soft cotton-wool, after which,when the picture has well appeared, a small quantity ofgallic acid is mixed with the nitrate of silver solution,and spread over the glass, which gives the developmentstrength, and renders it more rapid. At this stage of theoperation, a solution of hyposulphate of soda (50 grainsto an ounce of water) is poured over the picture, and care-fully spread with clean cotton; the process is then com-pleted by pouring some water from a jug very gently overthe surface.
The negative proof so obtained is transferred to paperby floating the latter on a solution of common salt (5 grainsto an ounce of water) for a space of two minutes; it isthen pinned up to dry and floated on a solution of nitrateof silver (70 grains to an ounce of water) for threeminutes; it is then dried in the dark, and afterwardsplaced with its prepared side to the prepared side of theglass negative, and screwed in the pressure frame with aplate of glass below to ensure its close contact. Thepressure frame should be surrounded with black boardsto cut off the rays of light from the sides. To fix theimpression, it should be first washed in cold water, thenin hyposulphate of soda (100 grains to an ounce of water)for 15 minutes. It is then washed once in cold water,five or six times in boiling water, and finally suffered toremain an entire night in cold water, so as to remove en-tirely the remaining hyposulphate of soda, which would, incourse of time, eat out the picture if allowed to remain.
The photograph thus obtained is afterwards mounted
upon card-board, and pressed on a warm plate of steel, tocommunicate a slight glaze, which may be considered animprovement to its appearance.
The process we have just detailed is good in manypoints, but defective chiefly in one—sensitiveness; everyeffort to increase which has hitherto been attended with usoftening of the albumen. This is a difficulty, but onewhich Messrs. Ross and Thomson will doubtless over-come.
The positives on glass are transferred and fixed in theusual manner (the albumen being mixed with salt insteadof iodide of potassium), with the addition of pure plasterof Paris, which being mixed with the solution is pouredon the face of the picture, and adhering to the albumenin a maimer hermetically seals it, and thus effectuallypreserves it from injury.
This admirable system is, we believe, entirely due toMessrs. Ross and Thomson, whose collection of Tal-botypes amply attests the superiority of their method; andindeed, as is the case of Mr. Bitches (301, p. 840), ofM. Martens, or of any highly-successful photographist, itis but fair to infer that the superiority observable in theirproductions is due to their improvement of the processeswhich they have adopted.
Whether the followers of Talbot will ever obtain a pre-eminence over those of Daguerre , or vice versa, is aquestion for time to solve; at present the two systemsappear in the British Department of the Exhibition to beequally well represented; the followers of each, with fewexceptions, laying claim to some improvement or pecu-liarity of manipulation. For example, in addition to thecases already mentioned may be included those of Mayall(pp. 439, 440), who calls attention to his crayon daguerreo-type, an invention of his own, and Beard (p. 440), whosepatent enamelled process is one of the very few instancesof a patent having been obtained for any improvementconnected with this art. Great as is the satisfaction withwhich we regard the efforts made for perfecting the pro-cesses of Daguerre and Talbot, still greater is that withwhich we observe experimenters divulging the processesthey have adopted; the hitherto all but total avoidance ofpatent enrolment must be considered a distinctive featureof this art, to which fact, doubtless, added to the readydivulging of improvements, is chiefly due the rapidityby whieli up to the present time its progress has beencharacterized. The publication of each new process opensa fresh field of philosophical inquiry, gives to man in-creased physical knowledge, and may work great changesin his moral destinies.
We cannot pass from the subject of photography withoutalluding to a loss recently experienced in the death of itsfounder, M. Daguerre , whilst the Jury were engaged intheir duties, and we feel it due from us not to let hismemory pass unnoticed. In him was lost one of the lightsof the age.
We now proceed to Electric Telegraphs, of which agreat variety are placed in the Exhibition; many of themare remarkable for novelty of construction, and for im-portant improvements. In the section devoted to theirdescription we shall speak of them at some length.
When Oerten, in 1820, linked together the sciences ofelectricity and magnetism, great hopes were entertainedof the application of electro-magnetism to the movementof machines; and as in the Exhibition there are severalarrangements for obtaining motive power in this way, weare far from despairing of its successful application tomechanical motion.*
When Faraday obtained the converse of electro-mag-netism, by induced electricity from magnets in motion,lie originated magneto-electricity, and it is possible thatits successful application to the purposes of the electrictelegraph will supersede the use of galvanic electricity;the experiments which were made before us with themagneto-electric telegraph were satisfactory.
The application of voltaic action, by coating the inferiormetals with the superior, is shown in the Exhibition insome beautiful electrotypes and intaglios; also in a recent