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362. —---- ndence, in the .■rest of g that ookthe ult will ich the / of the on with Mudd, Lady attest a ry few, hurston of the erpieces aes of Mayet, as exhit ng well reality 10 trace 1 as to it, inas- thought ihy h> ience it ograpb; ing and ographe graphy change e great hers to eat this graphs, ed with ably as Ils have a print perma- results ixpense, re come ispareni produc j lit fine 1 m. Er i, whies I r, ho* । mply 8 Field, d nance ition of sands 8 luction, i termed. I beauti- ■ of it to ne of a i, by * : plate, e ordi- pictures photo- perfat iss will on the sure to picture illation . The Avgust 15,1862.] THE PHOTOGRAPHIC NEWS. 389 process has been perfected, and a cheap and artistic orna- qsntation of our windows, whether in portraits of our tends, landscapes of familiar scenes, architectural objects, ostatuary, is brought within the means of the many. Mingled with the photographs, and closely packed on “o small floor space allotted for their display, are the Mstruments an d appliances used in the art. In lenses, In which the artist is so greatly dependent, there has great progress made since 1851. Hoss and Dall- meyershow some very fine specimens—marvellous proofs a combination of methematical theory with the skilful development of the practical optician ; Horne and Thorne- waite, veterans in the field of photography ; Murray and Heath, Bland and Co., attest what the English can do as takers of apparatus. All sides show a host of contrivances lhoroughly unintelligible to the uninitiated, but seemingly contrived with great ingenuity for extemporizing a labora- tory, workshop, and dark room, wherever the labours of the Photographer may carry him. One firm shows specimens ofalbumenized paper, an article much in use by the photo- Erapher, and it is said that this firm alone (and it is only Ine of a legion of others) uses for this purpose annually half a million of hen’s eggs. " Class 14 has a high position in the building, and, though Only to be reached by overcoming the labour of a long Staircase, will, we venture to say, well repay the toil of the “ndertaking." • DIREOT COLLODION POSITIVES UPON GLASS. BY DR. SABATIER. • siting preceded typography : painting preceded engrav- 18 and lithography. In photography, writing and paint- 1gdo not even exist. Objects are not copied directly ; we “aye to proceed through the cliche, or negative; and to “ rt ive at the result achieved by the scribe in an instant, the 1008 and delicate operation of printing must be undertaken, "riting, that cursive heliography, will it then become use- 288; or, rather, have we hitherto dreamed of seeking it? I Believed and foresaw the possibility of it, when, a year ago, .published my process for obtaining directly, and in the fourse of a few minutes, direct collodion positives upon glass. . Notwithstanding the modification I have introduced and Indicated in my last communication, this process leaves much 10 be desired, and cannot become popular; but the new im- Provements I have recently made reduces the manipulation 10 much, renders its production so rapid and easy, that the Sast experienced photographer may easily become familiar Jib it, and its adoption will, I hope, afford a pastime and Measure to all who undertake it. My direct positives upon glass were not very visible, and Could only be properly appreciated when viewed as transpa- ^cies. I now make them visible at pleasure, by trans- PArency or by reflection, like photographs upon paper. , “esc two kinds of positives require different manipulations. “hall now describe the method of obtaining them. Direct Dositives by Rejlected Light. This kind of positive, I must first premise, in order to pre- e “t misunderstandings, does not completely respond to the Bgencies of photography. It is in order to excite the im- Ecsvements o f which it is susceptible, that I proceed to ascribe the manipulations by which they can be produced ; an also, because these manipulations, well understood, posit in the comprehension of the production of transparent hen the development of the negative picture is com- a ted in the laboratory, there remains in the collodion film becartain quantity of uncombined iodide of silver, either hasAnse it has not been acted upon by light, or because it aianopbeen sufficiently 80 to be influenced by pyrogallic fori , inding a substance which, in acting upon this iodide, 18 a colour approaching that of a negative, and then wo have the means of producing a collodion positive upon glass, by reflection : for, necessarily, the new colour will be more abundant and more intense where the non-reduced iodide is most abundant; for the diffusion of the iodide in the collo dion film is such, that the new colour necessarily places itself in perfect harmony with that of the negative. Now, in the absence of more suitable materials, which yet remain to be found—pyrogallic acid, which has already given the colour of the negative by acting upon the iodide impressed in the camera—can also furnish another colour by combining with the iodide unacted upon by light, pro vided, that, before putting one into contact with the other, the plate be exposed to diffused light for a few seconds. Doubtless, it is an extraordinary fact, that pyrogallic acid reduces the iodide impressed in the camera, while it also combines with it, when it is impressed by diffused light, which seems to prove that the action of the light is not the same in both cases; but, although extraordinary, the fact is none the less true. These two reactions of pyrogallic acid may also manifest themselves under the influence of other causes quite as mysterious. To be convinced of this, take two test-tubes; pour into the one four or five c. centimetres of a solution of nitrate of silver, and into the other an equal quantity of solution of pyrogallic acid ; the strength of the solutions is unimpor tant ; then, drop three minims (or drops) of pyrogallic acid into the test-tube containing the nitrate of silver, and into the test-tube containing pyrogallic acid pour three drops of the solution of nitrate of silver; in each test-tube a different colour and combination will be evident. The pyrogallic acid poured upon the nitrate of silver does not appear to combine with it immediately ; the liquid remains for a few moments colourless, then the upper stratum commences to blacken. The black descends down the tube, communicating gradually with the lower strata, and after four-and-twenty hours’ repose, a precipitate will be found at the bottom of the tube, exactly similar to the reduced silver of which a negative is composed. The liquid, now become limpid, has only a very light tinge of green. The nitrate of silver poured into the pyrogallic acid behaves quite differently. The liquid mass immediately be comes thick, and of a dull yellow colour; a rusty-coloured precipitate gradually falls to the bottom of the test-tubes, and twenty-four hours after the experiment, the liquid be comes limpid, and assumes the yellow colour it presented at the commencement. The image has all the appearance of the combination which constitutes the positive image. To what is this difference in the mode of acting due ? Is it to the respective quantity of the elements put into con tact, or rather to the manner in which that contact is made? Will it be with the nitrate of silver and the pyrogallic acid as with the letters A and 13, which form a different syllable according as the first of these letters is placed before or after the other? M. l’Abb Despratz, in proving that the nitrate of silver poured upon the iodide of potassium gives rise to an electro-positive current, while iodide of potassium poured upon nitrate of silver gives rise to an electro-negative current, has rendered this hypothesis very probable. What confirms also the fact that the colour of the positive, and that of the negative are due to different combinations, is, that in leaving a transparent positive in a solution of hyposulphite, the positive portion of the picture disappears even before the negative portion is attacked, and that the sulphide of potassium, which lines the positive remains with out influence upon the negative. Pyrogallic acid, which forms two combinations, two dif ferent coioUi’s, and which has already served to develop the negative, serves also to develop the positive, I proceed as follows:— When the negative appears to have attained its highest perfection, I pour off the acid, and wash the plate in rain or distilled water, and drain it with one corner resting on blotting paper. It is next moistened with a solution of nitrate of silver, strength 5 to 6 per cent, in order to render