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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 206, August 15, 1862
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Zeitschrift
The photographic news
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Band 6.1862
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- Register Index 619
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Band 6.1862
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392 THE PHOTOGRAPHIC NEWS. [August 15,1862. in order to sooth him in his desolate condition ; Nitric acid follows her example, whereby they form a new and compact trio—the nitrate of the oxide of sodium; but the oxide of sodium is denominated soda, therefore the name of this new compound is generally called nitrate of soda; that of the other new compound is chloride of silver. This decomposition takes place as soon as contact is effected, and is, therefore, almost instantaneous. But observe well the difference in one of the new compounds ; it is in soluble in water, and is therefore precipitated, or falls to the bottom of the vial. The supernatant liquid is the water holding in solution the nitrate of soda, which can now be decanted from the residue; after this we can drive off the water from the nitrate of soda by boiling, when we shall have the nitrate of soda alone, tasting and acting very much like saltpetre. The residue, after decantation, we will wash several times, pouring off the water at each time after the white precipitate has settled. Now take two tea cups and pour into the bottom of either half of this white chloride; leave one cup in the dark room: I will take the other into the light, in fact, allow the sun.to shine upon it; you observe how quickly the colour is changing into a beautiful violet; the colour, however, is only on the sur face ; for by stirring the precipitate you perceive it is still white beneath. This change of colour has been effected by the light, and it is in proportion to the intensity of the light; and where the light is obstructed the change is not produced; so that if I were to place a ten-cent piece on a portion of the chloride before exposition to the light, the chloride beneath the coin would remnain white. Let us now return to the dark room, and see if the other half has changed in the meanwhile. No alteration is visible. And none will take place, as we know by experience, if light is excluded. But what you have seen is not all the change that has been effected in the chloride ; for if we convert all the white chloride into the violet chloride, by exposing it some time to the sun, and by continually stirring it all the while, it will undergo another very important change, as I will show you. I have here a solution of another salt called hyposulphite of soda; in this solution the white chloride is quite soluble, so that now not a single particle is visible ; on the other hand, the violet chloride is insoluble in a similar solution in this other vessel. On these two changes, produced by light, depends, in a great measure, the science of photography ; the light produces colour according to its intensity, ana renders this colour insoluble in the same proportion. Repeat these experiments at home until you are quite ex pert in their manipulation. Your next lesson I will give you in about two weeks from now. PHOTOGRAPHIC STUDIES. BY DB. SCHNAUSS. Examination of Various Formula. Wb know that the collodion and the silver bath must con tain a slight excess of acid, or of the element iodine which supplies the acid. M. Gaudin recommends chloric acid for acidifying the silver bath; but, in fact, this acid has the instability and volatility of those heretofore employed for the same purpose, namely nitric and acetic acid. Doubtless we should add to the silver bath only an acid whose salts are soluble in water, for upon adding an acid which forms an insoluble combination with silver, we set at liberty an equivalent of nitric acid. In this particular, chloric acid, Cl 0s, must not be confounded with hydrochloric acid, Cl H, which produces a precipitate of chloride of silver in the bath it is well suited for this purpose, for all its salts are very soluble in water. But it is different with regard to its instability, for chloric acid and its salts form some of the most unstable chemical combinations known. Strong * Continued from p. 380. friction, or the presence of an incandescent body, is sufi- cient to decompose the chlorates, and cause a terrible exple sion. Chlorate of pottassa, one of the most familiar salts ot this acid, is used in the manufacture of “ lucifer" matches. Chloric acid itself is very easily decomposed into chloric acid and oxygen. If a piece of paper be moistened with the concentrated acid, it ignites spontaneously on drying. The facility with which chloric acid gives up its oxygen greatly surpasses that which characterizes nitric acid. In this respect, the employment of the new acidifier will not be an improvement. But we perceive from this example, that a greater or lesser instability in these bodies, which are added to the silver bath in very small quantities, must not be regarded as important, for the action of chloric acid is the same as that of acetic acid or of free iodine. For those of our readers who desire to repeat the experiment, we give the preparation of chlorate of baryta (which is not nearly so dear as stated by M. Gaudin), and of chloric acid. Chlorate of baryta is prepared by dissolving parts of crystallized carbonate of soda in 24 parts of boiling water. As the carbonic acid is given off, a large vessel must be em ployed for making the solution in, 6 parts of chlorate of potassa are dissolved in IC parts of boiling water, and added to the solution of soda, well stirred, and left to subside; tartar is deposited, and chlorate of soda remains in solution, which is filtered, evaporated, and 14 parts dissolved in 27 parts of cold water. On the other hand, 19 parts of vinio acid are dissolved in 19 parts of cold water, and the sola tion added to the solution of chlorate of soda, and also double its volume of alcoholized spirits of wine is added. After 24 hours a precipitate is deposited, and the liquid, which is a dilute solution of chloric acid, is filtered. It 13 then saturated with carbonate of baryta, and filtered. The filtered liquid contains chlorate of baryta; we then add to it, cautiously, some diluted sulphuric acid, until a precipi tate of sulphate of baryta is formed. The filtered liquid is chloric acid.—Le Moniteur de la Photographic. (To be continued.) THE STEREOGRAPH AND THE STEREOSCOPE. The stereograph, as its name implies, is a solid picture, orA picture whose different parts retain their distances apart in space proportionately to those in the objects of which it is * picture. Such a picture naturally can never be printed, because it then would be on the same plane, and hence nol solid ; but it can be produced by two pictures of the sav) objects, these pictures being on the same plane, and endow with the requisite conditions. A combination of two su) pictures, mounted side by side, receives the appellation 0 that which they produce—the stereograph. The conditions thus required are, in the first place t regular difference in the distances between the correspondis points on the two photographs, or pictures, increasing 2 decreasing according to a certain law from the front objsie to those in the back ground; secondly, that, theoretics the maximum distance shall not be less* than that betvd the centres of the two eyes, whose average is about two inc and a half, nor the maximum greater than the sum of 1 ' distance between the centres of the two eyes and twice tangent of the parallactic angle to be described hereatto! and, thirdly, that an equal number of objects shall be Co tained in either photograph or picture. . , on The pictures of near objects in a landscape projected the retina of either eye, that is, as seen by the two eyes Sne rately and independently, possess, when mounted on is, same] cardboard side by side, the above conditions: tna the if the picture, as seen by the right eye, bo mounted onnce right side, and the other on the left side, then the dis de between the corresponding points of the two pictures * Practically, these maxima and minima distances admit °t 1 f onside (d i range of variability, arising from the expansive capability of 1 may so express myself; under dimicult conditions. Aug —— crease f gmaphs, villik The Mir of betweer ditions of diffe since tl scarcely foregrot The verging object; which । optical superve graphic cease to an obje increasi apart o graphs can be < effect; ; tical st< five as I greets, devoid 1 with su graphs For ins cular v which t one casi apart, 1 observa in both the pic buildin the reli a fac-si fact, a i relief, f thoroug As a human from th quire a tance f distanc if tai ne and 01 have th Paralla followil Bistan fee i 1 12 2 2] 3 31 4 4 5 5, 6 9 • Thl them sc
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