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The photographic news
- Bandzählung
- 7.1863
- Erscheinungsdatum
- 1863
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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. 245, May 15, 1863
- Digitalisat
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Zeitschrift
The photographic news
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Band 7.1863
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- Register Index 619
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Band 7.1863
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THE PHOTOGRAPHIC NEWS. 232 Gritiral Jlotites shows that insufficient heat was employed. Granting, how ever, that further experiments would confirm M. Mitscher- lich’s opinion that the spectral rays belong to the metal in its pure and simple state, another deduction springs from the fact. That is that the solar atmosphere does not contain sufficient oxygen to oxidise all the sodium contained in it, and that all the metals having less affinity for oxygen than sodium are free; it may, moreover, be admitted that if in the solar atmosphere there exist metals combined with electro-negative elements in spite of the presence of free sodium their affinities are inverted at the high temperature of this atmosphere. Moreover, if the rays of certain metals are not observed it is impossible to be quite certain of their absence ; for they may exist in a state of combination like chloride of potassium, which in the presence of some other bodies, as shown above, gives no spectrum. A most inge.nious barometer, for measuring small atmo spheric disturbances, has recently been devised by Dr. Joule. It consists of a large glass carboy connected by a glass tube with a miniature gasometer, formed by inserting a small platinum crucible over a small vessel of water. The crucible is attached to the short end of a finely suspended lever, multiplying its motion six times. When the apparatus was raised two feet the index moved through one inch ; hence he was able in serene weather to observe the effect corresponding to the elevation of less than one inch. The barometer is placed in a building, the slated roof of which affords, without perceptible draught, free communication with the external atmosphere. In this situation it was found that the slightest wind caused the index to oscillate, a gale occasioning oscilla tions of two inches, an increase of pressure being generally observed when the gusts took place. This barometer is un doubtedly very sensitive, and is highly spoken of amongst scientific circles in Manchester. It will however, of course, only show relative pressure, not absolute, as the indications would vary as much, or even more, by an increase or diminu tion of temperature. It would not be difficult we think to compensate it for temperature, and thus to render such a barometer an accurate measure of the height of the atmo sphere as well as of its passing waves. Mr. Sutton, who, as our readers know, has been the strong champion of simply iodized collodion against bromo-iodized collodion, has always insisted as one of the points of its excellence that it required the use of pure chemicals, simple and unsophisticated, the nitrate bath especially consisting only of pure nitrate, of silver and water, without doctoring of any kind. Mr. Matheson insists on the addition of acetate of soda in the bath as a condition of success. As this is a point to which he attaches considerable importance, we will quote his remarks upon the subject:— Best Chemical Condition or Bath.—We have found that for a negative bath to give a film sufficiently sensitive, yet at the same time to develop dense enough for printing at once, and without re-developing or strengthen ing, or whatever it may be termed, a small quantity of alkali—masked, how ever, by a slight excess of some organic acid—is indispensable. To prove this position, let us examine the results we get from the formul for bath and developing solutions which most beginners in photography are taught to use. Let us take the favourite one, which seems to be, pure nitrate of silver and distilled water, with a little iodide of some kind added to it (to prevent the silver eating away the iodide from the film of collodion), and perhaps a little alcohol or ether, or, maybe, an infinitesimal dose of acetic or nitric acid. Practically, what is the result? Why, on developing the pic ture taken with an iodized collodion (which, we repeat, is best for negatives), and a neutral, or simple silver and water bath, it will be found that the picture appears struggling to get through a cloud of all sorts of photographic difficulties, in the shape of fog, veils, haze, streaks, comets, &c., &c., and the picture appears under-exposed. The remedy for this, say some, is a little acid—well, let us try—say, nitric. We try another glass, and what do we get ? If sufficient is added to clear away the previous difficulties, we get another ; for if developed with pyrogallic acid, the picture is certainly free from the previous defects, but the picture vanishes with them, and we only get the extreme high lights, and those so faint as to be totally useless for printing. With the iron developer the matter is very little better, besides the greater length of exposure necessary in the camera. Suppose we had tried a little acetic acid instead, we should find the bath deteriorated in sensitiveness, without getting rid of our enemies. Let us now try the system advised by the writer, starting with a neutral, or plain silver and water bath. To a fifteen-ounce bath, of the strength of thirty-five grains to the ounce, let us add one or two grains of an alkali dissolved in a little distilled wateri after well shaking this with the bath for a minute or two, the bath should be well filtered. After preparing a glass, and giving it the right exposure in the camera, what do we now find on developing ? Positively nothing at al apparently. The film blackens instantaneously under the developer, and there is no picture to be seen, but we do see the character of the deposit i5 totally changed; instead of the previous greyish-leaden hue of the surfas we have, after the picture has been fixed and washed, a deposit of a brownish orange colour, and when held up to the light and looked through, the film a pears of a brownish yellow, inclining in some places to a purple. The bath now evidently requires a little acid of some kind to prevent the spontaneot) blackening of the film ; but as the alkali was added to the bath to remov all traces of free nitric acid, it is evident that nitric acid cannot be used.° any other which would liberate it. We have tried various acids, but fin" none equal to acetic, which, for reasons too numerous to be mentioned her we recommend as being the best. Acetic must be added very sparingly to the bath, just barely sufficient to mask the alkali and to develop clearly T" or three drops arc more than sufficient to neutralize the small portion 01 oxide of silver formed from the alkali. As the strength of acetic acid is very subject to variation in differet samples, and as it is not always possible, or convenient, to get pure cause potash, soda, or other alkalies, it will be found much more certain ifwetie an acetate of any alkali, say acetate of soda (as the most convenient obtained), because here acid and alkali are combined in equivalent proPed tions. To a fifteen-ounce bath add two or three grains of this salt, dissof in half an ounce of distilled water; this will combine with the nitrats,, silver when added to the bath, forming acetate of silver, which readily dn solves therein to the extent of nearly twenty grains to a pint. For thisretitt more than the two or three grains recommended may be added withoij injury, only that the proportion of acid which is to be added in addition " have to be increased in the same ratio, and will be found less manageabff Supposing, then, we have added to a fifteen-ounce bath two grainjus acetate of soda, we shall find, on developing a picture, the same spontanes blackening of the film, provided there was no free nitric acid in the cr?stsa of silver of which the bath was composed, as it very often happens therein trace. Should there have been any free nitric acid in the crystals, imay perhaps be found not necessary to add any more acid, as the nitric acid ling have liberated sufficient acetic acid from the acetate of silver by forper, nitrate of the oxide of silver, and setting acetic acid free. Should, how nce this not be the case, make a solution of a drop of pure nitric acid in ansue s of distilled water; add a drachm or two to the bath, occasionally tryi5 picture, until it develops satisfactorily. . t o It may be thought a paradox to add nitric acid, when we are trytnd secure ourselves against the presence of this very acid ; but it will belthe that, although we could not use it to neutralize oxide of silver formed 0, to addition of alkali to the bath (as it would have been only bringing it DEce its previous condition of a neutral nitrate), yet, in the case of the presnof of an acetate, the effect is quite altered, as was shown by the descripting the action of free nitric acid sometimes found in the bath, due to its " introduced in the crystals of some samples of silver. te- No matter, however, how or by what method we introduce the acetnr gn whether by an alkali to be masked by acetic acid, or by the addition set acetate (which is the mode we recommend), with a portion of its ad"the free by the cautious introduction of a minute quantity of nitric ac"mpic change in the picture is marvellously satisfactory; for now, instead of"rried ture flat, and too faint for printing, we get an intensity which maybecickeo- to opacity if desired, without any “re-developing,” “converting,” "Dations. ing," &c., &c., with all their attendant risks, uncertainties, and vex i The change in the colour of the negative is just as extraordinary—tne rttheit appears, when viewed by reflected light, to show objects in ao” PRACTICAL ADVICE TO AMATEUR PHOTO GRAPHERS ; or, the Direct Negative Process, v. Strengthening Positives. By Henry Matheson, eight years Principal Operator in the Photographic Depart ment, Crystal Palace, Sydenham. London : James How, Successor to G. Knight and Sons. The author of the little work before us is a professional photographer of many years’ standing, his experience, as he informs us, extending “ from the old daguerreotyping times to the present of cartes de visite." It is almost impossible for an experienced practical man to write upon his art without saying something interesting and useful, and Mr. Matheson says much in his book which will well repay perusal. The title of the book scarcely entirely conveys its cha racter, for, whilst it contains much advice for amateurs, it is practically a manual for beginners, commencing with in structions for obtaining collodion positives and proceeding onwards to the production of prints on paper. Incidentally, in the course of his instructions, the author introduces what appears to be the great aim of the work, an argument in favour of simply iodized collodion, and a method of using iron development so as to secure negatives at one operation, as superior to the use of bromo-iodized collodion, and the necessity of using intensifying processes which he conceives it involves. The author’s predilections are very strongly in favour of what he terms the direct negative process, in which bromo- iodized collodions are, he states, “ a delusion and a snare.”
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