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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
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- http://digital.slub-dresden.de/id1780948042-18620000
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- Bandzählung
- No. 202, Juny 18, 1862
- Digitalisat
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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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July 18,1862.] THE PHOTOGRAPHIC NEWS. 339 tizing the paper totes the dark colouring matter in the picture. More recently we are indebted for an important addition to our knowledge of the printing process to Mr. W. T. Mabley, "'ho has, through the medium of the Manchester Photo- graphic Society, communicated a series of quantitative results, which indicate clearly the direction in which economy may be practised. Irrespective of the labours of these gentlemen, I have for per cent, only of the silver originally employed for sensi- r is fixed in an insoluble form, and consti- Kmc time past, at intervals of leisure, been engaged in investigating the more prominent circumstances connected "iththe employment of silver and gold in photography, And although my results corroborate in the main the con- Slnsions lately arrived at by Mr. Mabley, there are points of difference, chiefly attributable to variations in manipulation, Fhich appear to me sufficiently marked to justify my sub- fitting them in the character of supplementary data. The operations of the photographic establishment of the 'I ar Department, of which to some extent I have the super- lsion, include of necessity the reproduction of a great number of impressions from plates, illustrating important Achievements in artillery practice, construction, and the means of defence; the printing branch at Woolwich is saried out therefore upon a tolerably extensive scale, and Nnmes the character of a manufacturing department. 1 ring the ordinary course of working, I have frequently Gyailed myself of opportunities of ascertaining and con- rolling the quantities of silver, gold, and other salts ex- Pended upon a known amount of photographic work, and ons results have throughout demonstrated the importance of Aserving a strict watchfulness in regard to precipitating wdcollecting the silver from the numerous waste solutions Ich. rapidly accumulate during a busy season of photo- nephic printing. In practising the system of recovery, to th I shall presently refer, we have been enabled to return nthe photographic laboratory many pounds weight of a irate of silver, made from the metal reduced from the Noride and sulphide of silver, which are separately for- Tded to us in the shape of residues. oA1 arge earthenware jar is provided, in which the whole MIL nitrate washings are collected, and therein precipitated 6 Common salt, the chloride of silver being allowed to ofPide during the night, the supernatant liquid is poured qnoen the morning to prepare the jar for the reception of te Ir day's produce. The hyposulphite solutions, and vitghausted toning baths arc mixed together, and treated tie hepar sulphuris ” (crude sulphide of potassium), when pleteplall proportion of gold contained in them will be com- 6 NeX, precipitated along with the sulphide of silver, will litre" Ied with it when fused with carbonate of soda and Ml and may be ultimately recovered on redissolving the "nitr ump, of metal in nitric acid. As a general rule the Propots Washings ” will Do found to yield by far the larger Mel/ 1011 of the silver, usually more than three times as chloriametal being procured in the state of precipitated Mm as that recovered from the fixing solutions in the • WitL sulphide of silver. nthesergard to the details of the printingprocess adopted Paper emxperiments, it may be stated that the albumenized lnakere Ployed was Spencer’s best quality, bearing the • he full dame " ‘B. F. K. Rives, 1862,” in the watermark; ndicatincd sheet measured 17} by 22, inches, and, as an ot substance, weighed from 335 to 345 grains. step of these commercial undertakings. There is small chance, however, of these nicely calculated results being announced in the columns of our scientific journals, and thus it happens that but few details have been published respecting the exact proportion of silver which may be economically recovered during the production of the ordi nary proofs upon albumenized paper. MM. Girard and Davanne were probably the first to show how small an amount of silver remains actually in the finished print; their analytical results led them to conclude that about five Quarter sheets of this paper were successively floated upon a 70-grain solution of nitrate of silver for five minutes, lifted up and suspended for the same time over another dish to drain, the droppings being returned to the bulk of the solu tion. The sheets of sensitized paper were used in the pres sure frame under negatives having a fair distribution of light and shade; the pictures were then washed in throe changes of common water, about a gallon in all being em ployed for twenty proofs, equivalent to five whole sheets of paper; they were toned in an alkaline gold bath, contain ing four grains of the chloride of gold, with excess of car bonate of soda; washed once or twice, and fixed in a solu tion of hyposulphite of soda, containing four ounces of the crystals to a pint of water. I append the results indicated as the mean of several ex periments, made with ordinary care, and with the object of observing the amount of silver which it would be practically possible to recover in the shape of reduced metal, or as valu able silver compounds. The numbers arc based upon the consumption of five sheets of paper. Diminution in bulk and strength of the nitrate of silver bath ... 240 grains Recovered from water used to rinse the dishes—chloride of silver... 10 „ The nitrate washings gave of— Chloride of silver 121 grains The fixing solution gave of— Metallic silver ... ... ... 27 grains Metallic gold ... •5 „ Total amount of silver recovered equal to nitrate 197 „ Unavoidable consumption and loss by difference 43 „ Equivalent to 17'92 per cent, of the silver employed. Other experiments made upon ten and fifteen sheets of paper respectively, furnished results in close accordance with the above. In the latter of these a small bulk of nitrate of silver solution was employed, with a view to ascertain more particularly the degree of exhaustion, or diminution in strength suffered by the 70-grain bath. It had lost in measure nearly six and a half ounces, and had become re duced in strength to a 57-grain solution of nitrate of silver. The amount of silver taken up by the sheet last immersed must therefore have been considerably below the 48 or 50 grains which I found to be usually abstracted from a 70- grain bath. As a general summary of these analytical and quantita tive experiments, it may be stated that the preparation of a full sized sheet of albumenized paper necessitates the em ployment of 50 grains of nitrate of silver, which at the rate of four shillings per ounce troy costs four pence ; of this amount, however, 10 grains only need bo actually expended, or one pennyworth of silver per sheet, since the remaining 40 grains, or its equivalent in metal, or silver compounds, are recoverable from the waste solutions and other products obtained in the course of these operations. The value of the chloride of gold expended in the process of toning the prints amounts likewise to one penny per sheet; whilst the whole of the remaining chemicals, viz. : the hyposulphite and car bonate of soda, common salt, hepar sulphuris, and kaolin, all taken together, fall within the limits of an extra half penny. FORMIC ACID IN THE NEGATIVE DEVELOPER. We have more than once recently called the attention of our readers to the great advantages claimed by many first-class photographers, for the use of formic acid in the iron deve loper. We have pleasure in calling attention to a formula, communicated by Mr. Henry Claudet, in which this acid is used with the pyro developer, and by which, it appears, very rapid and fine results are obtained. Our readers may remember a reference in our last to two very excellent groups, by M. Claudet, consisting of the photographic
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