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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- 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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- Seite 1-72 fehlen in der Vorlage. Vorlagebedingter Textverlust.
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- Bandzählung
- No. 211, September 19, 1862
- Digitalisat
- SLUB Dresden
- Strukturtyp
- Ausgabe
- Parlamentsperiode
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- Wahlperiode
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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
Band 6.1862
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446 THE PHOTOGRAPHIC NEWS. [September 19,1862. This difficulty was subsequently met by the use of a green formed of the oxide of chromium, which resisted the action of chemical re-agents. A geometrical pattern in this colour was printed first all over the paper, and the value, denomi nation, &c., of the note subsequently printed upon that in the usual way with black ink. This was an effectual check to ordinary photographic imitation, but it would be little or no check to the photolithographer, whose art would furnish him with means of evading this difficulty. A variety of means might be suggested of making the imitation difficult, but they would require more consideration than we can now give to the subject. We may remark, before concluding, for the informa tion of those of our readers who may be tempted to amuse themselves with experiments in this direction, that the pastime is a dangerous one; as the attempt to copy one of these notes by any process whatever, and for any purpose, is a felony, the consequences of which might be awkward. Stientifir Gossip, TO PURIFY WATER. Pubs water is as essential for the well-being of the photo graph as for the health of the operator, and a systematic perseverance in the employment of an impure source of this liquid will be attended in cither case with the most Serious consequences. The mortality of a town is, in the majority of cases, in proportion to the amount of impurity contained in the water with which it is supplied ; and those who are engaged in photographic printing on a large scale can speak from experience as to the parallel holding good, in a re markable degree, in the case of photographs. Of all the multifarious impurities which are liable to contaminate water, those which come under the class “ organic ” are by far the worst. These act not so much by what they them selves are capable of doing, as by the evil example they may be said to set other bodies with which they are brought in contact, acting, in this respect, after the manner of a ferment, and inducing a decomposition amongst a set of otherwise peaceably disposed atoms, of which no one can tell the end. Hence extremely minute quantities of such matter are capable of producing very extensive mischief. We have so often insisted in these pages on the paramount importance of pure water in all the operations of photo graphy, that it is with no little pleasure we' now draw attention to a plan, by which this necessary freedom from contamination can be secured by anyone, at a mere nominal expense either of money or trouble. The method is due to Mr. H. B. Condy, and consists in the addition of a solution of an alkaline permanganate to the impure liquid, when the organic matter will be rapidly destroyed. The process is as elegant as it is effectual. By the peculiar chemical properties of the permanganic acid it is capable, when em ployed in appropriate combination, of not only burning up every trace of organic matter in a water as perfectly as if it had passed through a furnace, but it also removes many of the mineral constituents which are sometimes almost as objectionable. An experiment of Mr. Condy’s shows this in a striking manner. He made a saturated solution of oxide of lead, by shaking common white lead in distilled water, and filtering; this, on being tested with hydrosul phuric acid, gave the well known reaction of lead—a black precipitate. Four ounces of this liquid were then taken, and to it were added a few drops of a very weak solution of permanganate of lime. Upon standing for half an hour, the pink colour had disappeared; and when filtered off from the precipitated peroxide of lead and binoxide of manga nese, there was only a brown tint communicated to it on testing with hydrosulphuric acid, A little more permanga nate of lime was added, and the liquid allowed to stand for some hours, when, upon filtering again, not a trace of lead was found in solution. This is a very remarkable experi ment, inasmuch as lead is a most difficult impurity to remove from water, whilst it is the most poisonous of ordi nary metallic contaminations. Water containing iron 111 solution can also be purified in the same manner, so as to render it fit for use in dyeing and other industrial purposes; but the chief use of the permanganates as purifying agents is when organic impurities are to be removed. Hitherto no methods of purifying water can be considered of much efficacy. Filters remove suspended impurities only; ebulli tion merely destroys the vitality of animal and vegetable impurities, and precipitates carbonate of lime; alum intro duces, in most cases, more than it removes; alkaline carbonates, lime, &c., merely touch some of the organic impurities ; whilst even distillation itself, as ordinarily con ducted, leaves much of the original organic impurity still in the water, whilst it deprives it of the dissolved gases which render it fresh and sparkling as a beverage. Of ah purifying agents, filtration through animal charcoal has hitherto been looked upon as the best; but this is only partially effectual, and is tedious and somewhat expensive. Nothing that we are acquainted with at all comes up to an alkaline permanganate (either of lime or potash) in value and perfection of result, and we consider that Mr. Condy, in drawing attention to this simple and ingenious method, deserves the thanks of all practical photographers. The rationale of the process is easy to understand. Permanganic acid consists of the metal manganese united with a large excess of oxygen. This has been joined to it by powerful chemical methods, and the affinities between the metal and metalloid are sufficiently feeble to cause the oxygen to fly off on the slightest opportunity being offered. Pure water being incapable, under ordinary circumstances, of taking up more oxygen, will dissolve a permanganate unchanged; but if organic matter be present, the case is different. This, no matter how complicated its composition, invariably consists of the elements hydrogen and carbon, in conjunc tion, sometimes, with nitrogen, sulphur, &c. Now all these are substances greedy of oxygen, and exercising, in con sequence, a powerful reducing action upon the highly oxygenized manganese compound, the carbon becoming acid, the hydrogen water, the other elements are burnt into perfectly harmless compounds, whilst the manganese is reduced to the state of binoxide, which falls down as a brown insoluble powder. When absolutely pure water is required for some special scientific object, it can be readily procured by mixing it with an excess of permanganate of potash, and distilling it once. This we have verified ourselves, and can vouch for the extreme purity of the product. For all ordinary pur poses distillation would not be required, and in this case the cost of applying the permanganate process on a large scale is very trifling. The quantity of permanganate necessary to purify 10,000 gallons of water would be con tained in one gallon of Condy’s fluid, the price of which is only 10s. ; at this rate 200 gallons, or one ton of water, could be purified at an outlay of 2}d. On a practical scale, Mr. Condy recommends a wine-glassful of solution of per manganate of potash to be poured into a hogshead of offensive drinking water, and mixed up with a stick. Generally this quantity will render it as sweet as fresh water; but should it be very impure, half a wine-glassful more may be added. So long as organic matter remains, which is known by the pink colour of the liquid gradually vanishing, add the fluid. If too much has been used, it need occasion no uneasiness, for it is merely necessary to continue stirring for a short time with a stick, or, on a small scale, to filter it through blotting paper, for the excess of permanganate to be decomposed. The precipitated per oxide of manganese must be left to subside, and the clear liquid may then be poured off. f One great advantage in employing permanganate o potash as a purifying agent is, that any excess of me ta which may be present, either by addition of too much 0 the pink liquid, or by not separating the precipitated per-
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