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The photographic news
- Bandzählung
- 6.1862
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- 1862
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 215, October 17, 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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52. meats re are must s our as to to be irtistic photo ¬ clean i time e been are; & st, aw t with of the i, they iy the words ailing bution iation ficent, ice in in im- 13. luable from which pared, oluble .rm of to free The^ iencel lit bf hould it to ion of ter, be : even sional which e and »wder, acids, huri, Yected m, fot i cod- takes twee 11 lphate ■> pro- comes varyta r any irmed ba^ It is when <1 for ution iso to October 17, 1862.] THE PHOTOGRAPHIC NEWS. 497 Lime is the oxide of the metal calcium. It is termed 'Icicle lime when free from water, and caustic lime when it contains no carbonic acid. It is prepared by heating the Carbonate to redness. On a small scale, and if a pure re- eult is desired, artificially prepared carbonate of lime should be used. This is packed in a crucible, heated to redness, then allowed to cool, moistened with water, and again heated for some time, to redness ; by this means the last Baces of carbonic acid arc removed, being carried off by (he steam. Lime on the large scale is made by ignit- Ing common lime stone (a native carbonate of lime) in kilns. When the lime-stone contains clay, the silica of the clay unites with some of the lime, forming a half fused Compound, which prevents the mass from evolving heat "hen wetted with water. This is technically called “ dead burnt" lime. Pure carbonate of lime, such as Carrara harble, does not become dead burnt, even if submitted to the highest attainable artificial heat. Pure lime is white, oft, and easily pulverised. It is infusable at any attainable tmperature, and on this account has been employed by the ”rench chemists as a lining for their oxyhydrogen furnaces, ke, When strongly heated, it emits a brilliant white light, "hich is so intense as to be employed for illuminating pur- Poses, being known as the lime light. The ignited jet of Combined oxygen and hydrogen gases, is used in this case 4s a source of heat. When a lump of quick lime is moist- kned with half its weight of water, this is at first absorbed by capillary attraction, into the pores which have been left 1,1 its substance by the escape of carbonic acid. The air Sontained in the pores is thereupon driven out with a kind of '‘Using noise, and in a few minutes combination between the Water and the lime takes place, with evolution of great heat, ‘he temperature sometimes rising high enough to inflame gun- Powder, sulphur, or wood. The purer the lime the more "pid and intense is this heating. This phenomenon takes Place even when ice is mixed with lime, and, therefore, can- kot be explained by the passage of the water from the liquid .o the solid state. The steam, which rises during the slak- tg, carries with it a considerable quantity of lime. When J>e phenomenon of slaking takes place in the dark a bright ahtis observed. The result obtained in these cases is a anbination of the oxide of calcium with water in equal •oms, known as hydrate of lime. This hydrate, when I Lcetate of Liai-yta.—In cases where a sulphate of a base I s required to be decomposed, and a weak organic acid substi- I tiled for the powerful mineral acid, chemists make use of ptate of baryta. For instance, in the preparation of acetate •f the protoxide of iron, for developing purposes, the best plan is to prepare it by means of double decomposition stween acetate of baryta and sulphate of iron ; upon filtering ofthe insoluble sulphate of baryta which will be precipi- uted, the acetate of iron is left in solution. Acetate of | baryta is very easily prepared. Carbonate of baryta, or ®«stic baryta is mixed with a slight excess of acetic acid, nd the whole evaporated to dryness over a water bath. The dry mass is then digested with hot water, and the iquid filtered from insoluble portions. The solution, which fill contain the acetate of baryta, must then be evaporated I again until it shows signs of crystallizing, when the heat 8 to be removed and the liquid left to cool. The salt teparates in the form of flat foursided bevelled prisms, con- kaining only one atom of water of crystallization, they foresee in the air, but retain their form. They have a Pungent odour, and produce a slight alkaline reaction with festpaper. They dissolve in about an equal weight of cold Tater, but are scarcely more soluble in boiling water. Alcohol dissolves the salt but very sparingly. The remaining baryta salts are of very limited interest, ’nd do not require further description in this place. We I therefore pass on to a much more important class of salts, I {hose of lime. Unlike baryta, this earth in its caustic state I »very common, and well known to all our readers. We I lnay, however, give a few of the chemical properties of lime, I vhich are not so well known as its physical qualities. formed by slaking quick lime, is a fine white powder, of an alkaline taste and reaction; it readily absorbs carbonic acid from the air, and becomes converted into carbonate of lime. It dissolves in water to a small extent, but is much less soluble than baryta. In order to prepare lime water for chemical or other purposes, it is advisable to wash the slaked lime once or twice with distilled water, in order to remove the alkalies, potash, and soda, which ordinary lime always contains. The best plan is to proceed as follows :— Place a small quantity of good slaked lime in a bottle, and fill up with water ; allow it to stand for some hours in a cool place, shaking it occasionally during the time ; then allow the excess of lime to settle, and pour away the pure supernatant liquid. Repeat the opera tion with a fresh quantity of distilled water, and then fill up the bottle a third time with pure water; and after allow ing it to digest, in the cola, with frequent agitation, on the residuary lime for a day or two, filter the liquid quickly, and with as little exposure to the air as possible, into a well stoppered bottle, and preserve it in a cool place for use. We have specified the necessity for keeping the liquids cool in these operations, for the following reason :— Lime dissolves in 778 parts of water at the ordinary tempe- rature, but requires 1,280 parts of boiling water for solution. Hence, lime water, saturated at the ordinary temperature, deposits, when heated to the boiling point, a considerable quantity of hydrate of lime, in small crystals. The mixtures known as milk of lime and cream of lime are prepared by stirring up slaked lime and water to the requisite thickness. They consist of mechanical mixtures of hydrate of lime and limo water. PHOTOGRAPHIC MANIPULATION. VARIOUS HINTS. BY J. C. LEAKE, ESQ.* When I undertook to provide a paper for this evening, I had no doubt but that I should be able to persuade some of our friends to come forward and place at your disposal, a paper on some subject of a far more novel and interesting character than I can hope to produce. In the absence how ever, of anything else, and rather than the meeting should go empty away, I will endeavour to make a few remarks, in the hope of raising a discussion which may elicit some useful information from those gentlemen present who are so well qualified to give it. It has been said of photographers, and truly, that they are in most cases ignorant of the theories of their art. That this is so, is a fact much to be regretted. Yet, let a man be ever so good a theorist, he will in all probability be in the habit of doing a number of odd things from fancy, and if asked why he did so and so, his reply would be, “ I fancy it is better,” but can give no reason for thinking so. This being my unfortunate condition, I propose stringing together a few of my photographic whimsies, and recounting them to you, if you will kindly listen for a quarter of an hour. Beginning with plates. I have a prejudice against every thing but the best polished plate glass. I have tried sheet and crown of almost every description, and in all cases have failed to produce satisfactory results. In fact I believe it to be impossible to produce as much fine and delicate detail upon either of the two last named varieties as upon the former. If, after development, a picture upon a piece of sheet glass be examined, it will be found that a film of re duced silver is deposited between the collodion and the glass. This being the case it is evident that some reducing action is set up, and that this is independent of the develop ment, may be proved by taking a piece of sheet glass, ex citing as usual, and after allowing it to remain in that condition a few minutes, fixing it, without development. * Read before the South London Photographic Society, on Thursday, October 0,1862.
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