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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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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. 188, April 11, 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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APRIL THE PHOTOGRAPHIC NEWS. [APRIL 11,1862. 172 the pavements of the streets, is likewise due to the presence of this sulphide of iron; the ready decomposition of which ON SU covered by Martius. He ON I LEAR Thour usually be traced . . _ hole, and the streets which mostly suffer in this way are those in which the sewers are imperfect. The same dis colouration is met with in photographic miniatures, in which white lead is one of the colours used. Owing to the annoy ance caused by this, the employment of lead compounds for this purpose is ceasing in great measure; the permanent zinc white taking the place of white lead. As explained above, sulphide of lead in the native state has a metallic lustre ; when formed artificially by the action of sulphuretted hydrogen on a surface of white lead, it takes various shades of slate colour or brown, according to the depth of tarnish, but seldom appearing black. When precipitated from solu tions by hydrosulphuric acid or an alkaline sulphide, it appear as a brown black powder. There are several sulphides of iron, only the most in teresting of which however need be noticed. Protosulphide of iron is prepared on the large scale in several ways. One of the most instructive modes of making it may be met with in most books of chemical experiments. If a poker be heated red hot in the fire, and a roll of sulphur pressed against the hot end, the two will unite and form this sulphide, which being readily fusible, falls in drops, giving an appearance as if the iron were melting. Sulphide of iron is of great value in the laboratory as a source for hydrosulphuric acid. When acted on by dilute sulphuric or hydrochloric acid, it evolves this gas in a state of considerable purity, and is thus of daily employment for chemical pur poses. According to Braconnot, the black mud at the bottom with hydrochloric acid tion of chlorine. Dragon's blood may be detected by the empyreumatic odour which it gives on the application of heat; it also communicates a red colour to alcohol. One of nay alsc beautiful and 4 pa which an twenty-fc the purer into watt and drier is very e: to imitat Naxy p developi prefer it ferable i of photo in order surface r it is in acetic et image, t from the quantity french. But tl sulphate cient ini little oj which t larger a iron bat Very we I hav substitu might < develop proof s place in I ha develop hut whi have ad inake it Disse water; into it strengt he allot parts o taining nitric e The served bottles. The sulpha meetin iron ag The very w may b formation of cinnabar in -uu wau -uino, -e packs them in a box which is fastened to the upper beam of a saw-mill. In 24 to 30 hours, at ordinary temperatures, the most beautiful cinnabar is produced; it is afterwards washed and dried. This method not only has the advantage PHOTOGRAPHIC CHEMICALS: THEIE MAXUFACTURE, ADULTERATTOXS, and Analysis. Sulphides (continued).—Sulphide of lead.—This sulphide is of importance to the photographer in a negative sense, as it is a body to be avoided rather than used; a knowledge of its properties may, however, on that account be very useful. It occurs native in the form of galena, a beautiful mineral of a metallic lustre, and breaking readily into cubes. From its pretty sparkling appearance, it is much used at the pre sent time for ornamenting ladies’ head-dresses, &c. Lead and sulphur have a great affinity for each other, and as there is almost always sulphuretted hydrogen in the atmosphere of large towns, compounds of lead are certain to absorb sulphur and tarnish. This is strikingly seen on the fronts of houses which are painted with white lead. At intervals of dispensing with the labour of trituration, but it likewise prevents the hitherto unexplained passage of the cinnabar into the brown state, which is so liable to take place on the application of heat. The ingredients employed vary slightly, according to different modes of preparation. In general they consist of metallic mercury with Howers of sulphur and potash ley, or a solution of pentasulphide of potassium. I nearly neutralising with ammonia and then adding acetate of soda and ferro-cyanide of potassium. Red-lead may be detected also by heating the substance, being left behind in the form of a fused protoxide. On boiling the cinnabar d it yields chloride of lead with evolu- of drains contains hydrated sulphide of iron, probably formed by the putrefaction of organic substance in contact with the ferric oxide of earthy matter’s, and to this it owes its black colour and peculiar smell. Hence when exposed to the air it loses its odour and colour, and afterwards resembles ordi nary vegetable mould. With acids it evolves abundance of sulphuretted hydrogen. The black colour of the soil io cesspools, pits, ponds, and morasses, and of the earth under Another sulphide of iron which possesses some interest is j the bisulphide. This, from its yellow colour, has been fre quently mistaken for gold; and we have even heard of con siderable sums of money being sunk in mining work, when a very slight knowledge of chemistry would have shown the managers that the only yellow body they had a chance of getting was iron pyrites, as this sulphide is called. The distinctions between this mineral and gold are numerous, and of ready application. In the first place, a touch with a penknife shows that gold scales are soft and easily indented, whereas iron pyrites is hard and brittle. Again, if the two are sprinkled on a red hot shovel, the gold will be unaltered,' whilst the sulphide of iron forms sulphurous acid, easily recognised by its powerful odour. If nitric acid be poured! over gold, no action takes place ; but if the yellow body be iron pyrites, a strong action, with evolution of red fumes, is at once produced, Gold also is about four times as heavy, bulk for bulk, as iron pyrites; so that to a person with very! slight chemical knowledge, the mistaking of the one for the other would be simply impossible. Sulphide of Mercury, or Cinnabar, is largely used as a pigment; it is one of those valuable colours which is un affected by a sulphuretted atmosphere, being already satu rated with sulphur. Cinnabar is also a very frequent ore of mercury. It is of a very beautiful red colour, the shade varying from deep carmine to yellowish red, according to the mode of preparation. When gently heated over a lamp it becomes brownish ; at 250° C., quite brown, and at a higher temperature black ; but if the heat has not bee# strong enough to cause it to volatilise, it recovers its fine scarlet colour on cooling. When strongly heated in the air it burns with a blue flame, yielding sulphurous acid and metallic mercury. Cinnabar is frequently adulterated with brick-dust, oxide of iron, red-lead, and dragon’s blood. Brick-dust may be detected by heating the cinnabar in an iron spoon, the sulphide of mercury going off whilst the brick-dust is left behind. Oxide of iron may be detected in I the same way ; or it may be dissolved out by boiling hydro- chloric acid, and then precipitated in the filtered liquid by | addition of ammonia, or converted into prussian blue by | along a street coloured in this way, there is occasionally an appearance as if a gigantic brush dipped in mud had been dabbed over the. painted surface. This discolouration may d to the presence of a neighbouring gully the most curious modes of formation of cinnabar is that dis- ; places the ingredients for the I bottles closed with corks, and | or chair, as the drained nitrate should not be encouraged to flow over the plate again, and if stood, as it often is, upon the ground, leaning up against the camera stand, it is very liable to be knocked over, a fate which also not unfrequently happens to the focussing-screen, when this latter is separate from the camera. The trays should, of course, be of a proper form to hold the plate-slide in a nearly vertical posi tion. The portable tripod stand for field use is admirably suited to its work, and it is difficult to imagine any great improve ment being made upon it. Care should be taken to select a triangle top suitable in size to the camera it has to sup port, as, if the former be too small, it is difficult to secure the perfect firmness of the instrument. As this triangle cannot conveniently be made to hold a spirit level, it is very advisable, for the reasons given above, if the photographer does not use a camera with a swing back, to carry in the pocket a small circular spirit level, and to place it upon the top of the stand before screwing on the camera, or upon the camera itself when fixed, to enable it to be adjusted quite level before taking the picture. The fall of the country is very apt to deceive the eye. Attention to this is more particularly necessary when working with a binocular camera. (To be continued.) . * 1 1 sulphide is the chief cause of the presence of sulphuretted hydrogen I solution in the atmosphere.
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