HAVING examined carefully the plate of glass, and removed from its surface any adhering fibre or dust, take it in the left hand, holding it with the forefinger and thumb by the upper left-hand corner, and with the bottle of iodized collodion in the other hand, pour from the bottle on to the glass, towards the upper right-hand corner, such a quantity of the solution as will run in a body freely.
Whilst pouring the iodized collodion on to the glass, tilt the glass slightly towards the upper right-hand corner, and when this is reached, incline the glass to the upper left-hand corner, but not touching it, to avoid coming in contact with the thumb of the left hand; this corner passed, run the iodized collodion down towards the lower left-hand corner, and finally incline the glass to the lower right-hand corner, at the same time holding the glass upright over the neck of the bottle (which should be retained in the right hand whilst the operation is going on), to allow the superfluous collodion to drain off into the bottle; during the time it is draining, move the plate vertically backwards and forwards over the neck of the bottle, to prevent the furrowed appearance the film is likely to assume if allowed to drain quietly to the lower right-hand corner.
To perform the above operation with certainty, requires a steady hand, and some little practice. After the glass has drained for a few seconds, and the collodion has ceased running from the plate, it should be immersed in the exciting bath; from five to twenty seconds may elapse between the two operations; if the drying is prolonged, the sensibility and evenness of the coating are injured, and the iodide of silver is liable to be thrown out from the film on to its surface.
Very often, in dry, hot weather, the plate will require to be immersed in the exciting bath directly the film has set; if the plate has been allowed to dry too much, the iodide from the upper part of the plate will most likely be thrown out on to the surface of the film, and be washed away by the liquid in the exciting bath. Care should be taken not to breathe upon the surface of the glass during the operation of pouring on the iodized collodion.
OXIDE OF SILVER.
Sym: AG + O.
Eq. 116. Silver 108 + Oxygen 8
Oxide of silver can be obtained from a solution of nitrate of silver, by the addition of a solution of pure potassa, or soda; oxide of silver is set free and falls as an insoluble brown powder; it should be repeatedly washed to remove all traces of the excess of potassa, or soda,and the nitrate of the alkali formed. After washing, it should be thrown upon a clean linen filter to drain, and afterwards dried; or it can be preserved in a moist state in a wide-mouthed bottle.
CHLORIDE OF SILVER.
Sym: AG + C.
Eq. 144. Silver 108 + Chlorine 36
Chloride of silver is most conveniently formed by the addition of a solution of common salt, (chloride of sodium,) to a solution of nitrate of silver. It falls readily as a white precipitate, and should be repeatedly washed, to free it from the excess of common salt, and the nitrate of soda formed during the process. After washing, it may be collected on a linen filter, and subjected to pressure to free it from moisture, and then dried, or it may be preserved in a moist state. It is soluble in ammonia, hyposulphite of soda, iodide and cyanide of potassium.
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