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away the distilled water, pour into the silvering vessel Solution A, and then add slowly B, stirring well together meanwhile with a glass rod ; directly the solution begins to change colour gently immerse one edge of the mirror, and then the whole surface, taking care that no air bubbles or specks of any kind remain between the surface of the mirror and the solution. Gently agitate the silvering vessel, so that the solution may be kept in motion for the first few minutes, until the film begins to form ; or the mirror suspended in the fluid may have a gentle rotatory motion imparted to it; but in any case this motion is a most important element towards obtaining a silver film of uniform thickness, and free from stains, especially if the back of the mirror be not dry. Care must be taken not to lift the surface of the mirror out of the solution during the motion, as this may cause a streaky film. When the deposition of silver commences let the mirror remain undisturbed until nearly all the silver in solution has been thrown down. To ascertain this, break through the stratum of silver formed on the surface of the ring of fluid surrounding the mirror, and should the fluid below be perfectly clear the deposition of silver is complete. The time the deposition will occupy will depend on the temperature of the solution and the process employed. In summer it will be completed much more rapidly than in colder weather, during which period the operation can be more satisfactorily performed in a warm room. Do not leave the mirror too long in the solution, for directly the silver is all thrown down, there is a tendency to cover the brilliant silver film with a white deposit, which is not readily polished off; to avoid the risk of this occurring it will be found preferable to take the mirror out of the solution before the silver is quite exhausted.

To prepare the Silvered Surface for Polishing.

If the solution is still warm, immediately the mirror is removed, pour over its silvered surface a little warm distilled water, several times, until about a pint has been used. But if the solution from which the speculum has been removed is perfectly cool, cold water may be allowed to flow on the surface for five minutes or more, from an ordinary tap, finally rinsing with distilled water. When clean, the film may be dried, by placing the mirror with its silvered surface resting on some filtering paper (Fig. 26), but it is far better to rapidly dry off the superficial water by means of a good draught of air, and soak off the water as it comes to the edge with some absorbent paper. After the water has disappeared from the surface, the film, being still damp, may be allowed to gradually dry, leaving it unpolished for a few hours; or the mirror may be held at some distance from a fire, so as to quickly drive off any remaining moisture, care being taken not to over-warm the mirror itself; the film can then be immediately polished. In damp weather it will ahvays be better to slightly warm the film before polishing it. •

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Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,44 %.

La langue de reconnaissance de l'OCR est l'Anglais.

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