3622. To Polish a- Silvered Surface on Glass

3622.    To Polish a- Silvered Surface on Glass. To accomplish this, rub the surface gently, first with a clean pad of fine cotton wool, and afterwards with a similar pad covered over with cotton velvet, which has been charged with fine rouge. The surface will, under this treatment, acquire a polish of intense brilliancy, quite free from any scratches.

3623. To Silver Glass for the Reflectors of Telescopes

3623.    To Silver Glass for the Reflectors of Telescopes. The solutions employed are four in number, and they require some care in their first preparation; but once made they are always ready, and can be used with great rapidity and certainty for depositing a lustrous, mirror-like surface of silver on a piece of glass of any desired shape or curvature :—

Solution No. 1 is prepared by dissolving 1 part, by weight, of nitrate of silver, in 10 parts of distilled water.

Solution No. 2 consists of an aqueous solution of. pure ammonia, having a density of 13.3° Baumé.

Solution No. 3 consists of 4 parts of pure caustic soda in 100 of distilled water.

Solution No. 4 is made by dissolving 121/2 parts of the best white loaf sugar in 100 parts distilled water. To this add 1 part, by measure, of nitric acid, boil for 20 minutes, in order to invert or alter the molecular arrangement of the particles of the sugar, and then add water to increase the volume to 500 parts by measure, and finally add 50 parts alcohol.

These solutions will remain unchanged for a long time. When required for use, prepare a silvering liquid by pouring into a flask 12 parts, by measure, of the silver solution, No. 1; 8 parts, by measure, of the ammoniacal solution, No. 2; then 20 parts of the soda solution, No. 3; and, lastly, add 60 parts of distilled water, in order to make up the volume to 100. If the proportions have been properly observed, the liquid so prepared will be perfectly clear, but will be rendered turbid by the smallest addition of nitrate of silver solution. It must be allowed to remain without disturbance for 24 hours, to permit the floating particles to settle. The clear liquid decanted from the sediment will then be ready for use. The surface of the glass which has to be silvered must be well cleaned with a tuft of cotton and a few drops of nitric acid, and then washed with distilled water. (See No. 3621 (To Clean the Surface of Glass for Silvering).) Drain it, and support it on the surface of the silvering bath, which is composed of the above described silvering liquid, with the addition of 1/10 or 1/12 its volume of the sugar solution, No. 4. The surface to be silvered, should, by preference, bo at the upper part of the liquid, so that the silver may be deposited on it from below upward. There are two advantages in this - first, the deposit is finer and more even: and, second, there is no danger of floating particles of dust settling on the surface. It is, however, scarcely necessary to say that silver will be deposited upon every part of the glass which is under the surface of the liquid, as well as upon the sides and bottom of the vessel; so that, as a matter of economy, as little as possible of the back of the glass should be exposed to the action of the liquid. The action seems to be more rapid in the light than in darkness. Under the influence of diffused light the liquid becomes yellow, then brown, and in a few minutes the whole of the exposed surface of the glass will be covered with a fine deposit of silver. In about a quarter of an hour the thickness of the metallic coating will be sufficient to bear the subsequent operations without injury; it must then be washed with plenty of water, and rested by one corner on several thicknesses of blotting-paper to dry spontaneously. The surface will now be covered with a thin whitish veil, which may be readily removed by gentle friction with chamois leather; it may afterwards be polished with jewelers' rouge, when a perfectly brilliant surface will be produced. (See No. 3622 (To Polish a- Silvered Surface on Glass).)