The object of this pamphlet is to give some new and additional advice not contained in my “Hints on Silvered Glass Reflecting Telescopes,” on silvering and adjusting them; and, as the results of continued and recent experience, it is hoped they may be useful, and may prove an acceptable appendix to my little book of Hints.
The first thing to do after fastening the mirror to the wooden support, is to suspend it in the dish in which it is to be silvered, and so to adjust it that there shall be one inch between the bottom of the mirror and the bottom of the dish; then pour in water to come a quarter of an inch up the sides of the glass—the quantity thus found is to be measured, and will be the exact amount of the bath when all the solutions are mixed; this will prevent any hitch at an important moment, and the glass can be immersed without delay or disturbance.
Next proceed to wash the surface with nitric acid, taking care that the acid does not run down the sides, as it is not so easily removed from the fine ground sides as it is from the polished surface. After gently but thoroughly rubbing the surface, add a little water, and again go over; then wash all off, and take a large piece of cotton wool and well sponge the surface and sides with plenty of water, and suspend in a dish or plate with water in it.
TO PREPARE THE SOLUTIONS.
The plan I adopt is this,—I dissolve a large quantity of the chemicals required in one-fourth or one-eighth the quantity of water employed by Martin, so that in a Winchester quart stoppered bottle I can keep a large supply ready. I make the silver and ammonia solutions eight times the original strength, the potash and sugar solutions four times only, as these latter solutions require more water to properly prepare them.
Enough solutions to silver a 6-1/2 in. mirror, eight times are to be made.
Dissolve 1400 grains of nitrate of silver in 10 ounces of water (it may be clean fresh rain water filtered, if distilled is difficult to obtain, and it will act very well), but do not put the silver into the exact 10 ounces, but make up to exact 10 ounces after the silver is dissolved. It is thus condensed eight times. Do the same with the nitrate of ammonia, by dissolving 2096 grains.
Next prepare the potash and sugar solutions, condensed to four times the initial strength.
Dissolve 8 ounces of potash, and make up to exactly 20 ounces of water; if this is dissolved in a glass measure it will evolve sufficient heat to break it; it is safely done in a clean white jug. Lastly, dissolve 4 ounces of white sugar candy with 416 grains of tartaric acid, and boil ten minutes in a clean glazed vessel; when cold, add 8 ounces of alcohol, and make up to 20 ounces with water.
Do not use the solutions till all are of the same temperature, nor on the same day as they are made; and do not silver until the glass, and everything used are of the same temperature. To insure this, get the mirror ready and suspend in water, with the solutions all collected in the room in which the silvering is to be done, and let them remain until next day.