42 THE MODERN REFLECTING TELE8COPE. 



in weight to one-half that of the entire amount of silver nitrate used ; this is also 

 filtered. The silver solution and reducing solution are now both diluted with 

 distilled water, prepai'atory to mixing ; the quantity of the diluted solutions, 

 together, should be sufficient to cover the glass about one inch deep. 



An assistant ])ours ofS the water which has stood on the glass, while the op- 

 tician quickly mixes the dilute silver and re<lucing solutions in a large pitcher or 

 granite-ware bucket. The glass being horizontal, the mixed solution is immediately 

 poured on, and the mirror is rocked slightly by means of the tilting frame. The 

 liquid quickly changes to a ti-ansparent light-brown color, then dai'k bi'own, then 

 black, after which the silver immediately begins to deposit. The solution gradually 

 changes to a muddy-brown color, and in three or four minutes after the solutions 

 are poured on the glass, begins to clear; the light mud(l3'-V)rowii precipitate 

 settling upon the film. With the proportions given, the silver film should be 

 sufficiently thick in about five minutes after the solutions are poured on the glass 

 provided that the I'oom, glass,- and solutions are all at a temperature of sixty-eight 

 degrees or seventy degrees Fahrenheit. When fiist formed the brown pre- 

 cipitate is so light that it moves about with the rocking of the glass; but it very 

 soon deposits in large areas on the film. As soon as this begins to occur, the solu- 

 tion must be very quickly poured oflp the glass, an abundance of distilled water 

 poured on, and a large bunch of absorbent cotton, held in the fingers, instantly 

 used to displace all streaks of the precipitate which adhere to the film. The film 

 is now washed again and again with fresh distilled water and a soft bunch of cot- 

 ton ; then an abundance of water is poured on and the film allowed to soak for an 

 hour. When this is poiii-ed off, the paper band is carefully removed, with the glass 

 horizontal so that no liquid from the edge can lun upon the silver film ; this must 

 be done quickly, before the latter has time to dry. A small amount of alrohol is 

 now flowed on the film; this is repeated several times to get rid of all water; the 

 glass is then turned on edge, and is quickly dried with a fan. 



After standing for an hour or two in a dry room the film is to be burnished. 

 A soft pad as large as the hand is made of the softest chamois skin ; this is used on 

 the film without rouge, with light circular strokes, to condense the silver. After 

 two hours of this work a little of the finest washed dry jewelei-'s rouge is rubbed 

 into the chamois-skin with a piece of clean absorbent cotton ; from thirty to sixty 

 minutes use of the pad with the same stroke as before should now bring the film to 

 a perfect polish, without scratches. 



If the back of the mirror is already silvered, the face can be silveied by the 

 method just described, without injuring the film on the back ; the mirror now rests 

 upon three curved and beveled blocks of soft wood which touch only the rounded 

 corner or edge of the back of the glass ; extra precautions are now taken to prevent 

 any of the solution from touching the back. I legard this method as much better 

 in the case of large mirrors than to attempt to silver both back and face at the same 

 time in a deep tray; in the latter method the difficulties of handling and pi'operly 

 cleaning the mirror are almost insurmountable. 



The back of the mirror does not usually need silvering oftener than once in 



