1868. | ois Physies. 421 
chlorine, neutralized with ammonic sesquicarbonate, and diluted to 
sp. gr. 1:115; or (b) 242 gr. ammonic sulphate dissolved in 1,200 
c.c. water (sp. gr. 1°105 to 1:106) ; III. Solution of sodic hydrate 
sp. gr. 1:050 prepared from sodic carbonate, free from chlorine ; 
IV. 50 grm. white sugar candy dissolved in little water, 3:1 gr. 
tartaric acid added, the mixture kept boiling for one hour, and 
diluted to 500 cc.; V. 2°857 gr. dry cupric tartrate, covered over 
with water, and solution of sodic hydrate gradually added till solu- 
tion has taken place, and the volume made up to 500 cc. These 
solutions are mixed in the following proportions :—Ist, 14 vol. of L., 
10 vol. of IL., and 75 vol. of III., = 99 vol. of (A) silvering solution ; 
2nd, 1 vol. of IV., 1 vol. of V., and 8 vol. of water = 10 vol. of (B) 
reducing solution. The silvering mixture is then made by diluting 
50 vol. of the silvering solution (A) with from 250 to 300 vol. of 
water, and adding 10 vol. of the reducing solution (B). If ammonic 
sulphate has been employed for solution (A), the liquid, after mix- 
ing the three ingredients, must be allowed to stand three days 
before being used; the clear liquor may then be drawn off. 
Professor Draper of New York, who has also paid great attention 
to this subject, recommends the following process as being very suc- 
cessful for silvering glass mirrors. He divides the process into five 
operations, viz. the cleaning of the glass, the preparation of the sil- 
vering solution, the warming of the glass, the process of silvering, 
and the polishing. (The description is for a 15}-inch mirror.) 
1. Rub the glass plate thoroughly with aquafortis, and then wash it 
with plenty of water and set it on edge on filtering paper to dry ; then 
cover it with a mixture of alcohol and prepared chalk, and rub it in 
succession with cotton flannel. 2. Dissolve 560 grains of Rochelle salt 
(tartrate of soda and potassa) in 2 or 8 ounces of water and filter ; dis- 
solve 800 grains of nitrate of silver in 4 ounces of water. Take an 
ounce of strong ammonia of commerce and add nitrate solution to it 
until a brown precipitate remains undissolved. Then add more am- 
monia and again nitrate of silver solution. This alternate addition is 
to be carefully continued until the silver solution is exhausted, when 
some of the brown precipitate should remain in suspension. Filter. 
Just before using, mix the Rochelle salt and add water enough to 
make 22 ounces. The vessel in which the silvering is to be performed 
should be a circular dish of ordinary tin plate, and coated with a 
mixture of equal parts of beeswax and rosin. At opposite ends of 
one diameter two narrow pieces of wood are cemented to keep the 
face of the mirror from the bottom of the vessel. 3. The glass is 
slightly warmed by putting it in a tub or other suitable vessel and 
pouring in tepid water to cover the glass; then hot water is gra- 
dually stirred in. 4. Carry the glass to the silvering vessel, into 
which the silvering solution has been poured, place the whole appa- 
ratus before the window, and keep up a slow rocking motion. Leave 
