Prepare two solutions.
1. Argentic nitrate is dissolved in distilled water, and ammonia added
to the solution till the precipitate first thrown down is almost
entirely re-dissolved. The solution is filtered and diluted, so that
100 cc. contain one gramme of argentic nitrate.
N.B.—100 cc. are equal to rather more than 3½ fluid ounces.
2. Two grammes of argentic nitrate are dissolved in a little distilled
water, and poured into a litre of boiling distilled water. 1·66 gramme
of Rochelle salt is added, and the mixture boiled for a short time,
till the precipitate contained in it becomes grey; it is then filtered
hot.
The glass, having been thoroughly cleaned with (1) nitric acid, (2)
water, (3) caustic potash, (4) water, (5) alcohol, and lastly distilled
water, is to be placed in a clean glass or porcelain vessel, the side
to be silvered being placed uppermost. Equal quantities of the two
solutions are then to be mixed and poured in, so as to cover the glass.
This should be done while the glass is still wet with distilled water.
In about an hour the silvering will be completed. Then pour off the
exhausted liquid, carefully remove glass, wash in clean water, rub off
silver where deposited where not required, allow to dry, and varnish
silvered side with any thin varnish which does not contract much in
drying.
The time required for the operation depends on temperature.
If the solutions be warmed to about 30°C., the silver is deposited in a
few minutes; but it is safer to use them cold.
The inside of test tubes, bulbs, &c., are silvered by putting the
solutions into them, no second vessel being then required.
Throughout the whole operation the most scrupulous cleanliness is the
grand essential.