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if stirred for several minutes. When ready for silvering add to the ammoniated solutions, freed from precipitate by subsidence or straining, solution B, which should be previously filtered, and may be also warmed if the weather is cold.

Both Draper’s and the Sugar of Milk processes take about three times as long as Martin’s.

The quantities of silver, etc., here given are sufficient for any amount of silvering solution up to 30 ounces ; but it must be noted that the solutions need not be over strong; it will therefore be better to keep to a standard strength, such as the above quantities of chemicals to 20 ounces of solution, and roughly estimate the amount of each substance that will be wanted when the quantity of solution required has been ascertained.

GENERAL HINTS ON SILVERING.

Be very careful not to employ too much ammonia in preparing solution A. Do not mind an inky colour so long as there is no visible precipitate undissolved.

Be very careful to clean the superficial edges, as stains are more likely to appear there than anywhere else.

Never leave the mirror too long in its bath, as the film is sure to tarnish directly all the silver is thrown down; and the polishing may then prove a tedious process.

Keep the back of the mirror dry during the entire operation, but especially at its commencement.

Be very careful the film is perfectly dry before any attempt is made to polish it.

As pitch is soluble in ammonio-nitrate of silver, great care must be taken not to let any particles fall into the solution, or come in contact therewith, otherwise a thin silver film will be the certain result.

All thin articles to be silvered should be cemented to their supports with pure gutta percha and not with pitch.

Never attempt, except with Martin’s process, to silver a mirror or “flat” in a room where the temperature is below 6o° F., as the film produced will be thin, uneven, of a blue tint, and incapable of bearing a high polish.

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