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Weights and

acid and white

WEIGHTS AND MEASURES.—The confusion existing in the English system of measure ment is, without doubt, very great. All solid chemicals are sold by avoirdupois weight, while most formulm are written in apothecaries' weight. Various suggestions have been offered to remedy this state of things. The adoption of the French metric system is, without doubt, but a matter of time.

It is then hung up to dry, and when thoroughly dry it is sensitized with Silver nitrate 3o grammes Water .5oo c. c.

Glacial acetic acid 2 to 10 grammes The amount of acetic acid depends upon the temperature. Exposure is made in a solar camera the time required varying from about 15 seconds in dull light to one minute with fine.

The developer is made up as follows : Pyro 3 grammes Glacial acetic acid... 15o c. c. Water .x000 c. c.

Potassium bromide z to 2 grammes The print is laid on a large glass plate, and the developing mixture poured over it.

WHITE INK.—The following will be found suitable for writing white letters upon the dark portions of silver prints : Potassium iodide xo parts Water .3o parts Iodine z part Gum arabic z part Chinese white can also be used for the same purpose.

WHITE LEAD.—Made by suspending rolls of thin sheet lead over malt vinegar or pyro• ligneous acid in closed vessels, the evaporation of the acid being kept up by the vessels being placed in a steam bath or arranged in rows under a manure heap, fermentation producing the necessary rise of temperature.

It forms a dense white powder, insoluble in water, but readily soluble in dilute nitric acid or acetic acid. It is largely used in painting backgrounds and for other similar purposes.

WHOLE PLATE.—The size of dry plate, 84. x 6i inches.