ch purposes, but in the apparatus
as constructed by Perkins, with adequate dampers and safety valves,
and used with common care, no such result can ensue. Paper bound round
an iron tube is not affected till the temperature exceeds 400 deg.; from
420 deg. to 444 deg. it becomes brown or slightly singed; sulphur does not
inflame below 540 deg..

SECTION V.

COLOURS FOR POLISHED BRASS--MISCELLANEOUS.

PAINTING ON ZINC OR ON GALVANIZED IRON.

Painting on zinc or galvanized iron is facilitated by employing a
mordant of 1 quart of chloride of copper, 1 of nitrate of copper, and
1 of sal-ammoniac, dissolved in 64 parts of water. To thin mixture add
1 part of commercial hydrochloric acid. This is brushed over the zinc,
and dries a dull-grey colour in from twelve to twenty-four hours,
paint adhering perfectly to the surface thus formed.

BRONZING COMPOSITIONS.

The following are the formulae for a variety of baths, designed to
impart to polished brass various colours. The brass objects are put
into boiling solutions composed of different salts, and the intensity
of the shade obtained is dependent upon duration of the immersion.
With a solution composed of sulphate of copper, 120 grains;
hydrochlorate of ammonia, 30 grains; and water 1 quart, greenish
shades are obtained. With the following solution, all the shades of
brown, from orange-brown to cinnamon, are obtained: chlorate of
potash, 150 grains; sulphate of copper, 150 grains; and water, 1
quart. The following solution gives the brass first a rosy tint, and
then colours it violet and blue: sulphate of copper, 435 grains;
hyposulphite of soda, 300 grains; cream of tartar, 150 grains; and
water, 1 pint. Upon adding to this solution ammoniacal sulphate of
iron, 300 grains, and hyposulphite of soda, 300 grains, there are
obtained, according to the duration of the immersion, yellowish,
orange, rosy, and then bluish shades. Upon polarizing the ebullition,
the blue tint gives way to yellow, and finally to a pretty grey.
Silver, under the same circumstances, becomes very beautifully
coloured. After a long ebullition in the following solution, we obtain
a yellow-brown shade, and then a remarkable fire-red: chlorate of
potash, 75 grains; carbonate of nickel, 30 grains; salt of nickel, 75
grains; and water, 10 oz. The following solution gives a beautiful
dark-brown colour: chlorate of potash, 75 grains; salt of nickel, 150
grains; and water, 10 oz. The following gives