Brass is perhaps the most useful and important alloy known. Its composition varies widely with the uses for which it is intended, but its constituents are copper and zinc, usually in the proportions of nearly two parte of the former to one part of the latter. Brass may also contain small quantities of tin and lead. The qualities which render this alloy so valuable may be briefly enumerated as follows:-It is harder than copper, and consequently better ab]e to resist wear and tear. It is very malleable and ductile, and therefore admits of being either rolled into thin sheets, shaped with the hammer, drawn into fine wire, or raised by stamping into objects of various forms. It is readily fusible, and therefore easily cast at a lower temperature than copper. It resists the influences of the atmosphere better than copper, although, if unprotected by lacquer or varnish, it rapidly tarnishes and blackens on exposure to the air. Finally, brass has a fine yellow colour, and is capable of receiving a beautiful polish.

The malleability of brass varies with its composition and with its temperature; it is also affected, to a sensible degree, by the presence, even in minute quantities, of certain other metals. Some varieties of brass are malleable only when cold, others only when hot, and others, again, are never malleable. At a temperature just below its fusing-point, brass, like copper, is brittle, and may be powdered in a mortar. Alloys of copper and zinc present a great variety of colour, ranging between the reddish hue of the former and the bluish-white of the latter; the transition is gradual, and passes through all the intermediate stages of yellow. The table on page 14 represents the intensity of colour, hardness, and fusibility possessed by these different alloys.

During the process of stamping brass, it must be hardened or tempered from time to time. At the end of the process, it has lost its colour, owing to the formation of a coating of oxide during the tempering operations. This coating is easily removed by plunging the metal into nitric acid, and then washing it thoroughly with water. A brilliant metallic surface is thus produced, ready to receive the customary layer of lacquer or varnish. This cleansing process, is known as "dipping." If the brass contain any impurities, dipping will not impart to it a brilliant surface. The colour produced by dipping varies according to the strength of the acid; this is due, it is believed, to the fact that the metals constituting the alloy are acted upon to a greater or less degree by acids of different degrees of dilution.

The operation of dipping is performed in the following way :-The object, with a black coat of oxide, is plunged into nitric acid containing 1 part of the pure acid to 7 or 8 of water. It is allowed to " pickle," as it is termed, in the acid solution until the crust can be detached by rubbing the surface of the metal gently with the finger, when it is withdrawn, and washed immediately in water. It is next dipped into a much stronger acid solution, where it remains until the *' curd " appears, or until the surface of the metal is entirely covered with minute bubbles of gas. This solution should be about twice as strong as the one previously used. The brass must then be washed with a plentiful supply of water, and roughly dried in cold sawdust. It is afterwards dipped, with the particles of wood still adhering to its surface, into strong nitric acid, where it remains only a few moments, then rinsed with a little water, and immediately afterwards thoroughly washed with water containing argol in solution.

It is finally dried in hot sawdust, after which the surface is ready for the lac-quer or varnish.

Atomic Constitution.

Percentage Composition.

Colour of Fracture.

Inverse' order of Hardness.

Inverse order of

Fusibility.

Nature of the Brass.

Cu

100.00

Tile Red

20

15

Copper.

10Cu + Zn

90.72 + 9.28

Reddish-yellow

1

21

14

Similor, etc.

Several of these are malleable at high temperatures.

9Cu + Zn

89.80 + 10.20

,, ,,

2

20

13

8Cu + Zn

88.60 + 11.40

,, ,,

3

19

12

7Cu + Zn

87.30 + 12.70

,, ,,

4

18

11

6Cu + Zn

85.40 + 11.60

Yelliowish-red

3

17

10

5Cu + Zn

83.02 + 16.98

,, ,,

2

15

9

Bath-metal.

4Cu + Zn

79.65 + 20.35

,, ,,

1

16

8

Dutch brass.

3Cu + Zn

74.58 + 25.42

Pale yellow

14

7

Rolled sheet brass.

5Cu + 2Zn

71.43 + 28.57

• •

• •

• •

Ordinary brass.

2Cu + Zn

66.18 + 33 .82

Full yellow

1

13

6

British brass.

19Cu + 12Zn

60.00 + 40.00

,, ,,

15

6

Muntz's metal.

Cu + Zn

49.47 + 50.53

,, ,,

2

12

6

German brass.

Cu + 2Zn

32.85 + 67.15

Deep yellow

10

6

„ (watch-makers').

8Cu + 17Zn

31.52 + 68.48

Silver white

1

5

5

Very brittle )

Too hard to file or turn.

8Cu + 18Zn

30.30 + 69.70

,, ,,

2

6

5

85U + 19Zn

29.17 + 70.83

Silver grey

1

7

5

8Cu + 20Zn

28.12 + 71.88

Ash grey

3

3

5

Brittle

Lustre nearly equal to speculum metal.

8Cu + 21Zn

27.10 + 72.90

Silver grey

2

9

5

,,

8Cu + 22Zn

26.24 + 73.76

1

8

5

Very brittle

8Cu + 23Zn

25.39 + 74.61

Ash grey

4

1

5

Barely malleable.

Cu + 3Zn

21.50 + 75.50

,, ,,

1

2

4

Brittle.

Cu + 4Zn

19.65 + 80.36

,, ,,

2

4

3

White button metal.

Cu + 5Zn

16.36 + 83.64

Very dark grey

11

2

Brittle.

Zn

100.00

Bluish-grey

23

1

Zinc.

Another dipping bath, which has been recommended, consists of hydrochloric acid and alum. It is said, however, that the lustre given is much duller and of a greenish hue, in comparison with that given by strong nitric acid. When dipping articles, have a bath of whiting and water close to the acid-bath. When the article has been dipped 4 seconds, remove it, and instantly plunge into the whiting and water,, which removes at once all the acid and oxide, and it comes out a beautiful dead-gold colour, requiring to be only dried, warmed, and lacquered. Should the first dip be not sufficient, repeat the process, and end by a dip just in and out again quickly, having previously cleaned the article in water and dried it. Don't put it into the acid wet, because some parts being wetter than others, the acid will attack them unequally, and the result may be a cloudy mottled appearance on the surface. Never use a pair of iron tongs or forceps for holding the work when dipping; either suspend it from a brass wire, or make a pair of tongs out of a piece of f by 3/16 in. brass, something like a long pair of sugar-tongs. If obliged to use this process indoors, get a draught to carry away the brown fumes; if you have a fireplace not in use, make a board to fit it exactly, and at a convenient distance from the bottom cut a hole in it about 6 in. square; place the acid-bath close in front of this, and the air rushing through will carry the hurtful fumes up. the chimney.

A mottled appearance is produced on brass by a " spotting " machine. A fair imitation can be made by the flat end of a piece of slate pencil. Put a piece of wood or metal, with a hole in it the size of the pencil, upon the piece of brass you wish to spot, and, having dipped the end of the pencil in water, place it in the hole, and turn it round a few times, when it will form a grey spot.

A dead appearance, called by the French mat, may be obtained by plunging the articles in a. mixture of strong nitric acid 200 parts; sulphuric acid sp. gr. 1.845, 100; common salt, 1; sulphate of zinc, 2. The articles will require thorough rinsing. Another recipe, suitable for large work, consists of: 3 parts nitric acid, 1 sulphuric acid, 1 water, 1/2 zinc sulphate. Dip the articles. and rinse, again dip and rinse until the earthy yellowish dullness gives way to a clear mat, without earthiness.