TABLF 77.-MELTING POINTS OF ALLOYS AND METALS, &C., FROM THE EXPERIMENTS OF POUILLET, CLAUDEL, &c., AND FREEZING POINTS OF LIQUIDS, &c.

Temperature of Furnaces, &c.-When the fire is at red heat = 1,300; at cherry red heat = 1,700; at orange colour = 2,000; at bright white heat 2,500; and at a dazzling white heat = 2,800 degrees Fahrenheit. Temperature of the hot blast for melting iron, from 900 to 1,200° F. Welding heat of iron, 2,700° F. Iron is bright red in the dark at 752° F. Iron is red in daylight at 885° F. Metals are red in daylight at 1,077° F. Wrought iron boils at 5000° F.: cast iron at 3,350° F.; sulphur at 570° F.; and phosphorus at 556° F. Temperature of Bessemer furnace, 4,000° F.; puddling furnace, 3,500° F; cupola, 3,000° F.; common fire, 790° F.; of ignition, 637° F.; of common oven, 460° F.; disinfecting chamber for clothing, 240° F.; laundry drying rooms, 110° to 150° F.; of the human body, 981° F.; and of a comfortable room. 70° F.

Metals when hot are weaker than when cold. Iron loses strength by every increment of heat above 550° F. Copper loses strength by every increment of heat above 32° F., the loss of strength being 5 per cent. at 212°; 20 per cent. at 450°; 30 per cent. at 600°; 50 per cent. at 800°; 75 per cent. at 1100°; and at 1335° it loses all tenacity and becomes a soft viscid mass, although it does not melt until it reaches 2050° F.

Table 78.-SHEWING IN SUCCESSive Order the PROPERTIES OF METALS,
VIZ.:-Malleability, being beat into thin plates;
Ductility, being drawn into wire;

Tenacity, resistance to pulling asunder.

Table 85.-BRAZING SOLDERS FOR BRAZING COPPER, GUN METAL, BRASS, IRON, STEEL, SILVER, AND GOLD.

Soft solder for brazing copper and brass
Soft solder for brazing copper and brass

Hard solder for brazing copper, gun metal, and brass
Harder solder for brazing iron, copper, gun metal, and brass
Hardest solder for brazing iron, copper, bronze or gun metal,
and brass

Another hard solder for brazing copper, gun metal, brass, &c.
Silver solder for fine bronze or gun metal and brass work
Silver solder for fine bronze or gun metal and brass work
Silver solder for German silver and for fine bronze or gun metal
Silver solder for steel and for jeweller's and fine work
Silver solder for jeweller's and fine work

Silver solder for jeweller's, instrument-makers, &c.; very tough
and fluid

Silver solder for plating

Soft silver solder

Parts of
Antimony.

I

6 aluminium

...

...

6 aluminium

6 bismuth

4

89/

In preparing solders, to prevent oxidation, soft solders should be melted under tallow, and hard solders under a thick layer of powdered charcoai. Fluxes for soldering.—For iron or steel, borax or sal-ammoniac; for tinned iron, resin or chloride of zinc. For zinc, spirits of salts: for lead, tallow, or resin for lead and tin pipes, and for pewter, resin and sweet oil for copper, gun-metal, brass, silver, &c., borax or chloride of zinc.: for aluminium, paraffin.

:

Finishing and Burnishing Gun Metal and other Metals.—It is frequently requisite to give a very high finish to metals: for instance, to prepare them for receiving a coating of silver or nickel-plating. This is accomplished by burnishing the articles on buffs revolving at a high speed, for which purpose the following buffs and burnishing compositions are the best.

Burnishing Bronze, Gun-Metal, Brass, Copper, and White Metal. The articles, after being well polished with a fine powder, made from old burnt plumbago crucibles, are finely polished by buffing on a leather buff, with rottenstone and oil, or crocus powder and oil, and are then burnished, by buffing with finely-powdered unslacked lime, or dry crocus powder, on a calico buff.

Burnishing Iron and Steel Articles.-The article, after being highly polished with fine emery, is burnished by buffing on a leather buff, first with glass-cutters' sand and afterwards with Trent or finer sand.

Buffs.- Calico buffs are made by cutting a great number of pieces of coarse calico into discs; they are then firmly pressed together, and screwed up on a mandrel, with a nut at each end, between two thick leather discs, with a brass washer at the end of the leather.

Leather buffs are made of a number of discs of walrus hide glued together to the required thickness, and firmly clamped until the glue is set, when they are turned up true, on a mandrel having a nut and washer at each end.

Finishing Brass Work by Acids.—Intricate brass work, which cannot oe finished in the ordinary way, is finished in the following manner by acids, viz., the work is first cleansed by heating and dipping in washing. soda and water, and afterwards well rinsed in clean water; it is next plunged for not more than 10 seconds into a solution of water, I part, nitric acid, 2 parts; then taken out and plunged, first into clean cold water, and then into hot soap and water, and dried in hot sawdust. Boxwood sawdust is the best, as it does not contain resin.

Clouding Brass.—A solution of charcoal and water is poured on to the surface of highly polished brass, so as to produce circular marks; slate pencil may be used to fill in part of the cloud. The work when dry, is lacquered.

The Weights to the New Imperial Standard Wire-Gauge of sheet-copper, brass, gun-metal, white metal, zinc, and lead are given at pages 290, 291, and the weights of bars of copper, brass, lead, and zinc, at page 301.

BLUEING, COLOURING, TINNING, BRONZING, LACQUERING SILVERING AND JAPANNING PROCESSES.

Blueing Iron and Steel Articles.-Fill an iron pan with either clean brass filings, sand, powdered charcoal, or mahogany sawdust; heat the same to a dull red heat, and pass the article through it, in and out, until the required colour is obtained. The article to be well polished, free from grease, and not to be touched with the fingers before inserting. The higher the polish the better will the colour be. For very light articles, such as spectacle frames, hot sawdust is preferable. To take away all traces of grease, the articles should be rubbed with powdered quicklime before blueing.

Blueing Iron and Steel by Boiling.-Place the articles in the following solution, kept at boiling heat. Dissolve 4 oz. hyposulphite of soda in 1 pints of water, and then add a solution of 1 oz. acetate of lead in 1 oz. of water.

Brown Tint for Iron and Steel.-Dissolve in 4 parts of water, 2 parts of crystallised chloride of iron, 2 parts of chloride of antimony, and I part of gallic acid. Apply the solution with a sponge and dry in the air. Repeat the process according to the depth of colour required.

Browning Gun Barrels.-The barrels to be well polished and free from grease, and not to be touched with the hands during the process. First rub with powdered quicklime to remove all trace of grease, then apply with a sponge one of the following solutions:

Solution No. 1.-Mix in 1 pint of rain water, muriate tincture of steel; oz. spirits of wine; oz. muriate of mercury.

oz. blue-stone; oz oz. strong nitric acid;

Solution No. 2.- -Sulphate of copper, 1 oz.; sweet spirits of nitre, 1 oz.; rain water, I pint

Solution No. 3.—Aqua fortis, oz.; sweet spirits of nitre, oz.; tincture of muriate of iron, 1 oz.; spirits of wine, 1 oz.; sulphate of copper, 2 oz.; water, 30 oz.

Solution No. 4.-Tincture of muriate of iron, oz.; spirits of nitric ether, oz.; sulphate of copper, 2 scruples; rain water, pint.

When dry, polish off the rust with a wire scratch brush, and repeat the process until the required depth of colour is obtained. After the last application pour boiling water over the barrels, dry, and while still warm polish with a little beeswax and spirits.

shellac, oz.; dragons' blood, barrels before applying.

Varnish for gun barrels after browning: oz.; rectified spirits, I pint. Warm the

Browning Iron and Steel Articles.-Immerse in a solution of tincture of iodine, with one half its bulk of water.

Japanning Metal.—A coat of thick coloured varnish, called japan, is laid on to the metal, and dried by baking in a suitable oven, heated to about 300° F. The high temperature evaporates the solvents of the japan,