THE Latin for tin is stannum, whence the chemical symbol " Sn." It has a specific gravity of 7-291, and melts at 442° F. Alloyed with lead it forms pewter and solder; with small portions of antimony, copper, and bismuth, it forms block tin, Britannia, etc.

Pure tin does not tarnish in the air, as plumbers very well know. It is proof against acids and liquids, such as vinegar, lime juice, etc., etc. Copper saucepans, baths, slop-sinks, or any kind of copper vessel, only require to be scoured and made clean and bright for melted tin to readily tin upon them; though, for removing the last film of oxide which so soon forms upon well-cleaned and well-brightened copper, it is necessary to sprinkle powdered sal-ammoniac upon the parts to be tinned; or to rub a piece of sal-ammoniac over the copper - a piece being held in a pair of tongs for the purpose - before passing the melted tin over it with a wisp of tow. Wrought iron and cast iron can also be tinned, the process being very similar to that of copper tinning. The articles to be tinned are thoroughly cleaned and washed with sulphuric acid, and then heated up to the melting point of tin, when the fluid tin is rubbed on the bright surface of the iron with a ball of cotton or a cork.

Sal-ammoniac is applied during the operation to keep the surface of the metal free from oxidation. Tinned iron articles which are deficient in tin oxidize more rapidly than iron without any tin coating, owing to a galvanic reaction, caused by the contact of the tin and iron.

Tinstone, which is the only ore of tin found in sufficient quantity to be the subject of mineral exploration, is found in many places; the oldest known deposit is in Cornwall, where it occurs in veins or small strata, from whence large supplies of some of the purest tin used still comes to London. It bears the well-known mark of the Lamb and Flag. Plumbers' solder and fine solder have been made in the firm, of which I am now the head, for a century and a half, of Truro tin. But for many years past large quantities of tin have been brought into London from Australia, the Straits Settlements, and the islands of Banca and Billiton, as shown by the following statistics.

The Cornish production is somewhere about 9,500 tons per annum.

Plumbers' solder is usually made out of two parts of lead and one of tin, but for seam or angle soldering, as well as for flange joints, and for upright joints, solder a little richer not only looks better, but it works better. Sixty-five per cent. of soft pig lead to 35 per cent. of Truro tin makes good wiping solder. It is generally made in casts, consisting of eight bars, and weighing about 7 lbs. per bar, from prints stamped in a large level bed of prepared casting sand; or the tin and lead, being well mixed into good alloy, is run into moulds made in flasks of sand. In the illustration, fig. 2, A shows the top, and b the bottom of a cast of solder. A stick of fine solder is shown at c.

Fine solder, for soldering with a copper-bit, is made out of about eight parts of tin to seven of lead. When the two metals have been well heated and well mixed in a melting-pot, the alloy is run out with a ladle into sticks (into small U-shaped grooves sunk in iron plates) about 18 in. long, 1/2 in. wide, and 3/8 in. thick. A stick of fine solder is illustrated at c, fig. 2, and when it is of good quality it gives forth a crackling noise most pleasant to the ear of the plumber, when he bends it to forecast its fluidity for flowing round a jointing when heated by a copper-bit or blowing-lamp.

Fig. 2. - Showing the Upper and Under Side of a Cast of Solder, and a Stick of Fine Solder.

Blow-pipe solder is made with about 7 1/2 per cent. more tin than fine solder, or fine solder is melted down in a pot and further enriched by adding from 5 to 10 per cent. of tin to it, as circumstances may require. It is then run out with a small ladle upon faced iron plates into thin narrow strips about 3/16 in. wide, 1/12 in. thick, and 18 in. long.

A Table of Alloys with Tin, and their Melting Point.

Soft Solders (Extracted Chiefly From Appleton's "Dictionary Of Mechanics ")