Common pewter consists of tin 80 parts and lead 20 parts. Holtzapfel states that some pewters are made nearly as common as that of equal parts of the metals; when cast they are black, shining, and soft; when turned they are dark and bluish. Other pewters only contain or of lead; these when cast are white, without gloss, and hard. Such are pronounced very good metals, and but little darker than tin. The French legislature sanctions the employment of 18 per cent lead with 82 per cent tin, as quite harmless in vessels for wine and vinegar. The finest pewter, called tin and temper, consists chiefly of tin, with only a little lead and copper, which make it hard and somewhat sonorous, but the metal becomes brown in colour when the copper exceeds a certain quantity. The copper with twice its weight of tin is melted, and from lb. to 7 lbs. of this alloy termed temper are added to a block of tin, weighing from 360 to 390 lbs. Zinc in small quantity is added to the molten alloy, and the mixture well stirred. The operator considers that the zinc removes impurities, bringing them to the surface as dross, and also that the burning of the zinc during casting lessens the oxidation of the pewter.

Unalloyed tin is now being largely used in place of pewter, and it is not only whiter in colour, but for domestic purposes it is certainly safer, on account of the poisonous nature of lead compounds, although, as before stated, lead when thoroughly alloyed with tin may be present to the extent of 18 per cent without injury. An alloy of 3 parts lead and 5 parts tin is used for tinning certain articles of copper. Alloys of lead and tin have a bright lustrous appearance, and are used for the manufacture of stage jewellery. The so-called Fahlum brilliants are made of an alloy of 39.6 parts lead and 60-4 parts tin. The molten alloy is poured into moulds faceted in the same manner as diamonds. Toys, such as tin-soldiers, and many other articles are made of alloys of lead and tin.

For tempering various articles of steel, where it is important to have a definite and uniform temperature, Messrs. Parkes and Martin have proposed the following alloys :—

The same authorities have determined the melting points of lead-tin alloys; their results are embodied in the following table:

Composition. Melting point. Composition. Melting point.

According to Tilden,' the most fusible alloy of lead and tin consists of very nearly 2 parts tin to 1 part lead, or 3.3 atoms of tin to 1 atom of lead. The melting points of this and other alloys are graphically represented by the following curve, Fig. 31:—

§ 98. Soft solders usually consist of lead and tin in various proportions, and to a certain extent the fusibility of the alloy increases with the content of tin; but this does 1 Chem. Philosophy, p. 15.

When a

not apply when the tin exceeds 67 per cent. more fusible solder is required, the metal bismuth is added in addition, and sometimes cadmium. Metallic tin is sometimes used alone, as in soldering fine utensils of tin plate. Lead is also soldered to lead by simply melting the edges by means of a blowpipe flame, as in the case of lead sheets for sulphuric acid chambers. This is termed autogenous soldering.

Soft solders are termed common, medium, or best, according to the amount of tin, those containing most lead being the cheapest. Fine or best solder is largely used for Britannia metal, best tin - plate, brass, and other metal articles. The commoner varieties are used by plumbers. An alloy of 1 part tin to 2 parts lead is termed "plumbers' sealed solder," and stamped by the "Plumbers' Company." The following table gives the proportions employed for different kinds of soft solder :

The quality of the solder is roughly judged by the appearance of the surface when cast into a mould and allowed to cool. With excess of lead, the surface shows a uniformly grayish-white colour. With excess of tin, the surface is bright with dull grayish-white spots; in fact, the appearance approximates to that of lead or tin according to the amount of lead or tin present.

§ 99. Alloys of Tin, Lead, and Zinc.-The presence of lead imparts more body and resistance to the alloys of tin and zinc than when tin and zinc alone are used, but the

triple alloys clog the file as much as the latter. The fractures are more decided than tin-zinc alloys. When the three metals are present in about equal proportions, the alloys are malleable, although not very ductile, and may be economically employed in some cases.

1 Various alloys are given in the following table :—

No. 2 is as hard and brittle as zinc, although more resisting. No. 3 resembles hard lead, leaves a mark on paper, appears to be uniform in composition, and has a leaden colour. Both these alloys are better adapted for castings than either of the three metals taken separately. Nos. 1, 3, and 7 appear to withstand friction very well. Nos. 2, 4, and 5 will do for work requiring more resistance than pure zinc. No. 6 will answer for small castings requiring a certain malleability. It is serviceable for ornaments, and will bear engraving and chasing. For these uses Nos. 2, 4, and 5 would be too brittle; and Nos. 1, 2, and 7 too soft and yielding. All these alloys of tin, zinc, and lead have little lustre when polished, and become readily tarnished by exposure to air. Some of them may be used as type metal. Most of them may be easily rolled.

It is preferable to melt the zinc at the lowest possible temperature, to add the tin, and then the lead. The metals should be covered with charcoal, or with resin, and a little

1 Guettier, Guide Pratique des Alliages, 1865.