Solders.—Alloys employed for joining metals together are termed " solders,' and they are commonly divided into two classes : hard and soft solders. The former fuse only at a red heat, but soft solders fuse at comparatively low temperatures.
The most easily fusible metal known is an alloy of 2 parts bismuth, 1 part tin, and 1 part lead ; tin is the most fusible of these three metals, melting at 228°, but this alloy melts at 93°, or a little below the boiling point of water. By diminishing the quantity of bismuth in the alloy, the point of fusion may be made to vary between 100° and 200°, and thus it is an easy matter to form a solder which shall fuse at any required temperature between these limits, for electrical purposes, steam-boiler plugs, &c. The following are the best recipes for the common solders :— Hard spelter solder: copper, 2 parts ; zinc, 1 part. This solder is used for iron-work, gun. metal, &c.
Hard silver solder : silver, 4 parts ; copper, 1 part ; or, silver, 2 parts ; brass wire, 1 part. These are employed for fine work ; the latter is the most readily fusible.
For brass-work : equal parts of copper and zinc ; or, for the finer kinds of work, silver, 1 part ; copper, 8 parts ; zinc, 8 parts.
For steel : silver, 19 parts ; copper, 3 parts ; zinc, 1 part.
For pewterers : bismuth, 2 parts ; lead, 4 parts ; 3 parts ; or, bismuth, 1 part ; lead, 1 part ; tin, 2 part's. The latter is best applied to the rougher kiiids of work.
For jewellers: fine silver, 19 parts ; brass, 10 parts; copper, 1 part ; or, for joining gold, gold 24 parts ; silver, 2 parts ; copper, 1 part.
alloy, used for printers' type, is composed of 6 parts lead, aud 2 parts anti mony. It is of a blackish-grey colour, aud is softer than tin and copper, but a little harder than lead.
Platinum is capable of being united to most other metals, the alloys being as a rule more fusible than platinum itself. It occurs in nature in combination with a rare metal called iridium, with which it is often alloyed ; the resulting metal is called tridio-platinum, and, though still malleable, is harder than platinum, and unattacked by aqua regia. It is also much less readily fusible than platinum itself, and is therefore likely to be largely used in place of this metal for the purpose of electric lighting by incandescence. Silver is hardened, but rendered brittle, by
being alloyed with very small quantities of platinum.
The following is a table of the proportions of the various metals in the alloys most commonly employed in the arts and manufactures.
The proportions of the several ingredients in the various alloys given above must be regarded as only approximative in many cases. Every manufacturer adopts the proportions which experi ence has taught him to be the most suitable for the purposes for which the alloy will be used, or perhaps, in some instances, which accident or caprice first led him to make use of. If we take, for example, half a dozen samples of that variety of pewter known as Britannia-metal from as many different manufacturers, we shall probably find that we have half a dozen alloys widely different iu their composition, though similar in appearance, and applicable to the same uses. The same remark holds good of such alloys as pinchbeck, tombae, Manheim gold, and some others. More than this, oven the products of the same manufaetory may vary considerably in composition at different times, when these products are not required to possess in a high degree any given quality. It is therefore not surprising that the proportions published in many works are so absurdly different and contradictory. Thus we have, for example, one acknowledged authority giving the composition of Britannia-metal as equal parts of brass, tin, antimony, and bismuth ; while another gives the composition as 150 parts of tin, 3 parts of copper, and 10 parts of antimony, omitting the bismuth altogether. It would be easy to find a third authority giving a composition of this alloy widely different from the above two. From out of this chaos it is impossible to evolve anything like order, or to give information that shall not be at variance with all that has preceded it from sources acknowledged to be trustworthy. Hence the recipes we have given must be regarded as having only an approximate value generally, though for the cases we have in view they are exact, i. e. they are the proportions which have been actually adopted in practice. Many of them have been ascertained by analysis of the finished product, while others have been obtained from sources that are worthy of confidence.