A metallic cement for joining separate pieces of metal together by fusion. It is a general rule, with respect to solder, that it should fuse at a lower temperature than the metal to be soldered. The solders of the plumber are composed of tin and lead, on account of their ready fusion. (See those metals.) The coppersmith's solder is an alloy of copper and zinc. See those metals.) In general, the solder is harder or softer, in proportion to the quantity of copper that is in it; the greater the quantity of copper it contains, the harder and more difficult of fusion it becomes. Solders of different degrees of fusibility are often required, particularly in cases where several joinings have to be made near to near other. The least fusible solder is employed in the first place, and the others in succession, according to their order of fusibility, to the subsequent joinings. If this precaution were not adopted, it would often happen that in soldering one joint, the heat communicated to the next thereby would cause it to become unsoldered.

Before soldering, the surfaces are rendered bright and clean, by scraping or filing them over; as a thin coat of oxide, or any foreign matter intervening, would prevent the union.

The solders used for brass are usually of two kinds, denominated hard and soft. The hard is composed of brass and zinc, varied in the proportions of from sixteen to two parts of brass to one of zinc. The soft solder is composed of six parts brass, one of zinc, and one of tin. The brass is first melted, then the tin, and lastly the zinc (previously well heated) is added. The mixture is then agitated to divide it into grains as it cools.