SOLDERING, is the process of the surfaces of metals, process the intervention of a more fusible metal, which being melted upon each surface, serves, partly by chemical attraction, and partly by co hesive force, to bind them together. The metals thus united may be either the same or dissimilar ; but the uniting metal must always have an affinity for both. Solders must be, therefore, selected in reference to their appropriate metals. Thus tin-plates are soldered with an alloy consisting of from 1 to 2 parts of tin, with 1 of lead ; pewter is soldered with a more fusible alloy, containing a certain proportion of bismuth added to the lead and tin ; iron, copper, and brass are soldered with spelter, an alloy of zinc and copper, in nearly equal parts ; silver, sometimes with pure tin, but generally with silver-solder, an alloy consisting of 5 parts of silver, 6 of brass, and 2 of zinc ; zinc and lead, with an alloy of from 1 to 2 parts of lead with 1 of tin ; plati num, with fine gold.; gold, with an alloy of silver and gold, or of copper and gold.
For the simple solders, each of the metals may be used, according to the nature of that which is to be soldered. For fine steel, copper, and brass work, gold and silver may be employed. In the large way, however, iron is soldered with copper, and copper and brass with tin. The most usual solders are the compound, which are distinguished into two princi classes, viz. : hard and soft solders. he hard solders are ductile, will bear hammering, and are commonly prepared of the same metal with that which is to be soldered, with the addition of some other, by which a greater degree of fusi bility is obtained.
The hard solder for gold is prepared from gold and silver, or gold and copper, or gold, silver, and copper.
The hard solder for silver is prepared from equal parts of silver and brass, but made easier of fusion by one-six teenth of zinc.
The hard solder for brass is obtained from brass, mixed with a sixth, or an eighth, or even one half of zinc, which may also be used for the hard solder of copper. It is sold in a granulated form,
under the name of speller solder.
The soft solders melt easily, hut are brittle, and cannot be hammered. Of this kind are the following mixtures :—tin and lead, in equal parts ; of still easier fusion is that consisting of bismuth, tin, and lead, in equal parts ; one or two parts of bismuth, of tin, and lead, each one part.
In the operation of soldering, the sur faces of the metal intended to be joined must he made very clean, and applied to each other, and it is usual to secure them by a ligature of iron wire. The solder is laid upon the joint, together with sal ammoniac and borax, or common glass, according to the degrees of heat intended, and these additions defend the metal from oxidation.
Glaziers use resin ; and pitch is some times employed.
Tin foil, applied between the joints of fine brass work, first moistened with a strong solution of sabammoniae, makes an excellent juncture, care being taken to avoid too much heat.
In joining lead plates together, when solder is objectionable, owing to corrosion occurring, after the surfaces have been cleaned, they are united by melting their edges together with the blowpipe, or by pouring a band of melted lead along the two edges placed in apposition. Chloride of zinc in solution is now used as the substance best adapted for cleaning the minces of metals to be soldered. SPECIFIC GRAVITY. (See Guavrry.) SPECTRUM. In optics, the mune given to an elongated image of the sun or other luminous body, formed on a wall or screen by a beam of undecomposed light through a small hole, and re fracted by a prism. For the different colors and fixed lines of the solar spec tribe, and for the refrangibility of the different rays, see the Handbook of Sci ence, of this series.