This is a very important kind of solder, used by many metal workers to solder brass, bronze, copper, iron, and steel. From its composition it may be considered a kind of bras-, to which are sometimes added small quantities of tin.

Brass, as we know, is an alloy of copper and zinc. Most kinds of brass have an average composition of 68 to 70 per cent of copper to 32 to 30 per cent of zinc; but there are certain special varieties in which varying quantities of zinc, from 24 to 40 per cent, may be found.

The less zinc there is in brass, the more it approaches copper in its general characteristics; increasing quantities of zinc tend to make it brittle and crystalline. As a rule, alloys for hard solders should not contain more than 34 per cent of zinc.

The fusing point of brass is raised as the amount of copper is increased; an alloy containing 90 per cent of copper melts at 1,060 deg. C. (1.940 deg. F.), with 80 per cent of copper the fusing point is 1,020 deg. C. (1,868 deg. F.), with 50 per cent 980 deg. C. (1,796 deg. F.), with 30 per cent 950 deg. C. ( 1.742 deg. F.).

As the alloy becomes more readily fusible with an increase of zinc, the color also changes essentially, and the alloy becomes much more brittle. The latter property may be modified by using partly zinc and partly tin, thus giving the alloy a resemblance to bronze. The durability of the solder is not affected, but it is made much less brittle and more readily fusible. If, however, more than a certain percentage of tin is added, the solder becomes thin and somewhat soft, gray-white in color, and very brittle again, so much so that the seams will separate if the article is bent. For this reason great care must be exercised in making the mixtures of zinc and tin.