A soft alloy, which adheres so firmly to metallic, glass and porcelain surfaces that it can be used as solder, and which is invaluable when the articles to be soldered are of such a nature that they cannot bear a high degree of temperature, consists of finely pulverized copper dust, which is obtained by shaking a solution of the sulphate of copper with granulated zinc. The temperature of the solution rises considerably and the metallic copper is precipitated in the form of a brownish powder; 20, 30 or 36 parts of this copper dust, according to the hardness desired, are placed in a cast-iron or porcelain-lined mortar and well mixed with some sulphuric acid having a specific gravity of 185. Add to the paste thus formed 70 parts (by weight) of mercury, constantly stirring. When thoroughly mixed the amalgam must be rinsed in warm water to remove the acid, and then set aside to cool. In ten or twelve hours it will be hard enough to scratch tin. When it is to be used it should be heated to a temperature of 375 degrees C., when it becomes as soft as wax by kneading in an iron mortar. In this ductile state it can be spread upon any surface, to which, as it cools and hardens, it adheres very tenaciously.
(2) A solder for various metals, particularly aluminum, consists in combining cadmium, zinc and tin mixed in substantially the following proportions: Cadmium, 50 per cent.; zinc, 20 per cent.; tin, the remainder. The zinc is first melted in any suitable vessel, when the cadmium is added, and then the tin in pieces. The mass must be well heated, stirred, and then poured.