A soft alloy which attaches itself so firmly to the surface of metals, glass and porcelain that it can be employed to solder articles that will not bear high temperature, can be made as follows: Copper dust obtained by precipitation from the solution of the sulphate by means of zinc is put in a cast-iron or porcelain-lined mortar and mixed with strong sulphuric acid, specific gravity, 1.85. From twenty to thirty-six parts of the dust are taken, according to the hardness desired. To the cake formed of acid and copper there is added, under the constant stirring, seventy parts of mercury. When well mixed the amalgam is carefuly rinsed with warm water to remove all the acid and then set aside to cool. In ten or twelve hours it is hard enough to scratch tin. If it is to be used now, it is to be heated so hot that when worked over and brayed in a mortar it becomes as soft as wax. In this ductile form it can be spread out on any surface, to which it adheres with great tenacity when it gets cold and hard.