LEAD. 



323 



this, if the nails are touched by a piece of iron, which has not undergone the 

 action of nitric acid, they are immediately acted upon, and a giving off of 

 nitrous vapour is manifested with great energy. Lead is a very soft metal, 

 and can even be scratched by the nails. It is also extremely pliable, and 

 so entirely devoid of elasticity that when bent it has no tendency whatever to 

 return to its primitive form. Lead is heavy, and has a density represented 

 by 1 1'4 ; that is to say, the weight of a quart of water being one kilogram, 

 that of the same volume of lead is 1 1 '400 k. 



Fig. 313 represents cylindrical bars of the best known metals, all 

 weighing the same, showing their comparative density. 



Fig. 312. Iron and nitric acid. 



Lead, like tin, is capable of taking a beautiful crystalline form when 

 placed in solution by a metal that is less oxydisable. The crystallization of 

 lead, represented in fig. 3 14, is designated by the name of the Tree of Saturn. 

 This is how the experiment is produced : Thirty grams of acetate of lead are 

 dissolved in a quart of water, and the solution is poured into a vase of a 

 spherical shape. A stopper for this vase is made out of a piece of zinc, to 

 which five or six separate brass wires are attached ; these are plunged into 

 the fluid, and we see the wires become immediately covered with brilliant 

 crystallized spangles of lead, which continue increasing in size. 



The alchemists, who were familiar with this experiment, believed that 

 it consisted in a transformation of copper into lead, while in reality it only 



