CRYSTALLIZATION OF GOLD, SILVER, ETC. 437 



arborescent forms as are represented in Fig, 6. As these branches 

 push into the yellow liquid, it becomes colorless even in advance of 

 their points, and it frequently happens that yellow crystals of some 

 salt shoot out in front of the crystallizing metal, which follows them 

 and builds up its advancing fronds at their expense. This is shown in 

 the figure. The gold will generally shoot its yellow branches rapidly 

 round the margin of the drop. Such a running branch has been seen 

 to stop on coming in contact with a loose piece of gold, which imme- 

 diately in its turn becomes active, and commences to sprout on its 

 farther side. Copper salts give round nodules, which have no crystal- 

 line appearance when deposited from moderately weak solutions, but a 

 very strong solution of the chloride — about forty per cent. — yields with 

 zinc, first a thick, black growth, then arborescent fringes of red metal, 

 terminating in crystals of very appreciable size. 



The fringes referred to in the case of these three metals are still 

 more characteristically developed by bismuth. When a solution of the 

 terchloride of bismuth acts on zinc there 

 is an immediate outgrowth of black fringes, 

 as in Fig. 7, where they are seen on an 

 illuminated field. As they advance, these 

 become more arborescent, and as the crys- 

 talline character becomes more developed 

 they change from black to gray. Some- 

 times bismuth presents itself in botryoidal 

 masses, but the tendency to form the fringes 

 is verv strons;. 



Chloride of antimony with zinc also 

 gives black fringes. Lead salts yield crys- 

 tals resembling those of silver, but leaves 

 of irregular, hexagonal plates prevail, and 

 frequently become of large size. 



A solution of acetate of thallium, of 

 twenty per cent, of salt, quickly gives a 

 beautiful forest of thorny crystals. Sul- 

 phate of cadmium gives rise to a small, 

 leaf-like growth on zinc ; but a strong solution of the chloride produces 

 an appearance of sticks covered with small spines or knobs. The new 

 metal indium is thrown down upon zinc in the form of thick, white 

 crystals. The deposition is promoted by touching the zinc with a piece 

 of iron. 



Tin gives beautiful results. If zinc be placed in a solution of stan- 

 nous chloride it is quickly surrounded with a growth of prolonged octo- 

 hedra, and as these advance into the liquid it is easy to observe that 

 the additions of new metal commence at the apex, and that the wave 

 of chemical change proceeds down the lateral edge, occupying some 

 seconds of time in depositing the new layer of material. Frequently, 



Fig. 7. 



