May 23, 1872] 



NATURE 



67 



Beside these various forms, there occur all kinds of 

 crystalline combinations, as, for instance, the spray 

 sketched in Fig. 4, where the rough branches have ter- 

 minated each in a large hexagonal plate, and the flowing 

 past of a weakened solution has afterwards caused the 

 growth of delicate fern-leaves. Often, too, a large ex- 

 pansion will take place in every direction, though joined 

 to the parent stem by an almost invisible thread ; or from 

 the point of a long crystal there will branch out to right 

 and left crescent-shaped structures, a process the com- 



mencement of which is seen in one of the side rays of 

 Fig. I. The last traces of silver in the liquid will fre- 

 quently give rise to delicate crystalline filaments wander- 

 ing over the surface of the glass, as in Fig. 5. 



If a piece of zinc be placed in a solution of neutral ter- 

 ohloridc of gold, containing q per cent, of salt, there is 

 an immediate outgrowth of black gold, which speedily 

 changes to an advancing mass of yellow or perhaps lilac 

 metal in lichen-like forms, from which proceed beautiful 

 fringes of yellow or black, ending generally in such 



Fig 7 



arborescent forms as are represented in Fig. 7. As these 

 branches push into the yellow liqu'd, it becomes colourless 

 even in advance of their points, and it frequently happens 

 that yellow crystals of some salt shoot out in front of the 

 crystallising 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 touching at one point a 

 loose piece of gold, which immediately in its turn became 



a"tive, and commenced ti sprout on its farther side. 

 Copper salts give round mdules, which have no crystal- 

 line appeirance when deposited from moderately weak 

 solutions, but a very strong solution of the chloride — ibout 

 40 per cent. — yields with zinc first a black thick growth, 

 then arborescent fringes of red metal, terminanng in crys- 

 tals of very appreciable size. 



The fringes referred to in the case of these three met lis 

 are stiU more characteristically developed by bismuth. 

 When a solution of terchloride of b'smuth acts on zinc, 



there is an immediate outgrowth of black fringes, such as 

 Fig. 8, where they are seen on an illuminated held. These, 

 as they advance, become more and more arborescent, and 

 as the crystalline character develops itself more they 

 change from black to grey. Sometimes bismuth presents 

 itself in botryoidal masses, but the tendency to form these 

 fringes is very strong. 



Chloride of antimony with zinc also gives these black 

 fringes. Lead salts yield crystals resembhng those of 

 silver ; but leaves of irregular hexagonal plates prevail, 



and often grow to a lirge size. A solution of acetate of 

 thallium, containing 20 per cent, of salt, quickly gives a 

 beautiful forest of thorny crystals. Sulphate of cadmium 

 gives rise to a small leaf-like growth on zinc ; but a strong 

 solution of chloride produces an appearance of sticks 

 covered with small spines or knobs. The new metal in- 

 dium 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 solu- 



