ON THE FOEMATION OF MOSS GOLD AND SILVER. 131 



Exijeriment. — I placed some lumps of native copper disulpliide 

 {^BedrtitJiite) in a hard-glass bulb tube, heated and passed current 

 of hydrogen gas. After the experiment the whole surface of the 

 mineral was found to be thickly covered with a nap of acicular 

 filaments of copper. No traces of fusion were exhibited. 



Dr. Percy also shows by a series of experiments that metallic 

 copper is- separated in a similar way by simply fusing some copper 

 disulphide (CusS.) in a crucible. And he further states that 

 there is at present no certain knowledge of the cause which 

 brings this about. 



The foregoing results obtained by diiFerent eminent scientific 

 observers, together with those yielded by my own experiments, 

 afford, I think, some very interesting information, m.uch important 

 matter for reflection, and a large field for future experiment. 



The conditions under which the formation of crystals have been 

 observed may be briefly stated to be comprised by the following- 

 divisions ; i.e., crystallization takes place under the following 

 conditions : — 



MetJiods hy ivJiicJi crystallization may he produced. , 



1. By condensation feom a state of vapoue. 



2. Feom solution. 



3. Feom a state of fusion. 



4. By electeolysis. 



5. By " spontaneous" CHANGE. 



6. By theemo-eeduction. 



1. Condensation of a substance from a state of vapour — e.g., 

 iodine, arsenic, water vapour yielding snow and hoar-frost. 



2. Crystallization from solution.- — As when crystals of a salt are 

 obtained by the evaporation of its solvent ; and as when a solution 

 of sulphur in carbon disulphide is allowed to evaporate spon- 

 taneously, beautiful crystals of sulphur are left. 



3. On solidification from a state of fusion. This is commonl}^ 

 seen when metals such as bismuth, antimony, and others are 

 allowed to solidify slowly. Beautifully crystallized examples of 

 such metals and of sulphur may be readily obtained in the fol- 

 lowing way : — Melt a considerable quantity of the substance in a 

 crucible or ladle, and when a thin coat has formed over the 

 surface by cooling, pierce the crust and pour out the still 

 fluid contents as quickly as possible. A large part of the metal 

 or sulphur, as the case may be, will be left lining the inside of 

 the crucible in the form of most beautiful groups of crystals 

 with sharply defined edges and angles, and not as the rounded 

 imperfect semifused-looliing bodies that we might naturally 

 expect when we consider the density and viscosity of the fluid 

 in winch they were formed and by which they were bathed. 



