5 
Mr Brooke on Crystallisation. 
conclusions which will explain the natural processes of crystalli- 
sation ; nor are the causes which produce the almost endless 
variety of crystalline forms capable of explanation, from the phe- 
nomena attending the production of artificial crystals. With a 
view, however, to investigate those causes, many experiments 
have been made, from which several curious and interesting re- 
sults have been obtained. 
Most bodies have a tendency to crystallise in passing from a 
state of fusion or solution into a solid state. 
Ice may, in the strict language of chemistry, be said to be- 
come fusible at 32° of Fahrenheit ; and water, on the other 
hand, may be said to crystallise at that temperature, although 
it does not exhibit regular cleavage-planes when broken. High- 
ly concentrated acetous acid becomes solid, and assumes a crys- 
talline form, at about 50° Fahrenheit; and mercury crystal- 
lises at about 72° below the freezing point of water, and when 
in a solid state it is brittle, and exhibits a distinct crystalline 
fracture, if broken. Lead, antimony, and most other metals, 
become fluid at different temperatures above that of boiling wa- 
ter ; and, when suffered to cool gradually from the melted state, 
they may be brought to crystallise with more or less regularity. 
For this purpose, they are to be melted in deep vessels, and 
when the metal has become solid at the surface by slow cooling, 
that surface is to be broken, and the metal which remains fluid 
within to be poured out. The hollow which remains will fre- 
quently be found lined with very regular crystals. 
Among the slags from furnaces regular crystals will also fre- 
quently occur, not only of metallic, but of earthy substances. 
The crystals of titanium, from the iron-works of Merthyr Tyd- 
vill have been already alluded to. I have seen, in the posses- 
sion of Mr Rose of Berlin, some crystals in a slag, which were 
black, opaque, and had the form and measurements of pyroxene. 
The same gentleman has also shewn me a portion of a fused crys- 
talline mass, resembling, in appearance and measurement, the 
pyroxene from Ala in Piedmont. This mass was produced, 
by fusing, in a porcelain furnace, a mixture of the elements of 
pyroxene, in the proportions in which they occur in that mine- 
ral ; and it is said to be similar to pyroxene in hardness and 
specific gravity. 
