But the
elements of this quantity of uncrystallized alum could not be computed.
Then we may define crystallization to be the operation of nature wherein
the chemical atoms or molecules of a substance have sufficient polarized
force to arrange themselves about a central attracting point in definite
geometrical forms.
Fresenius defines it thus: "_Every operation, or process, whereby bodies
are made to pass from the fluid to the solid state, and to assume_
certain fixed, _mathematically definable, regular forms_." It would be
folly for me to attempt to criticise Fresenius, but I give you both
definitions, and you can take your choice. The definition of Fresenius,
however, will not suit our present purpose, because the crystallization
of wrought iron occurs, or seems to, _after_ the iron has acquired a
_solid state_.
Iron, as you all know, is known to the arts in three forms: cast or
crude, steel, and wrought or malleable. Cast iron varies much in
chemical composition, being a mixture of iron and carbon chiefly, as
constant factors, with which silicium in small quantities (from 1 to
5 per cent.), phosphorus, sulphur, and sometimes manganese (e.g.
spiegeleisen) and various other elements are combined. All of these have
some effect upon the crystalline structure of the mass, but whatever
crystallization takes place occurs at the moment of solidification, or
between that and a red heat, and varies much, according to the time
occupied in cooling, as to its composition.
Pages:
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171