The ornamental alum baskets, whose manufacture was once so favourite a
pursuit of lady-chemistry, were made upon this principle; the forms of
the baskets being determined by wire framework, to which the crystals
readily adhere.
Why is sugar-candy sometimes in large and regular crystals?
Because the concentrated syrup has been kept for several days and nights
_undisturbed_, in a very high temperature; for, if perfect rest and
a temperature of from 120 deg. to 190 deg. be not afforded, regular
crystals of candy will not be obtained.
The manufacture of barley-sugar is a familiar example of
crystallization. The syrup is evaporated over a slow heat, till it has
acquired the proper consistence, when it is poured on metal to cool, and
when nearly so, cut into lengths with shears, then twisted, and again
left to harden.
Heat.
Why does hay, if stacked when damp, take fire?
Because the moisture elevates the temperature sufficiently to produce
putrefaction, and the ensuing chemical action causes sufficient heat to
continue the process; the quantity of matter being also great, the heat
is proportional.
Pages:
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66