ERA 
in different works, being determined by 
custom, by the quantity of materials, the 
size of the crucibles, and especially the na- 
ture of the calamine. In the great way 
from 10 to 24 hours are required. At Hol- 
lywell, in Flintshire, about 24 hours are 
taken. 
In the laboratory, brass may be made very 
well in the small way in a short time. Put into 
a crucible a mixture of calamine and char- 
coal, bury it in the requisite proportion of 
copper shot, cover the whole with charcoal 
powder, lute on a cover to the crucible, 
and heat slowly in a wind-furnace for half 
an hour, till the zinc begins to burn off in a 
blue flame round the top of the crucible ; 
then raise the fire and heat briskly for half 
an hour longer. This process of cementa- 
tion is also shewn by the following manage- 
ment. Put the mixture of calamine and 
charcoal into a crucible, cover it with a 
thin layer of clay, over which, when dry, 
lay a thin plate of fcopper ; cover the whole 
with fine charcoal powder, and lute on a 
cover to the crucible. Apply heat gra- 
dually, and the vapour of the reduced zinc 
will rise through the floor of clay, penetrate 
the red-hot copper plate above it, and gra- 
dually convert it into brass, which at the 
end of the operation will be found lying 
melted on the stratum of clay. The increase 
of weight gained by the copper in this ope- 
ration will afford a good practical test of 
the goodness of the calamine, and its fitness 
for brass-making in the great way. The 
most important properties of brass com- 
pared with copper are the following : the 
colour of brass is much brighter, and more 
approaching to that of gold ; it is more 
fusible than copper; less subject to rust, 
and to be acted upon by the vast variety of 
substances which corrode copper with so 
much ease ; and it is equally malleable when 
cold, and more extensible than either cop- 
per or iron, and hence is well fitted for fine 
wire. Brass, however, is only malleable 
when cold. Hammering is found to give a 
magnetic property to brass, perhaps, how- 
ever, only arising from the minute particles 
of iron beaten off the hammer during the 
process, and forced into the surface of the 
brass ; but this circumstance makes it ne- 
cessary to employ unhammered brass for 
compass-boxes, and similar apparatus. The 
expansion of brass lias been very accurately 
determined, as this metal is most commonly 
used for mathematical and astronomical in- 
struments, where the utmost precision is 
required. Mr. Smeatou found that twelve 
inches in length of cast brass, at 32°, ex- 
BRA 
panded by 180 degrees of heat (or the inter-, 
val from freezing to boiling water) 225 ten 
thousandth parts of an inch. Brass wire 
under the same circumstances expanded 
232 parts, an alloy of 16 of brass with 1 of 
tin expanded 229 parts. The expansion of 
hammered copper is only 204 such parts : 
but that of zinc is 253 ; so that brass holds 
a middle place in this respect between its 
two component metals. 
Analysis shews a vast variety in the pro- 
portions of the different species of brass 
used in commerce. In general the extremes 
of the highest and lowest proportions of 
zinc are from 12 to 25 per cent, of the brass. 
Even with so much as 25 per cent, of zinc, 
brass, if well manufactured, is perfectly 
malleable, though zinc itself scarcely yields 
to the hammer. Mr. Dize analyzed a spe- 
cimen of remarkably fine brass made at 
Geneva, for the purpose of escapement 
wheels, and the nicer parts of watch- making, 
the perfec 1 bars of which bear a very high 
price. This metal unites great beauty of 
colour to a very superior degree of ductility. 
It was found to consist of 75 Of copper with 
25 of zinc, and probably too the copper was 
Swedish, or some of the finer sorts. The 
common brass of Paris seems to contain 
about 13 per cent, of zinc, the English pro- 
bably more. The uses of brass are very 
numerous. It is applicable to a great va- 
riety of purposes, is easily wrought by cast- 
ing and hammering, and by the lathe ; its 
wire is eminently useful, and it takes a high 
and very beautiful polish. The appearance 
of brass is given to other metals, by washing 
them with a yellow laquer or varnish, a sub- 
stitution often very much to the detriment 
of the manufactured article. Many other 
yellow alloys of copper are used, such as 
bronze, bell-metal, &c. most of which are 
triple compounds, and will be noticed under 
the article Copper. 
BRASSICA, in botany, a genus of the 
Tetradynamia Siliquosa class and order. 
Natural order of Siliquosa or Cruciformes. 
Cruciferse, Jussieu. Essential character ; ca- 
lyx erect, converging; seeds globular; a 
gland between the shorter stamens and the 
pistil, and between the longer and the ca- 
lyx. There are sixteen species, among 
which are the various kinds of cabbages 
bore-coles; brocolis, and, turnips. To give 
a short account only of this important ge- 
nus would exceed the limits of our work ; 
we can therefore refer the reader with plea- 
sure to Dr. Rees’s New Cyclopedia, where 
he will find, under the words Brassica, 
and Cabbage, every information he can dc- 
