$2 Brass* 
then raise the fire and heat briskly for half an hour long* 
er„ 
This process of cementation is. also neatly shewn by the 
following management, as given by Cramer. 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 copper, cover the whole with fine charcoal pow- 
der, 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 gradually 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 operation 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 compared 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 on 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 copper 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 however only aris- 
ing from the minute particles of iron beaten off the ham- 
mer during the process and forced into the surface of the 
brass, but this circumstance makes it necessary to em- 
ploy unhammered brass for compass-boxes and similar 
apparatus.* 
The expansion of brass has been very accurately de- 
termined, as this metal is most commonly used for ma- 
thematical and astronomical instruments, where the ut- 
* The brass contains iron. T. C, 
