Brass . 
85 
most precision is required. Mr. Smeaton found that 12 
inches in length of cast brass, at 32°, expanded by 180 
degrees of heat (or the interval 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 22 parts- 
The expansion of hammered copper is only 204 such 
parts, but that of zinc is 253, so that brass holds a mi d» 
die place, in this respect, between its two component 
metals. 
Most of the zinc readily burns off from brass when kept 
melted in a strong heat with free access of air. When the 
heat is equal to that of melted copper, the zinc takes fire 
and slowly burns away. At last little else but copper re- 
mains, but still united with a small portion of zinc, which 
no further continuance of the fire will entirely separate. 
Some kinds of very fine brass are said not be made by 
cementation in the way already described, but by a more 
speedy and direct union of copper and zinc, care being 
taken to prevent the access of air to the materials while in 
fusion. Very fine brass may also be made by mixing to- 
gether the oxyds of copper and zinc, and reducing them 
with a carbonaceous flux. This idea is ingenious, and 
from the intimate mixture of the two metals which it pro- 
mises, it deserves to be further pursued. M_. Sage, gives 
the following experiment to this purpose. Mix together 50 
grains of the oxyd of copper, remaining after the distilla- 
tion of verdigris (which is very pure) with 100 grains of 
lapis calminaris, 400 grains of black flux, and 30 grains 
of charcoal powder ; melt the mixture in a crucible till 
the blue flame is seen no longer round the lid of the cruci- 
ble, and when cold a fine button of brass is found beneath 
the scoria, weighing a sixth more than the copper alone,, 
obtainable from its, oxyd in the same way but without 
the calamine. This brass has a very fine colour like gold 
