Marcu 28, 1912] 
NATURE 
IOl 
but the excellence of Corinthian bronze 
recognised long before. 
Whatever may have been the exact composition of 
this bronze, of which several statues are said to have 
been cast, | may say that no addition of gold or 
silver to any copper-tin alloy will cause it to resemble 
gold closely. Imagination must, I think, be respon- 
sible for the accounts given of this bronze by ancient 
authors, especially when we read also that its beauty 
was derived from being cooled in the water of the 
fountain of Peirene. 
With the fall of Greece and the rise of the supre- 
macy of Rome we enter an important period in the 
history of copper and its alloys. In Spain and in 
Britain we find copper-smelting being vigorously 
carried on by the Romans, and in Rome and the 
chief seats of the empire a further extension of the 
use of bronze, not only for statues and other objects 
of art, but for vessels of all kinds, furniture, and 
other articles of domestic life. Of special importance 
is the invention of a new alloy, brass, which comes 
into use for the first time in Europe. 
Among the varied remains which are representative 
of the Roman occupation of Britain, few are of 
greater interest to the metallurgist than the cakes 
of copper found in North Wales and Anglesea. These 
cakes afford us, in their form and character, un- 
mistakable evidence of their history. They had been 
obtained by smelting sulphide ores, or ores containing 
sulphides, in low hearths, in which they had almost 
certainly been allowed to solidify before removal. 
According to Pliny, who seems in this matter to 
have had access to fairly trustworthy sources of in- 
formation, the copper obtained by smelting was brittle 
and useless, and in order to obtain malleable metal 
from it, it was mixed with lead and melted several 
times, and the oftener the operation was repeated 
the better was the quality of the copper. This brief 
account of copper-refining by a non-technical writer 
gives us an excellent résumé of the process as prac- 
tised in Roman times. The operation was evidently 
conducted with free access of air, and the lead used 
would, by its oxidation, aid greatly in the removal of 
impurities from the copper. 
The earliest Roman alloys which have come down 
to us are copper, lead, tin, alloys of the fifth century 
B.c. Their chief peculiarity is their very large content 
of lead, namely, from about 19 to 25 per cent., the 
tin being about 7 per cent. They were worthless for 
practical purposes, but formed the alloy of which the 
large coin of the republic—which weighed from 8 to 
11 ozs.—the ‘‘As,’’ was cast. These copper-lead-tin 
alloys continued in use as coinage alloys until 20 B.c., 
but from that date until two centuries later lead is 
seldom found in coins except as an_ accidental 
impurity. 
The large percentages of lead were undoubtedly 
added in these cases on account of the cheapness of 
the metal as compared with copper and tin. 
The copper-tin-lead bronzes appear also to have 
been used by the Romans for engineering and indus- 
trial purposes. An interesting example of this use 
is afforded by the broken shaft of a water-wheel 
which was found in the lower Roman workings of 
the north lode of the Rio Tinto mine. The water- 
wheel was probably built in the first century of our 
era, as coins of the time of Vespasian (7o to 81 A.D.) 
were found near it. 
The bronze used for statues by the Romans also 
always contains lead in considerable proportions, as 
much as 6 to 12 per cent. being often present. In 
this they were doubtless influenced by Greek practice, 
the lead being added to the bronze to increase its 
fusibility and more especially its fluidity when molten, 
NO. 2213, VOL. 89] 
had been 
so that it might receive the sharpest possible impres- 
sions of the mould. 
I may point out here that the addition of lead to 
bronze was and is largely practised by the Japanese, 
not only for the reasons stated above, but also to 
' enable the objects cast of the alloy to receive a rich 
brown patina when suitably treated; and in this con- 
nection it is worthy of note that Pliny states that by 
the addition of lead to Cyprian copper, the purple 
tint is produced that we see in the drapery of statues. 
The alloy used by the Romans for mirrors does 
| not differ greatly from that in use in Europe for 
| metallic mirrors in comparatively recent times, the 
percentage of tin ranging from 
23) to) 28 per cent 
but lead is present in all from about 5 to 7 per cent. 
CopPER-zINC ALLOYS—THE BRASSES. 
Zinc as a distinct metal was unknown in early 
| times; in fact, as late as the sixteenth century it 
was not known in Europe; but there are strong 
reasons for the belief that the Chinese were acquainted 
with it as metal at least several centuries eariier. 
It is occasionally but rarely present in the implements 
and weapons of the Bronze age, and then only in 
small quantities as an accidental impurity, which has 
been derived from smelting copper ores containing 
it. 
In somewhat later times it occurs in rings, armlets, 
and other personal ornaments found in the ancient 
burial mounds of Germany and Denmark, but these 
mounds are of post-Roman date, and the objects men- 
tioned have really been made from Roman coins. 
In Greek alloys zinc is never found .s an inten- 
tional addition, but only as an impurity, about 1 to 2 
| per cent. or less; in fact, according to Gobel, all 
antique objects which contain zinc are not Greek; 
but this, in my opinion, is only true for those con- 
taining considerable proportions of the metal, and not 
for those with the small amounts just mentioned. 
In Roman times it first appears in the coins of 
the republic as an impurity; as an intentional addi- 
tion, however, it only begins in the time of Augustus 
(20 B.c. to 14 A.D.), when brass was made for the first 
| time in the world’s history. 
One of the earliest examples is a coin of 20 B.c., 
which contains 17°31 per cent. of zinc. 
The Romans were the first makers of brass. 
Although they were unacquainted with the essential 
constituent zinc, yet they had discovered that by melt- 
ing copper together with a certain ore (calamine), a 
yellow alloy of a more golden colour than bronze 
could be obtained. 
It was first employed for coins which appear to 
have had a higher value than those of bronze, even 
up to the time of Diocletian (286 to 305 a.D.), when 
six parts of brass are said to have been worth eight 
parts of copper. There is, too, a curious statement 
by Procopius in his De Gédificiis relating to its value 
in the fifth century a.D., in which he says that brass 
was then not very greatly inferior to silver. 
The method employed by the Romans in making 
this alloy from copper and calamine was a very simple 
one. 
It was conducted as follows :—The calamine was 
ground and mixed in suitable proportions with char- 
coal and copper in granules or small fragments. This 
mixture was placed in a crucible, and was very care- 
fully heated for some time to a temperature sufficient 
to reduce the zinc in the ore to the metallic state, 
but not to melt the copper. The zinc being volatile, 
its vapour permeated the fragments of copper, con- 
verting them into brass. The temperature was then 
raised, when the brass melted, and was poured out 
of the crucible into moulds. 
