DECEMBER 10, 1396] 
NATURE 
0 
ABCD being similar in the case of all the brasses. It 
may be seen that reheating has no effect on the tensile 
strength of copper unless the temperature exceeds 280, | 
when there is a progressive lowering of the tensile strength 
until the temperature reaches 420. Above that point a 
further increase of temperature has no effect on the metal, | 
Finally, when the tem- | 
the annealing being complete. 
perature is so high that the copper is ‘ burnt,” the tensile 
strength again falls off rapidly. 
It is remarkable, however, that the more thoroughly 
the test piece is hardened, and consequently the higher 
its initial tensile strength, the lower is the temperature 
(in the above instance, 280°) at which the annealing effect 
becomes sensible. M. Charpy suggests, therefore, that 
in pure, completely hardened copper or brass, any in- 
crease in temperature, above that at which the hardening 
was effected, would cause a reduction in the tensile 
strength, and that the broken curve CBA would then be 
a straight line, CBE. It would thus be predicted, as 
may be seen by a glance at the diagram, that the tensile | 
strength of completely hardened pure copper would be 
about 52 kilogrammes per square millimetre, and, asa 
matter of fact, A. Le Chatelier raised the tensile strength 
a 
1000. 
800: 
700: 
600. 
+ 500. 
30 
2 2s 30 3 
. Tensile strength. 
Fic. 
1.—Variations in the tensile-strength of metallic copper. 
of copper to 51 kilogrammes by successive wire-draw- 
ings. In spite of this close agreement, the inference 
must be accepted with some caution, for apparently there 
were no experiments made on copper annealed at tem- 
peratures between 280° and 420. Nevertheless the 
approximate correctness of the general direction of the 
line BC is attested by a number of results obtained on 
the analogous parts of the curves obtained by studying 
the brasses, whence, for example, it may be deduced that 
the maximum tensile strength of the alloy containing 
30°2 per cent. of zinc should be about 70 kilogrammes per 
square millimetre, or 44 tons per square inch. 
In tests made on completely annealed bars, in which 
M. Charpy believes that all accidental differences in the 
physical conditions are eliminated, he finds that the ten- 
sile strength increases with the percentage of zinc, passes 
through a maximum when the alloy contains about 45 
per cent. of zinc, and then decreases rapidly. The 
elongation increases similarly with the percentage of zinc, 
NO. 1415, VOL. 55] 
but passes through a maximum when the alloy contains 
30 per cent. of zinc, and then decreases rapidly. It 
follows that there is no advantage in using for industrial 
purposes alloys containing less than 30 per cent. of zinc, as 
they are more costly, and possess both less resistance and 
less malleability than those richer in zinc. On the other 
hand, if there is more than 43 per cent. of zinc present, 
the alloys are brittle, and should not be employed, so 
that only those with from 30 to 43 per cent. of zinc can 
be recommended for use. 
In the micrographical researches, in which enlargements 
of 30 diameters with obliquely falling light were studied. 
Fic. 
2.—Alloy containing copper 80 per cent., zinc 20 per cent., annealed 
at 700°. 
appearances were noted by M. -Charpy corresponding 
to many of the results of the mechanical tests. Thus, 
for example, on hardening alloys containing from o to 
35 per cent. of zinc by passing them through the rolls, 
the crystals are gradually deformed and disappear, a 
homogeneous granulated surface being obtained. When 
the hardened alloys are annealed, the crystals are re- 
formed, their size depending on the maximum temperature 
attained, and not on the length of time during which 
they were subjected to it. No striking change is pro- 
duced by reheating to temperatures below that at which 
;. 3.—The same annealed at goo’, showing increase in the size 
of the crystals. 
Fr 
complete annealing is effected, but above that temperature 
| the alloys become completely crystalline, showing no 
amorphous magma, and the crystals grow larger and 
larger as the temperature is raised and the tensile 
strength falls off. Thus Fig. 2 shows an alloy containing 
20 per cent. of zinc which has been hardened and 
annealed at 700°, and Fig. 3 shows the same alloy 
The crystals are octahedra with 
annealed at goo’. : 
and are obviously larger in the latter 
numerous macles 
case than in Fig. ; p 
When the reheating is carried to a very high tem- 
