422 — Mr. HK. H. Hall on the Rotation of the 
: Copper. Zine. 
eye bake Ter cent per cent. 
A SP) 
B 81:08 13-51 
C 72°86 27°02 
D 66°35 33°04 
F Sol 93°79 
G a trace 99°54 
Specimen E, which contained apparently about 50 per cent. 
copper, was so brittle that I did not succeed in getting it 
rolled into a thin sheet. 
Most, if not all, of these specimens were annealed one or 
more times during the process of rolling. None of the strips 
examined, however, were annealed after the final rolling. All 
of the strips which were used were cut in such a way that the 
arms a, a extended in that direction in which the strips passed 
through the rolls. 
As it is a somewhat troublesome matter to determine accu- 
rately the density of a thin strip of metal, and as my imme- 
diate purpose did not demand great accuracy in this respect, 
it seemed allowable to estimate the density of the alloys from 
their composition. After certain rough experiments the 
density 8°9 was assumed for the copper, and 7:2 for the zinc. 
Assuming, what we know to be not strictly true, that the 
density of an alloy decreases regularly as its amount of zinc 
per unit mass increases, we find :—. 
Alloy. Density. 
i Baetepinteont 8°6 
Ore aae ie 8°4 
Ditvcapetiate 8°3 
Ry bitte 73 
The description of particular strips will now be given. 
A Nor 1) 
Length of main strip when weighed . 4:20cm. 
Width of main strip when weighed. . 1:07 cm. 
Area, including that of the arms . . 4°98cm. sq. 
Weight manic dsc cuisaey ts, nym) jotee iene Deore 
Density (5 3. T.daee eatery > eee 
Average thickness from above . . . ‘00456 cm. 
By calipers the thickness appeared to be at one end ‘0046; 
other end -0044 ; between arms ‘0048; average 0046. Take, 
then, for true thickness between arms, ‘00476. 
