DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.619#0080
THE WEIGHTS OF NAUKRATIS.
71
Name.
Formula
Silver, chloride .
• AgCl
Silver, sulphide
• AgS
Copper, oxide (black)
. CuO
Copper, sub-oxide (red)
. Cu20
Wpi?ht of Percental
cubic inch, non-metallic.
1400 -21-7
1820 12-9
1640 20-1
1450 11-2
Copper, sulphide (black soft) Cu2S 1460 20'1
Copper, green carbonate . CuO, H20, CuC03 960 42'5
Copper, blue carbonate . CuO, H»0,2CuC03 960 44'5
Tin, binoxide . . . Sn02 1760 21-3
Lead, carbonate. . . PbCOs 1630 22-6
Lead, sulphate . . . PbSO, 1590 26'4
Zinc, carbonate . . . ZnC03 1110 48-0
The extent of the change is to he estimated by
measuring the thickness of the scale of compound
and its area, thus ascertaining its cubic volume;
and hence, by the weight of a cubic inch given
above, its weight.
To find the thickness of a scale or crust of
compound, a hole should be cut through it with
a hard-steel point in two or more places; then
examining it with a magnifier, and by a scale of
xinrths of an inch, the thickness may be estimated.
The general surface of a weight must also be
taken into account, and the crust examined at a
point which is likely to yield a fair average, and
not close to an edge, which is always more deeply
corroded. For leaden weights some estimate must
be made of the loss of carbonate of lead by solu-
tion or wear; and the same is sometimes requisite
for copper weights: any fragments of an original
outer surface must be observed, and the proportion
of loss judged by examination with a magnifier.
If the weight be of stone, the loss must be com-
pared with a set of samples of stone of different
textures and surface, ground or reduced to dif-
ferent amounts, which are duly recorded as a scale
of comparison. The loss is of three classes: (1)
wear of surface by rubbing, generally not over five
grains per square inch; (2) wear of edges by
bruising, generally not over three grains per inch
length; and (3) chips, which may be of any extent
up to the loss of the greater part of the weight.
Five or six examples of each of these sorts of loss
were prepared and used as standards of comparison
for all the stone weights here treated.
In some cases of metal weights it is desirable,
if they are deeply encrusted, to clean them. It
need hardly be said that to clean a weight without
using the balance is a vandalism worthy of Mum-
mius. The first step is to examine the surface
closely, and settle what fraction of the whole crust
has been already lost by rough usage; this may
be scarcely any, or may be the greater part. Then
weigh the weight; then remove the crust (gene-
rally by cracking it off by light blows), weigh the
weight again, and take the difference as the
amount of scale removed. Note what the com-
position of the scale is, and also what nature and
amount of compound may remain on the weight.
Sometimes copper weights may be found with only
a small core of metal, the greater part of the bulk
below the green carbonate when that is removed
proving to be red oxide, or in other cases the
whole of the inner mass is black oxide. A small
drill is required to test the thickness of the com-
pound when it is so considerable. Of course the
gain of weight in the crust is ascertained by the
percentage of non-metallic maUcr given in the
above table.
88. To take now some actual examples of the
methods followed in the present work. After
weighing a stone weight, and applying the cor-
rections for inequality of balance-arms and error
of weights used, we have 1259*2 grains for its
present weight; the bruising of the edges is esti-
mated by comparison at *3 grain per inch run,
their length is 7 inches, loss therefore 2'1 grains;
there is a chip of ■$ grains, and so the total loss
is 2-4 grains, and the original weight therefore
1261-6. Again, another is now 9G0-2; it has lost
2 grains per square inch of surface, and is 6}
square inches in area; adding therefore 13 grains,
we have 973' grains for the original weight. A
copper weight is now 2G8-5 grains; the thickness
1 It is a needless and misleading statement to enter tenths
of a grain when the uncertainties of estimating the loss
amount to many grains. In cases of allowances of 40 or
50 grains, it is best to state only the nearest 10 grains ; the
character of a statement should always correspond to it?
real accuracy.
71
Name.
Formula
Silver, chloride .
• AgCl
Silver, sulphide
• AgS
Copper, oxide (black)
. CuO
Copper, sub-oxide (red)
. Cu20
Wpi?ht of Percental
cubic inch, non-metallic.
1400 -21-7
1820 12-9
1640 20-1
1450 11-2
Copper, sulphide (black soft) Cu2S 1460 20'1
Copper, green carbonate . CuO, H20, CuC03 960 42'5
Copper, blue carbonate . CuO, H»0,2CuC03 960 44'5
Tin, binoxide . . . Sn02 1760 21-3
Lead, carbonate. . . PbCOs 1630 22-6
Lead, sulphate . . . PbSO, 1590 26'4
Zinc, carbonate . . . ZnC03 1110 48-0
The extent of the change is to he estimated by
measuring the thickness of the scale of compound
and its area, thus ascertaining its cubic volume;
and hence, by the weight of a cubic inch given
above, its weight.
To find the thickness of a scale or crust of
compound, a hole should be cut through it with
a hard-steel point in two or more places; then
examining it with a magnifier, and by a scale of
xinrths of an inch, the thickness may be estimated.
The general surface of a weight must also be
taken into account, and the crust examined at a
point which is likely to yield a fair average, and
not close to an edge, which is always more deeply
corroded. For leaden weights some estimate must
be made of the loss of carbonate of lead by solu-
tion or wear; and the same is sometimes requisite
for copper weights: any fragments of an original
outer surface must be observed, and the proportion
of loss judged by examination with a magnifier.
If the weight be of stone, the loss must be com-
pared with a set of samples of stone of different
textures and surface, ground or reduced to dif-
ferent amounts, which are duly recorded as a scale
of comparison. The loss is of three classes: (1)
wear of surface by rubbing, generally not over five
grains per square inch; (2) wear of edges by
bruising, generally not over three grains per inch
length; and (3) chips, which may be of any extent
up to the loss of the greater part of the weight.
Five or six examples of each of these sorts of loss
were prepared and used as standards of comparison
for all the stone weights here treated.
In some cases of metal weights it is desirable,
if they are deeply encrusted, to clean them. It
need hardly be said that to clean a weight without
using the balance is a vandalism worthy of Mum-
mius. The first step is to examine the surface
closely, and settle what fraction of the whole crust
has been already lost by rough usage; this may
be scarcely any, or may be the greater part. Then
weigh the weight; then remove the crust (gene-
rally by cracking it off by light blows), weigh the
weight again, and take the difference as the
amount of scale removed. Note what the com-
position of the scale is, and also what nature and
amount of compound may remain on the weight.
Sometimes copper weights may be found with only
a small core of metal, the greater part of the bulk
below the green carbonate when that is removed
proving to be red oxide, or in other cases the
whole of the inner mass is black oxide. A small
drill is required to test the thickness of the com-
pound when it is so considerable. Of course the
gain of weight in the crust is ascertained by the
percentage of non-metallic maUcr given in the
above table.
88. To take now some actual examples of the
methods followed in the present work. After
weighing a stone weight, and applying the cor-
rections for inequality of balance-arms and error
of weights used, we have 1259*2 grains for its
present weight; the bruising of the edges is esti-
mated by comparison at *3 grain per inch run,
their length is 7 inches, loss therefore 2'1 grains;
there is a chip of ■$ grains, and so the total loss
is 2-4 grains, and the original weight therefore
1261-6. Again, another is now 9G0-2; it has lost
2 grains per square inch of surface, and is 6}
square inches in area; adding therefore 13 grains,
we have 973' grains for the original weight. A
copper weight is now 2G8-5 grains; the thickness
1 It is a needless and misleading statement to enter tenths
of a grain when the uncertainties of estimating the loss
amount to many grains. In cases of allowances of 40 or
50 grains, it is best to state only the nearest 10 grains ; the
character of a statement should always correspond to it?
real accuracy.