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their primitive money long after the superiority of other metals
for coinage had been demonstrated by experience ; and long
after the real origin of their money had been forgotten. To
explain their own backwardness, they gave, as so many other
peoples have given, a religious and moral sanction to their own
lack of progressiveness."!"

After the introduction of metallic money there was room for
a long process of development. Man had still to determine
which of the metals was the most suitable for his purposes ;
and the actual selection which civilized man has made is the
result of the survival of the fittest There are certain qualities
which we have come to look for in money, qualities which all
metals seem to possess in a greater degree than any one sub-^
stance, but qualities which all metals do not possess in the same

•Del Mar: op. cit-.p. 147.
tEnc. Brit, Art. Money.



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THE NATURAL HISTORY OF MONEY— DAVIDSON. 203

degree. These are Utility, Portability, Indestructibility, Homo-
geneity, Divisibility, Stability of Value, [Cognizability. These
qualities are possessed in an especial degree by gold and silver,
and in a less degree by copper. Iron was used, and is still used
in many regions ; but it is not the best money material because
of its cheapness. It does not contain great value in small bulk,
and it is not indestructible. Lead was used in classical times,
and is still current in Burmah, but it is too soft to be made into
good coins which will retain their stamp and be always cogniz-
able. Tin was early adopted as a money material. It was
coined by Dionysius, of Syracuse, who was the first to use it of
whom we can speak with certainty ; and it has remained in use
as a money material ever since. In 1680, Charles II. issued tin
farthings, and his example was followed by William and Mary
in 1690; and it was employed in Java, Mexico, and elsewhere.
But it has the defect of being too soft. Copper, either pure or
in alloy, has been extensively employed, and it possesses almost
all the qualities requisite, except that it does not contain great
value in small bulk, and has comparatively little stability of
value. Platinum is in many respects suited for currency pur-
purposes, but it is in but slight demand, and the stock on
hand is very small. Consequently any change in the demand
is apt to cause great fluctuations in value. Russia, which owns
platinum mines in the Ural Mountains, began to coin it in 1828,
but abandoned the experiment in 1845, because of the cost of
striking coins. Nickel has been largely used in alloy, but it is
subject to the disadvantage of fluctuations in value owing to the
limited number of mines. Silver and gold are pre-eminently
the metals suitable for coinage. They possess all the qualities
necessary in a currency material. These qualities, of course^
they do not possess in a perfect degree ; but they possess them
in a higher degree than any other substances. They have great
ut'.lity. They contain great value in small bulk and are readily
portable. Except by the slow process of wear and tear they are
practically indestructible. They are almost perfectly homo-
genous after they have been reduced to uniform degrees of



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204 THE NATURAL HISTORY OF MONEY — DAVIDSON.

fineness, which can be easily done, so that equal* weights of them
have practically equal values. They can be easily divided into
the weights and fractions desired so as to express large values
and small values. They have a very large degree of stability
of value, not so much perhaps as wheat, but more than most
articles which could be employed as money. And lastly, they
are readily recognizable and cannot be easily counterfeited, and
above all, are soft enough and yet hard enough to be coinable,
" so that a portion, being once issued according to proper regu-
lations with the impress of the state, may be known to all as
good and legal currency equal in weight, size and value to all
similarly marked currency."*

The precious metals are simply those commodities which
experience has shown to be the most suitable for general money
purposes. This, or that money article, may have this or that
money quality in a higher degree than gold or silver, but taking
them all in all, the precious metals have been found to be the
most suitable. They have survived, not because of any prejudice
in favor of the metals, but because they have shown themselves
to be the fittest to survive.

*Jevon8 : Money and the Mechanism of Exchange, p. 40.



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VI— On the Presence of Acid Sulphate of Copper in
Mixtures of Aqueous Solutions of Sulphuric Acid
AND Copper Sulphaie —By Charles F. Lindsay, Dcd-
housie College, Halifax, N. S.

(CommunicaUd on 8th May, 1899^ by Prof, E, Mcuckay^ Ph. D.)

Anton Schrader* in a paper on the " Electrolysis of Mixtures,'*
measured the conductivity and other properties of solutions
containing mixtures of sulphuric acid and copper sulphate,
analysing his mixtures for the amount of acid present by titra-
tion. In his paper, no methods of any kind are given for the
analyses. Prof. MacOregorf- has held that Schrader's results
point towards the presence of acid sulphate of copper in
the solution. At the suggestion of Prof. Mack ay this work was
undertaken to find if any light could be obtained on this ques-
tion by chemical analytical methods.

The work was carried out in the Chemical and Physical
laboratories of Dalhousie College, and consisted primarily in
making up solutions of sulphuric acid and copper sulphate,
analysing them, and determining their densities. In the begin-
ning the densities were taken only as a means of calculating the
concentration of the mixtures from the concentration of the
simple solutions. The work also included the purification of the
materials used, and the calibration of burettes and pipettes.

Calibration of Burettes and Pipettes.

All burettes and pipettes were carefully calibrated, by weigh-
ing the amount of water of known temperature which they
delivered. The burettes used could be read to .01 c.c They
were calibrated for every 2 c.c. throughout their length.

The pipettes, in emptying, were held against the side of the
vessel into which they were being emptied, the last drops of
water being removed by blowing sharply once.

* Inaugural Dissertation, Berlin, 1897.
t Trans. Roy. Soa Canada, (2), 4, Sec 3, 117. 1898-a

(205)



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"206 SOLUTIONS OF SULPHURIC ACID

Purification and Analysis of Copper Sulphate.

The copper sulphate was obtained as chemically pure, and
after careful re-crystallization, was found to be free from iron
and the members of the ammonium sulphide group.

The copper sulphate solutions were analysed by precipitating
the sulphate, in known volume, with barium chloride, and weigh-
ing as barium sulphate.

The following are the results of three analyses of the same
solution : —

Cu SO4 in 5 C.C. of solution = .5782 grammes.

= .5788
= .5790



Mean = .5787

These figures would seem to show that my results might be
in error about 0.1 per cent.

Purity and Analysis of Sulphuric Acid.

The sulphuric acid was the best obtainable from Merck, and
was taken as chemically pure. The sulphuric acid solutions
were analysed volumetrically with standard caustic potash,
using as an indicator phenol phthalein.

The following results show with what accuracy such analyses
could be carried out : —

2 C.C. Hj, SO4 solution contained .1627 grammes H3 SO^

^^ u a u ,1(525 ** **

" .1624 " "



Mean = .16253 "

Thus, the possible error of a single measurement would seem
to be about 0.11 per cent.

Preparation and Analysis of Mixtures.

Equal volumes of the simple solutions, whose concentrations
and densities were known, were mixed at 18°C. The density of
the mixture being obtained, the concentration of the mixture
with respect to each of the constituents, was obtainable.



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AND COPPEB SULPHATE— LINDSAY. 207

The ordinary methods of acid titration are, of course, unavail-
able in this case, for not only does the copper sulphate itself
affect alkalimetric indicators, but the sulphate is precipitated as
hydroxide, by the base used for titration. The latter fact is the
one used in the method of titration which was employed.

Standard caustic potash solution is added from a burette to
the mixture, with constant stirring, until the solution just begins
to become cloudy, owing to the beginning of the precipitation of
the hydroxide of copper. 1 found that, using this precipitating
point as an indicator, very good determinations of the acid
prcvsent could be obtained, and would suggest that copper sul-
phate might be used as an indicator in the determination of free
sulphuric acid, in cases where the ordinary indicators are of
no use.

The following results of an analysis will show with what
accuracy the determination of this precipitating point could be
ascertained :

5 ac. of a mixture CUSO4 + ^2 ^^4, began to be cloudy on
addition of 43.88 c.c decinormal caustic potash.
43.97
43.99
44.86



43.92 = mean.

TnuSjin these determinations, the difference between the greatest
and least values would be about .3%.

A second set of determinations is added :

5 C.C. of a mixture CuSO^ + H^SO^, began to become cloudy
on addition of 28.94 c.c. of decinormal caustic potash.
28.91
28.99



28.95 = mean



In this case, the difference between the greatest and least
values is about .27%.



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208



SOLUTIONS OF SULPHURIC ACID



It is thus seen not only that the precipitating point is a per-
fectly definite one, but that it can be determined with consider-
able accuracy.

The next question is, whether it expresses accurately the^
amount of acid present.



Concentration.


H2SO4


Error.


HsS04


CUSO4


Calculated.


Found.


.416
.^7


.364
.727


.2036
.1356


.2039
.1357


+ .15%
+ .08%



Column I. contains the concentration of HaS04 in mixture in

gramme-molecules per litre.
" II. contains the concentration of CuSO^ in mixture ia

gramme-molecules per litre.
" III. contains the amt. of H2SO4 in grammes, calculated to

be in every 5 ac. of mixture.
" IV. contains the same, as found in every 5 c.c. of mixture.
" V. contains the percentage error.

We thus see that by this means, the sulphuric acid present
can be determined with considerable accuracy.

In the above analyses, the mixture under analysis was dilu-
ted very much, the reason being, that so far the work has been
only to find a good method of analysis, and not to prove or
disprove the presence of acid sulphate.

But now a number of analyses were performed on the above
mixtures, keepipg the mixtures concentrated, and in no case was
there any appreciable difference in the amount of caustic potash
needed before precipitation would commence.

The results obtained from analyses of the concentrated mix-
tures, gave, as a rule, slightly less quantities of sulphuric acid.
But this I would attribute to the fact that the precipitate would
be more easily noticed in the smaller volume than in the larger..



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AND COPPER SULPHATE — LINDSAY. 209

I also made a number of determinations, using standard
ammonia in place of the standard potash, but although the pre-
cipitating point could be fairly well determined, the results did
not agree as well with the amount of sulphuric acid known to be
present.

We thus see that this method of chemical analysis for sul-
phuric acid, while it gives us a good method of analysis for such
mixtures, sheds no light on the presence of acid sulphate in
solution.

While any recognizable decrease in the amount of sulphuric
acid given up to analysis from that known to be present, would
yield an almost conclusive proof of the presence of acid sulphate,
the result obtained here, does not of necessity lead to the reverse
conclusion.

Specific Gravity Measurements.

All specific gravity measurements were made at 18°, and are
referred to water at 18®. In these measurements, a pycnometer
of the form recommended by Ostwald, and holding about 25 c.c.
was used.

The pycnometer was brought to 18° by being placed in a
water bath, provided with a mechanical stirrer, whose tem-
perature could easily be kept constant to 1/20 of a degree.
When the liquid had come to the temperature of the bath, the
menfecus was brought to the mark, the pycnometer taken out,
dipped in distilled water, dried carefully with a linen towel, and
weighed.

From several successive measurements of the same solution,
it would appear that my measurements of density might be in
error by about 5 in the fifth place of decimals.

Favre and Valson* have found that, in the case of concentra-
tedjsolutions of K^SO^ and CuSO^, and K^SO^ and H^SO^, the
density of a mixture of equal volumes of the constituents, is less
than the mean value of their densities. From these results they

•Compt. Rend., 77, 907.

Proc. & Trans. N. S. Inst. Sci., Vol. X. Trans.-N.



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210



SOLUTIONS OF SULPHURIC ACID, ETC. — LINDSAY.



drew the conclusion that acid or double sulphate was present in
solution. Also McKay-f- has noticed the same for mixtures of
potassium and magnesium sulphates.

In the case of more concentrated solutions of CuSO^ and
HaS04, 1 have found the same result to hold. But from lack of
time I was unable to push this far.

I give two of my measurements, showing the concentration
and density of the constituents, the density of the mixture, and
its departure from the mean value.



Parts of
Ha SO4 in 100
parts Sortion.


Parts of
CUSO4 in 100
parts Sortion.


Density
HaS04

1.12586
L11525


Density
CUSO4.

1.19108
L14802


Mean
Value.

1.15842
1.13163


Density

of
Mixture.

1.16603
L 12952


DifTer-
ence.

.00239
.00211


17.41
16.23


16.063
13.877



t Trans. N. S. Inst ScL, 9, 318, 1897-98.



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VII.— On a Diagram of Freezing-Point Depressions for
Electrolytes. — By Prof. J. G. MacQregor, Dalhousie
College^ Halifax, N, S,

(Received June SOth, 1900.)

The object of this paper is to describe a diagrammatic method
of taking a bird's-eye view of such knowledge as we possess of
the relation of the depression of the freezing-point to the state
of ionization in aqueous solutions of electrolytes, and to show
that such diagrammatic study gives promise of throwing much
light upon the following questions : (1.)* — Has the depression
constant a common value for all electrolytes, and if so, what
is it ? And (2), What is the state of association, and what the
mode of ionization of electrolytas, in solution?

Construction and Properties of the Diagram.

If an extremely dilute solution contain an electrolyte whose
molecule, as it exists in solution, contains p equivalents, and dis-
sociates into q free ions, and if a is its ionization coefficient and
k its depression constant, the equivalent depression will be :



= i(l + «(,-!)).



If therefore we plot a diagram of curves with ionization coeffici-
ents as ordinates, and equivalent depressions as abscissae, the
resulting curves must, at extreme dilution {a = I), be tangential
to the straight lines represented by the above equation, provided
the proper values of k, p, and q be employed. These straight
lines, which, for shortness, we may call the tangent lines of the
curves, can readily be drawn in the diagram, with any assumed
value of k, and on any admissible assumptions as to the values
of p and q. In the diagram on page 235 the dashed lines are the

• On thw question, see also a paper recently communicated to the Royal Society
of Canada, and to be published in its Transactions for 1900.

(211)



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212 ox A DIAGRAM OF FREEZING-POINT

tangent lines for the electrolytes examined, on various assump-
tions as to constitution in solution and mode of ionization, and
for A;= 1.85. They are indicated by the inscriptions 1 — 2, 2 — 3,
etc., the fii'st figure in each giving the number of equivalents in
the molecule as it is assumed to exist in solution, and the second,
the number of free ions into which the molecule is assumed to
dissociate. Thus 1 — 2 is the tangent line for an electrolyte such
as NaCl, on the assumption that it exists in solution in single
molecules, each of which has therefore 1 equivalent, and disso-
ciates into 2 ions. If assumed to associate in double molecules,
with unchanged mode of ionization, its tangent line would be
indicated by 2 — 4, and if the double molecules were assumed to
dissociate into Na and NaClg, by 2 — 2. The line for HaS04, on
the assumption that its molecules undergo no association, and
have thus 2 equivalents, and that they dissociate each into 3
ions, would be 2 — 3 ; and 4 — 6 would be its line if it associated
into double molecules, dissociutiong each into 6 ions.

In a few cases dotted lines have been introduced, to show
what the tangent lines would be with other values of ^^ — 1.83,
1.84, 1.86, 1.87, the constant used in such cases being indicated.

The curve for any given electrolyte, must start at the inter-
section of its tangent line with the line : « = !, to which point we
may refer, for shortness, as the intersection of its tangent line.
What its form will be, may be anticipated from the following
theoretical considerations : — The equivalent depression in dilute
solutions of non-electrolytes, is proportional to the osmotic pres-
sure, P, and the dilution, F, which corresponds to the product of
the pressure, p, and the specific volume, v^ in the case of a gas.
If pv is plotted against v, the resulting curve is convex towards
the axis of v, and passes, in general, through a point of minimum
value of pv. Hence, if PV, and therefore equivalent depression,
be plotted against F, we may expect to get curves of the same
general form. And experiment shows, in some cases at least,
that we do. As in the case of gases the variation of pv is
ascribed to the mutual action of the molecules and their finite
volume, so in the case of solutions, the variation of PF is attrib-
uted to similar disturbing influences.



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DEPRESSIONS FOR ELECTROLYTES — MACGREGOR. 213

Owing to ionization, the curve of an electroly»/e will difler
from that of a non-electrolyte, (I) because of the change thereby
produced in the number of molecules (including free ions) in unit
of volume, and (2) because of the change produced in the dis-
turbing influences referred to. The former change is doubtless
the more important, and I shall assume the latter to be negligible
for the present purpose. Now dissociation increases continu-
ously with dilution. If, therefore, association of molecules does
not occur, and if the mode of ionization does not change, the
equivalent depression must be increased by the dissociation, in a
ratio which increases continuously with dilution. The change
produced in the curve by dissociation, therefore, will be a shear
parallel to the equivalent depression axis, and increasing with
dilution. The resulting curve will consequently remain convex
towards the axis of dilution, but it will Vie less likely than the
curve of a non-electrolyte, to exhibit the minimum point.

If, now, we plot equivalent depression against ionizJition
coefficient, instead of dilution, the result will be the same as if
we shortened the dilution ordinates of the various points of the
curve just mentioned, in ratios increasing with the dilution,
which process must leave the curve convex towards what was
the dilution axis, but is now the ionization coefficient axis.

If, therefore, no change occur in the association of molecules
or in the mode of ionization, the curve of an electrolyte on the
diagram must start at the intersection of its tangent line, tangen-
tially to that line, and bend away from it, as dilution diminishes,
to the right, possibly passing through a point of minimum
equivalent depression. We may speak of such a curve as the
normal curve for the tangent line, corresponding to the given
conditions as to constitution in solution, and mode of ionization.

If, the constitution of the electrolyte in the solution remaining
constant, the mode of ionization changes as dilution diminishes,
say, in such a way that the molecules dissociate, on the average,
into a smaller number of ions, the equivalent depression will
diminish more rapidly than it otherwise would. The curvature
of the curve will therefore diminish, and may possibly become



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214 ON A DIAGRAM OF FREEZING-POINT

zero, and change sio^n, the curve thus becoming concave towards
the ionization coefficient axis, and possibly crossing the tangent
line. In such a case, it will at the start coincide with the normal
curve of the tangent line determined by the initial conditions as
to association and mode of ionization, and at the finish, with the
normal curve of the tangent line, determined by the final con-
ditions ; and between the start and the finish it will gradually
change from the one to the other.

If, as dilution diminishes, association of molecules into double
or other multiple molecules occurs, the mode of ionization
remaining the same, the equivalent depression will be thereby
made to diminish more rapidly than it otherwise would, and the
general effect on the form of the curve, will be of the same kind
as under the conditions just considered. But the normal curves
of the tangent lines determined by the final conditions, will be
quite different in the two cases.

It follows that by plotting, so far as experiment allows, the
curves of observed equivalent deprCvSsion against ionization
coeflScient, and drawing in the tangent lines for different values
of the depression constant, and on different assumptions as to
association and mode of ionization, we may be able to determine,
with a smaller or greater probability, what the state of associa-
tion and the mode of ionization are, what are the tangent lines
to whose intersections the curves would run out if observations
at extreme dilution could be made, and what the values of the
depression constant are, to which these lines correspond.

Data for the Diagram,

To draw the experimental curves, we must have correspond-
ing values of the depression, and of the ionization coefficient, at
the freezing point, or, what in most cases would be sufficiently
near, at O^C. The former are obtained by direct measure-
ment ; but the latter only indirectly, from conductivity observa-
tions. It is not, of course, known how closely the ionization
coefficients, even during the passage of the current, can thus be
determined, or if the state of ionization during the passage of the



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DEPRBSSIONS FOR ELECTROLYTES — MACGREGOR. 215

current is to be regarded as being the same as when the current
is not flowing. But as it has been shown that electrically deter-
mined coefficients enable us to predict within the limit of error
of observation, not only the conductivity and the results of
electrolysis* of moderately dilute complex solutions, but also their
density, viscosity, and other non -electrical properties,"^ it would
appear to be probable that for moderately dilute and very dilute
solutions, electrically determined coefficients are approximately
exact, not only for a solution through which a current is passing,
but generally.

Jhe available data as to ionization coefficients at 0°, are
unfortunately few. Whethamf has recently published some
most valuable determinations, having measured the conductivity
at 0*^, of series of solutions down to extreme dilution, with what
one may call appareil de luxe, and found the ratio of the equiv-
alent conductivity to the maximum equivalent conductivity. For
neutral salts, his coefficients must inspire great confidence. But
in the case of the acids, they seem to me to be probably too high.
For the maximum equivalent conductivity of an acid is probably
lower than it would be, were it not for the disturbing influence
whatever it is, which makes the equivalent-conductivity-con-
centration curve not only reach, but pass through a maximum
point.

Archibald and Bamesj: working in my laboratory, measured
the conductivity at 0° and 18° for series of solutions, down to
dilutions, at which the ratio of the two conductivities became
constant; and assuming that the same ratio would hold at
extreme dilution, they calculated the equivalent conductivity at
extreme dilution for O*' from Kohlrausch's values for 18**. They
used this method only because appliances were not available,



Online LibraryNova Scotian Institute of ScienceThe Proceedings and transactions of the Nova Scotian Institute of ..., Volume 10 → online text (page 17 of 54)