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fPROM THE American Joor. op Sci. and Arts , Volume XLIX, March, 1870.]
Coiitrihutioiis to the Clieniistry of Copper; by T. Sterry
Hunt, LL.D., RRS. Part 1.
[Read before the American Associntion for the Advancement of Science at Salem,
« August 26, 1869]
§1. The resemblances between silver and copper in its cu-
prous form luive already attracted the attention of chemists.
The ordinary chlorid of silver (argentic cldorid) and the dichlo-
rid of copper (ciiproas chlorid) have many properties in com-
mon. Both of these chlorids are white, readily fusible, and
blackened by exposure to light; both of them are insoluble in
water but dissolve in ammonia and in aqueous solutions of
other chlorids, in which however the cuprous is far more solu-
ble than the argentic chlorid. A saturated solution of chlorid
of sodium holds at 90° Centigrade, 16 '9 per cent of cuprous
chlorid, at 40° C, 11'7, and at 11°, 8*9 per cent. A solution
containing fifteen per cent of chlorid of sodium retains at 90°
C, 10*3 })er cent of cupi-ous chlorid, at 40°, 6'0 per cent, and
at 14°, 3 '6 percent; vsdiile a solution with only live per cent
of chlorid of sodium holds of the cuprous chlorid at 90°, 2*6,
and at 40° only 11 per cent. These determinations are from
single observations and therefore require verification. From
the sparing solubility of the cuprous chlorid in dilute solutions
of chlorid of sodium it follows that the denser saturated solu-
tions are copiously precipitated by dilution with water, which
causes the separation of white cuprous chlorid in a crystalline
condition.
§ 2. The aqueous solutions of the chlorids of calcium, mag-
nesium, zinc, manganese, cobalt, feiTOsum and cupricum, also
freely dissolve cuprous chlorid, and it is probable that this
property is shared by otJier soluble chlorids. The strong af-
finity of cuprosiim for chlorine enables cuprous oxyd to decom-
pose all the chlorids just named, with the exception of those of
sodium and calcium, with separation of the corresponding oxyds
and formation of cuprous chlorid. In the case of zinc and
manganese, insolulde oxychlorids of these metals are formed
at the same time. These reactions require further study, and
the same may be said of the cupric and cobaltic chlorids with
cuprous oxyd. I have, however, partially investigated the be-
havior of cuprous oxyd with magnesic and ferrous chlorids,
and obtained the results about to be described.
§ 3. The cuprous oxyd for these experiments was prepared
by gently heating a solution of sulphate of copper mixed with
cane sugar and an excess of caustic soda,"''until tlie whole of the
copper was thrown down as a bright dense cinnabar-red powder
«•.
(34)
T. S. Hunt on the Chemistry of Copper.
which was carefully washed and dried. A concentrated solu-
tion of chlorid of nuigncsiiini dissolves this oxyd in the cold,
and more readily when heated, with separation of hydrated
oxyd of magnesium and cuprous chlorid, which latter is held
in solution by the excess of magnesic chlorid. By filtering
the liquid while hot, and washing with a strong solution of
chlorid oi sodium, the hydrate of magnesia may be separated,
and the dissolved copper subsequently precipitated by metallic
iron from the colorless filtrate, ferrous chlorid being formed.
Experiment shows tliat the reaction between the red oxyd of
copper and chlorid oi' magnesium may be represented as follows :
Cu,0-fMgCl=Cu2CH-MgO.
§4. A solution of magnesian chlorid nearly saturated when
liot with cuprous oxyd, and allowed to cool in contact with the
precipitated mognesian hydrate, deposits a portion of orange
colored oxyd, or perhaps an oxychlorid, which disappears as
often as the sohition is heated. The solid cuprous chlorid is
moreover decomposed when digested with water and magnesia,
hydrated cuprous oxyd and magnesic chlorid being formed.
The double chlorid of cuprosum and magnesium is however
stable, even in the cold, in presence of magnesian hj^drate, pro-
vided a considerable excess of magnesian chlorid be present.
From a filtered solution of cuprous oxyd in chlorid of magne-
sium water precipitates a large portion of the cuprous chlorid,
in this case colored orange-yellow from adhering oxyd, due to
the reaction of a little magnesia, which remains dissolved or
suspended in the concentrated solution even after filtration. A
solution of magnesian chlorid of specific gravity 1'23, retains
in solution at 12° Centigrade, about 7"10 per cent of cuprous
chlorid. A solution of magnesian sulphate with chlorid of
sodium may be employed to dissolve cuprous oxyd. This, like
all similar solutions of cuprous chlorid, rapidly absorbs oxygen
from the air and deposits a pale green cupric oxychlorid.
§ 5. With ferrous chlorid and cuprous oxyd it might be ex-
pected, from analogy with the magnesian salt, that we should
obtain cuprous chlorid and ferrous oxyd, but the reaction is
complicated by the tendency of the latter to pass to the state
of feme oxyd. When ferrous chlorid in solution with chlorid
of sodium is heated with a sufUcient quantity of cuprous oxyd,
the whole of the iron is precipitated as ferric oxyd, mingled
with metallic copper, whi'3 cuprous chlorid remains in solution.
Experiments made with an excess of ferrous chlorid show that
one third of the copper is reduced, while two thirds are dis-
solved as dichlorid. This reduction may be eftected directly by
ferrous oxyd ; if to a solution of cuprous chlorid in chlorid of
sodium, we add hydrated ferrous oxyd recently precipitated by
an alkaline base and still suspended in the liquid, it is at once
T. S. Hunt on the Chemistry of Copper.
8
converted into ferric oxyd, with precipitation of metallic cop-
per. The first stage in the action of ferrous chlorid on cuprous
oxyd niav be represented as similar to that of magnesic cliforid ;
CujO + i'eCl^^Cu.Cl + FeO. In the second stage CuyCl +
3FeO=Cu ^ + FeCl + Fe, O 3 . It follows from this that one-third
of the cuprous chlorid formed in the first stage is reduced to
the metallic state, and the final result may be represented as
follows: 3Cu30 + 2FeCl=2Cu,Cl+2Cu-fFe303.
A similar result is obtained if ferrous chlorid is added to an
unfiltered solution of cuprous oxyd in chlorid of magnesium.
The suspended hydrate of magnesia in this case liberates an
equivalent of ferrous oxyd, which reduces to the metallic state
one-third of the dissolved cuprous chlorid, in accordance with
the second reaction given above.
§ 6. The reducing power of ferrous oxyd is also shown with
cupric cblorid, which is at once converted by it into cuprous
chlorid in accordance with the equation, 2CuCl 4- 3FcO =
CUaCl-f FcCl-fFcaO,. The further action of ferrous oxyd
will, as we have seen, leduce the cuprous chlorid to the metallic
state: in fact, 2CuCl-|-6FeO = 2Cu-f 2FeCI+2Fe303. If re-
cently precipitated hydrated ferrous oxyd or ferrous carbonate
be added to a solution of cupric chlorid in the proportions indi-
cated by the last equation, the whole of the copper is separated
in the metallic state, mingled with ferric oxyd, while ferrous
chlorid is found in solution. The reaction with ferrous carbo-
nate, which requires a gentle heat, is accompanied by a violent
disengagement of carbonic acid gas. This experiment is best
made by dissolving in water feiTous sul])hate and sodic carbo-
nate or sodic hydrate in the proportions required, and adding
thereto a solution holding the proper amount of cupric chlorid.
Under certain conditions the cuprous preci})itate is brownish-
black in color, like that obtained by heating ferrous chlorid
with cuprous oxyd, but more generally it is of a bright red
color, and often coats the glass with a mirror-like film. A
warm solution of cupric chlorid with chlorid of sodium at once
conve]'ts the metallic copper of the precipitate into cuprous
chlorid, which is dissolved, leaving behind only hydrated ferric
oxyd. When a solution of ferrous chlorid with chlorid of
ammonium and excess of ammonia is added to a solution
of a cop})er salt the precipitated films of metallic copper some-
times possess considerable brilliancy and show a bluish ti-anslu-
cency. It is to be remarked that although the cupreous precipi-
tate thus obtained is bright red in color, that which is produced
by boiling cuprous oxyd with ferrous chlorid is nearly bliick.
§ 7. It was long since shown by Levol that hy<lrated feirous
oxyd will reduce cupric to cuprous oxyd, and this, as we have
already seen, can separate from its combinations ferrous oxyd,
4 T. S, Hunt an the Oiemtstry of Copper.
whose reducing power may be still further exerted upon the
cuprous combination thus formed. These facts serve to explain
the results obtained by E. Brann {Zeitschr. Chem., 1867, [). 568.
cited in Jahresberic/it for 1867), vviiicli were not known to me
at the time of making these experiments, lie found that by
digesting cupric hydrate or cupric carbonate with ferrous sub
phate in solution there was obtained a reddish mixture of basic,
ferric sid})]iate with cuprous oxyd, formed ap]>arently in accord-
ance with the equation,
2FeO, SO,4-2CuO=Cu,04-Fe,03, 2S0
3*
This, when boiled with a further })ortion of ferrous sulphate,
became black in color, and from the small amount of oxygen
present was supposed to contain metallic copper. By addmg a
large excess of carbonate of ammonia to a mixture of ferrous
and cupric sulphates, Braiin succeeded in obtaining solutions in
which all the copper was present in a cuprous form, and even
in reducing portions of it to the metallic state, a process which
we have seen is complete when tlie requisite amount of ferrous
oxyd is brought in contact with the chlorids of copper.
§8. In this Journal for March, 1867, page 308, I described
briefly the reaction between cupric oxvd and ferrous cldorid, ac-
cording to the equation, 3CuO-f2FCf= Fe.^0 ,+Cu,C\-\-OnG\.
I was not then aware that the same had been shown by Meyer
(Berg, und Hutt. Zeit., 1862, 182, cited by Kerl).* 'Further
studies of this reaction have given me interesting results. The
black oxyd of copper, even after ignition, is attacked by ferrous
chlorid in tlie cold, but the insolubility of the resulting cuprous
chlorid retards the action. If however the ferrous chlorid be
mingled with a strong solution of chlorid of sodium, and heat
applied, the cuprous chlorid is readily dissolved, and the reac-
tion is rapid and complete, the whole of the iron separating as a
bulky reddish-brown precipitate, provided three equivalents of
cupric oxyd have been taken for two of ferrous chlorid. The
greenish solution thus obtained readily dissolves precipitated me-
tallic copper, ill virtue of the cupric chlorid which it contains,
and, unless a large excess of chlorid of sodium be present, de-
posits white crystalline cuprous chlorid by cooling or by dilution.
When digested at a temperature of 50° Centigrade with carbon-
ate of lime, tlie greenish solution deposits one-third of its cop-
per as a pale gi-een insoluble cupric hydro-carbonate, while the
colorless filtrate retains the remaining two-thirds in the form of
cuprous chlorid. If a solution of ferrous chlorid with chlorid
of sodium is digested with a sufficient excess of cupric oxyd the
cupric chlorid formed unites with the latter to form an insoluble
cupric oxychlorid, and only cuprous chlorid remains in solu-
tion.
* Me tall. Huttenkunde, xi, 588.
T. S. Hunt on the Chemistry of Copper, 5
§ 9. For tlie ferrous chlorid in the experiments in §6 and §8,
a solution of ferrous sul})lmte with chlorid of sodium may be
substituted. When oupric o.xyd is heated with an excess of
ferrous cidorid, a small portion of ferric oxychlond is produced.
I he red brown precipitate may be waslied free from cupric, cu-
prous and ferrous chiorids by "a strong solution of chlorM of so-
dium, but will then yield to pure water a portion of soluble ferric
oxychlorid. By careful desiccation in a water-bath and subse-
quent washing with dilute alcohol the ferric precipitate may be
obtamed free from chlorid of sodium, and completely insoluble
in water ; but its composition appears to be variable. Of two
preparations the first contained one equivalent of chlorine for
eleven, and the second, one for twenty equivalents of iron. In
a,nother experiment where fine oxyd of copper from the calcina-
tion of malachite was dissolved inan excess of a mixture of fer-
rous sulphate and chlorid of sodium at a boiling heat, it was found
that for thirty equivalents of copper dissolv(;d there were pre-
cipitated twenty-one equivalents of iron, instead of twenty as
required by the formula given in §8; the additional equivalent
being separated as ferric chlorid in union with tlie ferric oxyd.
The production of a small and variable amount of ferric chlOrid
m the above conditions is apparently due to a secondary reaction
between cupric and ferrous chiorids in the presence of ferric
oxyd; 2CuCl+2FeCl = Cu,Cl4-Fe,Cl3. This point however
req^uires further investigation.
^ 10. The facility with which cupric chlorid parts with one-
half of Its chlorine and passes into the more stable cuprous
compound is shown by its well known power to chloi '-ze not
only metallic copper, but metallic silver and even suiphid of
silver. Its action on cuprous suiphid is not less remarkable.
A strong solution of cupric chlorid mingled with chlorid of so-
dium rapidly attacks pulverized copper-glance, ev.-n in the cold,
sulphur being separated and cuprous chlorid formed; 2CuCl-f
CujS = 2Cu2Cl-fS. Chalcopyrite, on i\v contrary, is but
slightly acted upon by such a solution, which, however, slowly
takes up a portion of iron, forming ferrous chlorid with a corres-
ponding amount of cuprous chlorid. %