Photography with emulsions : a treatise on the theory and practical working of the collodion and gelatine emulsion processes

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PHOTOGEAPHY WITH EMULSIONS.

PHOTOGBAPHY flTH EMOLSMS.

A TEEATISE ON THE

THEOEY AOT) PRACTICAL WORKING

COLLODION AND GELATINE

EMULSION PROCESSES.

Capt. W. de W. ABNEY, R.E , F.R.S.

TEIED EDITION.

L02SID0N :
PIPER & CAKTEE, 5, CASTLE STREET, HOLBORN, E.G.

1885.

LONDON :
PlPEll AND CAUTEK, CASTLE STREET, HOLEOKN, E.G.

PREFACE,

Another Edition of this work has been called for
by the Publishers, and, in preparing it, the Author
has endeavoured so to re-arrange and prune the
older matter, and to insert new, as to make it
useful to those whose knowledge of chemistry may
be limited, as well as to those who are experts in
that far-reaching science. Again, there are many
who at present care nothing about theory, and who
regard practical results as their sole aim. An
endeavour has been made to meet their views as
well, by, as far as possible, confining all theoretical
considerations to those chapters which are marked
with double asterisks in the table of Contents.
These chapters may be omitted without in any

VI PREFACE.

way interfering with the practical part of the
subject. Those readers who prefer to buy their
dry plates in the market to preparing them them-
selves, may omit the chapters marked with a single
asterisk.

The Author feels that there must be many short-
comings in the book, although he has tried to keep
it up to date. One thing, however, he may add,
that there is no process stated in it which he has
not thoroughly tried, and no theory which is given
which he has not endeavoured to confirm or refute
experimentally.

W. DE W. Abney.

South Kensington,

September, 1885.

CONTENTS.

**I. —Preliminary Considerations ... i

**II. —Alkaline Development ... .. ... ... ,,, 14

**III.— The Cause and Care of Fog in Emulsions 21

IV. — Dark Room and its Fittings 30

V. — Illumination of the Dark Room ... ... ... ... 41

**VI. — Introductory Remarks on Gelatine Emulsions ... ... 49*

**VII. — Silver Iodide and Chloride in Emulsions .58*

**VIII.— Gelatine 62*

IS. — Gelatino-Bromo-Iodide Emulsion 69*

X. — Bennett's Gelatine-Bromide Process 8L*

XI. — Paget Prize Emulsion 81*

XII. — Burton's Process 91*

XIII. — Dr. Eder's Emulsions ' 93*

XIV. — Cold Emulsifioation Process 101*

XV. — Mr. Cotesworth's Cold Emulsifioation Process ... .. , 101*
XVI. — A Process for Gelatine Emulsion Making in Hot Weather 105*

XVII. — Gelatino-Bromide Emulsion by Precipitation 107*

XVIII. — Dr. Van Monokhoven's Processes Ill*

XIX. — Preparation of the Plates (Gelatine) 114*

XX.— Testing Plates 122

XXL— Exposure of the Plates [ 127

XXII. — Development of .Gelatine Plates with Alkaline Developers 134
XXIII. — Development of Gelatine Plates with Ferrous Oxalate.,. 149

CONTENTS.

CHAPTER TAGE

XXIV. — Fixing, Intensifying, and Varnishing Gelatine Negatives 154

XXV.— Gelatino-Chloride Emulsions 163*

XXVI. — Aceto- Gelatine Emulsions 169*

XXVII. — Gelatino-Bromide and Gelatino-Chloride Papers ... 173*

XXVIII.— Exposure of the Negative Paper 179

XXIX. — Development of Gelatino-Bromide Paper for Negatives 183
XXX. — Development of Positive Paper ... ... ... ... 192

XXXI.— Defects in Gelatine Plates ... , 197

**XXXII.— Collodion Emulsions— Introductory 208

XXXIU.— PyroxyUtt 211

XXXIV. — Preparation of a Collodion Emulsion 219

XXXV. — Canon Beechey's Process — M. Chardon's Process ... 229

XXXVI. — Collodion Emulsions to which Preservatives are Added 233
XXXVII.— Cooper's CoUodio -Bromide Reliable Dry Plate Process... 237
XXXVIII. — Collodio-Bromide Emulsion Prepared in the Alkaline

State and with Excess of Bromide 2i2

XXXIX. — CoUodio-Albumen Emulsion 245

XL. — Preparation of the Plate 247

XXJ. — Preservatives used with Emulsions 255

XLII. — Development of the Plate 261

XLIII. — Collodio- Chloride Emulsion for Development 270

XLIV. — Defects in Collodion Emulsion Plates 274

XLV. — Emulsion Processes for Printing 277

XLVI. — Packing Plates 284

PHOTOGMPHY WITH EMULSIONS.

CHAPTEK I.

PRELIMINARY CONSIDERATIONS.

The term emtdsion is derived from the Latin word
" emulgere," to milk out, and the definition of it as found
in the dictionary is, " any milk-like mixture prepared by
uniting oil and water by means of another substance."
For our photographic technology this is hardly a correct
definition, for by it we mean a sensitive salt of silver in
very minute division, held in suspension in some viscous
body, such as gelatine, or, very often, collodion.

An emulsion in its most elementary form may be con-
sidered to be simply a pure silver haloid held in suspen-
sion in collodion or gelatine, and so well prepared that
when a plate is coated with it, a homogeneous film re-
sults ; a film which, in fact, is at least equal in sensi-
tiveness and in physical qualities to any which can be
prepared by any other process.

Emulsion processes are divided into two classes : one
in which the emulsion is made up and used without any
preliminary extraction of the soluble salts which are
necessarily present in their manufacture, owing to the

2 PRELIMINARY CONSIDERATIONS.

double decomposition of the salts employed, and the
silver nitrate ; and the other where these soluble salts are
extracted. In the first process the plates are washed
after coating, and is usually confined to collodion emul-
sions ; whilst in the second they are coated, and generally
left to dry spontaneously.

All emulsions at present in vogue for making negatives
may be considered to be simply bromide of silver, since it is
the basis on which all alterations by the addition of iodide
or chloride are to be made. It will be seen in the con-
text that these additions are not unimportant as regards
the range of sensitiveness.

The almost universal mode of producing an emulsion is
to dissolve certain soluble bromides (such as potassium
bromide) in the collodion or in a gelatine solution, and
then to gradually pour a solution of silver nitrate dissolved
in alcohol and water in the first case, or in water alone in
the second, into the viscous fluid, by which means solid
bromide of silver is formed, together with a soluble
nitrate (sucli as potassium nitrate). It is this latter solu-
ble product which in washed emulsions is removed, since,
if a film be left to dry without eliminating it, crystalliza-
tion sets up, and the surface of the coated plate is spoilt.
Silver chloride is readily emulsified in the same way,
substituting a soluble chloride (such as of sodium) for
the soluble bromide. Silver iodide is also easily formed
into an emulsion in gelatine, but it is formed with much
more difficulty in collodion. We give the chemical equa-
tion for the formation of silver bromide.

Potassium Bromide and Silver Nitrate give Silver Bromide and Potassium Nitrate
KBr + AgNOs = AgBr ■+■ KNO3

Bromide of silver may be produced in several molecular
states, all of which have different degrees of sensitiveness.
When we say different molecular states, we mean that
the silver bromide has precisely the same chemical com-
position, but that it is altered physically, the molecules

PRELIMINARY COXSIDERATIOXS. 3

being larger in some cases than others ; the particles are
built Tip of a greater or less nnmber of primary molecules,
according to the rapidity of the formation of the solid,
and its subsequent treatment by heat, ammonia, &c.
Thus, it is known that white light, when transmitted
through a film composed of gelatine, in which these parti-
cles are suspended, may appear of a ruby, orange, green,
purple, or grey colour ; and of these, three seem to be
different states of molecular aggregation- — viz., ruby,
green, and grey ; the others are probably mixtures of one
or more of the three. We must assume that the reader
is aware what a spectrum is. By exposing any of these
modifications to its action, we find that the range of sen-
sitiveness to the different coloured rays is varied. Thus

PEISMATIO SPECTRUM.

H C F E D B A

L

UUIIK — UOLET Via.ET BUIE CREEN YELIOV BED INFRA-RED
Fig. 1.

the rtiby and orange modification is sensitive to the ultra
violet, the violet, and blue rays, and a little to the green ;
the grey blue is sensitive to the same rays, but more
strongly in the green, whilst it is able to be impressed by
the yellow and by the red rays ; the green modification,
when in collodion, is sensitive to the ultra-violet, the blue,
very slightly to the green, and much more so to the red,
and infra-red regions — that is, those dark ra3^s which are
miscalled the heat rays.

In fig. 2 the range of sensitiveness of two of these
modifications (Nos. 3 and 4) is shown, as well as
that of some other salts of silver. The comparative
sensitiveness to different parts of the spectrum is shown
by the height of the curves.

In collodion emulsion the ruby and orange form of
bromide is that most sought after, whilst in gelatine emul-

PEELIMINAEY CONSIDERATIONS.

slon the form whict is supposed to give the most sensi-
tive films is the blue grey form ; though for our own part

we consider that a tinge of yellow is essential to get the
highest sensitiveness. The reason for selecting these
forms we shall touch upon by-and-Tbye.

PKELIMmARY CONSIDEPaTIONS. 5

Iodide of silver in its pure state is sensitive only to the
ultra-violet, the violet, and the blue rays, and it may well
be supposed that by adding iodide to the bromide, some
modification of the range of spectral sensitiveness must
be found. Such is the case, and it is more marked in
gelatine emulsion, in which, were no iodide added, the
emulsion would take the blue grey state (see fig. 2).

The addition of chloride of silver to the bromide modi-
fies the photographic qualities of the latter but little, and
since it is b\it rarely used in any quantity, we need not
consider it.

When white light is allowed to act on chloride of silver
for a sufficient time to blacken it, in the presence of
moisture, or moist air, as is all air unless chemically
purified, chlorine is given off. That this is the case is
never disputed, its proof being as old as 1780, when
Scheele made his classical experiments. We think also
it will be allowed that when bromide of silver is acted
upon similarly, bromine is given off ; a bromide plate when
darkened absolutely smells of bromine, or some compound
analogous to it. Let us take chloride of silver as the
example on which to found an argument, for any reason-
ing which may apply to the one will equally apply to the
■other principal haloid salts of silver — viz., the bromide
and iodide. Homogeneous matter is made up of mole-
cules, all having a similar composition, and such mole-
cules are themselves made up of atoms. In the case of
bromide of silver, for instance, the atoms are bromine and
silver. Now we are told in most text-books that silver is
a monad,* and that it requires only one atom of bromine
to combine with one atom of silver ; confining ourselves
to pure chemistry, without any reference to photographic
action, the evidence of this is based on the behaviour of
silver when combined with certain other elements.

* The opinion, however, that silver is a monad is not absolutely allowed
"by some chemists.

b PRELIMINAEY CONSIDEEATIONS.

The molecule of chloride of silver is, however, we are
constrained to believe, made up of at least two atoms of
silver and two of chlorine, and the question arises as to
what substance is left behind after the chlorine has been
dissociated from it by the action of light. Does such a
body as a sub-bromide or sub-chloride exist ? Now we
wiU not go into photographic evidence, but confine our-
selves at first to chemical evidence simply. In 1839, the
year when Daguerreotype was discovered, Wohler found
that if hydrogen was passed over argentic-oxalate,
mellitate, or citrate, when heated to the boiling point of
water, half the acid was set free, and a dark brown
argentous salt remained. The acid could be removed by
washing, only a small portion of the argentous salt being
removed, the solution of the latter forming a port-wine
coloured liquid.

Further, Wohler obtained argentous oxide (Ag^O) by
means of repeatedly boiling soda-ley with argentic
arsenite,* and Geuther found that argentous oxide is
formed by precipitating silver nitrate with cuprous
hydrate. Again, argentous oxide is produced by the
action of hydrogen peroxide on metallic silver. A bright
silver plate immersed in a neutral solution of hydrogen
dioxide becomes covered with bubbles of oxygen, and
coated with a greyish white film, while part of the silver
is converted into hydrated argentous oxide, according to
'the equation — 2Ag2+H202=2HAg20. Argentous salts are
also produced by passing hydrogen into ammoniacal
solutions of silver salts.

Such is an outline of the chemical evidence of the
existence of argentous oxide, and it would appear that
such evidence is very strong — in fact, as strong as
required under any circumstances. That this is not the
work of only one chemist adds more weight to the
existence of such a compound.

• Argentous oxide is, of course, the base o£ argentous citrate, oxalate, or
mellitate.

PEELIMINARY CONSIDERATIONS. <

Such being granted, the admission of the possibility of
the existence of sub-chloride or sub-bromide of silver is
at once apparent. Wohler describes a method of prepar-
ing it by adding to the argentous oxide a solution of
hydrochloric acid, or of common salt. In this case we
have : —

AgiO+2HCl=2Ag201-t-H2O and Ag40-t-2NaCl=2Ag2Cl+Na.O
Argentous chloride is also said to be formed by bringing
silver in contact with a solution of sal-ammoniac, as is
also the case by the first action of ferric chloride or cupric
chloride. The argentous bromide (sub-bromide) can be
formed in the same way. By chemical analogy, if there
is such a substance as the sub-oxide or argentous oxide,
there is the same reason for believing in the existence of
the sub-chloride and sub-bromide. Now comes the
question as to whether the same compound is produced
by the action of light.

When sUver chloride is exposed to the action of light,
we know well that a violet- coloured substance is pro-
duced, and that such a colouration is also found wheu
exposure takes place in the presence of nitric acid. We
also know that the metallic silver dissolves in dilute
nitric acid. Now, since chlorine is evolved, one of two
things must occur : either the total Hberation of the
chlorine from the silver salt, or else its partial liberation.
Which does it do ? Under any ordinary circumstances it
would be said that it was not metallic silver which was
left, since it was unacted upon by nitric acid ; however,
there are those who will accept a conclusion derived from
one isolated fact. Some thirty years ago or more,
Guthrie experimented on this subject, and ho put it
down that metallic silver was formed, but that it was in
a passive state, similar to that state which iron takes.
The connection between the two is not, however, very
apparent.

He found that the substance he got in every case of the
darkened chloride was insoluble in nitric acid, but that

O PBELIMINART CONSIDERATIONS.

after treatment with ammonia the residue was soltiLle-
This is exactly the hehaviour of chemically produced
argentous chloride, and is a striking proof that the light-
produced compound and this are identical.

It is usually said, if silver bromide he exposed to light
in nitric acid, that no change takes place in it — i. e., that
it remains as silver bromide. Now, to test this, silver
bromide was exposed to light in strong nitric acid, and
subsequently the acid was treated with silver nitrate. A
faint precipitate of bromide of silver immediately showed.
If dilute nitric acid be used, the silver is dissolved from
the sub-bromide almost at once.

Now we have an exceedingly interesting proof that
the salt formed by light and the argentous chloride are
the same, independently of chemical proof. If a collo-
dion film containing silver chloride be exposed to light
till it is lavender, and be then exposed to the action of
the spectrum, we get a coloured representation of that
spectrum. Further, if a similar film be exposed to light,
and the silver be reduced to the metallic state by a deve-
loper, and it is then immersed till it assumes a grey colour
in ferric chloride or cupric chloride, the same colourific
action takes place ; or, again, if a metallic silver plate be
treated in the same way, we have a coloured spectrum.
It would be curious that such should be the case if the
compounds are different.

The amount of the chloride converted into the coloured
salt, compared with the total amount to which a prolonged
exposure to light is given to produce it, is small, perhaps
not more than five per cent. ; but it must be recollected
that chlorine as it is liberated from the chloride by light
has always sub-chloride besides it, and it is always more
probable that a larger percentage will combine with the
sub-chloride and form chloride

(AgjCl+Cl^Ag^Clj)
rather than escape. For this reason there is no difficulty
in reconciling fact with theory.

PEEL13IINARY CONSIDERATIONS. 9

We may mention that Dr. Hodgkinson, by exposing a
large quantity of chloride to light, has been able to isolate
the sub-chloride by treating the mass with sodium chloride
solutions, which are able to dissolve the chloride
without destroying the sub-chloride, which remains
insoluble.

We may now assume that the prolonged action of light
is to reduce the haloid to a simpler type, which we may
call the sub-haloid. Thus —

Silver Bromide gives Silver Sub-Bromide and Bromine.
AgjBr^ = AgjBr + Br.

It is a pertinent question to put as to whether the visible
a,nd the invisible (or developable) image are of the same
nature ; which may be answered by another question :
Can the line be drawn where the image is invisible ? If
so, what is the boundary between the two ? If we admit
the theory of the formation of the visible image, it seems
hardly logical to deny a similar formation for the invisible
or photographic image. It is quite possible that beings
with more acute sight than ourselves might be able to see
the image which we cannot. As we know, certain insects
can hear sounds which do not affect our auditory nerves.
Coloured particles are visible when put together en masse ;
but if only a few coloured particles are present in a mass
of colourless particle, it is quite certain they may remain
undetected. If we take a couple of plates, and coat them
with emulsion, and place them in som^e conducting solu-
tion, connect the films with a very sensitive galvanometer,
and allow light for a second to fall on one plate, there
will be a deflection of the needle, showing that chemical
action is taking place on it ; expose for a time sufficiently
long to discolour the film, and the same result occurs.
There is chemical action, then, in both cases : what is the
difference between the two ? The chemical theory of the
photographic image is based upon the fact that where
light of a proper kind acts on a molecule the atoms are

10 PRELIMINARY CONSIDERATIONS.

made to swing, however short be that exposure. If it he-
for a second, the average number of vibrations which
light of a mean wave length makes is somewhere about
700 million millions, a goodly number, and which, if the
blows from the ether be well timed, is sufficient to make
an atom of chlorine or bromine fly off from the molecule,
or, in other words, sufficient to make it swing out of the
sphere of molecular attraction, particularly if some other
molecule is near which is ready to abstract it and
incorporate it with its atoms, and so to form a new
body.

Let us stop and see whether su.ch is the practical, and
not theoretical, action. Take bromide of silver emulsion,
in collodion, which latter, when pure, is almost an abso-
lutely neutral substance, and what occurs when it is used
dry V It is sensitive to a certain extent ; but add some
bromine-loving preservative to the film, and the increase
of sensitiveness is much increased. If the condition of
the bromide under the action of light were merely change
in the arrangement of the atoms, but not a chemical
change, there would be no use in the bromide absorbent,
and it ought to be positively detrimental.

Let ITS take another example still of this. If a washed
iodide of silver emulsion is prepared with excess of
iodide, and a plate be prepared and exposed, no image is
developable. Dip half of such a plate into a solution of
tannic acid or beer, and develop ; the half that has an
iodine absorbent will develop after exposure to light, the
other half will not. The chemical theory of the photo-
graphic image which assumes the liberation of an
atom of bromine from the bromide, explains it imme-
diately.

One of the most remarkable proofs of the truth of this
theory is found in the explanation of some experiments
made by the author on the effect of the spectrum on mix-
tures of the haloid salts of silver, an account of which is
published in the " Proceedings of the Royal Society," and

PEELIMINAEY CONSIDEEATIONS. 11

a diagram of wliicli is seen on page 4. It is there shown,
if you have a mixture of pure and dry iodide and bromide
of silver, and expose it to the spectrum, that at the place
where the iodide alone would show the greatest action on
development, the image on the iodide has been destroyed
by liberation of bromine from the bromide, which is in
contact with it, and which is also acted upon by rays of
the same refrangibility. Now no mere physical theory
of the photographic image would account for this. If a
mere change in the arrangement of the atoms took place,
instead of the developed image being almost nil at this
particular part of the spectrum, it would be increased in
intensity, and such increased intensity is to be found if a
lialogen absorbent is in contact with them.

We will merely mention that one form of the physical
theory of the formation of tlie photographic image is that
the light sets up vibrations, and that whilst no chemical
change is wrought, yet that it is the increased vibrations
which give the developing power, and that when the
vibrations cease the image is non-existent. This is one
of those pretty ideas which have to be relegated to the
same limbo as perpetual motion. We hear of a gelatine
plate being exposed and developed with unimpaired
vigour after a lapse of twelve or twenty months. We
ourselves have kept gelatine plates a year, and developed
some of them every three months. These plates were ex-
posed behind a sensitometer, and kept to ascertain if there
were any fading of the image. Plates which gave 22 on
the sensitometer at first, after the lapse of a year gave an
image showing 21. Hence, to accept this theory, we
should have to conclude that the vibrations commenced
at a certain time, kept of the same amplitude, or nearly
so, for the space of a year. If a collodion plate is treated
in the same way, the image will die out much more rapidly.
A couple of months is sufficient in most cases to obliterate
nearly every trace of an image, and yet it is the same
material acted upon in both cases. ^Vhy should it act

12 PRELIMINARY CONSIDERATIONS.

-differently in the two cases ? The answer is somewhat
hard on the vihration hypothesis, hut it is perfectly easy
on the chemical theory of the photographic image. Ex-
posure to the atmosphere, or to a substance which can
oxidize the image, we have shown destroys the developing
capacity of the image, and the difference of the enclo-
sures of the bromide when in the gelatine and collodion
fully explains the reason why the destruction is more
rapid in the one case than the other.

Again, we can absolutely show that if increased ampli-
tude of vibration be given to the atoms of a bromide
plate, such vibrations subside rapidly. If we take a hot
iron and press it to the back of a gelatine plate, and ex-
,pose the latter to light whilst hot, and then, after cooling,
develop the plate, we get an image of tlie iron shown by
increased blackening of those parts which were in contact
with the glass heated by the ffon. If, however, the hot
iron be applied to the back of the plate, which is then
allowed to cool, and if, after such cooling, it be exposed to
light, no trace of the iron shape is visible ; the silver salt
has returned to its normal condition.

In the one case, we have the amplitude of the vibra-
tions of the atoms of the molecules (which, when at any
temperature presumably above the absolute zero, are
■always vibrating) increased by the application of the hot
iron, but not sufficiently to make them separate entirely.
Where light of proper colour impinges on these atoms,
which are already swinging ^viih increased amplitude,
they are more readily swung off than when it has the
whole of the work to perform upon them, and as a re-
sult we have the image of the flat iron shown by the in-
• creased number of molecules which have been de-atomized.
In the other case the plate is heated, and the increased
amplitude of vibration must stiU be there, and, according
to the vibration theory, should continue ; but the fact is,
that it does nothing of the kind. The atoms resume
their normal swing when the plate is cold. It is for those

PKELI3IIKAEY CONSIDERATIONS. 13

who liold the physical theory of the formation of the
photographic image to explain why the increased ampli-
tude, due to the heating, dies away, whilst that due to
light does not. The chemical theory, then, fully accounts
for these experiments, which, as far as we are aware, no
other theory can do.

CHAPTEE II.

ALKALINE DEVELOPMENT.

It will be noticed that all emulsion plates are developed
•either by alkaline development, or by ferrous oxalate
development, and we propose to consider these two deve-
lopers from their theoretical point of view. It may be
said, first of all, that iodide is not readily amenable to
alkaline development, and we therefore do not consider
it ; the bromide and chloride are the salts which are chiefly
employed, and it is their part in it we shall consider.

An alkaline developer consists of a strong absorbent of
■oxygen, an alkali, and a soluble bromide or chloride. The
two first are the only essentials for the reduction of a salt
of silver to the metallic state. Thus, if we take precipi-
tated bromide of silver,* and add to it a solution of pyro
gallic acid and ammonia, we shall find that it is rapidly
reduced to the metallic state. If, however, we precipitate
the silver bromide in the dark, and add to the developing
solutions a little bromide of potassium, we find that the
mass is redaced more slowly, the soluble bromide acting
as a retarder to the rediiction. If we have a film which
has been exposed to a camera image, and develop by the

* Precipitated by dissolving a little bromide of potassium in water, and
adding to it silver nitrate, and then Trashing.

ALKALINE DEVELOrJMENT. 1,5

unrestvained solution, we shall find, as a rule with gela-
tine films, and always with collodion films, a reduction all
over the surface ; whereas, if we use one containing the
restrainer, we shall find that the image develops properly.
Whenever there is a reduction of the silver salt there is
■an alteration in the developing solution, due to a chemical
change in it.

Now what does this reducing action depend on? In
the alkaline developer, we repeat, we have three effectives
(putting on one side the water, Avhich enters into all three),
viz., the pyrogallic acid, the alkali, and the restraining
"bromide. When pyrogallic acid is mixed with an alkali, it
is in an unstable state, and greedily absorbs oxygen from
whence it can get it. During the process of develop-
ment it is in contact with water, and with haloid salts of
silver — viz., the bromide and the sub-bromide. Take
the former into consideration first, leaving out the action
of the restrainer, viz., the soluble bromide. We then
iave a vigorous oxygen absorbent, and a haloid salt of
silver and water. Now, all bodies when mixed together
have a tendency to enter into new combinations, which
take the most stable form they can. This is what the
three substances do. The oxygen absorbent will take up
oxygen from the water, which, at the moment of libera-
tion, reduces the silver bromide to the metallic state, and
the liberated bromine forms, with the hydrogen, hydro-
bromic acid. This, in its turn, forms bromide ot the
alkali and water again. Roughly, it may be expressed
thus —

Alkali Pyro Water and Silver Bromide give Oxidized Pyro Silver
2NHj,HO + Pyro+ H^O + Ag^Br^ . = Pyro + 2Ag +
Alkaline Bromide and Water.
2NHiBr + 2H2O

So far, we have treated merely of the reduction ot
bromide of silver (AgBr,), and not the sub-bromide
(Agi). Now the action of light on the bromide (AgaBrj)
is to cause one atom of bromine to swing off, and in doing
this a certain amount of work has been performed by the

16 ALKALIXE DEVELOPMENT.

light itself ; and that being the case the reduction of the
sub-biomide ought to be more easily effected than the
bromide. In other words, light has partially effected on
the silver bromide what the chemical action of develop-
ment has to do when light has not acted. Suppose,
then, we have an amount of work to be done on the
bromide in order to reduce it to metallic silver of (say)
100 units, and that light does 20 of these units, evidently
chemical action of developing has only to do 80 units.
So if we have bromide and sub-bromide of silver together,
and arrange that the chemical energy ot the developer
shall be (say) 95 units, the developer would be able to
reduce the sub-bromide and not the bromide ; and in
case the energy of the developer was more than 100 units,
it would attack the sub-bromide in preference to bro-
mide. With a very weak developer this is the case, and
it may be used without any (what is termed a) restrainer.
Now what is the action of the restrainer ? This is a
point which is more difficult to answer. We were now
talking of a chemical restrainer, viz., the soluble bromide.
Silver salts are known to form double salts very readily.
For instance, there are double chlorides of silver and
sodium, and they can be obtained in definite crystals, as
can the double bromides, and it seems more than probable
that the restraining action is due to this affinity. When
we have double salts formed, the energy of their com-
bination is shown by the heat which is given out during
the combination. Mow, in order to dissociate them from
each other, work would have to be done on the double
molecules ; in other words, the work that the two do in
combining, which is shown by a rise in temperature, the
same amount of work would have to be done on them to
separate them. The double salt is, therefore, more stable
than the bromide salt per se. The energy existing in the
developer has not only to do the work of separating the
bromine, but also of separating the double salt. It may
be said in objection to this that the bromide is in solution,

ALKALINE DEVELOPMENT. 17

and therefore cannot form a double salt. Tliat would be
valid if we could say that no double salt was formed.
We know, for instance, that two salts when in solution
will form a double salt, and that two solids form a double
salt. The question as to whether a salt in solution, such
as potassium bromide, can form a double salt with a solid,
such as silver bromide, is not quite so easily answered ;
but the evidence, as far as it goes, is in its favour.

In some electro-chemical experiments which we are
undertaking, the formation of a double salt seems to be
confirmed, and, as we have said, the temperature test
certainly favours such an idea. It must be quite under-
stood that this is not put forward except as a good work-
ing hypothesis, which, so far, is uncontradicted by known
facts. It may be found to be due to some other cause,
though we believe not.

We thus lay the action of the restrainer to the forma-
tion of a double salt during development, and a conse-
quent increase in work that the developer has to perform
to reduce it. A body like the sub-bromide does not appear
to form double salts ; its composition is not allied to the
soluble bromide. Now it may be taken that solubility of
the one body in the other is indicative of the possibility
of the formation of the double salts. Dr. Hodgkinson
finds that whilst the chloride of silver is soluble in sodium
chloride, the sub-chloride is not, and thus he arrives at a
method of separating the two. This points to a similar
action of the bromide and sub-bromide in soluble bromide,
or it must not be forgotten that bromide of silver is
soluble in bromide of potassium to a limited extent.

We have so far treated of the action of pyrogallic acid
alkali restrainer, or the bromide or sub-bromide of silver ;
but there is a further action in development that has to
be considered. The quantity of sub-bromide to be re-
duced is infinitesimally small when the brief exposure to
light alone produces it. The first act of the developer is
to reduce the sub-bromide, but at the same instant that

18 ALKALINE DEVELOPMENT.

the metallic silver is formed this metal combines with the
silver bromide in contact mth it, and fresh sub-bromide
is formed, which is then acted upon, and a visible image is
produced. The mere fact of a chemical restrainer being-
used, however, retards development, since the metallic
silver first deposited by the development of the sub-
bromide has, before it can combine with the adjacent
bromide, to undo the double salt, and as this is work to
be performed, the development is of necessity slower.
Thus, silver and silver bromide yield silver sub-bromide ;
or,

AgBr+Ag=Ag2Br

There are two kinds of restrainers : one chemical, and
the other physical. We have treated of the former ; no\v
as to the latter.

A physical restrainer is one by Avhich the developer is
deprived ot rapid access to the exposed sensitive salt, and
this is particularly the case when an emulsion is prepared
in gelatine. In this state the colloidal nature of the gela-
tine permits only a very slow access of the developer to
the embedded salt. In other words, the small portion of
developer which attacks the particle is obliged to attack
that portion of it which is more readily reduced, and in
the case of gelatino-bromide films, that is the sub-
bromide. Albumen acts in the same way, and a physical
restrainer is used when with the developer are mixed
solutions of gelatine or albumen.

It is thus evident that if an absorbent of oxygen, which
by itself is capable of reducing the sub-bromide at the
first shock without reducing the bromide, must be a better
agent to use than pyrogallic acid, which requires a re-
strainer. Such an oxygen absorbent has been found by
the writer in hydrokinone, which, under ordinary circum-
stances, has no tendency to reduce the silver bromide,
and it has a greater affinity for oxygen than any known
organic substance.

From chemical analogy it may be assumed that tlie

ALIOiilNE DEVELOPMENT. 19

molecular attraction of the metallic silver is strongest at
the instant of its reduction. With the weak alkaline deve-
loper the silver is reduced but slowly from the hromide,
and hence it hecomes less " nascent," if we may use the
term, than it is when it is rapidly reduced. It is found
from chemical analysis of the developer after it has been
used, that a weakly alkaline solution is only capable of
reducing a small amount of the bromide compared with
a concentrated solution ; in other words, whilst the same
amount of ingredients possess the same amount of total
energy, yet when diluted the time taken to use up the
energy is longer than with more concentrated solutions,
and thus the energy applicable at each small interval of
time is less in the former than in the latter case. If we
strike a moderately rigidly fixed target with a hundred
Ibullets fired at intervals of a minute, we should not ex-
pect to overthrow it, but if the 100 bullets were fired all
together, and with the same velocity, the united energy
of the bullets might probably cause the target to be laid
low. In both cases the total energies applied are the same,
but the effects are difiierent. In a rough way we may
apply this simile to the weak and strong developers when
acting on the silver salt.

It will be observed, that various formulas are given for
alkaline development ; in one ferro-cyanide of potassium
is mixed with the pyrogallic acid, and in another sulphite
of soda. The value of these appears to be either that
they form a new compound, or that they absorb oxygen.
In any case, the longer the pyrogallic acid remains unoxi-
dized, the more effectual should be the development.

The hydi'osulphite developer may be classed amongst
the alkaline developers.

We next have to consider the ferrous-oxalate developer,
and it matters but little, as regards theoretical considera-
tions, as to which way it is formed. It will be seen by
the formula given later that the ferrous-oxalate developer
is in reality a solution of ferrous-oxalate in neutral

20 ALKALINE DEVELOPMENT.

potassium oxalate. The latter salt exercises no develop-
ing action, but is rather a retarder to development than
otherwise. We have therefore only to consider the action
of ferrous-oxalate on silver sub-hromide, and it may be
expressed as follows : —

Ferrous Oxalate and Silver Sub-bromide give

3(Fe,GA) + 2Ag2Br

Ferric Oxalate and Ferrous Bromide and Silver

re.,(CA)3 + FeBr^ + 4Ag

By which it will be seen that a metallic bromide is formed,
together with ferric oxalate. This is subject again to a
change with the potassium oxalate, ferrous-oxalate and
potassium bromide being formed.

Experience has shown the writer that the addition of a
small quantity of hyposulphite makes development much
more rapid, and that a gelatine plate requires less exposure
with it. Let us trace what happens to the ferric salt
formed : —

Sodium Hyposulpliite

and

Ferric Oxalate

give

Na^SA

+

Fe2(C!A)3

=

Hyposulpliite of Iron
Fe,S203

and

Ferrou^-Oxaiate

Sodium Oxalate

+

■P8(CA) +

Na,(CA)3

We thus find that the ferrous hyposulphite and oxalate are
formed, and also a sodium oxalate. It seems likely that
the destruction of the ferric salt immediately On its forma-
tion is one cause of the increased activity of the 'deve-
loper. The ferrous citrate, ferrous citro-oxalate, and
ferrous tartrate act, chemically, in the same waj- as the
ferrous oxalate.

CHAPTER III.

THE Cause and cure of fog in emulsions.

Every student in emulsion work has found, and will find,
that the chief obstacle that he has to overcome to obtain
success is the tendency for the plates prepared with an
emulsion to fog, or veil over on development, and it has
taken a great deal of experimental work to enable it to be
overcome. The writer ventures to think that the re-
searches he has made on the subject have explained in a
^reat measure, if not entirely, its rdison d'etre.

Setting aside the collodion or gelatine from the question,
and merely taking into consideration the sensitive salts
■employed, we may arrive at very definite results. It has
been asserted that a neutral combination between two
substances can never take place ; for example, if we mix
potassium chloride with silver nitrate we shall never be
able to get pure silver chloride, however much we may
wash it — that either the soluble potassium or silver salt
will always be in excess, though probably in the minutest
quantities. This certainly is the case theoretically,
because do what you will, and wash as long as you like,
there still must be some infinitely small part of the
soluble salt left behind. Now, in ordinary chemical
analysis, where products have to be weighed, the re-
sidual impurity may be inappreciable, being so infini-

22 CAUSE AND CUKE OE FOG.

tesimal that no balance yet constructed can show them.
Though a halance may he inoperative, yet, as is well
known, light is able to show us impurities in a substance
which may not be one-millionth part of a grain in weight.
By passing the light emitted from heated vapours of the
substance and its impurity through a prism, and
noting its spectrum, we may be able to detect the
latter.

The spectroscope will not tell us at present, however,
whether the silver or potassium is present as nitrate,
chloride, bromide, oxide, &c.

Where we are dealing with silver salts which are sensi-
tive to light, and which are amenable to development, it
is possible to ascertain whether certain compounds of
silver are present. Impurities in the bromides, with
which the silver bromide, for instance, is to be formed,
can, in some cases, be shown by weighing. For, in a
paper read before the Photographic ISociety of Great
Britain on the 8th of February, 1876, Mr. Warnerke
stated that on testing the different bromides, he foimd
that considerable variation from the theoretical quantities
necessary to combine with silver nitrate was observable.

Potassium bromide is one of the most usual salts with
which to form silver bromide. Let us see how it may be
contaminated in its preparation. We find that the mother
liquor from the sea water brine is treated with chlorine,
and that this takes the place of the bromine which in sea
water is in combination with magnesium ; the yellow
liquid is agitated with ether, which takes up the bromine,
and this etherial solution is treated with potash in solution.
The bromine forms the bromate and bromide of the alkali,
and when the alkali is nearly saturated, it is decanted off
and further treated. Now, from what we have said be-
fore, it is more than probable that the bromide is con-
taminated with the alkali, however well it may be
separated : the traces of alkali may even be so small as
to be undetected by litmus paper.

CAUSE AND CURE OF FOG. 23

Again, the bromides of tlie alkaline metals are prepared
by acting on the alkalies with an excess of bromine, a
similar reaction to that above taking place. The bromate
is decomposed by ignition, and this heating alone tends
to decompose the bromide, in which case we should have
the oxide of the alkali left behind. In good preparations
it would be excessiyely small, but still sufficient for the
purpose we shall indicate presently.

The bromides of the metals may be similarly contami-
nated. Take zinc as an example ; the metal is easily
oxidized, and the zinc oxide is soluble in zinc bromide,
as it is in the chloride. In all these cases, then, it is
possible we may have traces of oxide with the bromide.
Again, there are some metals which form two bromides", as
that of copper ; and experience shows that it is very hard
to get all compounds fully saturated with bromine, a
part of it being generally in the less saturated state.

If such bromides, contaminated with the oxide, or con-
taining the lower combination of bromine, be brought in
contact with silver nitrate, we shall have two separate
reactions to consider. In the case of the oxide contamina-
tion, when silver nitrate is in excess, we shall have —

Potassium Bromide, Potassium Oxide, and Silver Witi-ate

xKBt + ' K2O + («-|-2)AgN03

give Silver Bromide, Silver Oxide, and Potassium Nitrate

»AgBr + AgjO -I- (a;+2) KNO3

Or, besides the silver bromide, we shall have silver oxide
formed.

We have seen that we may have oxides and sub-
bromides contaminating the bromides, and in a similar
way we may have oxides and sub-chlorides contaminating
the chloride. The writer has shown that it was possible
to develop an image on a film never exposed to light, but
which was in contact with a film (during the operation
of development) on which an invisible image had been
impressed. The explanation offered seems in every way
to meet the requirements of the case, which is, that where

24 CAUSE AND CURE OF FOG.

a nucleus, if it may he so termed, exists, there the silver
from the adjacent bromide during development will be de-
posited in preference to any other part of the film. Such a
nucleus is found in the silver sub-bromide or sub-chloride
when the one film is exposed to light. If it be chemically
produced, we may assume it will act in a similar manner.

The case of the oxide is not so clear ; but a little
experiment will throw light on it. Prepare silver oxide
as an emulsion in collodion ; dissolve (say) 6 grains of
silver nitrate in an ounce of plain collodion, and add to
it two grains of potash in alcohol. This will give an
emulsion of oxide of silver. Now wash it, and add a
drachm of it to an ounce of a washed collodion emulsion
which works perfectly free from fog; coat a plate, and
develop it. It will be found that a veiled image is pro-
duced. In this case the silver oxide (presumably partially
reduced to the metallic state, since the oxide is an un-
stable compound) acts as the nucleus on which the silver
bromide is reduced to the metallic state by the alkaline
developer.

It must be borne in mind that the invisible image must
necessarily be composed of very minute particles of the
altered silver salt. If, then, such a smaU number of such
particles distributed over a film are sufficiently powerful
to form nuclei for the development of the image, the same
minute quantity of oxide, or chemically-produced sub-
haloid of silver, might be capable of producing the same
results. The above, then, seems to be the explanation
of fog in emulsion plates. Now as to the remedies.

It is well known that when we have an excess of
soluble haloid, freedom from fog is secured. In some
experiments we carried out, we found that silver bromide
is formed before any other silver compound, except the
iodide, when the sensitive salt is formed from haloid salts,
and not from the halogens themselves. Thus, if potas-
siiun bromide be contaminated with potash, we shall have
both silver bromide and silver oxide formed, if an excess

CAUSE AND CURE OF FOG. 20

of silver nitrate be added ; but if there be a defect of the
nitrate, there will not be a trace of silver oxide, but only-
silver bromide. Again, if we take bromide of copper,
"which is usually contaminated with the sub-bromide, as
.already stated, it will be found that the bromide is all
utilized before the sub-bromide is attacked at all ; and
if, in addition to the bromide, we have a metallic chloride
present, which may be contaminated with sub-chloride,
the order in which they will combine with the silver
nitrate is : bromide, chloride, sub-bromide, sub-chloride.
Thus, if there be only sufficient silver nitrate added to an
emulsion to combine with the two first on the list, the
other two will be left in the emulsion as harmless com-
pounds. The method of eliminating fog from the finished
emulsion in which there is at first an excess of silver
nitrate is thus easy to guess, and we have the theoretical
•explanation of a statement made some years ago by Major
Russell, that a little soluble bromide ought to be left in the
film when silver bromide is formed by the bath in the
usual way. It may be remarked, parenthetically, that
whether the image be developed by the alkaline or acid
method, the same result must hold good. Supposing we
have a washed emulsion which contains bromide, sub-
bromide, and oxide of silver, and also a very slight excess
of silver nitrate. The addition of certain metallic chlorides
or of hydrochloric acid will at once convert the sub-
bromide and oxide into the chloride of silver, leaving harm-
less compounds behind. The metallic chlorides which are
of use are those which readily part with chlorine, and
which, therefore, preferably form more than one chloride,
such as gold, copper, platinum, &c. 'When other chlorides,
such as of the alkalies, are employed, the needful sub-
stitution may not take place, because the affinity of the
alkali for the chlorine is greater than for the sub-bromide ;
-and therefore the elimination of the sub-bromide is not
effected. Thus, if all the silver nitrate in original excess
be converted into silver chloride, we have the silver sub-

20 CAUSE AND CUEE OK FOG.

bromide to get rid of. Noiv, supposing Ave are using
sodium chloride as a corrective, then we should have

Silver Sub-bromide and Sodium Cbloride
AgoBr + NaCl,

which can form no new saturated silver compound, since
an atom of metallic silver, sodium, bromine, or chlorine,
cannot be left in a free state ; but if we use (say) copper
chloride, we have —

Silver Sub-bromide and Cupric Chloride
L'Ag^Br + CuCl„

which can form —

silver Bromide and Silver Chloride and Cuprous Chloride.
AgBr + AgCi + CuCl.

The CuCl, or sub-chloride of copper, is harmless, and can
be left out of consideration.

It will, therefore, be seen how it is that addition of
these chlorides to a washed emulsion will give freedom
from fog.

Secondly, if an excess of silver nitrate be used, it is
evident that something else besides a mere chloride will be
required, since the sub-salts and oxides would be formed.
This we find in the employment of an acid, or of a halo-
gen itself, or both together, added to the emulsion, to be
most rapidly effective. Whatever is used is best added
to the soluble salts before the silver nitrate is added.

Suppose nitric acid alone be employed, then any oxide
or carbonate will immediately be attacked, as also any of
the sub-bromides — such as of copper. Again, if aqua-
regia be employed, wc know that chlorine is evolved in
an extremely nascent state, and that this would attack
either oxide or sub-bromide, fully saturating the unsatis-
fied atom in the latter. If, now, silver nitrate be added,
silver bromide and chloride would result with some com-
pounds (perhaps such as the chlorate), which would be as
inert as producers of fog as the silver nitrate itself.

If a halogen be employed without any acid, the same
result would occur. Thus, suppose we had as impurities.

CAUSK AND CUBE OF FOG. 27'

an oxide and a sub-bromide, and that we added a solution
of bromine to it, we should get the oxide changed to a
bromide and bromate (the latter salt of which is experi-
mentally proved to be inert), and sub-bromide changed to
a bromide.

If the halogen be added last, when there is an excess of
silver, it is probable that until all the latter is converted it
will exert no unfogging action ; but if an acid, such as
nitric acid, be added, it will exert its proper influence,
though slowly ; for it will convert any oxide or compounds
of the oxide into nitrate, and froin the silver sub-bromide
dissolve away the loose atom of silver, converting the sub-
bromide into bromide and nitrate. Thus —

Silver , Nitric „• Silver , Silver . Nitrous „„;, -ar^^^^

Sub-tromide """i Acid S'^" Bromide ^""^ Nitrate ™"i Oxide ""^ ^^^"^
4AgBr + 6HNO3 = 4AgBr -|- 4AgN03 + N2O3 + SHjO.

(3r, at all events, a fresh combination will be made, which
is unacted upon by the developer.

There is also a method of eliminating fog from collo-
dion dry plates when coated, without doctoring the emul-
sion at all. This need not apply only to Avashed emul-
sions, but it can be effected during the washing of the
plates prepared by the unwashed emulsion. In addition
to the elimination by the acids, and by the metals forming
two bromides or chlorides, we can further effect it by
using a solution of potassium bichromate,*' permanganate
of potash, or peroxide of hydrogen, and other oxidizing
agents, such as ferric-sulphate and ferric-oxalate. The
reason of this seems to be due to oxidation, or to the
direct formation of a new product ; the writer is still
engaged in experiments on the subject. It may be, in the
first case, that a minute quantity of silver bichromate is
formed by the oxide, or that the free silver atom of the
sub-bromide is oxidized, and then formed into silver
bichromate ; with the second, it may be that the man-

* This can be used with gelatine emulsions.

2S CAUSE AN'D CUKE OP FOG.

ganese salt is substituted for the silver salt, and is inert ;
and in the next two cases it may Tbe that the silver salt is
per-oxidized, and forms an oxy-bromide, which is un-
affected by the developer. This seems probable, since
ozone has the same effect on the fog.

It may not be uninteresting to note an experiment which
throws some light upon this point, though it is not con-
clusive. If a plate be coated with collodion emulsion, and
be allowed to thoroughly darken in the daylight, and then
drops of the above oxidizing agent be placed on different
parts of the iilm, and allowed to act for a few minutes, it
will be found, after washing, that on these spots the colour
and appearance of the film will remain unaltered. (Where
the manganese has been, the film is slightly brown.)
Now, if the film be treated with sodium hyposulphite, the
parts where all have been will become transparent, show-
ing that everything except the collodion has been dis-
solved away, whilst on the rest of the plate there will
remain a delicate layer of metallic silver. This shows
that the loose atom of metallic silver attached to the sub-
bromide has been converted into a salt soluble in hypo-
sulphite of sodium.

Ee the theory what it may, the treatment holds good.
Perhaps with collodion plates the application of nitric
acid is the safest, where possible, but to that we shall refer
later on.

Dr. Eder has also shown tliat potassium ferri-cyanide
and potassium bromide will cause the same result. The
ferri-cyanide acts as follows : —

Silver . Ferri-cyanide - Ferro-cyanide . Ferrocyanide , Silver

.Sub-bromide^'"' of Potassium Si'« of Potassium *"" of Silver """^ Biomide,
iAg.,BT + aK^FeCy,, = 3KiFeCy„ + Ag^FeCye + 4AgBr

The potassium bromide converts the ferro-cyanide of
:silver into bromide, and ferro-cyanide of potassium is
formed. Thus —

Ferrocvanide „„;, Potassium - Ferrocyanide „_. Silver

of Silver ™'' Bromide ""'' of Potassium """ Bromide.
Ag^FeCyc + KBr = K.FeCye + AgBr

CAUSE AND CUEE OF FOG. 29~

From tlic foregoing it will be seen that fog may be
produced by inorganic matter present with the silver salt ;
and further on it will be seen that it may be produced
during development and in emulsification. Regarding
this last point there is more to be said in regard to gela-
tine emulsion, and which Avill be found more fully treated
of later on. Suffice it to say that gelatine itself, when
decomposed to any extent, has an alkaline reaction,
ammonia being one of the products, and that this will
reduce the silver bromide held in suspension in it, un-
less means be taken to overcome the effect of the alka-
linity, or to neutralize the alkalinity. In other words,
decomposing gelatine is a feeble developer (or reducer of
the silver salt), and may cause fog. The fog caused by
the reduction of the bromide to the metallic state is much
more difficult to treat than any other, for the mere con-
version ot the metallic silver into oxide is useless (see
page 24). More vigorous treatment is required. This
shows that a collodion emulsion is much more readily un-
fogged than a gelatine one, since in the former the reduc-
tion of the silver salt to the metallic state rarely, if ever,
occurs. With collodion the danger is minimized, and
acidity rather than alkalinity is to be apprehended.

With gelatine plates it is inadmissible to use any sub-
stance which may attack the gelatine ; thus the applica-
tion of acids is not to be thought of, nor hydroxyl, nor
permanganate of potash. Chloride of copper may be
employed, but the safest plan is to use either bichromate
of potash or the ferri-cyanide of potassium with the bro-
mide of potassium.

CHAPTER IV.

DARK-ROOM AND ITS FITTINGS.

It is of coiirse convenient to have a special dark-room
adapted for all photographic work, but in some cases it is
impossible, we are well aware. If, however, the amateur
will work after dark, there is no reason why a dressing
room, a bath room, or any spare room should not answer
the purpose without permanently disarranging them. For
the preparation of emulsion and plates the requirements
are of course greater than when merely development is to
be carried on. For the latter, a wash-hand stand andbasin,
five or six dishes, a drying rack, and a piece of mackintosh
(to prevent spoiling the furniture or carpet by any splash
from the developer), are sufficient for any purpose,
always provided, the light used in illuminating is made
subservient to the purpose for which it is to be employed.
In making collodion emulsions, any ordinary room will
answer ; and plates may be prepared if a drying cupboard
of some description or other is provided. For the manu-
facture of gelatine emulsions, much may also be done, only
in this case it is necessary to have some convenient gas-
stove for heating them, and hot water as well. One of
Fletcher's numerous burners may be employed with every
satisfaction in the majority of cases, and it need not be a
permanence in the room, since it can be attached to any

DARK ROOM AND ITS FITTINGS.

31

gas jet. "Tlie following description of a dark-room istaken
from " Instruction in Pliotography."

The size of the dark-room may, ol course, vary, but it
may he remarked that a place six feet square is the least
space in which to work.

A sample of an arrangement for such a size of room is
given in the figure. B is the sink : AA are the two work-

e FEET.

u

Fig. 3.

ing tables. On the left, over A, may be placed a glass
shelf, running along the left wall towards tue drying cup-
board, D. The right hand table, A, may be used for the
developing bottles and apparatus. The door of the dark-
Toom should open outwards, if possible, and be covered by
a curtain, which depends on to the ground, thus shutting
out all light which would otherwise get through the chink
between the door and the floor. Too many precautions
to exclude white light cannot be taken, since gelatino-
bromide, if it is to take the place of collodion, should be
extremely sensitive to it, however feeble it may be.

Water Arrangements. — It is always useful to have water
laid on to a dark room, but in many cases it is impossible ;
in that case we recommend that a two-gallon jar be placed
some three feet about A (fig.) on the right hand, a hole

32 DARK EOOM AND ITS FITTINGS.

Ibeing bored about two inclies from the bottom. A cork
"vritli a pierced hole, in which is passed a small piece oF
glass tubing, should fill up this orifice, and on the glass
tube should be drawn a piece of black india-rubber
tubing of a convenient length, to which an American clip
should be attached. If a hole be bored slantingly-
through the clip, so that the india-rubber tube, when
passed through it, comes to the termination of the jaws of
the clip, this arrangement, which was first described to
us by Mr. England, M'ill answer better than more elaborate
contrivances. When water is laid on from the main, a
rose is a very desirable adjunct to the tap, since it gives
a jet which has no force, and which is like a shower or
spray. _

Drying- Cupboards. — The principles on which a drying-
box should be made should be apparent, though in many
forms they are neglected. The first principle which
should be carried out is that the air passing through it
should be capable of taking up moisture. It very often
happens that the air which, in some contrivances, is
passed through the drying-box is nearly saturated with
moisture, hence it can take up but very little more, and
plates dry slowly. Air, of course, may be dried by
causing it to bubble through sulphuric acid, or by passing
it over dry chloride of calcium ; but in order for this to be
effective, the drying-box must not only be light-tight, but
also fairly air-tight, since the air would find its way im-
mediately through any small chink or cranny sooner than
force its way through these obstructions. A better mode
is to warm the air entering the box, so as to cause a
draught, and at the same time this slightly warmed air
will hold more moisture than cooler air. On this principle
sound efficient drying-boxes are constructed.

An excellent type is that due to Mr. England. If con-
structed as in fig. 4 it will dry plates up to 12 by 10.

A box is made of the dimensions given, and one side
is hinged, and opens as shown. This side has a fillet

DARK ROOM AND ITS FITTINGS.

33

placed round it, so that on shutting up no light can
enter the interior of the box. Through the centre of the
box runs a gas pipe, at the bottom of which is inserted a

I" CAS PIPE-'

Mg i.

small tube closed at the end, and on one side of which is
pierced a small hole. To this hole gas is led, and a very
small jet is lighted in the gas pipe. At the bottom of the
box, and at the top, are two holes of about three to four
inches diameter ; and above, two tin tubes, some twelve
inches long, are fitted into these tubes as shown in the
diagram. It will be noticed that the gas piping passes
through the centre of these two tubes. Round the gas
pipes are fitted two discs of blackened card or tin, one of
which is placed two inches above the bottom hole, and]the

34

DARK ROOM AND ITS FITTINGS.

Other the same distance from the top hole. These pre-
vent light striking down the tin tuhe into the box. The
plates, when set, are laid on pairs of wires stretched across
the hox, as shown in the diagram, and a box of the above
dimensions may take from half to one dozen plates on
each side of the central pipe.

Plates dried in such a drying-box are ready for use in
about twelve hours after coating. A small thermometer
should be hung on the cupboard door, to enable the
temperature to be noted.

The rationale of this fairly rapid drying is that the gas
piping gets heated, warms the air in contact with it, which
ascends through the top tin tube, and a current of fresh
air comes up through the bottom one. A constant change

Fig. 5.

of air, more than a very dry or hot air, is the object to
be attained.

We are in duty bound not only to give its excellencies,
but also to point out any defects. In hot weather we found
that the parts of the plates dried close to the central pipe

DARK ROOM AND ITS FITTINGS.

35

are apt to run; the heat is communicated to the iron
wires, and the glass takes it up, and the gelatine is apt to
melt when the plate touches the wires. This is evidently-
due to conduction, and we helieve that it is hetter to have
a non-conducting medium in contact with the glass. Small
loose cylinders, about half-an-inch long, of pipe-clay, can
be readily baked and slipped over the iron bars, and each
end of the plate supported by them. For summer weather,
when the air is, as a rule, dry, it is a good plan to have a
small gas jet placed just above the box in the iron gas
tube. This heats the air in the zinc tube, and a draught
is created through the box ; by this means the air is not
above the summer temperature, and is not so quick drying.
For our own part, when drying gelatine plates, we use
racks similar to that shown in fig. 5. A cupboard will
dry nearly double as many plates on these racks as when
they are laid to dry horizontally. Collodion plates may
also be dried in these racks.

^IL

c-

-^

e

e

^1

Fig. 6.

The plan recommended by Dr. Van Monckhoven is one

36 DARK ROOM AND ITS FITTINGS.

which has long been in use in England, hut he has de-
scribed it as follows : — " The drying-hox (fig. 6) is easily
made, and consists of a box of thick wood, on the top of
which is a zinc pipe to connect it with a chimney. At
the bottom is another pipe, but with an elboAv to prevent
light from entering. Horizontal shelves are placed in the
interior, so that the current of air obtained by the draught
in the chimney goes over each, one after the other. This
box ought to be placed in a warm and very dark room.
As to the necessity of warmth in the room, we demur.
Tt is not necessary if arrangements be made for burning
a gas jet in the top tube, so as to create a draught."

Mr. A. Cowan has also described in the Photographic
Almanac a drying box for dry plates which is essentially
correct in principle, and no doubt answers well. He says :

'' It often happens in very damp weather that gelatine
negatives refuse to dry for hours, and even when flooded
with spirit take a considerable time.

" To those who do not possess a good drying cupboard
the following is offered as a thoroughly efficient substi-
tute, which anyone can make for himself with a little help
from the blacksmith.

" The annexed diagram (fig. 7) will explain itself. The
box may be of any form most convenient, but the more
shallow the better. The one in actual use stands on an
ordinary work-bench, and the gas-burner, and iron cone,
&c., on the floor, enclosed with a few bricks piled up to
keep in the heat and protect any woodwork. A very good
proportion for the cupboard is thirty inches high, thirty
inches wide, and ten inches deep from back to front.
The front is closed up at the lower part about six inches,
and a sliding door running in grooves closes the upper
part all but about half an inch from the top, a balance
weight over a pulley supporting it in any position re-
quired. This is found a much better way than having
doors opening on hinges, for various reasons.

" The current of warm air is conveyed in at the bottonr

DARK EOOM AND ITS FITTINGS.

37

through a three-inch circular opening, the iron stove -pipe
arrangement being screwed on underneath. Ahove the
opening, at a little distance, is supported a thin shelf of
wood about an inch smaller all round than the inside of the

Fig. 7.;

box, which acts as a diffuser, and stops the current of hot
air from rushing up in one spot. Above this, at any-
convenient height, two bars are fixed to carry the feet of
the drying rack containing the plates. It will be found
that plates will dry without running at a very considerably-
higher temperature than that at which gelatine melts if
the heated air be kept in continual motion."

Another excellent drying box, due to Mr. Rogers, is
sho-wn in fig. 8.

The section of the box shows the general principles
adopted ; the exit pipe for the warmed air is at the top of
thebox. The drying-box may be of any dimensions. Pis
a one-inch piece of gas-piping standing on the box G, and
through it a small pipe, carrying a minute gas-nipple,

38

DARK EOOM ANT> ITS FITTINGS.

passes ; it is soldered in air-tight at the bottom of C, and
is connected hy an india-ruhber tube, I, with the gas ; Z
is a three-inch stove-pipe, soldered up at one end, and
open at the other, through which P passes ; a small leather
washer, W, makes the zinc-tube air-tight at the top ; D

is an outlet tube passing into the top of the box, over the
opening of which may be stretched muslin in order to
arrest the entrance of all dirt into the interior. At K is
a light-trap, to exclude all light which might be reflected
from G, the gas jet ; a current of warmed air thus per-
petually circulates in the box B. The gas is lighted by
raising the pipe P from off C, which is then replaced. In
summer the tube D may be closed, and an inlet pipe,
coming from the top of the box, be substituted for it,
thus causing only a current of air at the ordinary tem-
perature of the room to pass through it. We may mention
that the plates dry more rapidly at the top of this box

DARK EOOIM AND ITS FITTINGS.

39

than at tlie bottom. This is due to the warmer air having
a tendency to remain at the top.

Another excellent plan for a drying cupboard is the
following, which has been devised by the writer.

B is a zinc boiler, from which are taken two pipes, D
and H, leading to the coil of pipes, C C C C. A supply
tank, T, is fastened against the side of the cupboard, and
a supply pipe joins the coil pipe at H. From D another
pipe. A, is led, terminated with a tap, which allows any
air to be got rid of, which would otherwise stop the flow

*«tr

£3 ^1_

Sfl

lig. 9.

into CO. At H is a tap, which allows the whole appa-
ratus to be emptied at pleasure. K is a hot-air shaft,
being some four feet above the box. It is terminated by
a bend in two directions, and can be fitted with a cap, if
required, in which are pierced orifices. Beneath are a
couple of ventilating inlet pipes, likewise bent in two
directions. L L L is a false bottom, pierced with holes,
on which the drying racks are placed. F is a gas jet,
which heats the water. (The cupboard is shown with
only one door.) Each door is made light-tight by means
of fillets, which need not be described. The hinges are

40 DARK ROOM AND ITS FITTINGS.

pianoforte hinges. The piping is made of composition
gas-pipe, though perhaps iron would be better ; still, as
they are, they answer perfectly.

In this cupboard it is well to have the plates on hori-
zontal racks, so that the warm air may pass rapidly over
them.

CHAPTER V.

ILLUMINATION OF THE DARK ROOM.

In all emulsion processes, whether collodion or gelatine,
;great precautions have to be taken as to the light in
which the plates are prepared, since they are necessarily
exposed to its action for some considerable time. There
are many persons who attempt to prepare emulsions who
fail, and the failure may often be traced to the improper
lighting of the dark-room. For development, a light
which would slightly fog a plate during preparation
may be used, since it is not necessary that it should be
exposed to its action more than a second or two, which
would not be sufficient exposure to cause any percepti-
ble fog. When once development begins, the ingress of
more actinic light has but little effect, since there is
sufficient bromide used in the development, with the
alkaline development, to render the silver salt insensitive
or, if ferrous-oxalate be employed, the solution itself is of
a colour which effectually cuts off all light that would
rapidly harm the image. We have made these remarks,
not to discourage the idea that a perfectly safe light
should be used, but to show that when such cannot
be procured, as on tour, it is possible to develop
plates without any danger. It is necessary, first of
all, to know what kind of plates are to be prepared,

42 ILLUMINATION OF THE DAEK ROOM.

and worked, tefore deciding what light to admit to the
dark room. For instance, with collodio-hromide, an
orange or yellow light will suffice ; hut with gelatine
plates containing pm-e hromide, a ruddy light in which
there is hut little green is the safest. It is safe, however,
in all cases, to have a red light of the right kind, and
we recommend it for general adoption, since every kind
of plate can be worked in it.

If the quality of the light can he got by which the salt
of silver is unaffected, the quantity may he unlimited. To
make this more clear, a diagram from another work* is
reproduced, from which, together with a reference to
figure 2, page 4, a notion can he obtained as to the light
to which different plates are sensitive, and the media
which may be accepted to cut off that light.

No. 1 may be omitted from consideration, since it is
sensitive to all rays, and no filtered daylight is admissible
where it is employed ; but Nos. 2, 3, and 4 should be
studied. When a streak of white light is passed through
a prism it is spread out into its component colours, and
in 14 they are represented as white. The black portions
in 2, 3, and 4 of the diagram show the rays of light in
every case which do not appreciably affect a sensitive
plate. The white and half-tints represent, as approxi-
mately as can be shown in a wood-cut, the relative sensi-
tiveness of the plates, the different rays forming white
light ; the degree of sensitiveness being indicated by the
degree of whiteness. It will be noticed that the gelatino-
bromide and coUodio-bromide plates are sensitive to the
confines of the red, and some specimens of the former are
also sensitive well into the red, whilst the bromo-iodide
here shown is only sensitive to the confines of the
yellow. Next we need only turn our attention to Nos. 5,
6, 7, 8, 9, 10, and 12. In these are shown the rays of light
which pass through different coloured glasses and dyes.

* " Instruction in Photography " (Piper and Carter), 6th edition.

ILLUMINATION OF THE DARK KOOM.

43

2 3 4 5

1. Special collodio-bromide,

2. Gelatino-bromide.

3. Collodio-bromide.

4. Bromo-iodide.

5. Cobalt glass.

6. Ruby glass.

7- Chrysoidine.

8. Magenta.

9. Flashed orange.

10. Stained red glass.

11. Bottle-green glass.

12. Aurine.

13. Quinine.

44 ILLUMINATION OF THE DARK ROOM.

Buby glass would be as near peiiection as possible for
every plate were it not that a certain amount of blue
light passes through one thickness of it. When two thick-
nesses are used the blue is imperceptible. By the use of
a combination, orange glass and ruby, or stained red glass
and ruby, the light allowed to pass through is such as will
not affect most plates unless the exposure to it be pro-
longed, since the orange or stained red entirely cuts off
the blue which may permeate the ruby glass. The writer
has been told that somepeople prepai-e plates so sensitive to^
the red that the light passing through any number of thick-
nesses of ruby glass proves an ineffectual protection. Un-
less rubyglass were added till total darkness supervened,
there is nothing to surprise us in this statement, as the red
light which filters through three or four thicknesses of ruby
glass has the same quality as that which filters through two
thicknesses. What they really express is that they pre-
pare plates which are in reality sensitive to red light.
When this is the case the development and preparation
of such an emulsion become a nuisance, and are probably
more of a scientific than of a practical value, since the
same sensitiveness can be produced without any liability
to veiling of the image through the impact of light of such
low refrangibility on the plate. For an ordinary dark
room we recommend that, if a north light be obtainable
for the window, one thickness of ruby and one of stained
red or orange glass be employed. As to dyes, it will be
seen that if glass be coated with aurine on one side, and
magenta on the other, the same spectral quality will be
obtained. At the same time it must be remembered that
every aniline dye fades gradually in white light, the
fading being caused by those rays which they absorb.
Under these circumstances, if orange glass be placed out-
side the paper dyed with the foregoing, the means of
obtaining a room permanently lighted with a safe light
is increased. If plafes very sensitive to the red be pre-
j)ared, one thickness of cobalt glass and one of stained red

ILLUiXINATIpX OF THE DAUK ROOM. 45-

will be tlie best combination to use ; but, as we said before,
plates requiring such a light by which to develop should
not find a place in a photographer's hands. If the sun
shine on the window during any part of the day it is well
to have a screen, which can be placed against the window-
frame (it can be hinged from the top, and pulled up as a
flap by a small pulley arrangement), covered with orange-
coloured paper.* This diffuses the light, and renders any
chemically active rays which can possibly filter through
it less hurtful. It is not always practicable, however, to
work by day, and then it becomes necessary to resort t»
artificial light, and that must be of the same character as
the filtered daylight. Now, candle and gas-light have
not the same amount of blue in them as the light from
the sun, hence the screen used for shielding such sources
need not be quite so perfect. In our practice we have a
lantern made like a large sized stable lantern. Holes are
pierced at the bottom of it for the indraught of air, and
holes at the top of the sides for the outdraught. To pre-
vent any light striking the ceiling, we have had a tin cover
fitting round the lanternf at the top, and sloping 45°
downwards, by which means any light glancing through
the holes strikes the shade and is reflected downwards.
The sides are covered with two thicknesses of orange
paper, and a candle placed inside gives a very fan- work-
ing light for coating plates or for development. As may
be inferred from our previous remarks, the light must be
much more subdued lor the former than for the latter pur-
pose. There is a medium called canary medium which has
lately been revived for use in the developing and coating
room. It is a paper which is impregnated with chromate
of lead, and we have tested its capacity for cutting off
hurtful light. For most plates it ,answers well when two
thicknesses are employed, but it is inferior in illumination

* Common orange packing paper answers admirably,
t Some lanterns are made with this arrangement.

46 ILLUMINATION OF THE DAKIC ROOM.

to the orange paper. It is a pleasant light, however, to
work in, and it is to he recommended. Before packing
plates, it is always necessary to examine them lor dull
spots and imperfections. As a rule, the diffused light
coming through paper or other fabric is unsuited for this
examination. It is better for this purpose to have a lan-
tern with a transparent side, by which means the flame
of the light is reflected from the plate to be examined, and
this immediately throws in view any imperfections. As
the examination can be made in a couple of seconds, this
exposure does not injure the plate.

^ Some dry-plate men we know have gas burning close
outside a red glazed window which opens into an ad-
joining room, but it is not every one who can have such
an arrangement.

For developing plates at night, whilst on totir, we have

Fig, 11.

found that a useful piece of apparatus can be easily made.
Take a sheet of cardboard of the size of about 2 feet by

ILLUMINATION OF THE DARK ROOM. 47

1 foot 6 inches. Lay off from the 2 feet side distances of
8 inches from each corner, and with a penknife cut half
through the card in a line parallel to the ends. These
will form flaps, which can be folded over to meet in the
«entre. From the centre portion mark out a rectangle
of ahout 6 inches by 12 ; cut round three of the sides,
but only half cut through one side, the penknife
being applied from inside of screen. This will allow
a square flap to open outwards. On the inside of the
opening may be pasted or hung a sheet of orange
paper ; or a sheet of paper dyed deeply with a mixture
^f aurine and aniline scarlet may be glued to it. The
candle is placed behind the screen, which should stand,
supported by the two wings, in front of the operator. A
piece of board, or a piece of tin, may rest on the screen, and
thus cut off diffused light from the ceiling. We have deve-
loped many plates with such a light, and lost none by veil-
ing of the image. When packed for travelling, the flaps
are folded up, and it can be placed in the portmanteau.

Fig. 12.

A useful portable lantern is made from a Chinese lan-
tern. We first saw it adapted in Mr. Galton's hand ; but

48 ILLUMINATION OF THE DARK ROOM.

Dr. Hermann Fol has given a practical method of its con-
struction in the Photographic News. He describes it
as follows : — " The most portable lantern I make by
painting over common white paper Chinese lanterns with
collodion containing castor oil and fuchsine. The top
and bottom of the lantern are made each of two thin
metal plates fastened together by three small chains.
Each plate is pierced with holes, and each pair is fastened
to the chains so that the holes do not correspond, and
half-an-inch remains between the two plates. No white
light can then find its way out. The upper pair is, of
course, unfixed, and may be lifted out to get access to
the candle. This lantern folds up into the smallest possi-
ble compass, and when in use perfectly excludes all
actinic light without getting hot."

Dealers supply lanterns more or less efficient, but we
confess to liking home-made apparatus, since, if made by
oneself, they can generally be readily repaired.

CHAPTER VI.

INTRODUCTORY REMARKS ON GELATINE
EMULSIONS.

Histoi'ieal Outline of the Process. — ^A gelatine emulsion,
as it is somewhat crudely called, as first made by Dr.
Maddox in 1871, is in reality silver bromide, &c.,
emulsified in a gelatine solution, with which plates are
coated. We have already (page 3) stated that there
are various modifications of the molecular state of
the bromide, which are brought about in a variety of
ways. Mr. C. Bennett first showed how extremely sensi-
tive plates CO aid be prepared by keeping the gelatine
solution liquid at a temperature of about 90'' for six or
seven days. What he accomplished was in reality to
bring about a modification which was very easily acted
upon by light. It need scarcely be said that in certain
states of the weather this long emulsification was attended
with enormous risks of decomposing the gelatine, and
when gelatine decomposes, the products are apt to reduce
the silver bromide to the metallic state, and hence to cause
fog. Besides this, there is the danger, even if fog is not
produced, of the gelatine refusing to set. Col. Wortley
stated that he got the same rapidity in his plates by rais-
ing the temperature of the emulsion for a few hours to
160° F., and Mr. Mansfield first recommended the gelatine

50 EEMAEKS ON GELATINE EMULSIONS.

emulsion to be brouglit to the boiling point ; but then a
very short boiling is liable to destroy the setting qualities
of the gelatine. ■ ilr. W. B. Bolton, in an article in the
British Journal of Photography ^ first indicated the true
method of preparing emulsions by boiling. He emulsified
in a small quantity of gelatine, boiled, and then added to
the emulsion the proper quantity of gelatine to give it a
firm consistency when setting. We may say that the
publication of this article opened out a ne"w era in gelatine
emulsions. We need not further explain the rationale of
the process here. Dr. Van Monckhoven called attention
to the fact that by adding ammonia to the silver bromide,
a modification was obtained which gave great rapidity ;
and Dr. Eder carried the principle further, and gave a
really workable, though in some states of weather a
dangerous, process. The great desideratum^ according to
these authorities, was to obtain a grey emulsion by trans-
mitted light, and green by reflected ; but, as will be seen
from our remarks on page 3, this state is not what we con-
sider the most sensitive, and certainly we have never ob-
tained plates so rapid by the ammonia process as we have
by the boiling process. We have endeavoured in the
following pages to give an accurate description of the way
to carry out all these processes. But we here make a dis-
tinct record of our opinion, which is, that for rapidity
and good quality, the boiling or hot digestion processes
are the best and safest.

We have also given processes for precipitating silver
bromide in water or glycerine and water, and then adding
it to gelatine. The processes are effective, but they are
not so easily employed where iodide is used, as the iodide
is apt to settle down in large particles.

We here give one piece of advice, which is, that if the
reader has a process with which he is thoroughly satisfied,
he should keep to it, and not waste his time or energy in
following out more elaborate, but perhaps less successful,
processes.

REMARKS ON GELATINE EMULSIONS. 51

A pertinent question for everyone to ask himself is, as
to whether a very rapid process is always a desideraium.
For our own part we unhesitatingly say it is not. For
transient effects in a landscape, for instantaneous views, or
for portraiture in dull weather, rapid plates are iiseful ad-
juncts, but should be nothing more. We believe that
finer pictures, more mellow and truthful, are usually
produced by the slower plates, be they collodion or
gelatine.

On the Causes of Sensitiveness in Gelatine Emulsion. — It
may be said that in a gelatinp emulsion it is almost neces-
sary that the soluble bromide be in excess over the silver
nitrate ; that is, that when aU the nitrate is converted into
bromide, there should still be soluble bromide left in the
solution. It must be recollected that gelatine is a most
unstable body, and we believe we are correct in saying
that from the first time it is heated its decomposition
commences. This decomposition at first gives rise to an
acid reaction, and eventually to an alkaline one. In the
first stage no harm will ensue to silver bromide suspended
in it ; but when the latter stage is arrived at, there is a
great tendency for the silver salt to be reduced to the
metallic state, unless some body be present which hinders
it. Such bodies are found in acids and soluble bromide.
The addition of acid must be made cautiously, since acids
cause gelatine to lose its setting properties, and there is,
consequently, a greater safety in using excess of bromide.
Again, if there were any excess of silver nitrate, this ex-
cess would combine with the gelatine, and we should
have a product formed not particularly sensitive to light,
but acted upon by a developer at once, and have in conse-
quence a production of red fog. We may, therefore, take
it that in the production of gelatine emulsion an excess
of soluble bromide is essential.

In the first chapter we have already referred to the
differences in molecular structure that silver bromide
may assume ; and we repeat that the molecular structure

52 SENSITIVENESS IN GELATINE EMULSION.

is purely due to physical causes, and not to diiFerent
chemical composition ; in other words, hromide, chloride,
and iodide of silver emulsions have always the same pro-
portions of hromlne, chlorine, and iodine to silver present.
When silver hromide is produced with proper precau-
tions as an emulsion, or in the film at once, as in the wet
collodion process, we have the film transmitting red rays,
and ahsorhing the blue rays ; showing that the work per-
formed in the film is really done by the blue rays. If a
gelatine emulsion, however, be boiled, the bromide, unless
great care be taken in mixing, becomes a cold grey colour
by transmitted light, and yellowish-green by reflected light,
and this shows that some of the yellow and red rays are
absorbed, whilst some of the blue rays are transmitted; and
yet it is found that this silver bromide is more sensitive to
the blue rays than the redder form. Can any explanation
be given of this ? We think it can. It is not owing ta
the fact that the silver salt is slightly sensitive to the
yellow rays, for this woxild only increase the sensitive-
ness by about one-twentieth, as photographing the
spectrum shows us. It must be recollected that the
apparent colour of the bromide may be produced in two
ways — or rather, that it may be due to two causes : it may
be due to the colour of the silver bromide itself, which is
what we may call its molecular colour, or a variation in
colour may be due to the scattering of light by the
diiFerent sizes of the particles, each particle being pro-
bably composed of thousands of molecules. When an
emulsion is boiled, an inspection of the films after different
lengths of boiling wiU convince us that the longer an
emulsion is boiled, the larger the size of the particles
which are embedded in the gelatine. Hence boiling pro-
duces large particles. The cause is, probably, that silver
bromide is slightly soluble in water, and much more so in
water containing soluble bromide. Without doubt, during
boiling some portions of the silver bromide are dissolved
and re-precipitated on the coarser particles, other per-

SENSITIVENESS IN GELATINE EMULSION. 53

tions of tlie finer bromide being taken up, and they in
their turn deposited, and so on.

Mr. Wilson, in his description of his gelatine process
(which won the Paget prize), and which statement we
overlooked when we subsequently experimented in the
same direction, says : —

" The proportions of soluble promide and silver nitrate are
very important. Contrary to usual statements, the larger
the excess of silver bromide, the more quickly is the AgBr
converted ; if there be but little excess, a very long cook-
ing will be required ; and if exactly the equivalent
quantities could be used, the writerbelieves thatnoamount
of cooking would give the sensitive condition. Too large
an excess, on the contrary, tends to form fog, which is not
to be afterwards got rid of by the use of bichromate, but
which is more liable to occur with alkaline pyrogallic
<leveloper than with ferrous-oxalate."

Practically we have proved that by increasing the pro-
portion of soluble bromide to silver nitrate, up to a certain
point, a great increase of sensitiveness is brought about.

Now, we have shown (page 18) that metallic silver can-
not exist in contact with silver bromide, but that the
latter becomes at once amenable to development by its
conversion into sub-bromide. Suppose, then, that one
molecule of one of these particles is affected bv light,
the rest of the particle would be reduced and give the
appearance of-increased sensitiveness, since sensitiveness
is only recognized by a visible quantity of metallic
silver. Thus, if the particles in one were only one-
tenth part of the size they are in another, it is quite
within the range of probability that the sensitiveness of
the former might be concluded to be only one-tenth of
the latter, whereas the light might have done precisely
the same work on the two.

It might be supposed that a perfectly neutral state, or
an alkaline state of the emulsion, should be conducive to
sensitiveness, and seeing the use made of ammonia, there

54 SENSITIVEKESS IN GELATINE EJIULSIOX.

is, at first sight, much in it. Dr. Vogel, however, has, hj
the production of an acid emulsion (which he classes as-
sensitive as ordinary gelatine plates), proved that such is
not the case. The production of this emulsion, one solvent
of which is acetic acid, and in which silver hromide is not
soluhle, is most valuable in a theoretical point of view
(always supposing that no material loss of sensitiveness
is produced by it) being one more proof that the sensi-
tiveness is due wholly to a physical change, and not to a
chemical change, in the silver bromide.

There is another fact of especial interest, which is, that
keeping an emulsion after preparation previous to coating
the plate is conducive to sensitiveness. The following-
table will show the increase given by keeping. The
increase is gauged by taking the first day's sensitiveness
as unity. The emulsions were washed, and melted, and n.
small portion taken out of the jelly each day.

ist day. ind day. 3rd day.

1st experiment 1

2nd „ 1

.3rd „ 1

4th „ 1

5th „ 1

The growth of sensitiveness is here evident ; keeping-
longer than tliis appears to give no practical increase. We
wiU try and explain this, but it may be due to some other
cause. The editor of the Bntish Journal of Photography
explains it on the supposition that ammonia is formed in
the gelatine by keeping it, and that this re-acts on the
bromide. From what we have said before, this will be
seen not to be our view ; the amount of ammonia formed
would be very small, and as the water is in the jelly, the
solvent action would not come into play. Again, another
point is that we have found that if the emulsion be slightly
acidified the same result is obtained, though more slowly,
which is decidedly against the ammonia theory. Our own
ielief is that silver bromide, to be in the most sensitive

1-7

2-7

2-3

3-0

2-3

3-0

3-0

3-0

2-3

3-0

SENSITIVENESS IN GELATINE EMULSION. 55

State, must be placed entirely beyond any state of strain.*
It is during boiling that this strained state is probably
given to the particles of silver bromide, and by subse-
quently keeping the emulsion in a state of jelly this strain
wears off, in a similar way to that in which glass is annealed
by being kept in a semi-plastic state. When the bromide
is in dried gelatine it exists in the same state of strain as
that in which it hnds itself before the plate is dried.
When emulsion which has not been kept is spread on a
plate, and one part rapidly dried and the other more slowly,
it will be found that the part most rapidly dried is less
sensitive than the part more slowly dried. In the one
case the strain is taken off, and in the other it is not.
In the case of an emulsion kept two or three days, the
difference in sensitiveness of the slow and quick drying
portions of the plate is not apparent. Another cause of
apparent diminution in sensitiveness is the use of too hard
a description of gelatine, and also the use of too small a
quantity of water with it. The capacity for sensitive-
ness is present, but it cannot be utilized. The diminution
of sensitiveness is here also probably due to the strain
on the bromide. W^e made some interesting experi-
ments regarding this. We had some plates, the emulsion
for which was prepared in a very small quantity of water,
and the gelatine was very hard. Half of some plates were
immersed in water for half an hour, and half of others in a
mixture of 1 dr. of glycerine to half a pint of water for the
same time. The plates were then dried, and exposed.
Those portions of the plate which had been wetted with
glycerine and water developed out with proper density ;
the difference with those wetted with water alone was
not so marked ; the other portions lacked vigour, and were
apparently insensitive. To prove whether the sensitive-

* We -would invite a comparison of the effect of light on silver chloride
in the crystalline state as produced by fusion, and in the powder state ;
even when prepared with an excess of chloride, the latter will darken,
whereas the former remains nearly unchanged.

56 SENSITIVENESS IN GELATINE EMULSION.

ness had altered by the wetting, plates were exposed, then
half of them wetted, dried again, and then developed.
There was nearly the same result as before. It will he
seen, then, that to get a proper amount of density and
sensitiveness, the gelatine in the emulsion before coating
the plates should have a liberal supply of water with it.
Various other experiments have been made, all tending
to prove that if great sensitiveness is required, the gela-
tine should be as soft as is consistent with safety.

Another point which is conducive to sensitiveness
should be attended to. If the solution in which the
silver bromide is boiled be very viscous, the modification
will not take place with any degree of rapidity ; on the
other hand, fog is induced by having the gelatine too
dilute, since the particles are built up too coarsely. With
the ammonia process, the above holds good, for if an
emulsion be formed in cold solutions, according to Eder's
plan, with the minimum amount of gelatine, it will be
more sensitive by many degrees than if mixed warm with
the full amount of gelatine, and digested afterwards for
an hour.

There is one other important factor as to the cause of
sensitiveness in a gelatine emulsion plate, and that is the
fact that the bromine absorbent, which in this case is
gelatine, is in very close contact with the particles, and
we might even affirm that it is in close contact with the
molecules. For whether the boiling process or the
ammonia process be accepted, a certain amount of silver
bromide, as we have said before, dissolves, and is re-
precipitated whilst in a gelatine solution, and we can
scarcely conceive that such should take place without a
precipitation of a gelatine molecule or molecules with it.
In everv particle built up we should then have silver
bromide and gelatine in molecular contact, and the bro-
mine absorbent would be in the most favourable position
to do its work. In a collodion emulsion, on the other
hand, the cotton is not colloidal, and a microscope tells

SENSITIVENESS IN GELATINE EMULSION. 57

US that tlie particles of bromine lie in the interstices of
the cotton, and the cotton is not a bromine absorbent.
True, when we use a preservative over a collodion film
we have a bromine absorbent present, but it is only in
■contact with the particles, and not with the molecules
which make up the particles. When a preservative is
rendered strongly alkaline by ammonia, we do have in-
creased sensitiveness, and this is probably due to the
bromide being dissolved and re-precipitated, the presence
■of the bromine absorbent, particularly if it be a colloidal
body, such, for instance, as albumen.

CHAPTER VII.

SILVER IODIDE ATSTD CHLORIDE IN EMULSIONS.

Thebe has been some dispute regarding the advantage
of the use of silver iodide in gelatine emulsions ; but we
think we may say that its value is at the present time
scarcely disputed by any of the advanced Avorkers in
emulsion making. The introduction of iodide into rapid
gelatine emulsions was first generally brought to the know-
ledge of the photographic world in a paper read before the
Photographic Society of Great Britain, by the writer of
this work. At the time, the idea of its being useful was
energetically disputed by Dr. Eder and otliers, and cer-
tainly the experiments he brought forward tended to sup-
port his conclusion. On the other hand, the experiments
made by the writer showed its use.

Two emulsions were made according to Edcr's first
formula; the second containing about 10 per cent, of
potassium iodide, and called I. and II. Two emulsions
were made according to Eder's second formula,* one also
containing about ten per cent, of potassium iodide, and
called III. and IV.

A variety of emulsions were made and tested one

* These methods will be found in a subsequent chapter.

IODIDE AXD CHLOEIDE IX EMULSIONS.

59'

against the other in many ways. We give, in a tabular
form, some of the results : —

No. I. — Potassium bromide 93 grains

Swinburne's No. 2 isinglass... ... 30 ,,

Nelsons No. 1 photo, gelatine ... 120 ,,

Water 2i ozs.

And emulsified with —

Silver nitrate 115 grains

Water 2^ ozs.

No. II.— Potassium bromide ... ... ... 93 grains

Potassium iodide ... ... ... 10 „

Nelson's No. 1 photo, gelatine ... 120 „

Swinburne's No. 2 isinglass ... 30

Water

And emulsified with —
Silver nitrate
Water 'A-k ozs.

These had been made according to Dr. Eder's formula,
with ammonia.

Nos. V, VI, were made with the above formula;, but
boiled with 15 grains of gelatine for half-an-hour ; 105
grains of No. 1 photographic gelatine and 30 grains of
Swinburne's isinglass were dissolved in 2 ounces of water,
and added to them. They were each divided into two
parts, and one-half of each was digested with 1 drachm
of strong ammonia, as in experiments III and IV. The
other halves were washed without having been digested
with ammonia. All were allowed to set, and then washed
as usual. Those portions of V and VI of the emulsions
treated with ammonia we will call Nos. VII and VIII re-
spectively.

Plates were coated with all the emulsions : 1st, on the
same day on which the washing was complete ; 2nd, on
the day after, and then tested one against another. It

2-i- ozs.

127 grams.

2i

€0 IODIDE AND CHLORIDE IN EMULSIONS.

may be convenient to call the greatest sensitiveness 10,
and to show the others by lower numbers. ^Ye find the

wing results : —

No. VI

... 2nd day ...

... 10

No. VIII ...

... 2nd day ...

... 10

No. V

... 2nd day ...

!•

No. VII ...

... 2nd day ...

... 9

No. VII ...

... 1st day

... 8

No. VIII ...

... 1st day

7

No. IV

. . . 2nd day . . .

(5

No. Ill

... 2nd day ...

(■>

No. IV

... 1st day

5

No. Ill

... 1st day

... 5

No. VI

... 1st day

f)

No. V

... 1st day

... 5

No. I

... 2nd day ...

... u

No. II

... 2nd day ...

... 4"

No. I

... 1st day

... 3^

No. II

... 1st dav

... 3

It may be convenient to remember that the odd
numbers contain bromide alone, and the even ones iodide
with the bromide.

It will be seen, when boiling with a small quantity of
gelatine (Nos. V, VI, VII, and VIII), that on the second
day the plates containing iodide (VI and VIII) have a
little advantage over those which contain bromide alone,
and that the digestion with ammonia (VIII) gives no in-
crease in sensitiveness.* The same is apparent with VII
and V ; the digestion with ammonia does not increase the
sensitiveness with pure bromide. The tirst day's plates
(VI and VIII) with the iodide are in every way behind the
:second day's plates with the bromide alone ; but evidently
digestion with ammonia answers partly the same end as

* It should be said that Mr. W. K. Burton, who is a most careful expe-
rimeter, states, in a more recent communication to the Photographic Society,
Hiat increased sensitiveness is given.

ICUIDE AND CHLOEIDE IN EMULSIONS. 61

keeping the emiilsion. The same applies also to Nos. I
and II. Boiling with a small amount of gelatine, then, in
every case, is better than boiling with a full quantity of
gelatine, and then digesting with ammonia ; but this plan
is far better than digesting with ammonia alone. These
formulse are comparative ones, since they all contain
eventually the same amount of bromide of silver, and the
same amount of gelatine.

As regards development, the plates containing the
iodide were a little slower in coming out ; but, on the
other hand, they were certainly much brighter and
cleaner.

To test the value of the iodide ftirther, the same formula
as Nos. Ill and IV were used, and the emulsions brought
to the boiling-point Avlien the ammonia was present. No.
Ill fogged ; No. IV remained quite bright. The ammonia
undoubtedly makes plates mu.ch more rapid than when no
boiling is attempted ; the sensitiveness in which case
might, perhaps, be represented as 1 on the same scale as
that given before ; but it by no means gives the most
rapid kind of plate. We think for comparatively slow
plates, where good density is required, Formiila No. II is
excellent in every way ; and if any one has a prejudice
against iodide, let him use No. I.

It will thus be seen that we hold to introduction of
iodide into an emulsion ; except for experimental pur-
poses, we never omit it, believing it to be a sheet-anchor
for obtaining good and unfogged pictures. We are aware
that several commercial makers of plates which have a
great name in the market use the iodide, and if those who
condemn it would but give it a fair and unprejudiced
trial, we should have no fear of making converts of them
to its introduction.

CHAPTEE VIII.

GELATINE.

In gelatine emulsions one of tlie most prominent features
is the gelatine, and it is by no means iinimportant what
kind is selected. Dr. Eder has made long and exhaustive
researches on various qualities of gelatine, and Mr. T. F.
Elsden has also thrown light upon its variability in an
article in the Yeae-Book for 1881, and we cannot do
better than quote some of their conclusions. Gelatine is
compound of glutin and chondrin. The latter is dis-
tinguished from the former by its precipitation from an
aqueous solution by acetic acid, and its insolubility in an
excess of this reagent. Acetate of lead, alum, and sul-
phates of iron, aluminium, and copper also precipitate it ;
but not glutin. Mr. Elsden also remarks that a con-
venient test for the presence of much chondrin in gelatine
is to add a concentrated solution of chrome alum to a
.solution of 50 grains of gelatine in 1 ounce of water. If
chondrin be present in excess, the gelatine will set while
hot. Mr. Elsden further says : — Remembering that gela-
tine is a mixture of two substances of different composition
and properties, it must be expected to find great variation
in the behaviour of commercial samples. Most photo-
graphic gelatines, however, consist chiefly of glutin, and
their general character is not, therefore, affected to so

GELATINE. ()3

great an extent by the small quantity of cliondrin usually
present in addition.

Gelatine is extremely hygroscopic, and contains, at
ordinary temperatures, from fifteen to twenty per cent,
of water. In cold water it swells up, and absorbs from
five to ten times its weight of water ; good gelatine will
absorb enough cold water to dissolve it, if the temperature
is raised above 90'^ F. Very weak solutions of gelatine
will solidify to a jelly when cold, sometimes when only
one per cent, is present ; but long boiling destroys, to a
great extent, this power of setting.

Gelatine will keep indefinitely in a dry state ; but in
contact with water it soon putrefies, becoming first acid,
and then strongly alkaline, and giving off ammonia ; at a
temperature of 90° F., decomposition will often begin in
twenty-four hours. Hence it is evident that long boiling,
besides destroying its power of setting, also tends to pro-
duce decomposition of gelatine.

Alum, alcohol, carbolic acid, salicylic acid, glycerine,
fuchsin, hydrate of chloral, thymol, and salts of zinc act
as antiseptics, preventing the decomposition of gelatine,
even in small quantities. If glycerine be used, however,
it must be added in rather large quantities. Alcohol and
carbolic acid, in large quantities, precipitate gelatine from
solution in water.

Acetic acid, hydrochloric acid, sulphuric acid, and
oxalic acid dissolve gelatine even in the cold.

Acetic acid dissolves gelatine with great facility, whilst
ammonia acts as a weak solvent.

Sugar promotes the solubihty of gelatine, whilst gum,
in the presence of acetic acid, renders gelatine less solu-
ble, owing to the formation of a compound of glutin with
arable acid.

Silver nitrate, exposed to sunlight in contact with gela-
tine, causes a red discolouration, due to the combination
of organic matter Avith a sub-oxide of silver.

Chrome alum renders gelatine insoluble ; but long boil-

(54 GELATINE.

ing and hot dilute acids, potash, potassium permanganatey
are able to dissolve the mixture. Alum raises the melt-
ing point, but does not render it insoluble.

The quality of gelatine may be tested in several ways.
Dr. Eder, among other tests, recommends that the gela-
tine be incinerated, and the ash weighed, and he says that
this varies from ^ per cent, in good samples to 5 per cent.
in inferior kinds of gelatine, and to 10 per cent, if adulte-
rated with alum. Our own researches in this matter give
a greater margin for good gelatines, 2 '5 per cent, being
the ash of a certain gelatine which is excellent. We detail
some results in the table below. Another test which
should be applied is the amount of water it can absorb.
Good gelatine should absorb five to ten times its weight
of water. A very simple way of testing is to measure out
(say) 2 ounces of water, and soak 50 grains of gelatine
in it for some hours until it is thoroughly swelled. The
water not taken up should then be poured oif into a
measure, the gelatine being very gently pressed against
the side of the vessel in which it was allowed to swell.
The amount taken up is, of course, the difference between
the 2 ounces, and the amount returned to the measure. A
more scientific method is to allow the gelatine to take up
as much water as it can at a fixed temperature, drain it,
and surface dry it on blotting-paper, and then weigh it.
This is a more tedious method than that given above.

Name of
Gelatine

Coignet's gold label gelatine

,, special gelatine
Nelson's No. 1 photographic

„ opaque

„ amber
Ordinary French (not branded) 2
Swinburne's No. 2 patent ising-

glass

Cox's gelatine in packets

Ash,

Water absorbed

ler cent.

by

50 grains.

'.. nearly ,

... 7

drachms

1 „ .

... 7

))

2 „

... 5*

)>

2 „

... 8'

;?

1— 1

... 4

»

2 „

... 6

»

1 »

... 5f

)?

1 ,,

... 4|

)?

GELATINE.

t)D

Name of Ash,

Water absorbed

Gelatine. per

cent.

by 50

grains.

Eiissian isinglass ... ... 1

)j

... u

))

Gelatine supplied tliroiigh Jlr.

Henderson ... ... 2

;j

... 8

J)

Simeon's " Winterthur " gela-

tine

Heinrich's gelatine ... ... 1

j;

... 8

))

Batty' s gelatine 2

»

... 5

)>

The next test is that of solubility. A gelatine which by
itself is soluble at a low temperature is unfitted for gela-
tine emulsions, particularly if the temperature at which it
is prepared is at all high, since then it would not set.
Take, as an example of this, Nelson's No. 1 gelatine. In
warm weather it will dissolve in the water at the tempera-
ture of the room in which it is soaked. Take Coignet's
gold label as the other extreme, and it will be found not
to melt till the vessel has been plunged into water about
110°. As might be expected, as regards setting, these
two gelatines are the most opposite. At a temperature
of about 75°, No. 1 will scarcely set at all, whereas
Coignet's will set in a short time. A further most prac-
tical test is by noting the expansion of films of gelatine
which have been spread on plates. The greater the
lateral expansion in such films, the greater probability
there is of such films " frilling," i.e., wrinkling and leaving
the plate. The writer has carried out many tests in re-
gard to this point, and the results show that any gelatine
can be tested as to its capability of resisting trilling in a
very easy manner. Twelve grains of the following
gelatines were swelled in half an ounce of water and
melted. Quarter plates were coated with exactly half of
the bulk of each solution, and allowed to dry under the
same conditions as that in which plates are dried in the
drying box. The films were then stripped from oif the
plates, and different portions cut away and accurately
measured whilst dry. The films were then allowed to

66

GELATINE.

swell in water, ammoniacal water, or a solution of mono-
cartonates of soda and potasli, and again measured. The
following are tlie results : —

CJ

Water

Garb. Soda

and

and

Gelatine.

Dry.

Water.

Ammonia.

"Water.

Nelson's No. 1 ...

.. 1 .

. 1-2 .

.. 1-39

.. 1-29

Autotype ...

.. 1 ..

. 1-09 .

.. 1-28

.. 1-21

Heinricli's

.. 1 .

. 1-08 .

.. 1-22

... 1-15

Simeon's ...

.. 1 .

. 1-05 .

.. 1-14

.. 1-09

Batty's

.. 1 .

. 1-32 .

.. —

.. —

Nelson's X opaque

... 1 .

. 1-19 .

.. —

.. —

Crosse and Blackwell's

... -L .

. 1-09 .

.. —

.. —

Nelson's amber . . .

... 1 .

. 1-43 .

—

—

An important test is for acidity or alkalinity. For our
own part we strongly recommend a gelatine which is
slightly acid where an emalsion is to be boiled, and if not
in this state, we acidify the gelatine solution. When the
ammonia process is used, the condition of the gelatine
does not matter so much. In some gelatines, the acidity
(due to the hydrochloric acid used in its manufacture)
can be tasted by applying a piece to the tongue. A hard
gelatine can be at once identified when it is set after dis-
solving in the water, which it will absorb. Any exact
determination by applying weight to see where crushing
begins is misleading, unless the temperature is uniform
during all experiments.

We would here remark that gelatine has an affinity for
iodine, bromine, and chlorine, with each of which it com-
bines ; hence it is a preservative in the true sense of the
word.

The less fatty matter present the better, since it gives
rise to opaque spots on development, or else to scum-
markings on the plate. Where there is fatty matter
present, it may be got rid of by precipitating it in a fine
stream in alcohol, or by dissolving it in the quantity of
•water which has to be used, and skimming it; or by

GELATINE. 67

making it set, and, with a clean ivory knife, cutting off a
thin layer from the top.

To select suitable gelatine for an emulsion, we recom-
mend that a small batch of emulsion be made with the
specimens proposed to use, and that a few plates not
smaller than 7 by 5 be coated and tested before taking it
into use for larger quantities.

In our own practice we like to use a mixture of two
kinds of gelatine — one hard and one soft, and the propor-
tions of these we vary according to the weather. As a
rule, we like 1 part of hard to 2 parts of soft, as it will
then set with ease at a moderate temperature, and be hard
enough to resist the tendency to frill, and is at the same
time readily permeable by the developing solutions.

One fact must also be recollected, that frequent re-
heating of gelatine speedily detracts from its setting
powers, and that if too little water be added to it in mixing,
the film has a great tendency to become leathery, more
particularly if a little chrome alum has been added to it to
prevent frilling. A judicious mixture of alcohol to a
gelatine solution increases permeability, and should not
be neglected. The tise of a sufficient quantity of water
is, however, the great desideratum, and should be carefully
attended to, the quantity, of course, depending on the
temperature at which the plates have to be prepared ;
thus, in winter, more water should be used than in summer.
A very horny, glassy, film is objectionable in many ways,
and a moderately matt surface for the plates should be
aimed at. This depends almost entirely on the gelatine
-that is used, and at what temperature it is added, unless it
Ibe modified by additions such as glycerine, to which we
may at once say we object, on account of its affinity for
water.

It will be noticed that ammonia causes much greater
expansion than the carbonate of soda (the carbonate of
potassium gives almost identically the same results), and
the soda more than plain water. It is easy at once to see

68 GELATINE.

which gelatines would be most likely to cause frilling in
plates. The absorption of water does not coincide in all
cases with the expansion, but this we lay to the different
stress put on the different layers of gelatine during the
drying.

CHAPTER IX.

GELATINO-BROMO-IODIDK EMULSION.

We propose to give a detailed account of making an
emulsion at ordinary temperatures, say up to 65° Fahr.,
which may he taken as a pattern on which to form others
fey any other formula. It will he found to he exquisitely
sensitive to the hlue rays, and very slightly to the yellow,
which latter quality means that the development and pre-
paration of the plates can he conducted in a room fairly
illuminated with orange light. To prepare the windows
for this, the window maybe glazed with'stained-red glass,
or with one thickness of orange and one of ruby glass.
If this he undesirable, two thicknesses of common orange
packing paper may he employed. The reader should con-
sult Chapter V., on the Illumination of the Dark-room,
for further information on this subject ; but the reader
must remember that tricks cannot be played with the
light of the dark-room, such as are admissible when the
comparatively slow wet process is used. Thus he should
see that no light of the wrong colour penetrates at any
place ; he should pay particular attention, for instance,
to the chinks under the door, and in the sashes of the
window frame. When he has come to the conclusion
that no daylight is entering his room, he may think about
preparing the emulsion. First of all, he must make a few

70 GELATINO-BROMO-IODIDE EMULSION.

preparations. The jar or bottle in whicli the emulsioni
has to be mixed must be scrupulously clean. There
should be no patches of old emulsion left on it. If a
glazed jar be used, it should be seen that the glaze is not
cracked in any way, since fog may be expected if it be.
For dissolving the gelatine, &c., we like to use glass
beakers with a lip, since they are handy for pouring.
These also must be scrupulously clean and dry. The
scales in which the weighing has to take place should be
examined for dirt (chemical or otherwise), and a few
circular filter papers on which to weigh the materials
should be at hand. Weighing should never be done*
without a filter paper of equal size and weight being
placed in each pan of the scale. A saucepan of hot water
should be ready in which to place the beakers, &c., in
which the difierent materials have to be dissolved, and
care should be taken that it is not too full. It need
scarcely be said that all weighing can be done in ordinary
light. To commence operations, the following may be
weighed out separately and placed on cleanf paper after
weighing, it being supposed that a dozen or a few more
whole-plates are required.

1. — Potassium iodide ... ... ... 5 grains

2. — Potassium bromide 135 „

3. — Nelson's No. 1 photographic gela-
tine 30 „

4. — Silver nitrate 175 „

5. — AutotypeJ gelatine 240 „

Nos. 3 and 5 are rapidly covered with water, shaken or

* Especially on trass scale pans.

t Any contamination by dirt of any description, and pardcalarly that to
be found in a photographer's work room, is almost sure to spoil the emulsion,
or at all events its sensitiveness, and to cause endless evils. Hence clean
paper should be used, and the chemicals should not be left on the benches
or table in contact with the wood.

X In case this cannot be procured, mix 3 parts of Nelson's No. 1 gelatine
with 1 part of some hard kind, such as Heinrich's or Simeon's Swiss.

GELATINO-BEOMO-IODIDE EMULSION.

71

stirred in it a few seconds, and the water poured off as
quickly as possible. This gets rid of any adherent dust
on them. Nos. 1 and 2 are then dissolved in 1 drachm
and 1^ ounces of water, respectively. To the solution of
bromide (No. 2) 1 minim of strong hydrochloric acid is
added, together with sufficient of an iodine in alcohol
solution to make it a deep sherry colour. No. 3 is swelled
for ten minu.tes in 1 ounce of water, and then dissolved
by heat ; No. 4 is dissolved in ^ ounce of water, and
heated to about 120° Fahr.

In the dark-room. No. 3 is added to No. 4, and shaken
up in a bottle till a perfect mixture is secured. Three-
quarters of the solution containing No. 2 is then dropped
in little by little, and shaken iip after each addition ; and
then the solution of No. 1 is added to the remaining ^ of
the solution of No. 2. The mixture is then added as
before. The emulsion should appear of a ruby colour
when a thin film of the liquid emulsion is examined by a
gas light.

This bromide maybe placed in a spray apparatus, which
is made as follows : — Bend two thin glass tubes in a

common fish-tail burner of the shapes A and B (fig. 13).
The tube A should first of all be drawn out so that the

72 GELATINO-BKOMO-IODIDE EMULSION.

end is perfectly closed ; this may be done by the heat of
a Bunsen burner, by holding the straight tube over it at
about an inch from the end, in one hand, and at any con-
venient distance in the other, and, when thoroughly
softened by the heat at one point, by simply pulling the
tube outwards. The glass collapses, and the short bit is
pulled off. A flat file is then applied to the point, and
the glass filed away till a very small orifice is left. The
two tubes are then inserted in a cork, which is fitted into
a test-tube as shown. The bromide is placed in the
bottom ot the tube, and a very fine spray of liquid can be
forced through the orifice of A.

The solution of gelatine and silver nitrate should be
placed in a glass beaker or a jam-pot, and in the dark-
room the spray is blown on to it, and the liquid stirred,
at the same time, with a clean glass rod. This gives a
very fine emulsion indeed, and, if correctly carried out, a
drop of it, when poured on a strip of glass, should show
an orange-yellow colour by transmitted daylight, or a deep
ruby when a gas or candle flame is examined through it.
The possible sensitiveness of an emulsion depends almost
entirely on the fineness of grain of the bromide when first
formed. With a grey or blue-tinted emulsion extreme
rapidity can never be hoped to be attained. The emul-
sion should be transferred to a 20-ounce bottle,* and well
shaken for a couple of minutes, after which it is ready
for the next operation.

The method of mixing the silver with the gelatine
which we have given above is not practised by most
emulsion makers, we believe, though for our own part we
have no doubt that it is the best plan of getting the best
emulsification with the least trouble. In case the method
of mixing the bromide with the gelatine is preferred, the
following modification in mixing may be made : — Nos, 1

* Some recommend the use of an earthenware bottle, such as an old ink-
bottle. There seems to be no advantage in it, if ordinary precautions be
taken for keeping out the light.

GELATIN0-BR0310-I0DIDE EMULSION. 73

and 2 are dissolved in 1 drachm and 1^ ounces of water
Tespectively, and No. 3 is added to the sohition of tro-
mide, allowed to swell, and then dissolved. The silver
nitrate, No. 4, is dissolved in 1^ ounces of water, and by
means of the spray apparatus, or by caretul dropping, is
-added to the bromized gelatine. When half the silver
nitrate has been emulsified, the iodide, dissolved in 1 dr.
of water, is carefully dropped in, and then the remainder
of the silver nitrate is added.

Other Methods of Mixing. — There are other methods of
emulsifying which are given here. Mr. England finds that
if two 1-drachm measures be filled, one with the bromide
solution, and the other with the silver nitrate solution, and
then be poured into a bottle together and well shaken, and
this operation be repeated again and again till the two
solutions are exhausted, he gets a perfect emulsion with-
out grain, and very smooth, It will be noticed that in
this plan the silver and the bromide solutions are in
equal quantities. Another plan, adopted by Mr.
Warnerke (whether it is original with him is not of great
consequence) is to draw out two funnels to fine jjoints,
and support them on funnel-holders over a jar. These
are filled with the two solutions, which are allowed to
run into the jar, a stirrer being used to aid emulsification ;
other workers use the scent-diiFuser, by which to secure
fineness of grain. Any of these artifices may be employed.
A later plan which the writer has adopted, and which is
very efi'ective, is to shake the gelatine containing the bro-
mide into a froth, and then to add the silver nitrate little
by little. This makes a beautifully fine emulsion, and
seems to be equivalent to immersing a delicate film of gela-
tine into a silver bath, when we know that splendid films
are to be obtained, having the very finest grain.

A good Stirriiig-rod may be made by taking a glass rod,
and tying across it with clean string a strip of glass about
a couple of inches long and half an inch wide. This
•cross-piece eifectually stirs up the emulsion during its

74 GELATINO-BEOMO-IODIDE EMULSION.

formation by a motion of the rod between tlie first finger
and thumb. We recommend its use.

Boiling the Emulsion. — A saucepan of sufficient size to
hold the bottle must be procured, and filled with water
to a conyenient height, and a flame, such as a gas-burner,
placed beneath it.* After the water has been brought to
boiling point, the emulsion is kept boiling for 45 minutes ;
it being shaken at intervals (say once every ten minutes)
for half a minute or so. A thick cloth tied round the
hand prevents any scalding. The boiling, by-the-bye,
should take place without the cork being left in the bottle,
for if it remain in, it would be blown out by the force of
the steam. A cork with a slot cut in it is, however, not
open to objection.

Coolmg and Washing the Emulsion. — After the proper
time of boiling, the saucepan is removed. The gelatine
No. 5 should, as already stated, be rapidly rinsed in several
changes of water to get rid of any adherent dust. It
should then be placed in a pot with 2 ounces of cold water,,
and allowed to swell. After this it is melted at a tempera-
ture of about 100°, by immersing the pot or flask in hot
water, and added to the solution in the bottle. Both the
emulsion^ and also the dissolved gelatine, should be cooled
to about 70° to 80° F. by allowing water from the tap to
run over the jars before the addition is made.

After a good mixing by shaking, the froth is left to sub-
side, and the emulsion is poured out into a flat porcelain
dishjt and allowed to rest. The time which it will take
will vary according to the temperature| of the surrounding

* To prevent bumping and breaking the bottle, we place half a dozen
folds of blotting-paper at the bottom of the saucepan.

t There is no " fetish " in a dish. When the emulsion is to be squeezed, .
if it is set in a beaker, it turns out in a more convenient shape. In a dish,
however, it sets more rapidly, since a greater surface is exposed to the cool
air.

J In very hot weather, if the dish or jar be stood in iced water, no
difficulty in setting will be found. See subsequent chapter for particulars
of preparing emulsion at high temperatures.

GELATINO-BROMO-IOBIDE EMULSION.

75

air, but a couple of hours is generally amply sufficient,
and often a mucli less time will suffice. After a proper
consistency is obtained (such consistency being that the
gelatine should not tear with a moderate pressure of the
finger), the emulsion is carefully scraped off the bottom
of the dish with a strip of clean glass, and transferred to
a piece of very coarse canvas, or mosquito netting, which
has been previously boiled in hot water to get rid of any
grease or dirt. The character of the canvas and netting-
can be judged of by the accompanying figures, which are

Fiff. 14.

of their natural sizes. The emulsion is then twisted up
in this, and, by a gentle pressure, squeezed through the
interstices, the ball of emulsion being absolutely below
the surface of the water into which it is forced. The
water causes the threads of gelatine to remain tolerably
separate, and, as it passes through the liquid, most of the
soluble salts are at once extracted. Some emulsion-
makers use a thick ebonite cylinder, over one end of
which is stretched silver wire gauze, and into the other
Is fitted a piston. By placing this piece of apparatus in
a screw-press the emulsion is forced through the meshes,
and acts like the canvas or netting. For large bulks of
emulsion this is certainly the most convenient plan.

When all is squeezed through, the particles of gelatine
may again be transferred to canvas, stretched loosely over
the mouth of a jar or sieve, and be doused with water
from the tap or from a water jug. After a coiiple of
gallons have been thus passed over it, the emulsion should

76 GELATINO-BKOJIO-IODIDE E31ULSI0N.

again be squeezed through the canvas, and the same
-operation repeated, thus exposing fresh surfaces oi gela-
tine to the action ot water. After another skiicing with
water the emulsion may be considered as washed, though,
to make assurance doubly sure, the gelatine may be left
at the bottom of the iar, and the water changed two or
three times. We have ourselves found that there is a
great gain in using distilled water as the wash water.
The gain is not in sensitiveness, but in brightness of the
resulting plates. There being no lime in the water,_the
grease or saponified matter cannot form an oleate of lime,
to which we have traced some kinds of spots. To show
the importance of thorough washing, the following ex-
periment may be noted. An emulsion was made as above,
and after once squeezing through the canvas, a part was
immediately used for making plates. A second part of
the same was washed under the tap for five minutes ; a
third part was squeezed and washed a second time ; and a
fourth part was allowed to soak and squeezed a third time.
The relative sensitiveness of the four parts was as follows :

1 li 91 '^1

J. J., ^2 -2

The first washing increased the sensitiveness to 1-|, and
the second squeezing to 2^, whilst the third squeezing and
washing had no perceptible effect.

The writer considers this method of washing superior
to that given below. Two squeezes, it is believed, are
equal to twenty-four hours' such washing. Grelatine is
hard to permeate, and, being a colloidal body, the crystal-
line salt has hard work to get throiigh when the emul-
sion is not finely broken up.

Other Modes of Washinij the Emvlsion. — -There are several
modes of extracting the soluble salts from the emulsion.
Putting on one side dialysis as introduced by Mr. King,
owing to its tediousness, we pass on to the most ordinary
method. The emulsion when prepared is poured out into
a flat dish in a very thin layer (say) of about ^ of an inch

GELATINO-BEOMO-IODIDE EMULSION.

77

thick. When set, it is scraped off the dish with a piece
of glass, and transferred to a jar or Tbottle in strips. Mr.
England first scores it over with the prongs of a silver
fork so hreaking it up into fine strips. Cold water is then
poured on to it, and a stream of running water kept flow-
ing over it for twelve hoxirs, more or less.

The writer has converted a tin canister into an effective
washing apparatus, as shown in the figure. In the lid of

(P:tH--3-i:

Fig. 15.

a common canister a hole is perforated so as just to admit
of the insertion of a glass tube a, a ; a piece of india-
rubber tubing connects tJiis with the water tap, and covers
any small chink between the glass and the lid, as shown.
A spout is soldered on to the canister, as shown. A
bottle containing the emulsion to be washed is placed in
the canister, the tube being inserted in it. The ^v&te,x:
flows over the top of the bottle, and rises in the canister
to the level of the spout, where it trickles over into the
sink ; the heavy water containing the soluble nitrate is
thus perpetually stirred up and caused to flow over the
neck of the bottle. This answers admirably, and can be
used in the daylight if necessary, but is more applicable

78 GELATINO-BROMO-IODIDE EMULSIOX.

to emulsion that has been cut into strips than to that
which has been squeezed twice, as the small particles are
apt to be carried over the top of the bottle and choke the
exit tube. A combination of this method with that given
on page 143 can, however, be made by only once squeez-
ing the emulsion through the napless canvas.

Dr. Eder, to whose careful researches photographers are
much indebted, finds by absolute analysis that emulsions
passed through fine canvas are sufficiently washed in
about thirty-five minutes in running water, and nearly in
the same time in standing water ; through coarse meshed
canvas in one and a-quarter hours in running water, and in
a much longer time in standing water. When cut in strips,
it is probable that twelve to twenty-four hours may be
necessary to free it sufficiently from the soluble salts, in
order to obtain a maximum sensitiveness.

Precipitation of the Emulsion hy Spirits of I'i'ine. —
Another method is also due to Messrs. Wratten and Wain-
wright, and is as follows : — After the emulsion has been
allowed to rest for two or three hours, two ounces of
alcohol to each ounce of water used are poured into the
bottle containing it, and well shaken up. The gelatine
rapidly assumes a pasty appearance, and subsides to the
bottom. The bottle is then inverted, and the fluid, which
contains the soluble nitrates and excess of water, is
poured off, and may be preserved for distillation. The
explanation of the efficacy of this method is, that the
alcohol has a greater affinity for water than has the gela-
tine, and that in extracting the water the soluble salts
are extracted with it. Methylated spirit not containing
gum may be used, and the lower the specific gravity the
more effectual it is.

Draining the Emulsion. — When the emulsion is con-
sidered to be properly washed, it has to be drained. This
the writer generally does over the canvas or net used for
the squeezing operations, though some recommend a hair
seive, but it does not appear that there is much advantage

QELATINO-BROMO-IODIDir EMULSION. 79

to be derived from its use. The great point in either case
is to drain long enough. A couple of hours is sufficient
time, and then the emulsion is ready for melting.

It will sometimes happen that no amount of draining
over a hair seive or canvas will render the emulsion suffi-
ciently free from water to set well when dissolved up. We
have found that by pouring a couple of ounces of alcohol
through the emulsion when draining, that the excess of
water is taken up, and it becomes firm. It should be noted
that before re-dissolving the gelatine it should be firm and
free from all sloppiness (if such an expression may be
used) ; one dose of alcohol generally effects this, and, if
not one, two will. The alcohol may be saved if required.
In case this artifice be resorted to, only half the quantity of
alcohol given before should be added to the emulsion, when
it is re-dissolved for filtering and coating the plates.
Emulsion that is cut up into shreds is much more easily
drained than that which is squeezed through canvas. It
is not that the gelatine takes up more water, but that the
water clings mechanically to the small particles forming
it.

Dissolving the Emulsion. — After draining, the emulsion
should be transferred to a clean jar or jam-pot, and then
placed in boiling water till all the gelatine is thoroughly
dissolved. A temperature of 120" or more may be given
it vdth advantage. The emulsion, when all additions are
made, will be about 10 ounces. The addition of -J- grain
of chrome alum is to be recommended. This should be
dissolved in 1 drachm of water, and added with stirring;
6 drachms of absolute alcohol are next to be added in the
same way, and the emulsion is then ready for filtering.
This operation may be carried out in various ways. The
writer now uses wet chamois leather, or two thicknesses of
swansdown calico which has previously been well boiled
and washed. This is allowed to rest loosely in a funnel,
and the emulsion filters slowly through it, all coarse
particles being left behind. It is preferable to filter into

t)0 GELATINO-BEOMO-IODTDE EMULSION.

a Florence flask, as it will bear Iieat, though an ordinaiy
medicine bottle will answer if the flask be not at hand.
The bottle or flask is again placed in water at a tempera-
ture of 120?, and the next operation is to coat the plates.
There is one very remarkable feature about emulsions,
which is, the great variation in their covering powers. If
a plate be coated and found to gi^e great opacity when
the ordinary amount of emulsion is poured on and set, no
harm will be done by adding another 60 or even 120
grains of gelatine (which have been swollen in a couple
of ounces of water and melted) to it. This of course
increases the bulk of the emulsion, and at the same time is
economical. As a rule, it will be found that the emulsions
which remain of an orange tint by transmitted light after
boiling are those which possess most covering power.
The reason of this is not far to seek, as the orange emul-
sion is in finer particles than the blue or violet. This
addition should of course be made before filtering.

CHAPTER X.

BENNETT'S GELATINO-BROMIDE PROCESS.

The next process we shall describe is that brought out by
Mr. C. Bennett, and was the first process published (1878)
which gives extreme rapidity. His description of it is
extracted from the British Journal of Photography. Sen-
sitiveness is attained by slow digestion at a low tempera-
ture instead of by boiling. Mr. Bennett, after describing
the light required for the preparation of the plates, on
which we have already written (Chapter IV.), says : —

" To make ' assurance doubly sure,' use a ruby-coloured
hock bottle, and with two eight-ounce decanter-shaped
bottles made of test-tube glass to stand heat, weigh out
for a ten ounce solution —

Ammonium bromide ...
Best silver nitrate
^Gelatine
Distilled water...

Use Nelson's ' No. 1 photographic gelatine,' for with the
opaque sixpenny packets you have irregularity, red fog,

* It will be noted that the gelatine and the silver nitrate have the pro-
portion of twenty to eleven, or nearly two to one. In the bromo-iodide
emulsion of Chapter IX. the proportion is four to three, snpposing
the gelatine in which the emulsion is boiled ia destroyed. In developing, it
is evident the former wiU require less restraining than the latter.

a

70

grains

110

,j

200

■II

6

ounces

82 Bennett's gelatino-beomide process.

and frilling. Place aside four ounces of water for the
bromide, and two ounces for the silver ; dissolve the bro-
mide with heat in one of the flasks in 1 or H
ounces of water ; pour into the hock bottle ; swUl
out the test-tube with the remainder of the four ounces
set aside for the bromide, and also pour in. I do it by
heat to ensure all being dissolved, as it does so very
slowly after the gelatine is inserted. The four ounces of
solution being now almost cold, add the gelatine, shake
up well, and place in two or three gallons of water at 90°.
I use a fish-kettle with lid. [A good-sized saucepan with
a lid answered perfectly with the writer.] In two hours
the bromized gelatine will, after well shaking, be quite
liquid, and also nearly at 90". Now dissolve the silver in
the other flask in one ounce of water, cool to 90°, and
pour in ; use the remainder of the two ounces set aside
for the silver to rinse out the flask, heat to 90°, and pour
in. By being so particular we get regularity, and are able
to mix different batches of emulsion, which is a great
boon. Shake the emulsion very briskly, and replace
in the kettle for two, four, or seven days, according to
rapidity required. The temperature should never be over
90° ; if you do not let it exceed that, you will not have
red fog. ' Cosy ' it up with flannel, and it will not lower
many degrees during the night. I, however, use a stove
two feet across, and place it on that ; a faint gas jet below
keeps it always at 90°. I shake up every twelve hours.
If washed in two days, the emulsion is rapid and dense ;
in four days, more rapid and less dense — quick enough
for any drop-shutter known, when developed as below.
With some that I kept for seven days, with drop-shutter,
on a dull February morning, pebbles close to the camera
were perfectly exposed. The negative was thin under
ammonia, but bore intensifying to any extent.

" Cool the emulsion in a bottle not smaller than a Win-
chester quart, and wrap it up in brown paper to exclude
<illlight except the lip of the neck. Let an india-rubber

Bennett's gelatino-brojiide process. 83

tube go quite to the bottom of the bottle to stir away
those layers of water which, on account of greater specific
gravity (by reason of the salts they now contain), would
■otherwise remain there. Wash for twelve hours ; a dribble
is sufficient. Upon melting you have eight or nine
ounces of emulsion ; add three-quarters of an ounce of
pure alcohol heated to 90° ; fill up with water (also warm)
to ten ounces, and coat. The plates should be only luke-
warm, or you will have red fog. For beginners it much
helps the coating to double the quantity of alcohol, leav-
ing out water to that extent. The operator should not
be alarmed at the peculiar mottling of the film (due to
the alcohol) directly after coating ; this subsides in a few
seconds to an even surface. The extra alcohol does not
appear to alter the sensitiveness, and is a great help ;
but with experienced workers it is not necessary, and the
quantity is sufficient to draw the emulsion up to the
edges, which is the sole object of introducing it. When
no alcohol is used you always have thin edges, which is
very objectionable, as the negative, of course, will print
dark at those parts, and this small addition of alcohol
totally rectifies this fault. It is difficult to measure the
exact quantity of emulsion required for each plate ; one
ounce would probably cover eight plates of 65 by 4| size."

CHAPTEE XL

PAGET PRIZE EMULSION.

The following is the description of the process sent in
by Mr. Wilson, which won the Paget Prize Competition
in 1880 :—

To make a pint of emulsion —

Select a 20-ounce narrow-mouth stoppered bottle, with
a well-fitting stopper, and thin bottom. Make it per-
fectly clean.

Make a stock solution of —

Hydrochloric acid (pure) ... 1 fluid drachm
Distilled water ... ... 12^ ounces

Put into the 20-ounce bottle —

20 minims of the above dilute acid.

3 fluid ounces distilled water.

210 grains ammonium bromide.

80 grains Nelson's No. 1 Photo, gelatine.

Leave the gelatine to swell for (say) fifteen minutes or
longer.

Ihe Additionofa JraceofHydrochlm'ic Acidio the soluble
bromide and gelatine is recommended in the formula given,
for the following reasons : — If the soluble bromide be
absolutely neutral, and the gelatine a suitable sample (see

PAGET PEIZE EMULSION. 85

page 65), the hydrochloric acid is not necessary^ and better
omitted. If, however, the gelatine he ever so little alka-
line, or even apparently neutral, but yet does not give a
clear solution, acid is required. Its use is not to
produce silver chloride, hut to ensure a fine precipitate
of silver bromide. According to Mr. Wilson's experience,
a fine precipitate is hardly at all a question of the method
of mixing, and ela-borate contrivances for the purpose
he considers as quite unnecessary. A fine precipitate
is easily obtained, however rapidly the solutions be
mixed, if two conditions exist, viz., if the bromized
gelatine solution contain a trace of hydrochloric acid,
and the silver solution be not stronger than 110 grains
per ounce. If it be 50 to 60 grains per ounce, it may be
poured in all at once ; or if a little weak solution be first
poured in, the stronger may follow (as per formula). A
good test for the suitability of a gelatine is to see if a
fine precipitate can be obtained without having to add
hydrochloric acid. Too much hydrochloric acid retards
or prevents the conversiorf of the silver bromide into the
sensitive form in cooking; a large excess destroys the
gelatine.

It will thus be seen that the addition of hydrochloric
acid must be made intelligently^ according to the other
materials accessible.

It might be supposed that any acid would make the
precipitate fine, and that, therefore, acid ammonium
bromide would be good. Such is not the case, and,
moreover, the acid bromide has iu some way a powerful
effect in retarding the conversion of the silver bromide
into the sensitive form.

Ammonium Bromide should be as nearly as possible
neutral. It is usually more or less acid, even' though
otherwise pure, and frequently becomes strongly acid by
teeping. It is then quite unfit for use, and will not give
good results unless almost neutral.

Since sending in the formula for competition, Mr.

86 PAGET PEIZE EMULSION.

Wilson has arrived at the conclusion that, on the whole,
it is better to use hromide of potassiiim. The latter is
often alkaline, but may, without much difficulty, be ob-
tained neutral, and is free from tendency to alter.

Silver Nitrate is usually — if good — slightly acid with
excess of nitric acid. It may be so used; but it
was recently found that better results are obtained if the
silver solution be neutralized with carbonate of soda. A
slight excess does no harm, as the resulting trace of
carbonate of silver is converted into bromide ; indeed,
emulsion may be made by mixing washed carbonate of
silver with a soluble bromide.

The uses of neutralizing the silver are twofold. One
is, that as the amount of acidity of silver nitrate varies
with different samples, it ensures the same conditions in
all cases ; the other is, that the presence of nitric acid in
an emulsion produces a tendency to green and pink dis-
colourations in the finished negative.

In a clean glass vessel (beaker, measure, or flask)
dissolve 330 grains nitrate of silver (re-crystallized) in
3 ozs. distilled water.

Pour out about 2 fluid drachms of this silver solution
into another small vessel (say test tube), and dilute it to
half strength with an equal quantity of distilled water.

Take the 20-ounce bottle and the two lots of silver
solution into the dark room. Mr. Wilson prefers to use a
large paraffin lamp, protected by one thickness of ruby
and one of dark orange glass, to two thicknesses of dark
orange paper without any ruby.

In the dark room have a gas-boiling stove, and on it a
tin pot or saucepan deep enough to contain the bottle
when the lid is on. It should have a tin perforated false
bottom, to prevent the bottle resting immediately on the
true bottom; or a piece of wire gauze wiU answer. Let
the pot contain some three or four inches in depth of
boiling water.

Turn out the gas of the stove, if alight, and plunge the

PAGET PEIZE EMULSION. 87

bottle into the water two or three times, so as to avoid
cracking it by too sudden heating ; then leave it in for a
few minutes until gelatine is completely dissolved. Do
not leave it in longer than necessary for complete solution.
Take it out, shake up, remove the stopper, and set bottle
down on table near your lamp, so that you can see what
you are doing.

Pour in all at once the four drachms of dilute silver
solution. Put in the stopper and shake up thoroughly,
but not too violently, for about half-a-minute. Now
pour in the strong silver solution in quantities of about
half-an-ounce at a time, shaking as before after each
addition, and, when all is added, give a final thorough
shaking for (say) a couple of minutes.

If the instructions have been so far accurately followed^
there will he no coarse precipitate or grit in the finished
emulsion.

Now put the bottle into the pot of hot watei-, see that
the stopper is not jammed in, and put on the lid. Light
the gas, and boil up as quickly as possible. If the water
was previously boiling, and the gas only turned out for
the mixing operation, it should boil up in less than five
minutes ; then keep boiling for fifty-five minutes. At the
end of this time turn out the gas, take off the lid, take
out the bottle, and remove the stopper at once, or you
wiU not get it out afterwards. The bottle must now be
cooled down as quickly as is consistent with safety to
the glass. In very cold weather it may stand on the table
for ten minutes or so, and then be cooled with water ;
or in any weather, place it in a pan of nearly boiling
water, and cool gradually by allowing cold water to trickle
slowly in, shaking the bottle occasionally. Whatever
method is adopted, it shovUd be down to 90" F., or lower,
in fifteen or twenty minutes at most. It cannot easily be
made too cold, as the gelatine has lost its power of
setting.

In a glass beaker (about 12 or 14-ounce size) put

88 PAGET PRIZE EMULSION.

1 ounce of Nelson's No. 1 Photographic or " X opaque "
gelatine, and pour over it 10 ounces of clean ordinary water.
Leave it to soak until the gelatine has absorbed 4 ounces
of water, pour off the surplus 6 ounces, melt the swelled
gelatine by immersing the beaker in hot water, and pour
it into the 20-ounce bottle containing the cooled emulsion.
Shake up well, and pour all back into the beaker, draining
out the bottle thoroughly. Leave it to set in a cool place.
Mr. Wilson prefers to leave it for twenty-four hours. It
has next to be washed.

Ihe Addition of the Gelatine after boiling should be
made when the boiled emulsion and dissolved gelatine are
hotli at as low temperature as possible, and between the
time of this addition and that of washing the emulsion,
it should be kept as cold as possible. The reason of this
appears to be that the excess of alkaline bromide has a
most destructive effect on the new gelatine, and therefore
the lower the temperature and shorter the time during
which the two are in contact, the better.

There is a curious effect depending on the temperature
at which the emulsion and fresh gelatine are mixed, viz.,
that if quite cold the resulting plate will have a matt sur-
face, and the higher the temperature the more glossy it
will be.

A plain solution of gelatine in pure water is very little
injured by prolonged boiling ; but if an alkaline bromide
(or chloride) be added, it is speedily decomposed. Pro-
bably the alkaline nitrate, which is present in the emulsion
in large quantity, may be even more effective.

For the washing, clean ordinary water at a temperature
not over 50" F. should be used. The writer prefers at all
times to use water cooled down to below 40° by melting
ice in it. By so doing, uniform results are obtained, and
where ice can be procured the cost is trifling ; 3 lbs. of
ice will be sufficient for a pint ol emulsion in the hottest
weather.

In a glazed earthenware pan or other suitable vessel,

PAGET PRIZE EMULSION. 89

put about 3 pints of cold water, and add 3 ounces of
saturated solution of potassium bichromate (made by
saturating clean ordinary water with the bichromate.

Before squeezing the set emulsion through the canvas,
it shovild be cooled down so as to be as firm as possible.
The water into which it is squeezed will then remain al-
most clear, or but slightly milky. If the emulsion he soft,
€ven though the loater be ice cold, the water wiU be more
milky, and the emulsion take up too much. Too much
excess of acid bromide, too high a temperature at the time
of adding the gelatine, or keeping at too high a tempera-
ture between adding and washing, will produce the same
result.

The emulsion may, of course, be washed by precipitating
with alcohol, squeezing the clot, breaking it up, and soak-
ing in water ; but the writer prefers washing with water
and bichromate, as described, on account of the clear and
brilliant shadows so obtained.

Having cooled the beaker of set emulsion down to 40° F.,
run a bone spatula or paper knife round, and turn out
the emulsion, or cut it out in lumps. If cold, it will come
out almost quite clean from the glass. Place it on a piece
of coarse " straining cloth" or canvas, and squeeze through
the meshes into the water, the operation being performed
under the surface of the water. Leave it so for an hour.
Lay the straining cloth over the mouth of another pan
■or large jar, and pour the mixture of emulsion threads and
liquid on to it so as to let the latter run through. Squeeze
the emulsion a second time through the cloth into clean
cold water, and immediately repeat the operation a third
time, leaving the emulsion in the last water for half an
hour. When strained for the last time, place cloth and
all in a large beaker, and put the latter into hot water
xmtil the emulsion is completely melted and warmed to
about 115° F., i.e., not warmer than is pleasant to the
hand. With a clean hand take out the cloth and squeeze
it ; very little will be lost. The emulsion should now

90

PAGET PRIZE EMULSION.

measure atout 16 or 17 ounces. Add 2 ounces alcohol,
and mix thorouglilj. The alcohol may be either pure
ethylic alcohol, sp. gr. ahout "830, or good colourless
methylated spirit. The writer prefers the former. If the
emulsion now measures less than 20 ounces, make it up
to that hy adding clean water.

A good deal depends on the temperature at which
this is done, and by careful management much may be
effected. If the emulsion is sufficiently rapid, and free
from green fog, it is best melted and coated at a low
temperature, if it be slow and has a tendency to colour,
it will be improved "hj heating to 140° F. Mr. Wilson
has had emulsions which became more than three times as
rapid by this treatment ; but it is a somewhat dangerous
one, as too high a temperature, or too prolonged heating,
may result in hopeless grey fog. This kind of fog is more
apparent during development than after fixing.

The emulsion is now ready for use. It should be
filtered into the coating-cup through cotton-wool to free
from bubbles, and plates coated in the usual way, dried
and used as usual for rapid gelatine plates, using about
an ounce of emulsion for a dozen quarter-plates.

In drying arrangements, avoid the contact of gas, or of
the products of combustion of gas, with the moist plates.
The writer finds both to be very injurious.

The exposure is the same as for fairly rapid gelatine
plates, and the development may be conducted by any of
the methods to be described in a subsequent chapter.

CHAPTER XII.

BURTON'S PROCESS.

Me. Burton more recently worked out a process
which certainly simplifies the washing of an emulsion, but
which at the same time is rather more expensive, in that it
requires the use of spirits of wine or methylated spirits for
precipitation purposes. Mr. Burton kindly forwarded
a statement of his process, and we give it as he has de-
scribed it. He prepares the following solutions : —

1. — Silver nitrate ...
Water

2. — Ammonium bromide
Ammonium iodide
Gelatine (Nelson's No

graphic)
Hydrobromic acid
Water

2 photo-

212 grains

1^ ounces
120 grains
10 „

30 „
1 drop
1^ ounces

These are emulsified as given in Chapter IX., at page
72, or by shaking in a bottle as described at page 73.
There is no reason why the precipitation should not take
place by the reversed method (page 71), and we recom-
mend it.

The emulsion is boiled as given at page 74, and is then
allowed to cool to about 50° or 60° F. It is then poured
in a stream into 6 to 10 ounces of alcohol, the quantity
depending on the specific gravity of the spirit used ;
6 ounces of absolute alcohol suffice, whilst it is safe to use

■92 burton's peocess.

10 ounces with ordinary methylated spirit, since it usually
contains a large quantity of water. The emulsion settles
'down to the hottom of the vessel in a few seconds in the
shape of a dense flocculent precipitate. Most of _ the
soluble salts are, of course, at once extracted, hut it is
better to wash it further, either by decantation, or by
placing it on a hair-sieve in running water ; the precipitate
is coarse enough not to pass through the meshes.

In the meanwhile the following has been prepared and
made into a solution : —

Nelson's No. 2 gelatine 120 grains

Autotype or Swiss hard gelatine ... 150 „
Water ... ... ... ... 12 ounces

The bromide of silver precipitate is added to this, and
well shaken till it is dissolved and all granularity has
disappeared.

The diiference between this mode of washing and that
originally described by Wratten and Wainwright (see
page 78) is, that in the one case the emulsion containing
all the gelatine is precipitated, and in the other but a small
quantity of gelatine has to be thrown down, and conse-
€[uently the elimination of the soluble salts in the latter
case is far more perfect. There is also a saving in
alcohol. To prepare an emulsion in the shortest possible
time, this process meets the requirement, since it saves
much time in washing, and all the time of draining.

Again, too, it will be seen that this is a capital plan of
preparing dry pellicle which will keep indefinitely, and the
bromide will remain in its most sensitive condition,
since, after precipitation and washing, it will rapidly dry,
as the bulk of gelatine is so small, and is in a granular
state.

Mr. Burton recommends the use of acid, as it gives what
he happily calls a "robust character" to the emulsion ;
that IS, that the plate will stand more rough usage, and
more forcing in development.

CHAPTER XIII.

DR. EDER'S PLANS OF PREPARING GELATINE.
EMULSIONS WITH AMMONIA.

One of these methods is hased on the utility of allowing^
ammonia to re-act upon the bromide of silver in its
original condition, which enables the sensitive emulsion
to be formed more rapidly than by Monckhoven's method.
The second method, by which greater sensitiveness is ob-
tained, consists in boiling the gelatine emulsion by itself,
and subsequently treating with ammonia at 95" F. for
half an hour. We quote Dr. Eder's own words (see
Photographic Journal, November 19, 1880).

I. Method with Ammonio- Nitrate of Silver. — This
method furnishes very sensitive plates, which are at least
six or seven times as sensitive as wet plates. The
necessary operations are simple and and quickly executed,
requiring but few apparatus and arrangements, and
may be effected without continued warm digestion.
The requisites are an ordinary cooking-pot, a spirit lamp,
a thermometer, and a reliable dark-room. The plates
show great power and density, and keep wonderfully
clear. The emulsion works so clean, and is so free from
granulation, that not only landscapes and portraits can
be taken with it, but reproductions of line drawings can

?4 GELATINE E3IULSI0NS WITH AMMONIA.

Tbe made without intensification. The following is the
formula he recommends :-^

No. 1. — Potassium bromide ... 370 grains
Gelatine ... ... 520 to 700 „

Water ... ... ... 10^ ounces

This is dissolved (as given at page 139), and raised to
a temperature of from 95° to 120° F.

No. 2. — Silver nitrate ... ... 460 grains

Water ... ... ... 10^ ounces

Into this latter is dropped strong liquor ammonia till
the precipitate is just re-dissolved, and it is then, in a ruby
light, added drop by drop to No. 2, and shaken. The
flask containing the latter solution is rinsed out with
I5 ounces of water, and the emulsion is then placed in
a water-bath at a temperature of 95°, for from a quarter
to half-an-hour, gradually allowing it to cool down to 75°,
Tbut not lower.

The salts and the gelatine do not require to be so care-
fully chosen for this method as for that which follows.
Should the bromide of potassium have an alkaline reaction
it does no harm in this method ; neither is the neutrality
of the nitrate of silver imperative, nor the acidity of the
gelatine ; indeed, it may be alkaline,

The specific gravity of the ammonia, regarded as a
determinant of its strength, is a secondary consideration.
Take a strong solution of ammonia. The proper quantity
is defined sharply enough by the words — " as much
ammonia as will re-dissolve the precipitate produced in
the nitrate of silver solution." As one is deprived of
this indication by which to regulate properly the addition
of ammonia, whenever one adds the ammonia to the
gelatine containing bromide of potassium (instead of to
the nitrate of silver). Dr. Eder does not so much recom-
mend this manner of mixing, though, by the alteration
in the procedure, the same sensitiveness is obtained as by

GELATINE EMULSIONS WITH AMMONIA. 95

the former method.* Great care should be taken, when
adding the ammoniacal silver solution, that the tempera-
ture does not rise too high, and that, during the digestion,
the water-bath does not become too hot, otherwise log is
sure to result. The temperature should never exceed
105° F.

When the digestion is finished, the emulsion should be
poured into a gTass beaker (one made of not too thin glass)
or into a porcelain dish, which is placed in cold water to
accelerate the setting. When set it is pressed through
canvas as used for Berlin-wool work, and the operation
may be conducted as given at page 77, and then washed
in frequently-changed (or, better still, running) water for
twenty-four or forty-eight hours, whilst suspended in a
coarse stuif bag. A great deal of water adheres to the
gelatine particles, which should be allowed to drain for at
least half-an-hour, either from the bag or else through a
cloth filter placed loosely in a large funnel. If this
draining be omitted, the emulsion will most likely be too
fluid. The superfluous water may also be removed with
advantage by gentle pressure.

The finely-divided emulsion may be deprived of water
by placing it in a bath of alcohol, and then dried in thin
films in the air, either perfectly or only superficially,! or it
may immediately be liquefied by heating in the water-bath.
Filtration through flannel placed in a warm funnel is
good ; but it is generally sufficient to allow the liquefied
emulsion to deposit any sediment by standing quietly at rest.
If it be intended to keep the dissolved gelatine emulsion
for some time, an antiseptic must be added. To 10 ounces

* When gelatine, bromide of potassium, and ammonia are dissolved, and
the nitrate o£ silver is then added, the ammonia should not be allowed to
act too long upon the gelatine. The ammonia is best added immediately
before the addition of the nitrate of silver to the gelatine.

t Dr. Eder stated that he had not tested this method so minutely as to be
able to maintain that it furnishes exactly the same product as an emulsion
immediately re-dissolved ; but that he finds this preparation keeps better
than the dissolved aqueous emulsion.

96 GELATINE EMULSIONS WITH AMMONIA.

of emulsion add 10 grains of salicylic acid dissolved im
1 draclim of alcohol, or replace the salicylic acid by the
same weight of thymol oil, as a protection of the gelatine
against change caused by a long warming, putrefaction,
&c. Alcohol has a favourable action, accelerating
the setting of the gelatine and the drying of the film.

The proportion of bromide of potassium to nitrate of
silver is 4 : 5 ; it is not advisable to take less bromide,
as there is then a risk of fog. The difficulty of fixing
the proportion of the soluble bromide to the nitrate of
silver consists in finding the proper medium between the
too much bromide, which retards the sensitiveness, and the
too little, which it is not possible to overlook, on account
of the decomposition of the bromide of silver which sets
in, both in the case of treatment with ammonia, and boiling.
The proportions mentioned are those which have beem
found best both by Captain Toth and Dr. Eder.

The conversion of the insensitive modification (which
transmits red light) into the extremely-sensitive modifi-
cation (transmitting blue light) takes place in a very short
time when the above directions are followed. Even at a
temperature of 25° C. (77° F.), the complete conversion
generally takes place in from fifteen to twenty minutes.
A small sample poured as a thin film on a sheet of glass
is sufiicient to test whether the rays transmitted, be they
of daylight or of naked gas or candle-light, are blue or
not. In the former case the digestion may be stopped.
Generally, the prolongation of the digestion over thirty
minutes dev(4ops no further increase in sensitiveness
worth mentioning ; but if the temperature be not raised
above the point before mentioned there is, even after three
hours' digestion, no danger of fog.

If the liquid be too hot, or the solution too thin (that is
to say, too poor in gelatine), or if the added ammonio-
nitrate of silver be dissolved in too little water, the
bromide of silver will be too coarse in the grain. It then
quickly settles at the bottom, and the emulsion becomes

GELATINE EMULSIONS AVITH A:MM0NIA. 97

unequally mixed. The negatives also would be coarse-
grained, but there would be, nevertheless, no particular
increase observable in the sensitiveness.

By the gentle heat prescribed above, the gelatine should
not be injured or so changed that its setting power,
&c., suffers. It is, therefore, intentionally recommended
to add all the gelatine at once. By all methods of
emulsification with ammonia the separate addition of most
of the gelatine after the washing Is completed is impractica-
ble, since the greater part of the gelatine must be added
before the setting and washing, in order to impart the
necessary solidity to the mass, and a renewed heating of
the emulsion in order to dissolve the additional gelatine
would be unavoidable. The repeated or too prolonged
heating of gelatine emulsion containing ammonia, as is
known, is hurtful.

The emulsion must be washed with great care. It is
quite impossible to attain the full sensitiveness of the
plates in the presence of any considerable quantities of
soluble bromide ; besides which, the slight residue of
ammonia is an enemy to the keeping qualities of dissolved
emulsion, because, even in small quantities, it has a corro-
sive action, and combines with the salicylic acid, subse-
quently added as an antiseptic, to the great injury of its
property of retarding putrefaction.

II. MefJiod by Boiling and Subsequent Digestion with
Ammonia. — This is more complicated than Method I.,
and requires more care. It is based on the observation
that the modification of bromide of silver which transmits
blue light is produced very rapidly at a temperature of
from 60" to 100" C. (140" to 212" F.), and that the
sensitiveness of such an emulsion — already of itself highly
sensitive — can he increased by subsequent treatment with
ammonia at a gentle heat, while continued boiling would
bring fog.

The proportions of the separate ingredients are the
same as in Method I. (see page 94). The emulsion is

98 GELATINE EMULSIONS WITH AMMONIA.

then boiled ; but during the boiling the cork should not
usually be driven in quite tight, for fear of the bottle
bursting by the expansion of the steam. "When using
a common glass bottle, change the ordinary cork for one
which has a groove cut in it. The bottle, filled with
emulsion, is put in a perfectly light-tight tin saucepan
furnished with a tight-fitting lid,* and under the saucepan
is placed a gas jet or a spirit lamp, care being taken that
not even the reflected light from the spirit flame should
fall upon the emulsion. Of course it is understood that
the whole operation takes place in the dark room. The
boiling is continued for half an hour from the time the
emulsion reaches nearly boiling point.

The emulsion already possesses a high degree of sensi-
tiveness (similar to that of the best commercial gelatine
plates), and may be used without any further treatment
with ammonia. The latter, however, increases the sensi-
tiveness. When the emiilsion has become quite cool (the
temperature may fall to 70° F.), add to it two drachms
of ammonia, s.g. "880, place it in a water-bath of from
Do'' to 100'* F., and digest at this temperature for half-
an-hour to an hour. At the end of that time the emul-
sion is ready, and one then proceeds, after it has set, to
wash it, &c.

During the subsequent treatment with ammonia, caic
must be taken that the temperature never exceeds
lOo" F. Generally, digestion for half-an-hour suffices,
but with an hour there is more certainty of attaining the
desired sensitiveness. Even digestion for two hours does
not develop fog. The prolongation of the digestion with
uunnonia is particularly useful when the previous boiling
is interrupted before the bromide of silver is sufficiently
modified. It is assumed, however, that during the
whole process of digestion the water never sinks below

A linen rag laid at the bottom of the saucepan prevents the bottle from
tracking in consequence of coming in sudden contact with the hot metal
loimiDg the bottom of the pot.

GELATINE EMULSIONS WITH AMMONIA. 99

100° F. All tlie precautions described as applicable to
the adding of ammonia (Blethod I.) also apply here.

Here also all the gelatine must be added at once ; it
does not do (as in Method I.) to retain a portion, and to
add it later.*

With regard to other details (washing, qu.antity of
gelatine, &c.), the remarks made with reference to the last
method apply here.

Dr. Eder says that a gelatine emulsion prepared by
Method II. is more sensitive than one prepared by
Method I. The difference is, perhaps, not extremely
^eat, still the sensitiveness of that prepared by the
Method II. ought at least to be a fifth greater than by
Method I. It gives negatives with good gradation, and
free from that hardness which is often seen in less sensitive
emulsions, which are difficult of reduction by the deve-
loper. The whole picture generally comes out pretty
quickly under the developer, and even when the exposures
are very short, the shadows are sufficiently developed
hefore the lighter parts have become too intense. Di-.
Eder believes this emulsion will be found particularly
suitable for portraiture in the studio. It can be worked
to opacity, but is less apt to produce perfectly white and
hlack negatives than emulsion prepared by the first
method.

To sum up in a few words : — Emulsions prepared by
Method I. are most suited for the production of hard nega-
tives, and those prepared by Method II. for soft negatives.
The former has the same character as the most sensitive
emulsions at present in the market ; the character of the
latter is unusual. Still it cannot he said that with either,
both hard and soft negatives cannot be got according to the
way they are developed.

* Dr. Eder, however, expressly mentions that, with very easily-affected
sorts of gelatine, part of the gelatine may be beneficially added, when the
digestion is completely ended.

100 GELATINE EMULSIONS AVITH AMMONIA.

In the preparation of emulsions Iby Metliod II. great care
must be exercised. The gelatine and bromide of potas-
sium should not have an alkaline reaction, for fear of the
formation of fog during the boiling. The materials must,
therefore, be previously tested with litmus paper.* If the
nitrate of silver be added to the gelatino-bromide of
potassium, when heated to 60° or 70° C. (140° to 160°F.),
the formation of the extremely-sensitive modification is
sooner produced.

The ferrous oxalate developer is especially suited to
these fairly sensitive gelatine emulsions, though the
alkaline developer may also be used ; the former gives
particularly clear and brilliant negatives.

* Should one not be able to obtain any neutral or slightly acid prepara-
tions, the hot solution of bromide of potassium and gelatine may be carefully
acidified with dilute acetic acid or hydrochloric. The reaction should be
only slightly acid, otherwise the acetic acid will destroy the setting power of
the gelatine.

CHAPTER XIV.

COLD EMULSIFIGATION PROGESSES:

Me. a. Cowan has made a modification of Dr. Eder's
process which is certainly the easiest form of the am-
monia process, and gives excellent results as regards
rapidity.

The same proportions of gelatine, bromide, iodide, and
silver are taken as given at page 70, and dissolved up in
same amount of water ; the iodine mid hydrocJiloric acid are
omitted^ however. The silver should be dissolved in
■cold water, and the gelatine solution, after dissolving,
should be cooled. This can readily be effected by making
the vessels containing the different solutions to stand in
•cold water. To the silver is added sufficient ammonia —
equal parts of ammonia ('880) and water — just to dis-
solve the oxide first formed by the alkali. The bro-
mide and gelatine are then gradually added to the
ammoniacal silver nitrate, and a fine emulsion is formed.
The remaining gelatine is dissolved in the same amount of
water as given at page 74, and its solution also should
be cooled down. This is added to the emulsified bromide,
the two are well shaken up together, it is then poured
•out and set without further treatment, and washed in the
■usual manner. If the emulsion be kept for twelve hours
before washing, it will be found to have great sensitive-
ness.

The success of this method in giving sensitiveness
shows that the sensitive form of bromide formed by

102 COLD EMULSIFICATION PROCESSES.

ammonia is quickly arrived at in a but slightly viscous
fluid, whereas it is not fully formed until a quarter to lialf-
an-hour has elapsed (and even then not unless the solution
be rendered less viscous by warming), when the full
quantity of gelatine is employed. There is one thing
that has struck us in using the emulsion, viz., the large
number of plates that can be coated with this quantity of
emulsion.

Hendersons Process. — Mr. Henderson has a modification
of the cold emulsification process, which he published in
August 1882 ; his formula is as follows : — " Here I have a
solution of gelatine 10 grains dissolved in 1 ounce of
water ; when the gelatine is dissolved by gentle heat, I
add ammonia carbonate 20 grains (the ammonia causes
eiFervescence) : —

Bromide of potassium
Iodide „ „
Alcohol
Ammonia '880

Mix ammonia and alcohol before adding to gelatine.

This may be kept in bulk, ready for use ; it will keep'
a long time good. When it is quite cold, I stir in —

Nitrate of silver ... ... 200 grains

Water 2 ounces

I occasionally shake it, and in one hour it will be ripe'
enough for all ordinary pui-poses ; in fact, when finished,
it will give results twice as rapid as most commercial
plates. The maximum sensitiveness seems to be reached
in about ten hours. No further advantage is to be derived
by prolonging the emulsification, except that of con-
venience.

It should be apparent that, to have a large reservoir of
emulsion made in this way, to draw from daily, or at will,,
adding fresh to keep up the stock, perfect uniformity
must be obtained.

150

grains

2

»

3

ounces

60

minims

COLD EMULSIFICATION PROCESSES. lOJS

To the above quantities I add 4 to 5 drams of dry gela-
tine, and warm gently to dissolve tlie same. When the
gelatine is thoroughly dissolved, I stir in 12 ounces of
■warm methylated alcohol (100"). The emulsion, when
cool, will precipitate on the bottom of the vessel ; it is to
be broken up and well washed in a running stream from
two to twelve hours. Make tip bulk to 8 or H> ounces.
Gelatine dissolved in alcohol, ammonia, and water, will
not set so firmly as the same amount of gelatine in water ;
yet, if the salts and ammonia are removed by precipita-
ting with excess of alcohol, the gelatine recovers its setting
powers."

^Ye have tried this plan of emulsion making at various
times, and can say that it yields an excellent plate, and
very sensitive. At the same time we are not prepared to
give it such excellent qualities as is obtained by the
boiling process. The drawback to it is the large amount
of alcohol required to precipitate the emulsion, and its
consequent cost.

CHAPTER XV.

MR. GOTESWORTH'S COLD EMULSIFICATION
■WITHOUT AMMONIA.

Mr. CoTESWOETH described a plan of gaining sensitive-
ness by allowing an emulsion to gain sensitiveness by
remaining liquid at ordinary temperatures. We recollect
that a somewhat similar proposal was made of emulsify-
ing at a low temperature in gum-arabic. Following out
Mr. Cotesworth's general directions, we have arrived at
fairly satisfactory results. An emulsion is prepared, as
far as the boiling operations, according to Chap. IX., the
mode of mixing given at page 72 being preferred. An
emulsion which has a beautiful ruby colour, if kept liquid,
will, in twenty-tour hours, have attained a grey-blue
colour. A comparison with Bennett's process (Chapter X.)
will show that the difference between the two processes is,
that Mr. Cotesworth uses very little gelatine for emulsifi-
cation to begin with, whilst Mr. Bennett uses the full
quantity. ^ The consequence is that the latter gentleman
was obliged to have recourse to prolonged emulsification
at about db", in order to overcome the viscosity of the
gelatine, whilst the former can get sensitiveness in twenty-
four hours at (say) 60'' F.

In cold weather we have found it necessary to add a
couple of ounces of water to the sensitizing emulsion, in
order to prevent setting. In this case the extra gelatine
required is added dry, and, after soaking, the emulsion is
warmed, and the gelatine melts.

There is nothing different in the preparation or develop-
ment of the plates to call for any special remark.

CHAPTER XVI.

A PROCESS FOR GELATINE EMULSION "MAKING
IN HOT WEATHER.

The formula adopted is precisely that given in Chap. IX.,
€xcept that, before washing, 120 grains of autotjpe, or
other hard gelatine, are kept back. After boiling, if this
plan be adopted, or after using Cowan's cold emulsifica-
tion (see Chap. XIV.), and adding 120 grains of gelatine
in 1 oz. of water, the emulsion is poured out into a jam-
pot, which is immediately placed in iced water with a few
lumps of ice floating in it. In half-an-hour the gelatine
will be firmly set. The gelatine is loosened from the
sides of the jam-pot, and the lump of emulsion is trans-
ferred into moist canvas, and squeezed through into a
jar of iced water (the water having been run through
filter-paper to get rid of all floating matter) in which a
few small lumps of washed ice are floating. After ten
minutes the water is changed, and after another ten
minutes is changed again, when it is again collected in
the canvas, and squeezed through into water. One
more change of water should be sufficient to free it from
all except traces of soluble salts. It is then transferred
to the canvas, and allowed to drain over a jar for half-
an-hour to three-quarters. It is again transferred to the
jam-pot and melted, and the remaining 120 grains of
gelatine, which have been allowed to swell in about

106 GELATINE MAKING IN HOT WEATHER.

three-quarters of an ounce of water, is added, together
with two or three drops of carbolic acid (or other anti-
antiseptic), and then once more placed in iced Avater,
In half-an-hour it is set, when it is covered with alcohol
and allowed to ripen for a day ; and if the jar be placed
in water containing a lump of ice, so much the better.
When plates have to be coated, the slab on which the
plates have to be set is covered Avith small lumps of
ice for half-an-hour, and if the slab be thick it is only-
very gradually cooled ; but, on the other hand, it also
but very gradually gets warmed again. During this
time the emulsion is melted, six drachms of alcohol,
one grain of chrome alum in one drachm of water, added,
and filtered. When the plates are coated (alter the slab
has been dried from all water), it will be found that
the film of emiilsion will set in a couple of minutes, and
that the slab remains cool enough to enable five or
six batches of plates, each batch filling the slab,
to be prepared; that is, supposing your slab to hold
eight plates, yoix can coat forty to forty-eight without
re-cooling the slab. The gas of the drying-box may be
lighted immediately, and the drying of the plates wiU
proceed rapidly, and they will not re-melt. If gelatine be
once loell set, it requires a high temperature to re-melt it ;
and the more the water is evaporated, the higher the tem-
perature required. As the current of Avarmed air passes
over the plates, the moisture is rapidly absorbed, and
hence the drying can be effected Avith safety.

CHAPTEE XVII.

GKLATINO-BROMIDE EMULSION MADE BY PRE-
CIPITATION ■WITHOUT THE PRESENCE OF GELA-
TINE.

The next emulsion is one described in the Pliotograpliic
JVeu's by the writer. It is a method of prej)aring an
emulsion by adding washed silver bromide to gelatine.

Let us suppose we are going to make up about 7 ounces
ol gelatine emulsion. Weigh out ammonium bromide,
140 grains (or its equivalent in zinc, potassium, or any
other bromide), and dissolve in 20 ounces of water (not
necessarily distilled water). Next weigh out 250 grains
of silver nitrate, and dissolve in 6 ounces of water, and
add 6 drachms of glycerine to it, and stir thoroughly with
a glass rod. We prefer to put this mixture in a glass jar
holding about 40 ounces (an empty French prune bottle
would answer every purpose).

The bromide solution should now be added very cau-
tioasly. Take a 10-ounce measure, and fill it up to six
ounces, or thereabouts, so that it is not too full, and
gradually drop, little by little, the solution into the silver
solution, stirring very thoroughly the whole time. A
milky emulsion forms, and gets thicker and thicker
till the whole bromide in the 20 ounces is added, though,
of course, the fluid is per se thinner ; a quarter of an

108 EMULSION MADE WITH GLYCERINE.

'Ounce of nitric acid is next added, and well stirred up.
This addition is made to save any chance of fog, which
anight be caused by the excess of silver present. The
reason of this has already been described in Chapter III.

This emulsification is better carried on in a dark room,
though it is not absolutely necessary. The bromide solu-
tion must he poured into the silver solution, andnotvice versa,
■or a failure loill be most probable. The glass jar and its
contents may now be placed away into a cupboard, and
left for as long a time as is convenient, but not for less
than a quarter of an hour. By the latter time the silver
bromide will have fallen to the bottom of the jar, with the
exception of a very slicjlit milkiness, which will subside in
a couple of hours. The silver bromide, however, left in
suspension at the end of the quarter of an hour is so small
that it may be decanted off without detriment to the emul-
rsion. The jar may be tilted, and the liquid poured off, or
a syphon may be introduced (and this is a neater way),
and the liquid syphoned off close to the precipitate.
About 20 ounces of water are again poured into the jar,
the precipitate well stirred up, and again allowed to sub-
side. As soon as ever the subsidence takes place, the
water is again decanted or syphoned off. This operation
is repeated four or five times, after which the decanted
water may be tested for acidity, and for silver nitrate.

To try for the former, moistened litmus paper is held
over an open ammonia bottle till it is thoroughly blue,
then well washed in distilled water ; this is thrown into the
-decanted water. The faintest trace of acid will redden it.
If it does turn red, the washing must be repeated. To
test for free silver nitrate, add to the wash water 1 drop
of potassium chromate. A red colouration indicates the
presence of. silver nitrate. In case of the presence ol

* It should be remembered that the wider the diameter of the jar, and
the shallower the water, the greater will the precipitate collect at the
bottom.

EMULSION MADE WITH GLYCERINE. 10f>

eitlicr one or the other, as is. shown by the litmus paper
and the chromate, the washing' must be continued.

The original plan we adopted, and of wliich the above is a
modiiication, consisted in precipitating silver bromide in
pure water, and without the help of glycerine. This is
still one of the best methods we have tried, and we give
a re'<nme here.

AYeigh out the materials given on page 70, except the
gelatine. Dissolve 1 and 2 m 4 ounces of water, and 4 in
another 4 ounces of water. Take 20 ounces of water in
a glass beaker and a stirring rod, and add to it first ^ a
drachm of the silver nitrate solution, and then, drop by
drop, ^ a drachm of the bromide solution, then another ■§■
drachm of the silver solution, and another of the bromide
solution, and so on, till the solutions are exhausted.

A still better plan is to have the solutions in pipettes
on a stand, and allow each solution to drop into the water,,
stirring all the while.

The precipitate will be so fine that in some cases a
coiiple of days will elapse before it subsides. It may be
hastened by raising the water containing the precipitate
to the boil. The particles then will coagulate togetlier,
but this does not signify, since if they have been preci-
pitated in a fine state of division, they will separate again
in subsequent operations. The washing takes place as
nbove described.

The next part of the process has now to be taken in
hand. 100 grains of gelatine are soaked in 2 ounces of
water ; this 100 grains should be Nelson's " No. 1 photo-
graphic gelatine," and another 100 grains of harder gela-
tine, such as Autotype or Swiss hard gelatine in 3 ounces
of water. The No 1, when it is soaked, is taken up on a
rod, and the vessel containing the precipitate is placed in
hot water, and the gelatine used as a mop to collect it.
The gelatine gradually melts, and the bromide becomes
emulsified. It is then trainsferred to a flask, and heated
in boiling water for five minutes, and well shaken up.

110 raiULSION MADE AVITH GLYCERINE.

When the froth has subsided, the bottle is again shaken,
and the warming process repeated. After two or three
such shakings, a little of the gelatine emulsion may be
th-opped upon a glass plate, and examined for granularity.
If absent, so much the better ; but if present, half the
second lot of the harder gelatine, which has meanwhile
been dissolved, must be added, and the shaking repeated.

If the emulsion be raised to boiling (as at page 142) for
^ive minutes, then shaken, and the same operation repeated
-a second time, we believe that an emulsion is obtained
which, for rapidity, will bear comparison with any other
process. This plan will give as smooth an emulsion as
any other method, provided the operator's fingers are not
all thumbs when the bromide is dropped into the silver.

When the emulsion is ready, the remainder of the
gelatine solution not already added should be poured into
the bottle, together with half an ounce of alcohol, and
after a final shake, and filtering through washed cotton-
wool, it is ready for coating the plate.

CHAPTER XVIIL

DR. VAN MONCKHOVEN'S PROCESSES.

^st Process. — Dr. Van Monckhoven, in trying the
writer's original plan of Avashing the silver bromide before
adding it to the gelatine, failed, but hit upon the following-
ingenious methods, which arc given in his own words : —

"I prepare very pure and dilute hydrobroraic acid,
and I determine accurately the amount of it required
to precipitate exactly 150 grains of silver nitrate. I
then dissolve this quantity of acid in 7 ounces of M'ater,
with which I incorporate, by heating, 40 grains of gela-
tine. On the other part — and from this moment I entirely
operate in the dark room — I precipitate 150 grains of
silver nitrate by a very slight excess of bicarbonate of
soda ; I let it settle for twenty-four hours, and then renew
the water to the same amount, after which I let it settle
again previous to decanting. On this precipitate of silver
carbonate I pour a hot solution of 30 grains of gelatine in
7 ounces of water. This is Avell stirred, and then 1 pour
on it the solution of gelatine and hydrobromic acid. The
mixture is thoroughly shaken every quarter of an hour,
and is kept at the constant temperature of 120" Fahr.
The silver carbonate dissolves slowly in the hydrobromic
acid, and the silver bromide is formed in the colloidal
liquid in a state of extreme sub-division. At the end of

112 monckhoven's processes.

ten or twelve hours the mixture, when flowed over glass
plates, has a greenish white colour. 1 next introduce
, 150 grains of gelatine, cut into very thin shreds, which I
dissolve by stirring, and then, without washing the emul-
sion, I flow it over the glass plate.

" In order to obtain a success with this method, it is
necessary to take some precaution. The hydrobromic
acid must be free from phosphorus and sulphiir; the
water used for washing the silver carbonate must contain
no trace of carbonic acid.

"In an emulsion prepared by this method there is
always an excess of hydrobromic acid and of silver car-
bonate, but 1 have satisfled myself by other experiments
that the presence of these substances does not affect the
results. This is not the case if carbonate be replaced by
the oxide of silver ; the emulsion is then grey, and gives
rise to fogging. The plates that I have prepared by this
method are twenty times as rapid as the best wet collo-
dion, and, compared with the best English plates, I have
found them to be three or four times as rapid. For the
rest, the same observations and the same methods apply
also to coilodio-bromide."

2nd Process. — Dr. Van Monckhoven's second process is
as follows : —

" Procure some of Nelson's No. 1 photographic gela-
tine. I insist upon this point, because you will not suc-
ceed with German or French gelatines, which are pre-
pared in a diff'erent manner from those of Nelson. Weigh
out exactly 153 grains of this gelatine, and 122 gi-ains of
pure and well-dried ammonium bromide. Put these two
substances into a bottle, and pour upon them 10 ounces
of distilled water. In a quarter of an hour the gelatine
will have swollen, and you can now put the bottle into a
warm water bath and agitate, in order to dissolve the twO'
substances.

" Weigh out 184 grains of silver nitrate, and dissolve
in If ounces of distilled water. Now pour the silver

monckhoven's processes. 113

emulsion into the tottle containing the bromide, a little
at a time, well shaking it after every addition. When
all the silver solution has been added, pour in 1 drachm
of pure ammonia of a density of -880, and well shake
up the solution. The ammonia exercises a special
action here ; its effect is to render the emulsion ready to
be used in a few minutes, or, if great sensitiveness
be required, it can be obtained in a .few hours instead
of days, and thus decomposition of the gelatine is
avoided.

" Now pour the solution of gelatine into a porcelain
dish, and place it upon cold water, and let it set. When
set, detach it from the dish, place it in a strong linen
sack, and wring it so that the gelatine is expelled in
shreds, which are easily washed on a fine sieve. A
washing of five hours in water three times changed
suffices. Collect the pellicle on a clean linen cloth, and
dissolve it at a temperature of 35° Centigrade, and it is
fit for use. This process is a combination of those of
Mr. Bennett and Messrs. Wratten and Wainwright, with
this difference — that I add the ammonia in order to have
the emulsion ready to work in a few hours instead of
days."

CHAPTER XIX.

PREPARATION OF THE PLATES.

Cleaning the Plates. — A good emulsion is often con-
demned for frilling when the methods used in cleaning the
glass plates are, in reality, at fault. It is our own prac-
tice to immerse the plates in nitric acid and water (1 to 10),
then to wash, and next to rub them once with a 10 per cent,
solution of caustic potash or soda and a little methylated
spirit. After a wash under the tap the water should flow
quite evenly from off them, when, after a rinse with distilled
water, they may he set up to dry, which they will do very
rapidly if allowed to stand on clean hlotting-paper. Polish-
ing a plate is a mistake ; it only encourages the formation
of blisters, as it prevents the adhesion of the film to the
glass. Avoid French chalk, or anything but pure water,
and then one of the causes of frilling and blistering will
have been eradicated. The plates having been cleaned as
above, they are brought into the dark room, which should,
if possible, be kept at a temperature between 50" and 65",
as this is the heat which is most convenient at which to
coat the plates and to ensare setting.

Substrata. — With emulsions made with certain kinds of
gelatine, the tendency to frill is not easily overcome,
in Avhich case it is necessary to coat the plates with a

PEEPAKATION OF THE PLATES. 115

suLstratum of some sort. The following is one formula
(Mr. Forrest's) which may he used : —

White of egg ... ... ... 1 ounce

Water ... ... ... ... 20 ounces

Methylated spirit ... ... 1 ounce

Carbolic acid ... 20 drops

The carbolic acid is added with stirring to the spirit, and
then the mixture is poured into the albumen and water,
which has been previously mixed.

Dr. Vogel gives another substratum, which is also
efficacious and easily applied : —

I.

Gelatine ... ... ... 50 grains

Acetic acid ... ... ... ^ ounce

are placed in a bottle and warmed till solution takes place.

This keeps a month.

II.
Chrome alum ... ... 10 grains

Water ... ... ... ... A ounce

is next prepared.

Take of No. I 2^ parts

No. II 1 part

Methylated spirit ... ... 70 parts

and filter; coat the plates, after cleaning and drying, as
with collodion, and allow the substratum to dry.

The late Mr. Henry Cooper introduced a gelatine sub-
stratum, the preparation and application of which he
describes as follows : —

" Soak 60 grains of Nelson's photographic gelatine in
water, drain, and pour on enough boiling water to make
8 fluid ounces. Now add 2 drachms of a ten-grain solu-
tion of chrome alum, and stir vigorously for a minute
or two. Filter the solution through paper into a clean
measure, keeping it warm and avoiding air-bubbles.

116

PEEPAEATION OF THE PLATES.

" To save trouble, a large quantity of each of the solu-
tions, the gelatine and the chrome alum, may be prepared,
and will keep for a long time if a little pure carbolic acid
be added to each. No more must be mixed than is re-
quired for the batch of plates, as when the compound
solution has once become cold, it cannot be again lique-
fied with heat. The measure and filter used must be well
washed with warm water as soon as done with, for the
same reason."

Levelling Shelf. — The next point to look to is the shelf
on which to lay the plates after coating. In our own

S)ractice, we have a piece of thick plate glass about 3 feet
ong by 1 foot broad, and |-inch thick.* We level by
means of three mahogany wedges and an ordinary spirit
level.

The level L is placed first across the plate, and the two
wedges X and Y are altered till the bubble B of the level is

Fig. 16.

central ; the level is then turned lengthways along the
plate, and the bubble caused to occupy its proper position
by shifting Z, not touching X or Y. This should cause
the plate, if true, to be accurately level ; but it is as well to
repeat the operation. A couple of supplementary wedges
are sometimes useful if the glass " spring " at all.

Level Cupboard-shelves. — Instead of a levelling shelf as
given above, it is perfectly feasible to alter the cupboard

* A ground elate slab answers equally well.

PKEPABATION OF THE PLATES. 117

shown at page 22, and the alteration does away with the
drying markings sometimes found, and due to the iron
wires. The wires are removed, and glass or slate strips
siibstituted for them. For plates 8^ by 6^-, slips 3 inches
wide are sufficient, and they should he a :^-inch thick to
prevent bending. One end of the slip is supported in a
stirrup shown in fig. 17, in the top of which is a slot.

Fiff. 17. Fiff. 18.

through which a screw is passed into the cupboard ; oppo-
site to this is another stirrup (fig. 18), into which are in-
serted two thumbscrews as shown. This is placed exactly
opposite the first stirrup in the cupboard. The strip is
placed between these two stirrups, and is first levelled
crossways by means of the thumbscrews. When level in
this direction the length of the strip is levelled by raising
or lowering the first stirrup, and when in position the
screw in the slot is screwed home. When once levelled,
the strip will always fall level into position. In our own
cupboard we have seven of such strips across the cup-
board, and they answer admirably. The coated plates
are at once placed on these shelves, and allowed to set in
the position in which they are to be dried.

It has been stated (though we have never found it so)
that markings may be met with owing to the emulsion
setting more rapidly in those parts of the plate which are
in contact with the strips. If such should be feared, we
recommend that triangular pieces of card of 3^ inches
size should be cut, and drawing-pins passed through
them at each corner, and that these, with points upper-
most, should be laid on the strips where the plates have
to be placed. The setting will then take place without
^ny chance of drying markings, since the plate will be

118 PEEPAEATION OF THE PLATES.

supported by points. Drawing pins may be got by the
gross, all of the same height. This plan is very suitable
for warm weather when plates take long to set, as a
levelling shelf in such weather often becomes filled before
the plates are sufficiently set to be moved to the drying
cupboard.

Some dry-plate makers prefer to dry their plates in a
nearly vertical position in racks, and there is no doubt
that when drying takes place in this manner there is less
chance of dust settling on the plates (see page 34).

Coating the Plate. — The emulsion, having been filtered,
is kept in a jar at a temperature of about 90° F. by means
of a hot-water bath. Tt should be tested for its flowing
qualities ; i. e., whether it has enough alcohol, and whether
it is thin enough. It is hard to describe when an emul-
sion is of exactly the right consistency. It 'should flow
like oil ; and, when the plate is drained by tilting, a thin
film of emulsion should be left. As a rule, the emulsion,
during washing at about 60° F., will have taken up just
enough water, whilst at 20" lower, perhaps a drachm to
the ounce of water will have to be added ; and at 70" it
is probable that about 15 per cent, of dry gelatine may
have to be added. To coat a plate by hand, a plate is
taken on a pneumatic holder, or held upon the tips of the
fingers. We will suppose the plate is of the 6J by 8^ size
that is to be coated. About 2 ounces of emulsion are poured
into a warmed measure,* taking care that no bubbles are
formed (which can be secured by pouring out the emulsion
against the side of the measure), and a pool of gelatine is
made at the top of the plate. It is then, by careful pouring,,
made to fill up the centre of the plate, and flow to the
right-hand top-comer, next to the left-hand top corner,,
then to the left-hand bottom corner, and, finally, to the

* Small emulsion pourers are now to be had. They are like small tea-
pots, with an innner pot into which the emulsion is poured. The emulsion
used to cover the plate is thus taken from the bottom of the bulk ; and
bubbles which may be on the surface are thus avoided.

PEEPAEATION OF THE PLATES. 119

right-hand hottom corner, where it can be partially poured
back into the measure. The amount used should be
noted ; about three drachms should be sufficient to well
cover the plate. The plate is then detached from the
pneumatic holder (if used), held by the two corners of
the diagonal, and quietly rocked till an even coating is
seen to be secured. It is then cautiously slipped on the
level shelf, and left to set. Another plate is taken and
similarly treated ; and when the shelf is full, the emulsion
on the first plate will have set, and it must be removed to
the drying-box or cupboard. This operation, when the
operator is an adept at it, can be very rapidly performed.
A quick coater will coat 150 8|- by 6| plates m an hour
with ease.

There are other modes of coating the plate to which
we may refer. After a central pool is formed on the
plate as above, the emulsion may be guided by a glass
rod along each edge, and thus the chance of spilling is
lessened. For our own part, we think that this is not a
good plan ; first, because the glass rod is liable to collect
dust, as it must be wiped between the coating of every
plate ; and secondly, if the central pool of emulsion be not
spread out rapidly, coating marks are apt to be seen on
the finished negative.

Another plan which is advocated is to brush the plate
over with a very thin film of emulsion by means of a wide
badger-hair brush (kept in a small quantity of warm
liquid emulsion), and then to pour over the plate the full
quantity. This is not a bad plan if the brush be kept
clean. If resort must be had to any aids, our pre-
ference is rather to use a ruler or squeegee, somewhat
longer than the plate, and covered with swans-down
calico. This should be moistened with clean water
and swept along the surface of the plate, and then the
emidsion poured on immediately afterwards. With plates
to which a substratum is given, some such artifice is
necessary, since the emulsion Invariably drags.

120 PREPARATION OF THE PLATES.

If any quantity of plates is to be prepared, it may be
advisable to use a coating machine, which, for its princi-
pal parts, consists of a very finely turned india-rubber
roller. A, and a trough, C, in which the roller works
(fig. 19). The trough is filled with emulsion, which is

-' -- ~€

Fig. 19.

kept warm by a water jacket, D, below it. This in its turn
is kept warm by a small gas jet or by a spirit lamp. The
roller turns on its axis in slots, E E, in the water jacket,
is made to revolve by a grooved wheel, B, about twice or
three times a second, either by connecting B with a water
motor, or by turning by hand, the movement being towards
the operator, by which means it is covered with a uniform
coating of emulsion. A plate is taken on a pneumatic
holder, and the plate made to pass rapidly over the top
of the roller, and is immediately turned with the coated
side up, and rocked to give an even surface. It is then
placed on a slab to set.

Drying the Plates. — Should a room be available which
can be darkened, and in which the passage leading from
the door can be darkened, there is nothing better than
this for drying plates. It is well, however, to provide for
a constant change in the air by means of an inlet tube on the
principle of Tobin's ventilators, and an exit tube. A
small coil of water pipes in a small room will much aid the
change of the air ; and, in fact, some such artifice must be
adopted when many plates have to be dried. The plates
may be racked in some such racks as given at page 34.
Great care should be taken against dust. A boarded floor

PEEPAEATION OF THE PLATES. 121

is not safe ; kamptulicon should be laid down, and, if prac-
ticable, the walls and ceiling should be papered with a well-
varnished paper. This enables all parts of the room to be
washed down, and so to be deprived of any adherent
dust. Should a room not be available, then resort must
be had to a drying cupboard, such as described in
Chapter V.

The temperature of the cupboard should be kept as
even as possible, sudden changes being detrimental —
producing markings. Opening the drying cupboard door
before the plates are dry, when once the gas has been
turned on, is a mistake ; the plates should be left until
it is judged they are quite dry. Very quick drying
is a mistake, as the different layers of the film get an
uneven strain, and cause frilling. Six hours is about
the minimum time which we can recommend, unless
drying by alcohol is resorted to. The temperature should,
if possible, not exceed 80" F., and the gas must be regu-
lated accordingly. Drying by alcohol is eifected by
placing each plate, after thorough setting , in a dish of methy-
lated spirit free from resinous matter for ten minutes, when
it will dry in an hour without difficulty.

CHAPTEE XX.

TESTING PLATES.

All plates, whether commercial or otherwise, should he
tested before a hatch is taken into use. We have often
found plates blamed simply because such testing has not
been carried out. Plates should be tested (1st) for speed,
(2nd) for brightness, (3rd) for density giving qualities,
(4th) for frilling and other imperfections.

Testing for Speed. — In our own practice we always test
plates by means of one of Warnerke's standard sensito-
meters, but anyone may make a sensitometer for himself

Fig 20.

which will be sufficient. Warnerke's sensitometer consists
of a plate A, marked out into small rectangles of different
opacities. These opacities are so arranged that each

TESTING PLATES

12a

succeeding space is just ^ more opaque to white light than
the one immediately before it. They are numbered in
distinct numbers in the order of opacity. This mask is
placed in a pressure frame, B, in front of which, and fitting-
into a groove, is a phosphorescent plate, E, which is placed
behind C. The light of this can be made to pass through
the sensitometer screen on to a gelatine plate in contact
with it, by withdrawing a shutter (shown open in the
figure). To use this instrument, the phosphorescent plate
is excited by an inch of burning magnesium wire held
close to the surface of the plate. It is then placed in the
groove cut for it, the illuminated surface being towards
the shutter. Between exciting the phosphorescent sur-
face and the exposure of the plate to its action exactly a
minute is allowed to lapse. The shutter is then with-
drawn, and the plate receives the light through the screen
for half a minute, when the shutter is closed, and the plate
is developed. The last figure which can be read after
fixing the plate is the " sensitometer number " of that
plate. The following table, compiled by Mr. Cadet, can
then be used to compare the sensitiveness of one plate
with another : —

ij

16
12
9
7
5
4

Number of times more sensitive than

25
24
23
22
21
20
19
18
17
11)
15

25

24 23

1

}* 1!
... 1

22

21

20

19

18

17

16

2i

8

4

6

7

9

12

If

2J

3

i

5

7

9

1*

H

3

4

5

7

1

If

n

3

4

5

r

1} i»

n

3

4

... r 1 li

If

2J

3

1

H

If

2J

1

ll

n

1

14

...

...

1

2*
If

1

The numbers down to 15 only are given, this being more
than sufficient for comparison of most plates. Supposing
it is desired to comparetherapidity of two plates showing
difierent numbers, look for the higher number in the
column on the left side of the table, and the lower one in

124 TESTING PLATES.

the top horizontal row of numbers, then run the eye_ along
the line of the number in the left-hand column until_ you
come to the figure under the lower number ; the figure
will then show the number of times more sensitive is the
plate showing the higher number than the plate showing
the lower number. For instance, a plate showing 21 is
four times more sensitive than one showing 16 ; one show-
ing 20 is three times more sensitive than one showing
lb, and so on. In both cases the development should
be by a developer which is suitable to the plates.
A good standard developer will be found in the
chapter on Development. It is sometimes doubted,
though we believe incorrectly, that the sensitometer re-
sults are not in accordance with those given by the
camera. For our own part, we do not believe in any great
discordance, though it is possible that there should be a
slight one. If any doubt exist in the mind, a plate of
known sensitiveness may be placed in one half of a dark
slide, and the plate whose sensitiveness has to be judged in
the other, and an exposure made in the camera. It is then
easy to tell at a glance which is the better exposed picture.

I esting for Brightness. — The brightness is ascertained
readily by examining the plates already tested in the sensi-
tometer. In case a sensitometer is not at hand, it is a good
plan to expose a plate in the camera ; pull out but half of
the front of the slide. On development, the least trace
of fog (green or grey) is seen on the unexposed parts.

Testing for Densiti/. — It is unfair to test for the density-
giving qualities of a plate by exposure in the camera un-
less the light is bright. Our own practice is to use a dense
negative, from which a transparency is taken with the
plate to be tested. A good exposure is given by passing
a lighted match over the surface of the negative, which
is in a pressure frame with the plate in contact with it.
In the positive, after development and fixing, the
deepest shadows of the picture should be sufficiently
opaque to very greatly dim the light from a candle

TESTING PLATES, ]25

flame when looked at through the densest portions. If a
long exposure and plenty of restraining bromide be used,
most plates will give good density on fixing if the plate
be not starved of the sensitive salt of silver. When a
plate is looked at by reflected light before exposure, a
finger pressed against the back should not be visible. If
this be the case the plate has not been sparingly coated.

Testing for Frilling, 8fc. — We have already stated
(page 46) how dull spots which give opaque spots on
development can be distinguished on a gelatine plate —
viz., by shining the plate to the light coming irom a gas
flame through stained red glass. The spots, of course,
can be seen on development, and need not be remarked
upon further.

Plates which frill, usually do so after withdrawal from
the hyposulphite bath, and on immersion in the wash
water. The reason of this is due to the property that
gelatine has of allowing pure water to diffuse through a
layer of gelatine more rapidly than a salt solution wiU
diffuse out. The cure for this is to use a second bath of
weak hyposulphite, or even of common salt, and then
wash the plate. Plates with a substratum on them rarely
blister or frill. It plates frill with the developer made
alkaline with ammonia, the plates should be tried with
the developer made alkaline with carbonate of potash or
carbonate of soda. If the tendency to frill or blister with
ammonia be slight, these last developers should give im-
munity from it. In every case of a tendency to friU, the
plate, before fixing, s/jomW he immersed . in the alum hath
for five minutes.

Our advice, however, if plates friU or blister, is to reject
the batch, and make or buy others, as it will save dis-
appointment.

In conclusion, we would earnestly recommend any
photographer not to rely on any plates without previously
testing them. The trouble is small, as is the expense,
but the worry and annoyance of unsuccessful negatives

126 TESTING PLATES.

due to this cause are great. There are excellent plates
in the market, but they vary in their quality and rapidity
at times, as is almost inevitable. The manufacturers
may have the most perfect machinery and chemical appli-
ances, but as plates are dependent for their excellence
to a great extent on the quality of gelatine employed,
and as no two samples of gelatine are absolutely alike in
composition, and on no two days is the temperature exactly
alike, it can be well understood that such variations are
almost certain to occur.

There is one defect which arises in negatives, to which
special allusion is here made, viz., small pinholes in the
densest parts — generally in the sky. The plates are
usually blamed for these, but in the majority of cases it
will be found that they are due to dust (see next chapter).

OHAPTER XXI.

EXPOSURE OF THE PLATES.

Whether the plate be made at home, or hought, there
are certain necessary precautions to take when exposing
it in the camera.

hxamination of Slides. — The iirst thing to he done is to
examine the dark slides, and this should not he done in a
casual manner, hut should he done thoroughly before they
are filled. The greatest enemy to clean work is dust in
the slides, and much care should be taken in searching
for it, and for getting rid of it. In the fronts of the slides
the rabates should be carefully passed over with a bristle
brush, and the woodwork and separating partition of the
double back should be equally well dusted. If a journey
is contemplated, it is well to pass a rag moistened with
glycerine over the rabates, and, in fact, over the inside of
the whole of the slides, to act as a dust trap. Of course
but a very slight film of glycerine should be left, but the
faintest trace is sufficient to catch any fine dust that may
enter. For better security, too, of the plates, the slides
should be tied up in bags (thin waterproof sheeting is a
good material of which to make them). The plates them-
selves should each be dusted with a badger hair brush,
and, if practicable, each one should be shined by reflected
light, and viewed by transmitted light, to make certain

128 EXPOSURE or the plates.

that no surface imperfections, such as dull spots, are on
the plates, and that the plate has heen uniformly coated,
and has no pits or other markings which would spoil a
negative. No one who has not practically proved it, can
he aware of the disappointment that is caused hy taking
a negative on such a plate which, if the blemishes caused
hy such imperfections were absent, might be ranked as a
perfect one.

Focussing the Ficture. — It is beyond the scope of this
work to teach the artistic side of photography, and for
it a reference should be made to such works as '' Pictorial
Effect in Photography," or " Picture Making by Photo-
graphy."* We will suppose, however, that a landscape
has been chosen, that the lens is a good one, and that
the camera is not one of those ricketty articles which
may be described as cheap and nasty. We will, more-
over, suppose that the legs are light, and yet firm ; and
that the base of the camera fits tightly on them. In the
days of wet plate photography the rule to be followed was
to focus with the largest stop that would give passable
definition. In these days of rapid plates the rule is to use
a small stop, so as to enable the exposure to be slightly
prolonged. When the writer fo cusses a picture, he uses
the largest stop, which gives decent definition, and before
exposing the plate alters it to a stop of half that diameter,
or nearly so. By this means the sharpest definition is
got, and the resulting negative is one which will bear
enlargement if necessary. Some landscape photo-
graphers make it a point to use the smallest stop of their
lenses in all cases. If they err, they err on the right side.
As a rule, every lens has some stop which, when used,
gives the crispest, and yet sharp image. With instanta-
neous pictures the largest stop consistent with fair defi-
nition should be used, particularly if the plates are not
exceeding rapid. With plates that register 24 on the

* By H. P. Kobinaon (Piper and Carter).

EXPOSURE OF THE PLATES. 129

Warnerke sensitometer, No. 4 stop, or -^ of a " rapid
rectilinear " lens, should admit sufficient light to obtain
a picture in the vo of a second if the light be good, and if
the views be tolerably open.

It may not be out of place to give a few general remarks
as to the methods of" placing " the picture on the focussing
screen when photographing a landscape picture. First
of all, if the principal object is a building, a doublet com-
bination of lenses should be used, in order that the lines
may be straight, and not curved, which is the case when a
single lens is used. Then care should be taken that the
top and bottom of the focussing screen are parallel to the
horizon. This canbestbeascertainedbyusingasmaUlevel.
Now, if the building is a high one, the camera may have
to be tilted so as to include the whole, in which case care
should be taken to use the swing back (with which every
camera should be provided), so that the focussing screen
is vertical (plumb). This ensures that the vertical lines
of a building, besides being straight, will also be parallel,
a point which is insisted upon in proper perspective.
When this is done, then insert a stop, and focus the image
as sharply as possible.*

Note if the sun be shining into the lens, and if it is,
carefully shade it. (There are sky shades supplied with
cameras now which are very useful.) Be particular to
focus sharply the object which is to be the " nucleus " of
the picture, and note whether any improvement can be
made by a shift in position of the camera. For a pure
landscape, if a building be not in the margin of the focus-
sing screen, a single lens may be used, as any small curva-
ture to straight lines which may be given will not be per-
ceptible. Focus the principal object sharply, and if a
large stop has to be employed owing to want of light or
a required rapidity in exposure, the slight want of sharp-

* I£ the swing-back be used, it will be found that a smaller stop will
have to be used than if the focussing screen is in its ordinary position.

130 EXPOSURE OF THE PLATES.

ness In the remaining portions will not tell mucti against
the picture.

One more word : never take a picture without some

principal object in it ; every good composition should have

some point of prime interest, and the lines and general

sweep of light and shade should lead up to it. One ohject

of interest in a picture is hetter than a dozen, as then the

eye is not distracted, but can dwell on it and remember it.

Exposure in the Camera.— y^htn gelatine plates are

used, there is an addition to the camera which well repays

the preliminary cost, when comfort and ease of exposure

axe taken into consideration ; we allude to the use of a

shutter worked by a pneumatic arrangement, by which

any desired exposure can be given. At the risk of being

told that we are advertising a particular article, we

honestly say that one of Cadett's shutters, which works

inside the camera and at the back of the lens, is that

one which fulfils the object in view' better than any other

with which we are acquainted. With it exposures can he

given from any number of seconds to about the ^ of a

second by merely pressing the ball of the pneumatic

arrangement. This prevents any shake that might be

given to the camera at the moment of uncapping the

lens, a point of very practical importance when the

exposure is short. We will suppose that the camera is

provided with some such arrangement, or with a substitute

for it. When the box containing the slides is opened,

direct sunlight should not be allowed to play upon them,

but they should be kept in the shade ; for no matter how

carefully a slide is made, it frequently happens that a gleam

of sunlight is able to penetrate by reflection through some

apparently light-tight crevice to the plate, causing a

marking. The slide should be immediately covered with

the focussing-cloth, and whilst so protected placed in

the camera, where it should remain covered up. It is

here presumed that before taking out the camera it has

been thoroughly examined in bright light to see that

EXPOSURE OF THE PLATES. 131

there are no pin-holes in the bellows ; that the interior
is of a dull black ; and that the aperture of the lens in
which the diaphragm is placed has been provided with a
covering to prevent light penetrating to the plate by re-
flection when the front of the slide is withdrawn previously
ready for giving the exposure. We may remark that a
pneumatic shutter placed behind the lens (as we have
suggested it should be in our ideal camera) lessens any
danger of fog from this cause, as the light from the stop
will only act during the time of exposure, and would pro-
bably not hurt the picture. It is far different, however,
with a shutter in front of the lens, or where a cap is used ;
in these cases, from the moment the slide is drawn the
fogging action of such light commences. A good pro-
tection to the Waterhouse diaphragm is an india-rubber
band, whilst to rotating stops a cover is almost a necessity.
Now as to the time of exposing a plate it is impossible
to say very much, since all depends on the rapidity of the
plate ; but this ought to be known to the operator by
previous trial, and then a keen judgment as to the in-
tensity of light in which the exposure is to be made
ought to enable him to give an exposure not far wrong,
at aU events. In any case, it is better to over-expose
than to under-expose ; and with iodo-bromide plates,
such as given in Chapter IX., six times, or even more,
exposure than is absolutely necessary to give a perfect
picture, is better than giving even one-third too little.
In developing such over-exposed plates, a proper grada-
tion can readily be obtained; whilst with an under-
exposed plate, nothing can make it better than bad.
Violent contrasts are the most difficult to manage properly.
Thus, a snow mountain in sunlight in one part of the
picture, with dark fir trees in shade in another part, are
objects which not only try the expertness \)f the operator
in development, but are extraordinary tests for the quality
of the plates. It may be said that a thinly-coated plate
should never be chosen ior such a subject, but rather a

132 EXPOSURE OF THE PLATES.

plate which is thickly coated. In the latter, the reversed'
action caused Iby prolonged exposure, though extant on
the surface, may not reach the layers of gelatine emulsion
next the glass surface. Any how, in every case it is
necessary to time the exposure so that in no part of the-
deepest shadows is there any large amount of bare glass.
The golden rule, then, is to give sufficient exposure, and
to regulate the developer so as to correct any over-
exposure.

When the plate is to be exposed, the front of the slide
should be withdrawn, whilst the focussing cloth covers
the whole of the back of the camera. It is absolutely
necessary that all danger of light entering the slide be
avoided by taking this precaution. The cloth should re-
main over the camera whilst the exposure is made. It
is an excellent plan to have an elastic loop attached to-
the focussing-cloth to fit over the lens, and thus to pre-
vent any slipping of the latter.

Exposure of Instantaneous Fictures. — ^A picture is said
to be instantaneously taken when the exposure is very
short, and to obtain these short exposures some kind of
instantaneous shutter should be employed. There are
many in the market, many of which are good. All are
dangerous, however, if the camera is not very rigid, or
unless they are detached from absolute contact with the
lens. This may be effected by using a velvet bag to con-
nect the opening in the shutter with the hood of the lens.
If an instantaneous shutter is to be used, we like a drop-
shutter form in its simplest form. Some shutters act as
diaphragms to the lenses, and thus the full value of the
exposure is not gained, as much as half the light being
lost. The theoretical form that a shutter should take is
that the full aperture of the lens should be exposed for
as comparatively long a period as possible, whilst the un-
covering and covering should take place as rapidly as
possible. With this in view, the writer designed a shutter
shown in fig. 21. C is the aperture for the lens ; P, the

EXPOSURE OF THE PLATES.

133

pin to which an 'elastic band, E, is attached ; T, the re-
leasing catch. In this we have a long drop shutter, the
velocity of drop heing augmented by an elastic band.
With an opening of five inches an exposure of about one-

Mg. 21.

fifteenth of 'ei second can be given. The shutter is attached
to the lens bj|a velvet bag carrying an elastic ring, and,
at the moment of exposure, is held by the hand. For
ordinary rapid exposures, we like the flap shutter behind
the lens, which we have alluded to.

Witlidrawing the Slide. — The same precautions should be
taken in withdrawing the slide as were taken in placing
it in the camera.

CHAPTEE XXII.

DEVELOPMENT OF GELATINE PLATES WITH
ALKALINE DEVELOPEKS.

In Chapter II. we have already shown the theory on which
development proceeds ; but here we must enter a little
more fully into the matter. We have shown, when the
alkaline developer is used, that, as a rule, a restrainer,
in the shape of soluble bromide, to prevent the primary
reduction of the silver bromide unaltered by light, is
requisite. We have italicized " as a rule," since, in some
cases, this restrainer, which acts chemically, is really
unnecessary, as a restrainer which acts physically can
take its place. This was the case in the old albumen beer
process, which was well known till emulsion superseded
it; the iodide in the plate separates the particles of
bromide one from the other, and the albumen wraps these
up, as it were, in a colloidal sheath, through which the solu-
tion finds its way more slowly than it would if they were
unshrouded. Gelatine is also a colloidal body, and we
may expect to find the same hold good ; as a fact, with
many plates it does, and more especially with those plates
which are prepared with an emulsion containing a large
proportion of gelatine,* as compared to silver bromide.

" If we take emulsion, for instance, prepared by Beanett's process, we find
that the proportion of silver nitrate to gelatine is 11 to 20 ; in the formula
we have given at page 139 it is 20 to 16 ; that is, in one case the silver
nitrate is about i the weight of gelatine, and in the other jths. It can thus
be easily understood how in one case no potassium bromide is required^
whilst in the other a little is requisite.

ALKALINE DEVELOPMENT. 135

With some commercial plates, for instance, where the
silver bromide is minimized, alkaline development may
proceed with the greatest ease without any chemical
restrainer, the physical action of the gelatine being
suiEcient. It is for this reason that it is difficult to give
any definite formula which can apply to all plates. In
alkaline development, we may take it that there are three
components: 1, pyrogallic acid; 2, the alkali (usually
ammonia) ; 3, the restrainer (usually potassium bromide).
There are developers made with the carbonates of potas-
sium and sodium, instead of ammonia. These are ordin-
ary carbonates with an additional atom of the alkali tacked
on them. It appears that it is these tacked-on atoms
which is the active ingredient of the developer when
combined with pyrogallic acid, the carbonate being actu-
ally a restrainer. This may be proved by a simple experi-
ment of using with an ammonia developer bi-carbonate
of soda instead of potassium bromide, when the restrain-
ing action of the former will be seen.

Let us consider the different functions of the pp'OgaUic
acid, the alkali, and the restrainer.

The alkali and the pyrogallic acid we will take first.
As already pointed out (p. 15), pyrogallic acid combines
with the oxygen, and the bromine from the reduced silver
bromide combines with the alkali. Suppose we have just
sufficient of both to complete the reaction indicated, what
will be the effect of increasing the one or the other ?

If the alkali be increased we shall have a more rapid
absorption of oxygen by the pyrogallic acid. The oxygen
may be obtained from the air, or from the alkali by the
act of developing the image ; we may conclude that the
two sources from whence the oxygen is obtained will be
used fairly equally. Hence, increase in amount of alkali
means increased rapidity of development. But at the
same time, mi cases of over-exposure^ it means that the
effect of even a faint action of light is taken cognisance
of at once, and the image becomes flat. Moreover, in

136 ALKALINE DEVELOPMENT.

cases of extreme over-exposure, a large proportion of
alkali means a reversal of parts of the image, whicli can
often be avoided by using a weak developer, and conse-
quently slow development. The developer can de-oxidize
the oxidized molecules which cause the reversal before
they are required to aid in building up the image.
With a properly exposed picture more alkali gives an
Increased amount of reduced silver, which may increase
density, since the pyrogallic acid will be used up to the
greatest extent possible. It will also be seen that the
addition of successive doses of alkali to the developer
will give the same result when the exposure is correct ;
but vastly different if the exposure is too long.

The addition of pyrogallic acid to the normal solutions
means an increased power of reduction and a larger
amount of oxygen to be absorbed, and consequently more
silver to be reduced ; but It will be reduced more slowly
than where the ammonia is in excess. Now slow deve-
lopment, m a properly permeable plate, means density
in the high lights. It must also not be forgotten that
pyrogallic acid is per se an absorbent of bromine when
it has no oxygen to absorb.

In an 8 J by 6^ plate, on an average, about 8 grs. of silver
bromide are reduced to the metallic state, and from this
about 3^ grains of ammonium bromide would be formed.
Taking an ammonia developer, a little calculation will
show that the presence of 2 minims of strong ammonia are
necessary to cause this conversion in the presence of pyro-
gallic acid ; and allowing for loss by vapourizing, at
least 4 minims should be employed. The amount of
pyrogallic acid to effect the same may probably be placed
at about 2 grains, and allowing for oxidation, by contact
with the air, 4 grains at least would be necessary for the
full amount of ammonia. The bromide of potassium, or
other chemical restrainer, slows the development, pro-
bably through a formation of a double salt of bromide of
silver and potassium, which being reduced with difficulty

ALKALINE DEVELOPMENT. 137

retards reduction, and hence a greater apparent density of
deposit is given through the slower development.

PP/«'c/t of the Ingredients of a Developer sliould he first
applied ? — The question arises, should the pyrogallic acid,
the restrainer, the alkali, or a mixture of all three, be first
applied to the film ? We believe that the application of
pyrogallic acid first has a slight tendency to slow the
plate ; but, on the other hand, it is safe to do so, and then
subsequently to add the other solutions together, little by
little, till proper density is obtained. There can be no
doubt that flooding the plate with a bromide solution
first, is wrong in principle, since bromide has a tendency
to destroy the photographic image ; but with a carbonate
this is not the case. On the other hand, a first soaking
with a solution of the alkali, even in conjunction
with a restrainer (which does not destroy the image),
has much to recommend it, as pointed out by Colonel
Wortley. When ammonia is used, it takes a minute quan-
tity ot silver bromide into solution, which, on the addition
of pyrogallic acid (and bromide if necessary), is ready to be
deposited on the image, and at the same time the reduction
of the photographic image of sub-bromide to the metallic
state commences. A safe plan, perhaps, is to flood the
plate first with ammonia and bromide, or with an alkali,
such as the carbonate of soda, and then to add the pyro-
gallic acid. But on the whole, for a properly exposed
plate, we should recommend that all three ingredients
should be applied at once to the film, but not of necessity
in the full proportions. Wetting the plate before develop-
ment is equivalent to diluting the developer, and, as a rule,
is not to be recommended except in cases where there is a
very horny film which requires softening, and then a
slightly more concentrated developer should be used.

Development of a gelatine plate is in reality an art and
science combined. The art consists in getting proper
gradation, and the science in mixing your solutions to
obtain it. There are only two kinds of exposed plates

138

ALKALINE DEVELOPMENT.

whicli deserve attention at all : one when it is exactly-
timed rightly, and the other when it is over-exposed. An
under-exposed picture should be washed off as quickly
as possible, or else framed to illustrate a " horrid ex-
ample."

Before accepting what has been laid down, the reader
is strongly recommended to make a few experiments him-
self. First let him take formulse such as the following : —

P. — Pyrogallic acid...

Water

B. — Potassium bromide

Water

A. — Ammonia 'SSO ...

Water

50 grains

1 ounce

50 grains

1 ounce

2 drachms
2^ ounces

These nearly correspond to 10 per cent, solutions.

Expose an 8^ by (i|- plate, and cut it by the diamond into
six parts. Obtain a small dipping bath such as is used
for quarter-plates, or a glass cell such as is used in
physical laboratories.

The first experiment, perhaps, would be to take
20 minims of P, and add to it 1 ounce of water, place it
in the dipping bath, and then immerse the end of one of
the pieces of the plate in it for one to two minutes. Take
it out and pour the pyrogallic acid solution into the cup,
in which have been dropped 40 minims of B and 80 of A.
Develop the plate in the dish, and note the result.

Other experiments of the same type are, to use the bro-
mide first, then the bromide and the ammonia, and then
the ammonia alone. Further experiments should then be
made by increasing or diminishing the proportions of the
pyrogallic acid, &c., when no doubt the reader will be
able to confirm what has been said of the matter, or to
make his own deductions.

Practical Development of a Plate. — The writer adopts the
following method of developing plates, and which he has-

ALKALINE DEVELOPMENT.

139

found applicable to any he has tried.

The following are

prepared : —

1. — Pyrogallic acid ...

• • dry

2. — Potassium bromide

.. 10 grains

Water

... 1 ounce

3. — Ammonia -880

... 2 drachms

Water

... 18 „

If a plate has received good exposure, the following is
made • up : —

No. 1

3 grains

(which is measured out by taking the amount on a slip

of glass)

No. 2 2 drachms

No. 3 „ ... 1 „

Water, to make up to ... ... 2 ounces

This is flowed over the plate, and the appearance of the
outline is carefuUy watched; if itappearsbeforelS seconds,
the plate is rinsed in water, and 2 more drachms of No. 2
are added, and development continued. This checks the
rapidity of development, and allows sufficient density to
be attained before the deepest shadows are at all dimmed.
If the plate begins to develop in fifteen seconds, the
action of the developer is allowed to continue till such
time as the action begins to flag, when another ^ drachm
of No. 3 may be added ; or, if the developer be very
muddy, a fresh solution is employed after rinsing the plate.
Suppose the picture does not commence after (say)
twenty seconds, this developer is made up : —

Pyro
No. 2
No. 3
Water

3 grains
1 drachm

1 „

2 ounces

And after the image begins to gain strength, the plate is

140 ALKALINE DEVELOPMENT.

lifted out of the solution, and the development allowed
to proceed with the solution imbibed by the gelatine film.
By this plan all the detail can he got out without the
high lights becoming choked up. When all details are
out, the developer is once more applied, and proper
density obtained. For instantaneoiis work, or where the
exposure is known not to be full, we commence by soak-
ing the plate in —

No. 3* 1 drachm

Water 2 ounces

After a minute's Immersion in this, 3 grains of pyrogallic
acid and 1 drachm ot No. 2 are added, and the develop-
ment proceeded with. In this case also it is often advisa-
ble to lift the plate out of the dish till all possible detail
has appeared, when density can be given as before.

In developing small plates, white porcelain dishes are
capital to work with, since any slight want of flatness of
bottom does not cause much waste of solution ; but with
large plates (say, 12 by 10) these dishes are inadvisable :
first, on account of their weight ; and second, on account
of the usual want of flatness of the bottom. For large
plates shallow ebonite dishes have been manufactured,
and these are everything one can wish for, if kept out of
the sun, and away from heat, when they are apt to flatten
out. Care should be taken to keep such dishes clean ; an
occasional swill with nitric acid and water helps matters
much in this respect. It should be remembered that a
dirty dish means a muddy developing solution.

Carbonate, of Soda Developer. — The use of alkaline
carbonates is gaining attention, and they certainly possess
some advantages over the ammonia developer, in that
they do not give rise to green fog, and that their action
is slower than ammonia. Most use these developers
without any restraining bromide ; bat we confess to liking

* Some plates will stand 2 drachms.

ALKALINE DEVELOPMENT. 141

a slight dose of it. Tlie formula we prefer is a very
simple one, and stands as follows :

1 . — Pyrogallic acid 3 grains

2. — Saturated solution of dry mono-
carbonate of soda or potash... 1 drachm

3. — Potassium bromide solution

(10 grains to the ounce) ... 1 to 20 minims

4. — Water ... ... ... ... 2 ounces

It may be objected that the strength of a saturated solu-
tion of the alkaline carbonates varies according to the
temperature, and this is no doubt true, but not sufficiently
to be of any importance. Some use sulphite of soda with
the above, No. 2, and there is no objection to this course.
About ten grains of it to the ounce of saturated carbonates
is sufficient to ensure immunity from yellow stains. It is
the yellow stain which is the greatest objection to these
developers, though, if the carbonates are pure, there is
less liability to it ; and even if there be a stain, a 10-grain
to the ounce of water solution of citric acid after washing
the plate should entirely eliminate it. There is one ad-
vantage in the use of carbonate developers, viz., that the
tendency to frilling of the film is much diminished (see
page 66). We have developed plates which inevitably
frilled with ammonia, without a wrinkle when using the
carbonates. Further on will be found a formula for
developing plates with hydrokinone and ammonia. We
may say that by using 1^ grains of hydrokinone instead
of the 3 grains of pyrogaUic acid in the above formula,
there is a perfect immunity from yellow or any other
stain, and the negative presents the appearance of a
beautiful grey black. The cost of hydrokinone is rather
more than twice that of pyrogaUic acid, but as only half
the amount is employed there is no extra cost incurred in
using it. The method of developing over-exposed,
rightly-exposed, and slightly under-exposed negatives

142 ALKALINE DEVELOPMENT.

witli these developers will be readily guessed by reading
the plan we adopt with the ammonia developer. For a
fully exposed picture we begin with half the alkaline
carbonate given above, and if necessary add a few more
drops of potassium bromide to restrain the action. For
instantaneous work we soak the plate in the solution of
carbonate and water, and subsequently add the pyrogallic
acid or hydrokinone without any bromide.

W/iat is Correct Density. — It is often asked as to the
length development should go. This is a somewhat
difficult point to answer, as it is really dependent on the
thickness of the coating given to the plate, and to the
fineness of division of the particles of the emulsion. A
plate that is properly coated should give sufficient
density when the image appears at the back of the
plate. With some kinds of emulsion the development
appears to take place all through the film at once, and in
this case the plate may look almost black from reduced
silver before the density is complete. It must be also
recollected that some plates, though apparently very
dense after development, yet when they are fixed out
give thinnish images. In cases of this description the
development should be pushed on as far as possible. With
a very thinly-coated plate, this pushing of the image to
the back of the plate would give a hard negative.

The glycerine developer of Mr. Edwards, which some
photographers still like, is described by him as fol-
lows : —

Make two stock solutions, and label them No. 1 and
No. 2.

No. 1.

Pyrogallic acid

... 1 ounce

Glycerine

... 1 „

Methylated alcohol

... 6 ounces

Mix the glycerine and spirit, and add to the pyrogallic
acid.

ALKALINE DEVELOPMENT. 143

No. 2.

Bromide of potassium (or ammo-
nium) ... ... ... ... 60 grains

Liquor ammonia, '880 ... ... 1 ounce

Glycerine ... ... ... 1 „

Water ... ... ... ... 6 ounces

The ahoye stock solutions will keep any length of
time.

To make the developer, add 1 part of No. 1 to 15 parts
of water, and label this bottle D (developer). In another
bottle mix 1 ounce of No. 2 with 15 ounces of water,
and label it A (accelerator).

It will be found convenient, to avoid mistakes, to have
these two bottles of different shapes. Either of the above
solutions will keep two or three days. When required for
use, pour into a clean glass measure equal parts of D and
A, adding the A last just before using. Place the dry,
exposed plate face up in a shallow dish or tray, and pour
the mixture steadily over the plate, avoiding air-bubbles.
Should any adhere to the surface of the plate, at once
remove them with the finger, or a camel's-hair brush kept
for the purpose. Rock the dish gently, taking care to
keep the plate well covered with the solution. In a few
seconds the image will appear, and, if the exposure has
been well timed, all the detail will be out and the deve-
lopment complete in about one minute, when the negative
should be well washed under the tap, and placed at once
in the fixing bath.

Do not hurry the development, but allow the plate to
remain in the solution after all the details are visible
until the required density is obtained. With this deve-
loper, used in the above proportions, there is no danger
of fog, except from the action of light.

If, on the application of the mixed developer, the image
flashes out and the details in the shadows appear too
quickly, it will indicate that the plate has been over-

144 ALKALINE DEVELOPMENT.

exposed ; therefore at once throw off the mixed developer^
and, without stopping to wash the plate, flood it with D
alone, when the development will be checked, and will
proceed more slowly, while the image gains in density ; if
too slowly, or the negative appears to be getting too
intense, add a very little of A. There will, however,
usually be sufficient of the latter left on the plate tO'
complete the development with the simple addition of a
sufficient quantity of solution D. A very little experience
will enable the operator to produce a good printing
negative from a plate which, if developed with the full
proportion of A, would have been utterly useless from
over-exposure. In very warm, bright weather, it will,
perhaps, be found an advantage to use rather more D than
A in the mixed developer, giving just sufficient exposure
to avoid hardness in the negative. Under-exposure can
be corrected to a certain extent by increasing the propor-
tions of A in the mixed developer, but the addition should
be made at once before the development has proceeded
too far, or the effect will be to increase the density, and
cause too much contrast in the negative.

These concentrated stock solutions will be found very
convenient to use, and a great saving of time in weighing
and measuring small quantities.

We have used the terms over-exposure, under-expo-
sure, and proper exposure in the foregoing in this sense.
A plate ■ should develop with a developer of normal
strength (such as we have given above) with the full
amount of ammonia and bromide added, and the margins
of the plates, which are not exposed, but covered by the
rabbets of the slides, should then be free from fog, except
from any small amount which may be due to halation from
the sky, or other light parts of the picture. When a plate
is under-exposed, the developer is insufficiently strong,
and a greater strength has to be resorted to, giving a
danger of general fog. An over-exposed plate means one
in which there would be fog if the plate wei'e developed

ALKALINE DEVELOPMENT. 145

witli the developer used full strength (except on the mar-
gins of the plates).

The great enemies of this developer are the air-bells
which form on the plate, and they are to be feared in all
developers which contain glycerine or sugar.

To develop plates made with a large proportion of gela-
tine, we give Mr. Bennett's directions for development
with his long emulsifying process.

He soaks the plate for a minute in water in the deve-
loping dish, and then pours the following quickly along
that side of the tray which is not occupied by the plate.
By rocking the dish suddenly it sweeps over the plate
(it is developed in five to twenty seconds) : —

Pyrogallic acid ... ... ..._ 1 grain

Bromide ... ... ... ... none*

Ammonia (-880) 1 to 10 drops f

Water ... ... ... ... 1 ounce

He says : — " Do not flood with pyrogallic acid first, or
you will render the plate slower ; nor add more pyrogallic,
or you will again slow the plate, and, moreover, have it too
dense. It the exposure has been sufficiently short, you
should have a dense negative, with bare glass for shadows,
almost as soon as the developer has covered it. If much
ammonia be used, and the plate be not developed in half
a minute, fresh developer should be made, and the plate
be washed."

Mr. Henderson introduced the use of ferrocyanide of
potassium with the ammonia, and we give a formula.
Some find it has a tendency to produce fog, whilst others
have not found this difficulty. We do not much care for
it ourselves : —

* For reasons for this omission, see beginning of this chapter.

t The quantity of ammonia depends on the shortness of exposure and
the sensitiveness of the plate. About i drops may be considered as the
average amount required.

146 ALKALINE DEVELOPMENT.

A nearly sat. sol. of potassium

ferro-cyanide 10 ounces

Ammonia 10 drops

Pyrogallic acid 15 grains

He states that if this developer be kept from light and air,
it retains its developing properties a long time. If it
refuses to develop, a few drops of ammonia will set its
developing power in action. If free ammonia be present,
and it still refuses to develop, then a little pyrogallic acid
must be added.

Nelson's developer is made as follows : —

No. 1.

Pyrogallic acid ... ... ... 1 ounce

Methylated spirit 7 ounces

White sugar ... 1 ounce

Distilled water Bounces

No. 2.

Ammonia "880 4 ounces

Ammonium bromide ... ... 1 ounce

White sugar ^ ounce

Water ... ... ... ... 2 ounces

Use 40 minims of No. 1, and from 30 to 40 minims of
No. 2, mixed in 2 ounces of water.

Messrs. Wralten and Wainwright, with their ordinary
or slower plates, recommend the following : —
I. — Pyrogallic acid... ... ... 2 grains

AVater ... ... ... ... 1 ounce

used freshly mixed.

II. — Potassium bromide 15 grains

Water ... ... ... ... 1 ounce

in. — Ammonia ("880) ... ... 1 drachm

Water ... ... ... ... 1 ounce

The plate is softened for one minute in water, 1 ounce
of No. I. is applied for one minute, and then 3 minims ot
II. and III. are dropped into the developing cup, and the
pyrogallic eolution poured back. This is again poured

ALKALINE DEVELOPMENT. 147

on, and the image develops. When development flags, 3
minims more of No. II. and III. are again added till suffi-
cient density is ohtained.

For these rapid plates (and, indeed, for most rapid plates
to be found in the market), and also for plates prepared
as in Chapter XXVII., use the following : —

I. — Ammonium ('SSO) ... ... 1 ounce

Potassium bromide ... ... 60 grains

Water ... ... ... ... 3 ounces

II. — Pyrogallic acid ... ... ... 3 grains

Water ... ... 2 ounces

The plate is soaked in water for a minute, when the
water is poured off, and No. 2 is substituted. From 15 to
20 drops of No. I. are poured into the cup, No. I. returned
into it, and applied again. The plate develops rapidly.
For our own part, we like to add No. I. at two intervals of
time, as the development is more under control.

All the above formula are given in the simplest possible
form, no additions being made. Many photographers, how-
ever, add nitric acid or citric acid to the pyrogallic acid
to keep it from discolouring. When using them, however,
it must be remembered that a certain amount of ammonia
is thereby neutralized. If nitric acid be used, 4 minims
will be sufficient to keep 60 grains of pyrogallic acid free
from colour.

If citric acid, about 10 grains should be used ; Mr.
Berkeley for the same purpose uses about 880 grains of
neutral sodium sulphite to each ounce of water employed.
Of all additions, we may say we prefer this last, since it
has no neutralizing effect on the ammonia.

The following is a formula in which carbonate of soda
is used with sulphite of soda : —

Saturated solution of washing soda ... A.

Saturated solution of sulphite of soda 15.

Bromide of potassium ... 20 grains) p

Water 1 ounce) "

148 ALKALINE DEVELOPMENT.

Tor development, take —

16 di-aclims of A

6 drachms of B

3 or 4 drops of C

And add dry pyro 2 grs. to the oz. of solution.

If the'pyro is preferred in solution, mix as follows : —

36 ozs. saturated solution of sulphite.

1 drop to each oz. commercial sulphuric acid.

2 drms. of pyro.

And keep in a well-stoppered bottle. Use in same pro-
portion as given above.

In either of the formulae given, which include carbon-
ate of soda, carbonate of potash may be. substituted.
Carbonate of potash does not stain the film so much as
commercial carbonate of soda.

The hydrokinone developer for bromide plates is mada
as follows : —

1. — Hydrokinone ... ... ... 10 grains .

Water ... ... ... ... 10 ounces ; ,

2. — Carbonate of potash, a saturated solution in water.

To each ounce of No. 1, one drachm of No. 2 is added, and
about 10 drops of a (10 grains to tlie ounce of water)
solution of chloride of sodium.

For removing the yellow colour so often seen in alkaline
developed gelatine negatives, also for the use of ithe
alum bath to avoid frilling, see the chapter on " Defects
in Grelatine Negatives." ^i

The fixing bath used will be found at page 154.

CHAPTEK XXIII.

TDKVKLOPMENT OF GKLATINE PLATES WITH
FERROUS OXALATE.

'Development with ferrous oxalate is umquestionaWy the
favourite method with the writer, though his partiality for
it is not shared hj a great many photographers. For
purity of image and general excellence of quality, he
believes that no developer can he compared with it.
There can be no doubt that it is rather more expensive
than the alkaline pyrogallate developer; but not very
much so, since several plates may be developed with the
Same quantity of developer. It must not, however, be
forgotten that after each plate is developed, a considerable
amount of soluble bromide finds its way into the solution,
-owing to the combination of the bromine liberated from
the reduced bromide combining with the potassium oxa-
late (see page 20). After many plates have been deve-
loped, the solution, however, is not beyond use, since a
few drops of a weak solution of sodium hyposulphite are
most effectual in giving it fresh developing power, and
placing in sunlight, with a few grains of tartaric acid,
seems to reduce the ferric salt to the ferrous state. The
following are different methods of preparing the solutions.
Simple form of Ferrous- Oxalate JJeveloper. — A saturated
solution of the neutral potassium oxalate is first pre-
pared. A crystal of oxalic acid is next added, to prevent
the slightest trace of alkalinity. At one time we used to

150 FEREOUS-OXALATE DEVELOPMENT.

add ferrous-oxalate to a boiling potassium oxalate solu-
tion, only so much of the oxalate being added as to leave
a slight portion of the ferrous compound undissolved.
We prefer now to add the ferrous oxalate to the cold satu-
rated solution of the potassium salt, and to allow them
to remain in contact with one another for twenty-four
hours, shaking occasionally. The clear solution can be
decanted off. This method prevents the deposition of
crystals on the sides of the bottles, which always is
the case if the ferrous oxalate be heated with the potas-
sium oxalate. The solution will be of a deep red colour.

The ferrous oxalate solution rapidly oxidizes by con-
tact with the air, as already hinted at, and our own prac-
tice is to fill 4-ounce bottles with it, cork them up, and
then to lute the corks with solid parafiin. Mr. Warnerke
has a still better plan. He uses a stoppered bottle having
an opening near the bottom, such as can be procured at
any chemical dealer's. Into this opening he fits a cork
carrying a small glass tube ; on to the end of this (out-
side the bottle, of course) he fits a piece of india-rubber
tubing, and connects this with a similar piece of bent
glass tubing, which reaches nearly as high as the top of
the bottle. He fills the bottle two-thirds way up with
the ferrous oxalate solution, and then pours in a layer of
liquid paraffin oil. This prevents any access of air to the
solution. To get at the solution, the bent tube is turned
down below the level of the paraffin, and the developing
cup or bottle filled.

Dr. Eder's Ferrous Oxalate. — Mr. York, working on the-
directions of Dr. Eder, gives the following formula : —

No. 1.
Ferrous sulphate ... ... 160 grains

Water ... ... ... ... 1 ounce

No. 2.
Potassium oxalate (neutral) ... 1 ounce
Water ... ... ... ... 3 ounces

FEKEOUS-OXALATE DEVELOPMENT. 151

This makes up 4 ounces of developer, and by using these
quantities, saturated solutions are olbtained. Personally,
we prefer 4 parts of No. 2 to 1 of No. 1.

Strong Ferrous Oxalate Developer prepared with Feri'ous
Sulphate. — A still stronger form of ferrous oxalate deve-
loper can be made by taking a saturated solution of potas-
sium oxalate, and adding to it crystals of ferrous sulphate.
These must be added cautiously, since part of the potas-
sium oxalate is converted into ferrous oxalate, . and the
remainder holds it in solution.

Mr. York's formula for the potassium oxalate may be
taken, and to it 200 grains of sulphate of iron be added
(powdered up in a mortar by preference). It will pro-
bably be found that some of the yellow oxalate will pre-
cipitate, in which case crystals of potassium oxalate must
be added to the solution till such precipitate is re-
dissolved.

Practical Instructions for Developing with Ferrous Oxalate.
— We wiU now suppose that we have a plate to develop
by ferrous oxalate, and trace the manipulation from the
beginning.

The plate is taken out of the slide in the properly-
lighted dark-room, and placed in a flat dish a little larger
in bottom area than itself. If the plate has a glossy sur-
face, and has been prepared with hard gelatine, we recom-
mend that it be soaked for five minutes in ordinary water,
in order to cause the gelatine to expand vertically, and
thus to soften the film. If the surface be matt, we
recommend that the plate be not wetted.

Two developing solutions are prepared. Enough
ferrous oxalate (by preference that prepared by the
second method) is diluted with half its bulk of water,
when the slight precipitation of the yellow ferrous
oxalate may take place. Sufiicient of the dilute solution
to well cover the plate is poured over its surface, and
watched for half a minute. If the image appears to be
developing fairly well, and detail coming out, this deve-

152 FEREOUS-OXALATE DEVELOPMENT.

loper is continued till all detail appears, when it is poured
iback into a developing cup, and density obtained with
fresh undiluted solution of ferrous oxalate, to which^ 20
drops to each ounce of a 20-grain solution of potassium
bromide are added. This gives density. The develop-
ment should be continued till the image appears well on
the surface of the gelatine next the glass plate, supposing
the film to be of medium thickness. Many people recom-
mend the dish not to be rocked to and fro ; but we think
it better to give a gentle motion to the liquid, as we have
found that sometimes fog and stains like marble are
induced by not so doing. The plate is next rinsed under
the tap, and placed in the alum bath, made as follows : —
Potash-alum, a saturated solution in water. It must not
be supposed that this bath merely prevents frilling. It
cloes more : it decomposes any calcium oxalate which may
Tbe formed by the water (containing lime) with which
the developer is washed oif. After a couple of minutes'
immersion in this bath, it is placed in the fixing bath,
and when all the silver bromide and iodide have been dis-
solved, it is washed under the tap, and the operations
given at page 155 repeated.

Instead of the image coming out properly with the
developer as indicated above, we will suppose that after
a half a minute the high lights only slightly appear. In
this case, to each ounce of concentrated developer 20 drops
of a solution of sodium hyposulphite made as follows are
dropped into a cup, and the dilute developer poured on
to the hyposulphite : —

Sodium hyposulphite ... ... 2 grains

Water ... ... ... ... 1 ounce

The mixture is once more poured on to the plate, and if
not much under-exposed for the normal developer, the
details should appear rapidly and with good gradation.
When all detail is out, the plate is washed, and the strong
ferrous oxalate solution, with the bromide, is applied as
Lefore, to secure density.

FEEROTJS-OXALATE DEVELOPMENT. 153

Supposing the plate to be over-exposed, wheu the first
developing solution is applied, the details will begin to
appear too rapidly. It should be immediately poured off,
and the plate flooded with a solution of potassium bro-
mide (5 grains to the ounce of water), which should be
allowed to soak into the film for a couple of minutes. It
is then drained off. To each ounce of the weak solution
20 drops of the same solution may be added, and the
developer applied again. This should allow the image
to come up properly without flatness, but it may be
•desirable to finish with the strong solution as before.

Some photographers like to use old ferrous oxalate
solutions, to which sodium hyposulphite is added at the
•commencement. This no doubt gives brilliant pictures,
but is apt to cause exposure to be prolonged. On the
whole, we recommend tolerably fresh ferrous oxalate if
the greatest benefit is to be obtained from the developer.
The developers made by mixed solutions of ferrous sul-
phate and potassium oxalate are not so strong as those
prepared by the first method, and an allowance should be
made for the difference. The latter is the more energetic
developer of the two, and for instantaneous views it is
recommended. Either developer, however, can be used
vrith the sodium hyposulphite, and the difference between
their detail-giving powers is then very small.

There are some plates which are unsuited for ferrous
oxalate development. They are generally those which
are prepared in hot weather with soft gelatine. The
film shows reticulation, and the image appears granular.
In that case resort should be had to alkaline development,
by which this evil will be lessened. A plate worth
using, however, should always stand development with
ferrous oxalate.

CHAPTER XXIV.

FIXING, INTENSIFYING AND VARNISHING
GELATINE NEGATIVES.

Fixing the Negatives. — A fair fixing Ibatli is as follows : —

Hyposulphite of soda ... ... 1 ounce

Water ... ... ... ... 10 ounces

A weaker solution, however, may be used with some plates.
This reduces the chance of frilling. The use of potassium
cyanide was said to he inadmissable, as it attacked the
image. With some plates the following is successful : —

Potassium cyanide ... ... 50 grains

Water 10 ounces

Before fixing the negative, it is advisable, in order tO'
avoid all danger of frilling, as we have said in the pre-
vious chapter, to immerse it in an alum bath, which con-
sists of a saturated solution of crystallized potash alum.
The negative should be rinsed both before and after
immersion. Two to five minutes in such a bath should
be sufficient. The plate is next rinsed, and placed in the
fixing bath. A flat dish may be used ; or, what we prefer,
is a dipping bath such as used for the old wet process, as
there is no evaporation, to speak of, when it is used, and
the hyposulphite solution may be used until its fixing
power is exhausted. And here it is that the use of iodide

FIXING NEGATIVES. 155

in the emulsion is disadvantageous. The hyposulphite
attacks iodide much less rapidly than it does bromide ;
hence a plate prepared with iodide takes longer to fix.

After fixing the negative it has to be thoroughly
washed (unless it has to be intensified by Edwards' in-
tensifier, see page 158). There are various contrivances
for effecting this. A trough with vertical grooves to fit
the plate is sometimes employed, the water entering in at
the top, and being withdrawn hj a small tap from the
bottom. This is a good plan where many negatives have
to be washed, since the heavier saline solution sinks to the
bottom of the water with which the trough is filled.
Where only a few negatives are to be washed, flat dishes
answer, about four changes of water being given, each
change being made at the end of every half hour. To en-
sure thorough elimination of the hyposulphite, the plate
may be subsequently immersed in the alum bath, and again
washed. It must be recollected that thorough washing of
any film depends on its thickness, and we may say that, as
a rule, we consider six hours not too long washing for a
thick film. When the plate is considered washed, and
is not to be intensified, it may be placed in a rack and
allowed to dry spontaneously. If rapid drying be re-
quired, it may be flooded three times with methylated
spirit, when it will dry very readily, and can even be accel-
erated by a gentle heat.

Silver Intensification. — When the intensification of a
gelatine negative by any plan other than with silver is-
employed, the stability of the image is somewhat iin-
certain ; though, as we shall point out, there are methods-
which seem to give it ; but so far the test of time is
wanting in them. We shall commence with silver in-
tensification, which is uncertain in many cases, owing to
the tendency of the silver to combine with the gelatine^
and thus to stain the film. Now, as a rule, a gelatine
negative has to be intensified after fixing, since the
opacity of the film is usually so great that the operator

156 SILVER INTENSIFICATION.

is unaware what density his negative has taken under
development. It may be laid down as an axiom that,
to be successful, the whole of the hyposulphites of soda and
silver must be eliminated from the film, and where the
film is of any thickness, this is by no means rapidly effected
by simple washing. After the plate has been thoroughly
washed, the gelatine film may be made more secure by
applying to it a solution of peroxide of hydrogen in water.
A drachm of what is called a " 20-volume solution " to 5
ounces of water is sufficient. When it has soaked in this
for half an hour, it is again washed, and intensification
can commence. Another plan is, after thorough washing,
to immerse the plate in fresh alum solution for half an
hour, again washing thoroughly, and allow to dry, and
then the intensifying may be proceeded with. Those
who may have endeavoured to intensify with pyrogallic
acid and silver a negative treated in the ordinary way, will
find that red stains occur almost invariably where the
film is thickest — that is, where the hyposulphites have
not been thoroughly eliminated ; and to eliminate them
this extra precaution above indicated is necessary. The
following intensifying solution is recommended : —

Ferrous sulphate ... ... 5 grains

Citric acid ... ... ... 10 ,,

Water 1 ounce

To this, one or two drops of a 20-grain solution of
silver nitrate are added per ounce of solution, and the
plate intensified as if it were a wet plate ; that is, the
solution is kept in motion over the surface till sufficient
density is attained. Now, it by no means follows that a
film thus intensified would befree from a liability to change
in the presnce of light, since the silver might partially
combine with the gelatine. After density has been at-
tained, the plate is washed, and put in a dish containing
common salt, and once more passed into the fixing bath
lor a few seconds, again washed, and then dried.

SILVER INTENSIFICATION. 157

The following intensifying solution may also be
used : —

Pyrogallic acid ... ... ... 1 grain

Citric acid ... ... ... 1 „

Water ... ... ... ... 1 ounce

Sufficient of this is taken to cover the plate, and to it is
added 2 or 3 drops per ounce of solution of a solution
(20 grains to 1 ounce of water) of silver nitrate. We
may remark that some people flood the gelatine films,
before applying either of the above intensifying solutions,
with a pale sherry-coloured solution of iodine, which is
dissolved in a solution of 20 grains of iodide of potassium
in 1 ounce of water. There can be no harm in this, and
there may be good.

Success in intensifying by either of these methods the
writer has found to be more certain when the ferrous
oxalate developer has been used in lieu of the ordinary
alkaline developer.

We have heard of failures with these methods, and
when traced to their source have almost invariably found
that they arise from intensifying negatives which have
been exposed to the air. It is no uncommon thing to
see on such an iridescent film, to which, if silver be
applied, staining is certain. In this case a very dilute
solution (5 grains to the ounce of water) of potassium
cyanide should be applied, and, after well washing, the
intensification may begin ; cyanide will generally remove
any red stain which may occur if the above hyposulphite
destroying solutions have been applied first.

Mercury Intensifiers. — The next intensifiers are the
mercury intensifiers, some of which are most uncertain in
their action, and in the permanency of the acquired
density. The negative can be intensified either imme-
diately after the washing which follows the fixing, or it can
be employed upon a negative which has been dried. In
the latter case the negative must be steeped for a minute

158 MERCDEY INTENSIFIEKS.

or two in water. Mr. England recommends the following
as giving him what he desires : —

Mercuric chloride (bichloride of

mercury) 20 grains

Ammonium chloride ... ... 20 ,,

Water 1 ounce

After the negative has been thoroughly washed, the
above solution is poured over it till the surface assumes
a grey tint. After a thorough wash (see page 154) a weak
solution of ammonia (10 drops to 1 ounce of water) is
applied till a dark tone is assumed by a reflected light, and
brown by transmitted light. With collodion the intensity
thus given is unstable, and the film has a tendency to
bleach ; but with gelatine negatives it is said to be per-
manent, though we do not vouch for it.

The next intensifier is one in which we have the
greatest faith, as it gives a negative a beautiful black
colour. Two solutions are made as follows : —

No. 1. — Mercuric chloride (bichloride of
mercury)

Bromide of potassium

Water

No. 2. — Nitrate of silver...

Water

100 grains
100 „

10 ounces
100 grains

10 ounces

To No. 2 is added cyanide of potassium, but not suffi-
cient to dissolve the last trace ot the precipitate which is
formed on the first addition of the cyanide. It is conveni-
ent to make up a 100-grain solution of cyanide of potas-
sium (which, be it remembered, is a deadly poison, and
should be handled with caution) to 1 ounce of water, and
to add this to the silver nitrate solution till the desired
end is attained. The plate, after being dried, is soaked in
water for a couple of minutes, and then immersed in a dish
containing No. 1. After a few minutes the image will
be found thoroughly bleached, when it is taken out and

3IEECURY INTENSiriERS. 159

washed for a quarter of an hour. It is then placed in
a dish of No. 2 till the bleaching at the back of the
plate gives place to a blackening, when it is taken out
and washed thoroughly. It does not do to leave the plate
too long in No. 2, as it is apt to reduce the intensity after
a certain point is reached. Should the negative be now
too dense, the density may be gradually and evenly re-
duced by immersing it in a weak solution (20 grains to
the ounce of water) of hyposulphite of soda. This will
take away all the acquired density if the immersion is pro-
longed. The negative, after this method of intensifica-
tion, looks denser when wet than when dry ; allowance
must be made for this.

To Mr. B. J. Edwards, we believe, is due the credit of
adding sodium hyposulphite to the mercury intensifier.
This formula is as follows : —

No. 1.
Mercuric chloride (bichloride of

mercury) ... ... ... 60 grains

Water ... ... ... ... 6 ounces

No. 2.
Potassium iodide ... ... 90 grains

Water ... ... ... ... 2 ounces

No. 3.
Sodium hyposulphite ... ... 120 grains

Water ... ... ... ... 2 ounces

The iodide solution is poured into the mercury solution,
and then the solution of hyposulphite, which dissolves the
iodide of mercury which has been formed.

The negative is fixed and washed, and the plate im-
mersed in the above solution. Mr. Edwards says of it : —
^' The intensifier acts very quickly, a few seconds being
sufficient to give printing density to the thinnest negative.
If required to work slower, add more hyposulphite, which
will also alter and improve the colour of the negative.

160 URANIUM INTENSiriEE.

The shadows remain quite clear, there is. no loss of detail,
and the colour of the negative is all that can be desired.
The negative must finally he well washed."

This intensifier we, however, do not like, as the nega-
tives turn yellow after a time.

The Platinotype Company supply an intensifier, which
is also a mercury one, but it is in combination with a
platinum salt. We have tried it, and it is excellent, and
apparently gives permanent intensity. The solution sup-
plied is diluted to half its bulk, and the negative, after
thorough washing, immersed in it. A chocolate colour
is assumed by transmitted light, and a jet black by re-
flected light. The density-giving qualities of this intensi-
fier are very great.

Uranium Intensifier. — Dr. Eder, in his " Modern Dry
Plates," has recommended an uranium intensifier, which
is made as follows : —

Uranium nitrate... ... ... 15 grains

Potassium ferricyanide... ... 15 „

Water ... ... ... ... 4 ounces

Before using this, the plate must be thoroughly washed
(see page 155), as traces ofhyposulphite cause a reduction
of the uranic salt, and a consequent slight chocolate-
coloured veil over the shadows. The plate is immersed in
the solution ; the details in the shadows are first attacked,
and then the half-tones, and finally the high-lights. This
intensification is permanent, and can be used with much
advantage. We prefer this one on account of its simplicity
and permanency. Dr. Eder says that if a negative will
not acquire suificient intensity with uranium, it rnay be
laid aside as useless, and with this we agree.

Varnished negatives may be intensified by removing
the varnish first in warm methylated spirit, and, after
rinsing under the tap, a tuft of cotton-wool should be
applied to the surface. We think that there is but little
more to be said regarding intensifying a negative. If

VARNISHING THE NEGATIVE.

161

it be weak and full of detail, we mucli prefer to make a tliin
transparency in the camera, and from this another
negative by contact. By this means intensity can be
given to the reproduced negative, which it is almost^ im-
possible to give to the original, so that all the rapidity
of the gelatine plates is secured, together with the ad-
vantage of the collodion film for intensifying. We can
strongly recommend this plan to our readers, as it has
been most successful in our hands.

Varnishing the Negative. — In order to prevent staining
of the film by contact with silver paper during printing,
a coating of varnish should be applied to the negative ;,
but in order to avoid any chance of marking of the film,
and before any varnish is applied, it is preferable that it
should receive a coating of plain collodion. If it has
received one to avoid frilling, it will be unnecessary to
give it another. When collodion is used, the writer's
experience tells him that almost any varnish will answer.
Enamel collodion is, perhaps, the best to employ ; or it
may be made by dissolving 6 grains of tough pyroxylin
in half-ounce of ether ("725) and half-ounce alcohol (•820).
The collodion is poured in a pool at the upper end of the
dried plate, and flowed first to the right-hand top corner,
next to the left-hand top corner, third to the left-hand
bottom corner, and finally, as much as possible is drained
off in the bottle at the bottom right-hand corner, giving
the plate a gentle rocking motion in order to cause all
lines to coalesce. The plate is then set up and allowed
to dry. For a varnish, Mr. England uses seed lac in
methylated spirit (a saturated solution), and then thinned
down till it is of a proper consistency. The Autotype
Company prepare a special varnish for gelatine plates, as
do other commercial houses. To apply the varnish, the
plate should be gently warmed over a spirit-lamp or before
the fire to such a heat that the back of the hand can only
just bear the touch of the plate. The varnish is applied
like the collodion. After draining off all excess, and rock-

162 VARNISHING THE NEGATIVE.

ing the plate, it is warmed till all spirit has evaporated, and
till the lilni is glossy. A lack of warmth will cause the film
to dry " dead." "Where many prints are not to be taken,
it is believed that the film of collodion alone is a sufficient
protection against the silver nitrate of the paper combining
with the gelatine, and so causing a discolouration. If a
negative does get discoloured through this, a very dilute
solution of potassium cyanide will usually clear away
any marking that may have been made. But great care
must be taken to use this solvent in a dilute state, as when
strong it attacks metallic silver when in such a fine state
of division as that in which it is to be found in the a;ela-
tine plat p.

CHAPTEE XXV.

GELATINO-CHLORIDK EMULSION.

Dk. Edee and Cavtain Pizzighelli worked out a
gelatino-chloride emulsion, and a satisfactory method of
developing it when made. The formula they gave is as
follows : —

Sodium chloride ... ... 7^ grains

Gelatine, hard and soft (mixed) 25 „
Water 3^ di-.

This is emulsified by adding to it 15 grains of silver dis-
solved in 2 drachms of water. The silver may be precipi-
tated and re-dissolved by ammonia, or it may be boiled
and treated with ammonia, as given in Chapter XHT.,
page 97.

The method we adopt is the same as given in
Chapter IX., viz., the boiling process.

I. — Sodium chloride ... ... 80 grains

Nelson's No. 1 gelatine ... 30 „

Hydrochloric acid ... ... 5 minims

Water ... ... ... ... 1-^ ounces

n. — Silver nitrate 200 grains

Water ... ... ^ ounce

III. — ^Nelson's No. 1 gelatine ... 30 grains

Water ... ... ... ... 1 ounce

The above are made into solutions, and in the dark room.

164 GELATINO-CHIiOEIDE EMULSION.

II. and III. are mixed at a temperature of albout 100°, and
then I. added, as described in Chapter IX. The emul-
sion may he boiled for a quarter of an hour, or left un-
boiled. In either case, 240 grains of mediumly hard gela-
tine, or a similar total quantity of equal parts of hard and
soft gelatine dissolved in two ounces of water, are added.
After setting, the emulsion is washed, and plates coated
as described in Chapter XIX.

The plates, when made from unboiled emulsion, are very
transparent, and of a deep orange colour by transmitted
light, whilst those made from the boiled emulsion are blue
or sap-green.

Though extremely sensitive to daylight, they are much
less so to gaslight ; so that more artificial light may be
used during development than with bromide plates. This
will be found to be of great advantage, as the plates may
be examined from time to time within a reasonable dis-
tance of a gas flame, and the density thus regulated to-
great nicety.

The exposure of the plates (made with unboiled emul-
sion) to diffused daylight will vary from one to five
seconds, and the plates prepared with the boiled emulsion
for from a quarter to two seconds, according to the density
of the negative ; whilst to an ordinary fish-tail gas biirner
or paraffin lamp at 12 inches distance the former will
require from five to twenty minutes' exposure, and the
latter from half-a-minute to three minutes. Mr. A.
Cowan states that a very reliable method of exposing
when a number of pictures are required exactly alike — or
when it is necessary to work at night — is to burn one
inch of magnesium ribbon at from 9 to 24 inches from
the negative, according to its density.

Development is effected by the ferrous citrate or ferrous
citro-oxalate developers, or by hydrokinone diluted to-
quarter strength, to which a few drops of a saturated
solution of sodium chloride are added.

UELATINO-CHLOEIDE EMULSION. 165

The feiTOUs-citro-oxalate developer, as introduced by
the writer, is made as follows : —

Potassium citrate (neutral) ... 100 grains
Ferrous oxalate ... ... 22 „

Water ... ... ... ... 1 ounce

The potassium citrate is first dissolved in a flask by
heat, and, when nearly boiling, the ferrous oxalate is
added, and shaken up in it, a cork being used to prevent
the access of air to it. This quantity of ferrous-oxalate
should just dissolve. It may be cooled by allowing cold
water to flow over it, and should then have a citrony-red
colour.

A weaker solution is made the same way with the
following formula : —

Potassium citrate ... ... 50 grains

Ferrous oxalate... ... ... 12 ,,

Water 1 ounce

These solutions keep well when corked up in bottles.
There is no deposit from keeping even when oxidized,
which is shown by the solution turning an olive green
colour.

The development is carried out in a dish, which is kept
locking. An unboiled emulsion gives a warmer tone
than a boiled one.

The following is the method of making ferrous citrate
■developer according to Dr. Eder and Captain Pizzighelli's
plan : — 600 grains of citric acid are dissolved in 4| ounces
of water with the aid of heat, and exactly neutralized with
ammonia ; 400 grains of citric acid are then added, and
the bulk of the fluid made up to 9 ounces of water ;
3 drachms of this solution are mixed with 1 drachm of a
saturated solution of ferrous sulphate and 12 minims of
a solution of sodium chloride (30 grains to the ounce of
water).

Ferrous citrate may be purchased and dissolved in a

166 ■ GELATINO-CHLOEIDE EMULSION.

saturated solution of ammonium citrate, adding a little
citric acid to give a clear picture.

Mr. A. Cowan has made a large number of experiments
with, chloride emulsion, and by a modification in develop-
ment has been able to produce images which, by trans-
mitted light, give any tone, Irom warm to black.

No. 1, for Cold Jones.
Potassium citrate ... ... 136 grains

Potassium oxalate ... ... 44 „

Hot distilled water ... ... 1 ounce

No. 2^ for Warm Jones.

Citric acid ... ... ... 120 grains

Ammon. carb. ... ... ... 88 „

Cold distilled water ... ... 1 ounce

No. 3, for E/ctra Warm Jones.
Citric acid ... ... ... 180 grains

Ammon. carb. ... ... ... 60 „

Cold distilled water ... ... 1 ounce

To 3 parts of each of these add 1 part of the following

at the time of using : —

1. Sulphate of iron, 140 grains ; 2. Sulphuric acid, 1 drop ;
3. Distilled water, 1 ounce.

During development, keep the dish rocking ; the time re-
quired will vary from one to ten minutes, according to the
developer used and the density required. • No. 1 is the
quickest. No. 3 the slowest developer.

A great variety of tones may be obtained by mixing,
the first and last developers together in different propor-
tions, and altering the exposure to suit the developer.

The addition of from five to ten minims of a 10 per
cent, solution of sodium chloride to each ounce of deve-
loper considerably modifies the colour, and allows of a
much longer exposure. It is valuable when very rich,
warm tones are required.

GELATINO-CHLORIDE EMULSION. 1G7

btill further differences in colours may be obtained by-
mixing one of the following with any of the preceding.
The first three are, however, what Mr. Cowan recom-
mends : —

No. 4.

Magnesium carbonate... ... 76 grains

Citric acid 120 „

Water ... ... ... ... 1 ounce

■ No. 5.

Sodium carbonate (common)... 205 grains

Citric acid 120 „

Water 1 ounce

To '6 parts of these 1 part of the sulphate of iron solution
is added, as with Nos. 1, 2, and 3.

After development, the plates are washed, and fixed in
clean hyposulphite of the usual strength (page 154).

The plates are then finally washed as usual.

The hydrokinone developer is made as follows : —

1. — Hydrokinone ... ... ... 6 grains

Water ... ... ... ... 10 ounces

2. — Potassium carbonate, a saturated solution in water,

?). — Sodium chloride ... ... ... 20 grains

Water ... ... ... ... 1 ounce

To every ounce of 1, half a drachm of No. 2 and 4 drops
of No. 3 are added. The image should develop a beauti-
ful black colour, without any stain. The ordinary alka-
line developer may also be used with these plates, omitting
three-quarters of the ammonia solution recommended.
The image will be of a sepia brown colour, as a rule.

Mr. Arnold Spiller has introduced a developer which is
somewhat expensive, but gives excellent results for these
plates. The tones he obtains are beautiful, varying from
purple to orange.

168 GKLATINO-CHLOEIDE EMULSION.

For the development of gelatino-chloride films, the
following solutions are required : —

D. — Hydroxylamine hydrochloride ... 15 grains
Alcohol ... ... ... ... 1 ounce

E. — Potassium carbonate ... ... fi drams

Water ... ... ... ... 1 ounce

F. — Ammonia '880 ... ... ... 1 dram

Water ... ... ... ... 1 ounce

A normal exposure for use with this developer is about
ten minutes, one foot from a fish-tail burner. For a
sepia-brown tone take half a dram of D, 40 minims of E,
and 1 ounce of water. For chocolate tones, the above
mixture, to which has been added 1 minim of F. A
purple image is obtained with half a dram of F and half
a dram of D diluted with 1 ounce of water. To obtain
the dichroic* tone, expose fivefold normal, and develop
with half a dram of 1), 6 minims of F to 1 ounce of
water.

Plates prepared with the emulsion, if kept exposed to
the air, are apt to tarnish, and then develop badly. They
should bo carefully wrapped in. paper, and sealed up in
^infoil.

Lantern slides and transparencies may be taken in
the camera or by contact with these gelatino-chloride
plates.

* Mr. Spiller remarked that a dichroic image was formed when the tol-
. lowing proportions of developer were used. When moist, the colour given
was chestnut ; and when dry, deep purple.

CHAPTEE XXVI.

ACETO-GELATINE KMULSIONS.

Dr. H. W. Vogel experimented in the production of
emulsions which should combine the rapidity of the ordin-
ary gelatine plate with the ease of coating of a collodion
emulsion. His emulsions are made as follows, according
to the English specification of his patent, lie rightly
claims for himself the novelty of being able to rtiix a solu-
tion of pyroxyline with one of gelatine, and thus getting
the advantages of both emulsions. Any gelatine emul-
sion (such as that described, for instance, in Chapter
IX.) is prepared as usual, and the pellicle dried. This
dried emulsion is then dissolved in one of the fatty acids
(such as formic, acetic, or propionic ; acetic acid, how-

. ever, by preference, on account of its cheapness). To
effect this it is warmed in the acid, using three to ten
times as much acid as pellicle. The quantity of acid
depends on the kind of gelatine originally employed.
Sufficient alcohol is now added to this, till it is of proper
■consistency for flowing over the plate when heated to a
temperature of about 90° F. When cold, the emulsion
sets in a gelatinous mass. Plates may be coated with this
emulsion like collodion, and any excess drained into the

, bottle. In very hot weather, however, it is better to lay
the plates flat lor a short time, since sufficient emulsion
is with difficulty retained if they be thoroughly drained.

170 AOETO-GELATINE EMULSIONS.

In order to give tenacity, Dr. Vogel, as before stated^
mixes pyroxjline with his emulsion.
His Ibrnmla is this : —

Pyroxyline 20 grains

Acetic acid 1 ounce

Alcohol ... ... ... ••• 1 „

This form of collodion is mixed with equal quantities of the
gelatine emulsion just described. The plates formed by
this coUodio-gelatine emulsion can be used wet or dry.
Another method Dr. Vogel describes, which is as follows.
Collodion emulsion is prepared in the ordinary way, and
dried ; 70 grains of the pellicle are dissolved in 3 ounces
of alcohol, and If ounce of acetic acid. 20 grains of
gelatine are dissolved in 3| drachms of acetic acid, and
added to it. Plates are coated in the ordinary manner
by it.

A plan which we adopted before the publication of the
formula was to take gelatine pellicle (say 50 grains), dis-
solve by aid of the heat of hot water in the smallest
quantity of acetic acid, adding drop by drop till the solu-
tion is perfect. Methylated spirit was added tiU it flowed
nicely over a trial plate, when it was filtered through
cotton wool, washed, and was then ready for use. The
plates must have a very adhesive substratum ; Vogel' s,
given at page 115, is effective, whilst another is india-
rubber in solution made by dissolving india-rubber paste
in benzole till it has the consistency of cream. There is a
tendency, however, with the latter for the film to crack,
with the former none whatever.

The drawback to this process is the smell of the acetic
acid, which is decidedly objectionable. Again, too, it is
of necessity a more expensive process, since the solvents
of the gelatine are not as common as tap water. On the
other hand, the negatives obtained by it are excellent ;
the gelatine is apparently changed in quality, and allows
the developer to permeate easily. The sensitiveness of

ACETO-GELATINE EMULSIONS.

171

the emulsion is slightly diminished according to our ex-
perience, but there is a perfect immunity from spots of
any description. There is one great convenience in this
emulsion, which is, that it can be kept in a bottle corked,
and used for coating plates as required, instead of having
to coat more plates than sometimes may be convenient.
Care must be taken, in coating the plates, that the emul-
sion does not run into ribs. The plates should be rocked
as ^^'ith collodion emulsion, and then there is no danger
of this defect.

For developing. Dr. Vogel recommends the following
as giving the best results : —

1. — Sodium mono-carbonate

(crystalline) ... ... 200 grains

Potassium bromide IJ to 2 ,,

Water ... ... ... f ounce

2. — Pyrogallic acid ... ... 50 grains

Alcohol ... ... ... 1 ounce

o. — Four parts of No. 1 are mixed with one part of
No. 2 for a normal exposure. The development must be
modified according to circumstances.

Dr. Vogel also uses Nelson's developer (page 146), and
the ferrous oxalate (page 150). In regard to this latter
he uses it in a somewhat different form to that given.
His formula is as follows : —

1. — Potassium oxalate (neutral) ... 10 ounces
Water 30 „

2. — Potassium bromide ... ... 12 grains

Water ... ... ... ... :|- ounce

3. — Sodium hyposulphite ... ... 2 grains

Water ... ... ... ... 1 ounce

4. — Ferrous sulphate ... ... 1 ounce

Water ... ... ... ... 3 ounces

172 ACETO-GELATINE EMULSIONS.

To develop, he mixed

No. 1 H ounce

No. 2 15 drops

No. 3* 15 „

When well mixed, he adds J-oiince of No. 4, and again
Taixes and applies to plates.

M. Konarzewski also gives a formula for a coUodio-
_gelatine emulsion : —

Alcohol -805 2 ounces

Glacial acetic acid ... ... 2 „

Pyroxyline ... ... ... 18 „

To this collodion 180 grains of gelatine emulsion are
added, and dissolved by aid of heating in hot water. He
recommends a substratum of albumen and silicate of
soda, which is also most effective for ordinary gelatine
emulsion plates, and may be added to the list given at
pages 113 and 114. It is made as follows : —

Stock albumen ... ... ... ... 1 part

Water 20 parts

Silicate of soda (satui'ated solution) ... 1 part

These are mixed, and after allowing any precipitate to
settle, the solution is flowed over the plate. With this,
as, indeed, with all substrata, the plates are free from any
tear-marking containing any nuclei of dust, if they are
-dried off over a Bunsen burner or a hot fire.

* If the plates be hard, he uses 30 drops of No. HI. instead of 15.

CHAPTER XXVIl.

GELATINO-BROMIDE AND GEL ATINO- CHLORIDE
PAPERS.

There are in the market at the present time two or three
gelatinized papers containing silver bromide, and it is to
be presumed that these papers are prepared with gela-
tine emulsion. At first sight, nothing would appear
simpler than to coat paper with an emulsion, but we may
at once say that it is not by any means so simple as it
seems. We will endeavour to give a description,
however, of a plan by which it can be accomplished in a
satisfactory manner. Firstly, the emulsion may be
gelatino-bromide, gelatino-iodo-bromide, or gelatino-
chloride, and may be prepared by any of the methods
given in the previous chapters. It may be boiled or not
boiled, according as great or little sensitiveness is required.
For our own part, we like a paper which is only moder-
ately sensitive, since there is no great need to take ex-
tremely rapid pictures. One thing, however, we may
remark, that with all emulsions the resulting colour of a
picture from a boiled emulsion has a greater tendency to
black than one prepared without boiling. This remark
also applies to gelatino-chloride emulsion, but with not
such force.

The amount of water with which the finished emulsion
is made will be found tu be about correct ; but the operator

174 GELATINO-BKOMIDE PAPERS.

must, by an experiment with an emulsion, judge whether
the gelatine he uses should be increased or diminished.
A hard gelatine, for instance, may allow dilution with
water. A golden principle to remember is, however, that
the thicker you require your film, the less water there
should be with the gelatine. If a film is Avanted as thick
as that for carbon printing, it can be obtained by using
100 grains of gelatine to each ounce of water, instead of
about as much to 4 ounces of water. If a thick film,
however, be required, we i-ecommend that the operations
we are going to describe be repeated twice — or even
three times. It must also be recollected that a paper
which is required for positive printing need contain less
sensitive salt than if it be required for the production of
negatives. In the former case, the emulsion may be
mixed with dovible the amount of gelatine given at
page 70, and be rather thin.

The paper to be coated should be thick Saxe paper, or
paper of that description, with not too high a glaze on it.
It should be cut up into the sized sheets required, and
carefully dusted from every particle of dust. The emul-
sion should be heated and placed im a shallow dish some-
what larger than the sheet to be coated, and the fluid
should be a quarter of an inch in depth. The dish must
be kept warm by placing it on a closed shallow tin box
containing water heated by a spirit lamp beneath, or some
other similar means. When heated to about 130° F.
(the temperature depending on the kind of gelatine em-
ployed), the paper is turned up for about a quarter of an
inch at one end, and the sheet coiled up in a roll, the coil
being made towards the turned-up end. The turned-up
end is placed on the emulsion, and the coil gradually
allowed to unrol itself till the whole surface except the
turned-up end rests upon the emulsion. After resting a
minute the end is seized by two hands, and a glass plate
(to the front of which is fastened a wooden roller, the
top on a level with the glass plate) having been made to

GELATINO-BEOMIDE PAPERS. 175

Test on the dish, the uncoated side of the paper is drawn
on to the plate, where it remains till it is set,* when it
is hung up by clips to dry in a cupboard or other place
free from dust.

The paper thus prepared should present an even iilm,
free from aU " ridges " or " tear-markings," and, when
developed, should present a vigorous image by transmitted
light. Another plan, and one which answers very admir-
ably in our hands, is to damp a piece of paper slightly
larger than the size of sheet required, and stretch it over
a glass plate, turning down the edges over the plate.
This damped plate is given a thin coating of gelatine
emulsion as in the ordinary way of using an emulsion,
-allowed to set, and then dried while still on the plate.
For this plan the emulsion may be made rather thinner
than usual. Another plan is to wax a plate with white wax
and ether, leaving but little on. Coat the plate as usual ;
when well set, lightly squeegee a piece of damped paper
on to the surface, and allow it to dry. By this means the
paper carrying the film can be stripped off from the plate.
To secure freedom from markings caused by the grain of
the paper, the paper may previously be coated with a
thin layer of gelatine by floating as above. The gelatine
in this case should have three-quarters of a grain per
■ounce of chrome alum added to it.

Another very convenient method of preparing sheets of
paper for negatives is by means of a perfectly straight

J)

Fig. 22.

glass tube of the width of the paper, round the ends of
which are two india-rubber rings, of the thickness of
which the film is desired to be.

* It is a good precaution to take to place a muslin-covered frame over the
glass holding the gelatinised paper to protect it from dust.

176

GELATINO-BROMIDE PAPERS.

If thought advantageous, a rod may be passed through
the tube, and bent round to join, and so to form a handle^
by means of which the tube will revolve as it passes over
any surface.

The paper is damped as before, and stretched on per-
fectly flat plate glass, the emulsion is poured gradually in
front of the roller, and the emulsion takes a fine layer of
a uniform thickness. For preparing paper for positives,
a couple of sheets may be placed back to back, and to-
gether passed through a trough of emulsion, the two being
raised vertically together, and dried together. The emul-
sion will not penetrate between the two sheets if properly
manipulated.

Another plan, which we first saw in Mr. H. Starnes's
hands, is very simple. The accompanying figure shows-
the section of a box. The emulsion is poured into A, and

Fig. 23.

the box, with the emulsion in it, is placed on damped paper,
the end, C, being placed at the edge of the paper. The
box is then tilted ; the emulsion flows into B, and flows-
through G, which is a fine slit (made by inserting a thin
card during the making of the box, and afterwards with-
drawing it). The slit may be covered with two fine pieces
of muslin if thought necessary, and the flow is thereby
regulated, as the end of the box is drawn over the paper,
leaving a track of emulsion. It will be seen that the box,
which in our case is made of well-shellaced wood, could
be made of metal (nickelled iron, for instance, or silver),
and a heating box introduced so as to keep the emulsion
at a proper temperature. When the box comes to the
end of the paper, the emulsion is tilted back from B into-
A, This plan also answers for coating plates.

GELATINO-BROMIDE PAPERS. 177

General Hints on Coating Paper. — When coating paper^
regard should be had as to whether it is for use in the
production of negatives, or merely for positives. In the
former case, it is evident that the paper should have on its
surface sufficient silver bromide, or its equivalent, to give
a dense image by transmitted light, and this can be done
in two ways, either by coating the paper with a film which
is equal in thickness to that of an ordinary plate — as
must be the case in some methods of coating we have
indicated — or else by reducing the amount of gelatine
in the emulsion. For a negative paper, we reduce the
gelatine given at page 70, viz., 240 grains, to 120 or even
100 grains. It is not more wasteful than using the bigger
bulk, as a thinner film is required, and the paper is more
pliable. For positive paper, the amount of gelatine may
be much larger when the film is of the same thickness.
Approximately, it may be said that a positive only requires
quarter of the density by transmitted light which a nega-
tive requires, hence the gelatine used for the former may
be 400 or 500 grains, as against 100 for the latter, to an
equal amount of bromide gelatine. When a bulk of emul-
sion is used (as it must be when paper is floated) a great
consideration is to keep the emulsion homogeneous. If
the temperatures be high, the small particles of bromide
have a tendency to sink to the bottom of the vessel, and
hence there is danger that a layer of gelatine may be
at the top surface, which will contain but little of the
sensitive salt. Hence our advice is to keep the tempera-
ture of the emulsion as low as possible during coating
the paper, consistent, of course, with keeping it fluid. A
thick layer of gelatine is very unmanageable on paper.
The paper, when drying, is apt to cockle, and unless a
small proportion of glycerine is added, the film is apt to
break and tear. For this reason, we add to the emulsion,
when the film is thick, about 20 drops of glycerine to each
ounce of emulsion ; and when the film is to be thin, a
couple of drops are sufficient to ensure a certain amount of

178 HINTS ON COATING PAPEK.

pliability. We do not like glycerine, as a rule, but in this
case there seems to be no help for it, particularly when
the paper is to be used in a dry climate. It may also be
said that a thin paper is iU adapted for coating, as then
the difficulties of liianipulatiou are much increased, and
there is'very little chance of getting uniformity of result.
In these methods of preparing the paper the desicca-
tion takes place much more rapidly than with a gelatine
plate, since there are two surfaces by which the drying
eifect of the air is utilized.

CHAPTEK XXVIII.

EXPOSURE OF THE NEGATIVE PAPERS.

At first sight there is a difficulty in exposing paper in the
tamera, hut there are three very ingenious contrivances
in which to overcome it. The home-made negative paper
is usually prepared in sheets, and not in lengths, and the
foUowing artifices may he employed to utilizing it.

Blocks of Sensitive Paper. — Blocks of sensitive paper
are very readily prepared in a similar manner to that
adopted for drawing blocks. To prepare a block, two
sheets of flat zinc or tin are cut of very slightly less (say
1-1 6th inch) than the size of the plate which the camera
is constructed to take. A dozen sheets of sensitive paper,
and a similar number of smooth orange and black paper,
are cut rather larger than the zinc on the plates. One
sheet of zinc is placed against a couple of battons fastened
on a board exactly at right angles to one another, and a
sheet of orange paper is put on the zinc plate, butting
also against the two battons. This is followed by a sheet
of sensitive tissue, sensitive side out, and then by an
orange and black paper, and again by a sheet of sensitive
tissue, and so on, taking care to keep the sensitive side
against the orange paper. When the last orange paper
is in position, the second plate is placed on the top, and
with a knife the block is trimmed, which, it may be

180 EXPOSUEE OF NEGATIVE PAPEK.

remarked, will only have to be done at one side and one
end. The top plate is marked, and strips of paper are well
coated with india-rubber solution, turned over each plate,
and well pressed into the paper edges held between them.
The india-rubber solution fastens the sheets of paper and
tissue together at the edges. To use the block, the top
tin and orange paper are removed by a point of a knife,
and it is placed in the slide. When exposure has been
given, the sensitive paper is removed in a similar manner,
and then the black and grange paper, and another sheet
is ready for exposure. Half a dozen blocks can be placed
in three double backs ; thus, in the slides, sensitized sur-
faces to take seventy-two pictures can be conveniently
carried. We have found that the ordinary orange paper
used by stationers has no noxious effects on the sensitive
films.

Holders for Single Sheets. — These can be made by any
one. Cardboard, a wooden board, or ebonite of exactly the
same size as the paper, are used as the backing. A mask
is made in brass or galvanized iron, and curled over this
board ; the paper is placed on the board, and the two are
slided into the mask. Again, a flat zinc mask of the
size of the plate, cut out within :^-inch of the margin,
may be placed in the slide, the paper on this, and then it
may be backed with a glass plate.

llie Roller Slide. — ^Many years ago Mr. Melhuish intro-
duced a roller slide for endless paper, and more than ten
years ago Mr. Warnerke introduced one which was very
admiralile in its working, and of which we have a most
excellent specimen which was adapted for. collodion emul-
sions. Lately Mr. Warnerke has still f ui-ther modified the-
slide, and made it more adapted for the gelatine. On the
Continent, several have been made in the same direction.
The latest, however, is the Eastman-Walker slide, which
is ingenious in construction, and very effective. The
following is taken from their printed description.

" The roll-holder consists essentially of a metal frame

EXPOSUEE OF NEGATIVE PAPER.

181

canying the spool wound with the supply of paper, and a
reel for winding up the exposed paper, suitable devices
for maintaining a tension upon the paper, and measuring
and registering mechanism.

The frame is hinged at both ends to the panelled board
which forms the back of the enclosing case. Fig. 24

Fig. 2i.

shows the holder with the case partly raised, fig. 25 the
movement raised for changing the spool.

" To fill the holder, the movement is raised as shown, the
spool inserted in its place under the brake, and fastened
with the thumb-screw on the side of the frame ; the pawl
on the tension barrel is thrown off, the band on the spool
broken, and sufficient paper drawn out to reach over the
bed to the reel ; the movement is shut down and fastened
.and raised at the reel end ; the paper is then drawn over
the guide roll and slipped under the clamp on the reel, and
the reel turned sufficiently to give the clamp a hold on the
paper. The pawl on the tension drum is now thrown in,
the tension put on by turning the tension barrel over to
the left until the paper is taut ; the movement is shut
•down, the case put on, the key is inserted, and turned \intil
;an alarum strikes once. The slide is drawn, and the
limits of the first exposure marked with a lead pencil.
The holder is then ready to attach to the camera. After
the first exposure, turn the key until the alarum strikes

182

EXPOSUEE OF NEGATIVE PAPER.

four times (three in the 4 by 5 holder), and this brings a
fresh sheet on to the bed for exposure. When the required
number of exposures have been made, take the holder
into the dark room, take off the case, and insert the point
of a pen-knife in the slot in the guide roll, and separate

Mg. 25.

the exposed from the unexposed by drawing it along the
slot. Throw off the pawl from the reel, and draw out
the exposed paper, and cut it oif at every fourth mark
(third mark in the 4 by 5 holder) with a pair of shears.
If any unexposed paper remains on the spool, draw over
the end, and attach it to the reel as before, and the holder
is ready for work again. The holder should be carefully
dusted out before filling."

CHAPTEE XXIX.

DEVELOPMENT OF GELATINO-BROMIDE PAPER
FOR NEGATIVES.

To develop any of the negative papers, whose manufac-
ture we have briefly described, the ordinary alkaline
developer, to which sulphite of soda has been added, may
be employed (see page 147), or the developer recommended
by Mr. Warnerke, or the Eastman Dry Plate Company.
The ferrous -oxalate developer is also excellent, but care
must be used to avoid stains, due to oxides of iron being-
formed. This is best attained by the use, after develop-
ment, of a saturated aqueous solution of alum, to which
one per cent, of sulphuric acid has been added. In every
case, before development, the paper is soaked in water,
and the developer applied. Density can be judged by
looking through the paper, but allowance must be made
for the density of the paper itself. A negative should
appear denser than it does on a glass plate. The develop-
ment should continue till but faint glimmers of white
paper are seen on the image, and therefore it will appear
under-exposed when fixed. After developing, it should
be passed through the alum bath, and be allowed to re-
main there for a quarter of an hour, when it should be
thoroughly washed for half an hour, and then be fixed, and
again washed. Several negatives may be developed at
one time, if two solutions in separate dishes are at hand,

184 GELATINO-BROMIDE PAPERS.

one being old restrained developer, and the other new.
If the image appears too quickly in the fresh solution,
it is immediately passed into the restrained solution, when
the development will progress more slowly.

One advantage of this paper, on which to take nega-
tives, is that commercially it can be made in long strips,
and used in a roller slide, and in any case the weight of
glass is avoided ; another advantage is that the negatives
may be used as reversed if required ; and a final one is that
the storage of these films is easy, a dozen or more going
in an envelope.

Mr. Warnerke has recently introduced into the market
several kinds of paper coated with gelatine emulsion, for
producing negatives.

Negative Tissue. — The first paper he calls negative tissue.
It consists of stout paper coated with gelatine and gelatine
emulsion, and so prepared that after development, fixing,
and drying, it can be peeled off from the paper, and is a
flexible negative, from which prints can be taken. The
following is the method of developing employed by Mr.
Warnerke : —

The exposed sheet of tissue is placed in a developing
dish and moistened under a tap with water (both sides),
so that it will adhere to the bottom of the dish. It is then
developed like an ordinary glass plate.

The following developer is especially recommended : —

A,

— Pyrogallol

... 6 grains

Citric acid

... 1 grain

Sodium sulphite...

... 12 grains

Water

... 1 ounce

B.

— Potassium carbonate

... 22 grains

Sodium sulphite...

... 6 „

Water

... 1 ounce

Eqiial proportions of A and B are mixed together and
applied to the plate. After development, the tissue is
rinsed in two or three changes of water, and immersed in

GELATINO-EROMIDE PAPERS. 185

^ strong solution of common alum, washed, then fixed
with hyposulphite of soda, and washed again thoroughly.
The tissiie bearing the image is next spontaneously dried.
In hot and dry weather it is advisable to add a small
■quantity of glycerine to the last washing water to render
the film more pliable. The film will be much improved
if the tissue, after the last washing, is squeegeed to a glass
plate prepared with talc (French chalk), and allowed to
dry on it. It may happen, especially when washing has
been too long, that the tissue will curl so much, that it
will be difficult to attach it to the glass or to lay it flat.
In this case it wiU be useful to press it for some time
between two glass plates, putting some blotting-paper
behind to remove the excess of water absorbed by the
film. When the tissue is quite dry, the film is detached
from the paper support, beginning hj one of the corners,
and slowly, but steadily, proceeding until all the film is
■detached.

The printing can be made from either side of the film,
making this negative tissue specially useful for many pro-
cesses in which reversed negatives are required. Finished
film negatives are best kept between sheets of stout un-
sized paper. Retouching on the film can be made as on
.a glass plate.

Negative Paper. — Mr. Warnerke also prepares another
paper which is very useful in some ways. It consists of
a film of gelatine emulsion, the portions' of the film which
do not contain the silver reduced by development being
removed.

In case an ordinary negative is required, the image
is first transferred to the flexible support as in carbon
printing, which is paper coated with an insoluble form of
gelatine, and to which the adhesion of another layer of
gelatine is incomplete ; that is to say, it can be separated
from it after drying. The paper negative, after it is deve-
loped, is squeegeed on to this, in the same way as on to the
glasSj in the following manner : —

186 GELATINO-BEOMIDE PAPEKS.

The two pieces of paper — i.e., the developed paper and
the flexible support — are placed face to face with a layer
of water between them, and then placed on a glass plate
or other smooth surface. A squeegee — a bar of thick
rubber let into a wooden holder — is then brought to bear
on the back of one of them, the water squeezed out, and
the two left in contact for a short time. The papers are
then placed in hot water of about lOO'^ F., the paper on
which the emulsion was originally coated is stripped off,
and the soluble gelatine, which is free from any image, is
washed away, leaving the image on the temporary sup-
port. When moist — either being moistened after drying,
or immediately after development — the surface of the
paper on which the image rests is transferred to a glass
plate, to which has been given a thin coating of gelatine,
the squeegee being again brought into requisition to bring-
the image in close contact with the surface of the glass.
When dry, the transfer paper peels off, and leaves the
image on the jDlate.

If a reversed negative is required, all that is necessary
is, after development, to squeegee the developed paper on
to a sheet of clean glass, instead of on to the temporary
paper support, and then to allow it to soak in warm water.
The paper backing is stripped off, and the gelatine film
left behind.

A paper which can be used for this process may be
prepared by giving it a coating of india-rubber solution, or
gelatine, and then a coating of normal collodion (10 grains
of pyroxyline to 1 ounce of ether and 1 ounce of alcohol).
The paper thus prepared may be coated by turning up the
edges to form it into a little dish, and holding it on a glass
plate. The emulsion is then allowed to set, and even-
tually hung up to dry.

The object of this process is that, no matter Avhat deve-
loper is used, the negative should be without stain, and
can be intensified by pyrogallic acid and silver (see page
157) without any chance of injury to it. The rationale of

GELATINO-BEOMIDE PAPERS. 187

the process is this : that a pyrogallic acid and also a hydro-
kinone developer renders the gelatine insoluble where the
metallic silver is reduced, the remainder being left soluble.
Now as the reduction of the silver takes place first on
the surface of the gelatine film, it is quite evident that
the soluble portion must be enclosed between the top sur-
face and the paper support, and that to get rid of it, the
back surface of the gelatine must be exposed, as in carbon
printing.

The warm A\-ater dissolves away the soluble gelatine, and
leaves the image of metallic silver and insoluble gelatine
behind, the latter being exactly proportional to the amount
of silver precipitated. Besides this, there is the silver
bromide which has not been reduced, left behind en-
tangled in the film, which gives greater density. This
may be removed by fixing in sodium hyposulphite as
usual if required. The insolubility of the gelatine seems
to be greatest 1st, where the pyrogallic acid (or hydro-
kinone) is in excess of that usually employed ; or 2nd,
where the alkali is in excess. With the ordinary strength
of developer, the insolubility appears to be but partial.

The developer for this negative paper is the same as
that for the negative tissue. The relative proportions of
the solutions A and B is very important. The object of
the developer is not only to render the image visible, but
also to render it insoluble. Excess of one solution over
the other can produce either total insolubility of the
whole film, or the reverse, too much solubility.

Double Surface Negative Paper. — The latest negative
paper which Mr. Warnerke has introdiiced is one which he
has patented, and consists of a paper coated on both sides.
It is claimed that by this means the grain of the paper
is done away with — or, rather, that it does not show. Th&
reason of this is that the gelatine emulsion with which the
back surface of the paper is coated receives the light ob-
structed by the grain. Where the grain is thin, the light
acts more vigorously than when it is thicker, and on deve-

^88 GELATINO-BKOMIDE PAPEES.

lopment the result is that the opacity remains nearly the
same in every adjacent part. This of course is more par-
ticularly true when the image is vigorous than when it is
weak. The paper used in this process is chemically pre-
pared, and made transparent to begin with, which is an
important point, since the more transparent it is •the
quicker it will print. Any developer may be used with this
tissue, either ferrous-oxalate or ordinary alkaline developer,
or the alkaline carbonate developer (see page 184). After
development the negative is fixed in the ordinary way
-after passing through the alum bath, and then washed, and,
if necessary, to remove any slight stain, is passed through
•a bath containing two or three drops of sulphuric acid to
the ounce of water, when it is again washed. The paper
may be dried in contact with glass, or not ; in the latter
case, and in order to render it flat, it is placed between
sheets of blotting-paper very slightly damped and put
under pressure, and, when limp, transferred to a pressure
frame, and kept there tiU dry. The negative prints very
nearly as rapidly as if it were on glass. Care must be taken
that both sides of the paper are well wetted before deve-
lopment, and that the bottom of the developing dish is
well covered with water, otherwise the gelatine surface
will stick to the bottom of the dish, and mar the negative.
During development the paper should be turned over fre-
quently to secure an evenness, and the image should appear
strongly on the surface of the paper which was away from
the lens.

Eastman! s ISlegative Films. — Eastman and Co. have intro-
duced negative paper which gives very good results. The
paper is ordinary unglazed paper, and for printing requires
making transparent by oiling. They recommend the fol-
lowing developer for it : —

^0. 1 — Sodium sulphite crystals (pui'e) ... 6 ounces
Distilled or boiled water ... ... 40 „

Pyrogallic acid 1 ounce

GELATINO-BEOMIDE PAPERS. 189'

No. 2 — Sodium carbonate (pure) :| pound

Water 1 quart

To develop, take in a suitable tray —

No. 1 ... ... ... ... ... 1 ounce

No. 2 1 „

Water 1 „

Immerse the exposed paper in clean cold water, and
with a soft camel's hair brush gently remove the adhering
air-bells from the surface. As soon as limp, transfer to
the developer, taking care to avoid bubbles, by gently
lowering the paper by one edge, so as to slide it under the
surface of the developer.

The image should appear in ten to twenty seconds, and
the development should be carried on in the same way as
for a glass dry plate. If the image appears too quickly,
and is flat and full of detail, add five to ten drops of the
restrainer —

Potassium bromide ... ... 1 ounce

Water ... ... ... ... 6 ounces

This will keep back the shadows, and allow the high
lights to attain density.

If the exposure has been too short, and the image does
not appear except in the highest lights, add, instead of
the restrainer, not to exceed one ounce of No. 2 ; this will
help to bring out the details, and compensate in a measure
for the short exposure. As soon as sufficient density is
obtained, slightly rinse the negative, and put in the fixing
bath-
Sodium hyposulphite ... ... 4 ounces

Water ... ... 1 pint

Common alum*... ... ... ■§■ ounce

To be mixed fresh for each batch of negatives.
* We do not recommend this.

190 aELATINO-BROMIDE PAPERS.

The completion of the fixing operation may he ascer-
tained hy looking through the film. When fixed, wash
in five or six changes of water for fifteen or twenty
minutes, and then lay the paper negative, face down, upon
a clean plate of glass or hard rubber that has been rubbed
over with an oily rag. Press the negative into contact
with the plate by the scraping action of a squeegee, and
allow to dry, when it will peel ofi^ from the plate with a
fine polished surface.

The ferrous oxalate developer also works well with
Eastman's improved negative paper, and we recommend
it for trial.

Oiling. — Lay the negative down on a clean sheet of
paper, and give it a coat of castor oil, applied with a rag.
Then press it with a hot iron until it shows an even dark
colour. Use plenty of oil. If the iron is too hot it will
dry out the oil, and it will be necessary to go over it with
the rag again. If the iron is not hot enough, it will fail
to cause the oil to penetrate the paper sufficiently. When
an even colour is obtained, wipe off the excess of oil with
a soft cloth, and the negative is ready to print.

Instead of using a hot iron, the negative may be held
over the stove until the oil sinks into the paper. The
hot oil expels the air in the paper and fills the pores, so
that on examination it will be found that the grain has
disappeared, leaving a fine ground glass effect. No oil
should be allowed to get on the face of the negative ; in
case it does, it may be removed with a cloth and a few
drops of alcohol.

Printing. — Thus prepared, Eastman's negative paper
will print remarkably free from grain, and quicker than
most pyro and ammonia developed glass negatives. To
print, simply lay the negative, with the glossy side up, on
a piece of glass in the printing frame, and print the same
as a glass negative. The negative does not require
fastening to the glass in any way. These negatives
should be kept between paraffined paper, or back to back

GELATINO-BEOMIDE PAPERS. 191

in a printing frame, or suitalDle box. If the oil dries out
after continued use, the negative may be re-oiled.

Retouching. — When the negative is to be retouched, as
in portraiture, it should be done after oiling. The paper
takes the pencil freely, and persons unskilled will find it
comparatively easy to " work " these negatives. Amateurs
can spot their own negatives, and work-in fine cloud
effects with a stump on the paper surface.

Intensification. — When it is necessary to intensify, it
may be done before oiling by soaking the negative in a
saturated solution of corrosive sublimate, washing, and
then blackening the image with a solution of ten drops of
strong ammonia per one ounce of water.

Where strong negatives are desired, add five drops of the
restrainer to the developer before using.

■ Wvxing the Negative.- — We have found that the negative .
may be waxed, instead of oUed, as the Eastman Company
recommend, and for most paper, such as we have pre-
pared, it is very efficient. A flat iron is heated, and
whilst drawn over the back of the negative a piece of
white wax is held against it. This leaves a layer of wax
on the paper. There will always be an excess of wax,
but this can be well removed by clean blotting-paper
being placed on the waxed surface, and the flat iron,
moderately heated, being drawn over the surface. Instead
of this method, a cream of white wax in turpentine, made
with the aid of heat, may be applied with cotton-wool or
a soft rag, all excess being wiped off.

CHAPTEE XXX.

DEVELOPMENT OF POSITIVE PAPER.

Fcm direct enlarged positives, the thinly-coated hromide-
papers are extremely useful, an optical lantern can he used,
and good prints secured with but short exposure. As
an example of the exposure necessary, we have pro-
duced an enlargement of six diameters by an exposure
of three minutes when using a triple-wick oil lamp as the
source of illumination. They also should take the place of
collodion transfers for working upon in oils or crayons.

Bromide Positive Paper. — To develop a .bromide or-
bromo-iodide emulsion, we recommend a ferrous oxalate
developer, using to every ounce employed about 10 drops
of a 20-grain solution of potassium bromide. This gives
a blacker image than the ferrous oxalate alone. One firm
recommend the following developing solutions : —

Stock Solutions-

1. — Chrome alum

Boiling water ...
2. — Oxalic acid

Water

A. — Potassium oxalate

Glycerine

Chrome-alum solution (No. 1)

Oxalic-acid solution (No. 2)...

Water...

100

grains

5

ounces

30
5

grains
ounces

4

ounces

i

ounce

15

11

11

ounces

DEVELOPMENT OF POSITIVE PAPER. 193

B. — Ferrous sulphate 4 ounces

Sulphuric acid ... ... 10 minims

Water ... ... ... ... 16 ounces

To develop, 8 parts of A are mixed with 1 part of B.

An excellent developer may be made by mixing equal
portions of the ordinary oxalate developer and the above.
For fixing —

Sodium hyposulphite ... ... 4 ounces

Water .. 20 „

They further recommend the following for bleaching
if necessary : —

A saturated solution of borax or

sulphuric acid ... ... 1 ounce

Water ... ... ... ... 100 ounces

And to harden the film, common alum (a saturated solu-
tion), or chrome alum of a strength 20 grains to each
ounce of water.

The bromide and bromo-iodide papers may also be deve-
loped with the usual alkaline developer, using citric acid,
to keep the solutions from discolouring. The addition of
sodium sulphite, as recommended by Mr. Berkeley, will
answer the same purpose. Hydrokinone and the car-
bonates of potassium or sodium (see page 148) are
also excellent, leaving no stain on the paper. The fixing
bath should be the same as above. When the washing is
complete, which will take two or three hours, the prints
may be toned if required. A beautiful brown-black tone
is given by a weak solution of ammonium sulphide, the
colour being permanent. All excess should, of course, be
well washed out. A solution of sulphuretted hydrogen in
water will answer the same purpose. Against the use of
such solutions we are aware that many photographers will,
metaphorically, hold up their hands, as they will remember
the dread they have of bringing any sulphur compounds in
contact with a print on albumenized paper. They should

194 DEVELOPMENT OF POSITIVE PAPER.

recollect, however, that tlie conditions are totally different.
It is the organic compound of silver which gives riBe to
fading, and not the sulphuration of the metallic silver.
Sulphide of silver is about as permanent a silver com-
pound as can exist, and there can be no danger oi its fading.
Grreat care must be taken to eliminate all traces of iron
salts by washing after development, when using the above
solutions, otherwise the whites will be dirty. This dirty
green appearance, however, may be got rid of by passing
the print through dilute hydrochloric acid.

An improvement in the tone may also be given by
using the uranium intensifier (see page 160). Resort
may also be had to gold toning ; but the above will give
almost every variety.

Chloride Positive Paper. — Recently there have been
brought into the market several brands of rapid printing
paper for development. Most of them are gelatino-
chloride papers ; some, however, have mixtures of bro-
mide with them. The advantage of this brand of paper is,
that it may be developed and then toned to almost any
desired colour. •

We have prepared paper which answers every requu'e-
ment by the formula given at page 163, using three times
the quantity of added gelatine. It is preferable that it
should be unboiled, or, at all events, only very slightly
Tboiled, in order to get a warm tone.

The following developer is recommended : —
No. 1. — Potassium oxalate ... ... 125 grains

Potassium bromide ... ... 5 „

Water ... ... ... ... 1 ounce

No. 2. — Ferrous sulphate ... ... 50 grains

Water ... ... ... ... Ij ounce

3 parts of No. 1 are mixed with 1 part of No. 2, and
2* ounces of water.

• Some recommend 2 ounces of a 5 per cent, solution of sodium sul-
phite to replace these 2 oances of water.

DKVBLOPMBNT OF POSITIVE PAPER. 195

The longer the exposure within limits, the more warm is
the tone produced ; a warm tone is not produced if the ex-
posur eis short. An exposure of half a minute in diffused
daylight should he sufficient to give a warm tone. The
image should be developed till it appears rather darker
than it should finally be. It is next well washed, and then
placed in a saturated solution of alum, where it is left for
a quarter of an hour. It is taken out and washed for a
quarter of an hour, when it may be toned. The follow-
ing toning bath (the sel d'or) is recommended : —

A. — Hyposulphite of soda ... ... 30 ounces

Water 30 „

B. — Gold chloride 15 grains

Water ... ... ... ... 20 ounces

To solution A add, slowly and well stirring, 4 ounces of
B. The bath is then ready for use. It improves by keep-
ing, and, when necessary, is replenished by the addition
of fresh hyposulphite of soda, and of gold solution B.

The print is to be kept in this bath for ten minutes,
when it will be both toned and fixed.

The following acetate of soda toning bath also answers
well: —

Gold chloride ... ... ... 1 grain

Acetate of soda... ... ... 30 grains

Water ... ... ... ... 8 ounces

Chloride of lime a slight trace.

The lime toning bath, and the borax bath,* may be used.
After the print is toned in any of the above baths
(except the sel d'or), it must be fixed in a two per cent,
solution of hyposulphite of soda.f It is again washed,
and then dried in contact with some smooth flat sur-

* For details, see " Instruction in Photography " (Piper and Carter).

t Mr. Ashman finds, we believe, that if the prints, before toning, were
immersed in a weak solution (say, half per cent.) of ammonium snlpho-
€yanate for a short time, the toning colour was more satisfactory.

196 DEVELOPMENT OF POSITIVE PAPEE.

*

face. It was originally recommended to use a glass
surface which had heen rubbed over with powdered talc,
but we have found that the gelatine was liable to stick to
the glass. If the glass be rubbed over with castor oil,
however, it may be used, and a fine surface is given to the
print. Perfectly smooth ebonite or ferrotype plates may
also be used. A print after washing is placed, face down,
in a dish with the surface to which they are attached
beneath. The two are raised out together with a layer
of water between, when a squeegee is brought to bear on
the former, the water squeezed out, and the two surfaces
brought into close contact. They are then placed to dry,
and when desiccation is perfect, the two can be detached.
The mounting of these prints is somewhat difficult, on
account of damp spoiling the gloss of the surface. Mr.
Wamerke finds that if the prints are not burnished,
sufficient surface is given to the prints, and there is no
need to dry them in contact with the support.

This printing by development is still in its infancy, and
before long we may expect much improvement in the
preparation of the paper and also in its development. It
may be remarked that prints on this paper may be taken
in the camera, thus avoiding the necessity of taking en-
larged negatives.

CHAPTEE XXXI.

DKFECTS IN GELATINE PIATES.

Frilling. — What is meant by frilling is the gelatine film
leaving the glass plate in folds or wrinkles ; and a greater
nuisance than this cannot be met with. It generally
occurs when fixing the plate, though we have sometimes
met with it during the development, especially in hot
weather. We will endeavour to state the causes of frill-
ing as far as they are known. Frilling is often caused
by the use of unsuitable gelatine, possessing but little
tenacity. The more the qualities of gelatine are like
glue, the less chance there is of meeting with this vexa-
tious evil. If gelatine, however, were like glue in respect
to hardness, the difficulty of developing a plate would be
very great, since it is too hard. The addition of chrome
alum to an emulsion also prevents frilling to a great ex-
tent. The objections to chrome alum are that it increases
the tenacity of the gelatine, and prevents easy develop-
ment ; hence it should be used sparingly.

Gelatine that has been heated for a long time has a spe-
-cial tendency to frill, and, unless fresh gelatine be added
to the emulsion, in some cases frilling is inevitable. Long
cooking (in warm weather particularly) means decompo-
sition of the gelatine, and decomposed gelatine is very
■detrimental in preparing a dry plate. Boiling for a short

198 DEFECTS IN GELATINE PLATES.

time has much the same effect on the gelatine as cooking^
at a lower temperature; hence, to avoid frilling, it is
better not to boil the emulsion with the full amount of
gelatine.

Another source of frilling is the plate being improperly-
cleaned. If water will not flow in a uniform sheet from a
plate, it may be well understood that there will be but
little adhesion between it and an aqueous solution of
gelatine. This we believe to be one fruitful source of
evil.

Another source of frilling is unequal drying. Thus, if
plates be dried in an unventilated box, it will usually be-
found that a central patch refuses to dry till long after
the outsides are completely desiccated. At the junction
of this central patch with the neighbouring gelatine frill-
ing is to be looked for. It will spread to the paits which
have been the longest in drying. This is due to a false-
tension set up in the film, and can only be conquered by-
drying the plate by means of alcohol, or by using a proper
drying cupboard.

Again, when plates are coated in hot weather, unless
precautions are taken of cooling the slabs on which they
are placed, they take long to set. The emulsion remains
liquid on the plate for sufKcient time to allow the heavier
particles of silver bromide* to settle down on the surface
of the glass. This of course diminishes the surface to
which adhesion can take place. We believe that most of
the frilling which takes place in plates prepared in hot
weather may be traced to this cause. When washing
after fixing, frilling is often caused by allowing a stream
of water from the tap to impinge on the plate. This
should never be allowed if the film is at all delicate.
Plates which frill or blister will often not show any signs
of so doing if kept for a few months.

* This is particularly liable to happen when the emulsion has been long
boiled or carelessly mixed.

DEFECTS IN GELATINE PLATES. 199

A general remedy for frilling is to coat the plate with
normal collodion containing about six grains of tough
pyroxyline to the ounce of solvents. The formula would
he thus : —

Tough pyroxyline 6 grains

Alcohol (-820) bounce

Ether (-725) i „

This may be applied to the film immediately before
developing the plate : the solvents are washed away in a
dish of clean water first, and, when all repellent action is
gone, the developing solutions applied. If the film has
been allowed to dry, a solution of one part of ether to
three of alcohol will render it pervious to the developing
solutions.* In some batches of plates frilling is so obsti-
nate that, although collodion be applied, the film has a
tendency to curl off from the edges of the plate. It is
advisable, when such is suspected, to run a brush with
an india-rubber solution round the edges, to prevent the
water having access to that part of the film. When fixing
such plates, it not unfrequently happens that blisters
appear, and, if allowed to remain as they were, will spoil
the negative. To avoid this, we wash the plate under the
tap till all the blisters join, and the film presents the
appearance of a sack containing water. A prick at one
corner of the plate lets this liquid free, and the washing
can take place as usual.

Some writers state that, by immersing the plate in a
saturated solution of Epsom salts, frilling is avoided ; we
have not succeeded ourselves in proving its efficacy.

Blisters on the Film. — Blisters on the film are the usual
preliminaries to frilling. When they commence, further
damage may usually be avoided by flooding the plate with
methylated spirit. This extracts the water, and Vi^ith it

* We have found this essential in intensifying negatives which have beea
treated with collodion after fixing and drying.

200 DEFECTS IN GELATINE PLATES.

any soluble salt that may be left, and the plate speedily
dries, which is an advantage if it be fixed. Blisters are
usually found to follow the rubbing marks of the polishing
cloth, if such be used. The cure here is self-evident.
They also are to be found in places between which the
fihn has dried quickly and slowly.

Red Fog. — The writer fortunately knows very little
about this disaster, but it is found to occur if the silver
nitrate is in excess of the salts with which it should com-
bine. Cyanide will sometimes eliminate it from a film,
but this remedy must be used with caution.

Green Fog. — This fog is green by reflected light, and
pink by transmitted light, being dichroic. Experiment
points to it beingreduced metallic silver in an exceedingly
fine state of division, this reduction being aided by decom-
posed gelatine. In some cases we have immersed the film
in a strong solution of bichromate of potash, and on after-
wards washing, the fog has disappeared ; but whether it
is a certain cure, we hesitate to say ; it is, at any rate,
worth trying.

The writer found that green fog can be eliminated from
a plate if, after fixing and washing, it is treated with a
ferric salt. The following seems to answer satisfactorily :

Ferric chloride ... ... ... 50 grains

Potassium bromide ... ... 30 „

Water ... ... ... ... 4 ounces

This converts the image into silver bromide, and at the
same time bleaches the green fog, which, seemingly,
is a deposit of silver mixed with a constituent of
gelatine. The plate is then washed to get rid of any
great excess of the iron salt, when it is treated with ferric
oxalate developer. This reduces the bromide, with
slightly increased density, to the state of metallic silver,
and the green fog is replaced by a very faint deposit of
metallic silver, which in no way interferes with the
printing. Green fog is never seen when using ferrous

DEFECTS IN GELATINE PLATES '201

■oxalate, which has not an alkaline reaction on the alka-
line carbonates.

General tog. — By general fog we mean the fog pro-
duced in development, caused by the partial reduction of
the silver salt all over the film. This is probably due to
the decomposition of the gelatine by long cooking, the
products of which in the presence of a developer are apt
to react on the silver salt, and produce a partial reduction
in it. The production of this kind of fog, and electrical
disturbance in the atmosphere, are apt to go together.
In unfavourable weather, a few drops of a solution of
carbolic acid should be added to the gelatine during
boiKng or prolonged emulsification ; this will generally
check or entirely prevent the decomposition. An excess
of silver is likewise very likely to produce the evil, but
the presence of iodide in the emulsion will almost certainly
cure it. Another fruitful source of fog is the light ad-
mitted to the plates during preparation or development.
The light should be tested by putting a plate in the dark
slide, and drawing up half the front, and exposing the
half-plate to the light for ten minutes. If the fog be due
to this cause, the plate on development is sure to show it
by a slight reduction of metallic silver in the part so ex-
posed.

Whatever may be the cause of fog — if the emulsion be
not hopelessly in fault, or if the plates have seen light —
we have found that, as in the coUodio-bromide process,
there is one certain siu'e cure. If the emulsion be slightly
at fault, squeeze it into water containing ten grains of
potassium bichromate to each ounce, and about an equal
part of some soluble bromide, and allow it to rest for
an hour, and then wash again for a couple of hours
more. If all the bichromate be not taken out by this
washing, it is not of much consequence, since, when dry,
it is inactive. The sensitiveness after this treatment is
not much diminished, and the negatives taken with it are
beautifully bright. Plates may be treated in precisely

'202 DEFECTS IN GELATINE PLATES.

the same manner, and give unveiled pictures. There is a
slight diminution of sensitiveness if the Tbichromate be not
all washed out, but nothing to hurt except where very
great rapidity is required.

A cure for any emulsion is the addition of a few grains
of cupric chloride. This diminishes the sensitiveness,
but is most eifectual, negatives yielding bright and
brilliant images. A remarkable fact about the addition
of the cupric chloride is, that the grey form of bromide
is converted into the red form if much of the copper salt
be employed. The addition of a few grains of ferri-
cyanide of potassium with a little bromide of potassium
(according to Dr. Eder) is also a perfect cure, but this
slows the emulsion.

Another method is to add two drops of a mixture of
hydrochloric and nitric acids slightly warmed so as to
change the colour of the emulsion, or to slightly acidify
the first wash water with it ; about one drachm to a pint
of water is generally ample. The length of time which
the emulsion should be in contact with the acidified water
depends on the size of the mesh of the canvas through
which the emulsion is squeezed. For a medium size,
half-an-hour suffices. The emulsion has a tendency to
become insoluble by this method.

Flatness of linage is usually due to over-exposure and
development with the alkaline developer : the use of
ferrous oxalate mitigates the evil, whilst if iodide be ia
the film, we have never found any great lack of density
to arise. An over-exposed picture can be made to yield
a dense image by slow development. Feebleness of the
image is also often caused by too thin a coating of emul-
sion, or an emulsion poor in silver salt. A thick film is eu
desideratum, giving all the necessary density to the image
with facility. When a vigorous image is required, it is
most readily obtained by using a freshly-prepared and
strong ferrous oxalate solution (see page 149).

loo Great Density of Image ia sometimes met with, and

DEFECTS IN GELATINE PLATES. ZQA

can be remedied by applying ferric chloride to the film,
and then subsequently immersing in the hyposulphite of
soda fixing bath.

The formula recommended is —

Ferric chloride... ... ... 1 drachm

Water ... ... ... ... 4 ounces

This is flowed over the plate a short time, and then, after
washing, the plate is immersed in the fixing bath. The
solution acts very vigorously, and should be diluted if
only a small reduction is required. Local reduction may
be effected by using a paint brush charged with this solu-
tion on the moistened film. This practice is not, how-
ever, much to be recommended, as it is rather working in
the dark.

Density may also be diminished by the use of a strong
solution of cyanide. Local reduction may be given by
moistening the parts required to be reduced with water by
a paint brush, and then applying the cyanide in the same
manner. The reduction can be seen progressing.

There are a variety of formulaj extant for reducing
negatives. Perhaps the best is eau-de-javelle, which can
be obtained of all chemists, but which is made as fol-
lows : —

Dry chloride of lime ... ... 2 ounces

Carbonate of potash ... ... 4 „

Water 40 „

l^he lime is mixed with 30 ounces of the water, and the
carbonate dissolved in the other 10 ounces. The solu-
tions are mixed, boiled, and filtered. The filtering solu-
tion should be diluted, and the plate immersed in it till
reduction takes place. The plate should bo fixed, and
again washed.

Yellow Stains. — Usually a yellowish veil appears to dim
the brightness of the shadows when the development has
been effected by the alkaline developer. This may be

204 .DEFECTS IN GELATINE PLATES.

removed, if thought requisite, hy the application of one
orjtwo drops of hydrochloric acid to an ounce of water,
and floating it over the surface of the plate. This must
Tbe done after the negative has been freed from hyposul-
phite, otherwise the acid decomposes this salt, and there
is a deposition of sulphur. Mr. Coweli has recommended
another clearing solution, which is made as follows : —

Alum 1 ounce

Citric acid ... ... ... 2 ounces

Water 10 „

Mr. B. J. Edwards makes this solution sherry-coloured
with ferric chloride, but we do not find any marked ad-
vantage in so doing. The film must be washed almost
immediately, as the acid is apt to cause frilling.
Another formula is —

Saturated solution of alum ... 20 ounces
Hydrochloric acid ... ... ^ ounce

The negative should be well washed in all cases after
the application of either of them.

loo Granular an Emuhion is usually due to bad mixing
of the soluble bromide and the silver nitrate ; but it may
also be caused by over-boiling, and also by too small a
quantity of gelatine in the boiling operation. Digesting
too long with ammonia, as in Van Monckhoven's process,
has the same effect. There is no cure for this evil.

Opaque Spots on a plate are almost invariably due to
dust settling on the film when drying ; they also may be
due to imperfect filtering of the emulsion.

Semi-transparent Spots on the plate before development
are generally due to (1st) defects in the glass plate, or
(2nd) to the use of gelatine containing grease. We have
found that the use of a substratum is a certain cure for
these transparent spots.

As has already been pointed out, certain gelatines are
apt to contain grease, and that so intimately that soaking

DEFECTS IN GELATINE PLATES. 205

in ether or washing witli ammonia will not eliminate it.
A specific is as follows : — We will suppose that 80 grain*
of Coignet's gelatine are required : 90 grains are weighed
out, soaked in water, drained, and melted. The liquid is
then very slowly poured, almost drop by drop, into methyl-
ated spirit, free from resin, where it is precipitated in
shreds of a white pasty character ; after it is all precipi-
tated the spirit is poured oiF, and a slight rinse with fresh
spirit given, and then it is covered with water, in which
it should remain till the whiteness disappears. The water
should then he changed, and the gelatine drained and re-
dissolved ; about 10 grains out of the 90 seem to be dis-
solved in the mixture of alcohol and water. Emulsions
made with this gelatine will be markedly free from grease
spots. The same method may be adopted for large quanti-
ties of gelatine, omitting the final wash with water, and
leaving it to dry spontaneously. This is best done on
glazed dishes. The gelatine can be broken up, weighed,
and used in the usual manner. Another plan is to soak
the gelatine in water with a full quantity of water ; drain
oft" what can be drained off, pressing the gelatine during
draining. The gelatine is next melted, and to every 100
grains used ^ ounce of strong ammonia is added. When
set, the gelatine is squeezed through netting, and washed
till an alkaline reaction is only just shown on red litmus
paper. All grease is saponified and washed out to a great
extent. The gelatine may be added to the boiled emul-
sion in the moist condition.

Dull Spots on the Negative are also due to the use- of
gelatine which contains greasy matter. They seem to be
formed by the repellent action of the gelatine for the
silver bromide. If a plate be carefully examined by day-
light, the dull spots can be seen before development, and
are seen to be placed where the surface is denuded of
gelatine, and, there being no restraining action by the
gelatine, these are first reduced by the developer. If a
plate which shows such repellent action be coated with a

&

206 DEFECTS IN GELATINE PLATES.

weak solution of gelatine or albumen, and tlien he dried,
the evil will be nauch mitigated. These dull spots are
usually met with in most aggravated form in hot weather,
when the emulsion takes long to set, and, consequently,
when the repellent action has longer to develop its power.
In hot weather the slab should be cooled with ice to avoid
this evil.

Fits are, in reality, an aggravated form of dull spots.
The repellent action in this case is able not only to cause
the gelatine to be repelled, but also to carry with it the
bromide as well.

Tf'ant of Density in a negative may be caused by over-
exposure, but it more often arises from the emulsion
itself.

A rapid emulsion has a tendency to give a feebler
image than a slow emulsion, although to form the image
the same amount of silver may be reduced. This shows
that the silver is in such a state of aggregation that it
does not possess what may be called covering powers.
We have found that the addition of a chloride emulsion
materially aids the production of density. If one-fifth
part of an emulsion prepared according to Chapter XXV.
be added to an emulsion lacking density-giving qualities,
it will be secured without detriment to the sensitiveness.
The range of sensitiveness will be slightly altered. A
hard gelatine is also conducive to feeble images. If
prepared plates give feeble images, resort must be had
to intensiiying.

Irregular-shaped Spots, which refuse to develop, are often
caused by the use of chrome alum in emulsions which
contain free alkali. Ammonia causes a precipitate with
chrome alum, and this encloses particles of bromide, and
prevents the action of the developer upon it.

Iransparent Finholes on the ^Negatives after Fixing may
arise from minute air-bells in the emulsion, or from dust
which finds its way into the slides or changing-box. The
former disappear if the emulsion is kept before coating.

DEFECTS IN GELATINE PLATES. 207

The latter can be avoided hj rubbing the dark slides witli
a minute trace of glycerine. This acts as a trap for the
dust, and prevents its finding its way on the plates.

Dark Scratches on the Negative. — Sometimes plates on
development show dark scratches, which appear un-
accountable. If the plates have been rubbed together, or
if any grit has been rubbed on them, this will account
for the markings.

CHAPTER XXXII.

COLLODION EMULSIONS— (INTRODUCTORY).

A GREAT variety of formulse for collodion emulsions have
been published at one time or another. It would be im-
possible to give all which have from time to time been
given in the various photographic publications, but a
selection has been made of what the writer conceives to
be the most successful ; at least, which have proved most
successful in his hands.

These may be divided into two classes : one, in which
the emulsion is formed in collodion, and the plate coated
and then washed ; the other, in which the same emulsion
is dried and washed, and re-dissolved, the plate being-
coated with the emulsion as required. With the former
method, unless the bromide is in excess, the emulsion has
to be prepared from time to time aS required, and
if the bromide be in excess, the emulsion works very
slowly. With the latter process, where it is washed, the
emulsion will keep any time, always supposing no decom-
position sets up in the pyroxylin. We have ourselves
kept some emulsions of this class seven years which are
just as sensitive, if not more sensitive than when freshly
prepared.

2he plain collodion with which the emulsion is to be

COLLODION EMULSIONS. 209

made shall be first dealt witli, distinguishing the qualities
necessary for the unwashed and for the washed emul-
sion.

Some emulsion workers have laid it down as an axiom
that the pyroxylin for the two processes should differ,
while others declare that this is unnecessary. Again, some
declare that to gain good density the pyroxylin should
contain a percentage of organic matter, presumably to be
capable of acting on the silver bromide during develop-
ment, or by forming some definite compound with silver.
Our own experience is, that for securing density, organic
matter is unnecessary, though it may improve sensitive-
ness ; and we have found in some instances that density
was absolutely impossible to attain where organic matter
was present. We shall touch on the question of density
of the image further on.

If a preservative be used as a sensitizer, there can be
no doubt that a collodion should be used which is as
porous as possible, to enable it to surround the particles of
the sensitive salt. This porosity has also another advan-
tage, which is, that when the preservative is washed off
previous to development, the sensitive salt is immediately
accessible to the action of the developer. It is such a
collodion that is recommended for dry plates prepared
with the aid of the bath, more particularly in the coUodio-
albumen process, though in this process the sensitive salt
is more especially contained in the albumen, and it is
therefore necessary that a fair quantity of the latter
should be on the plate, which is accomplished by this
porosity of the collodion film. For any emulsion process,
we consider a horny collodion objectionable, owing to the
difficulty that exists in making the developer penetrate
through the film. A horny collodion has, however, one
advantage in that it acts as a varnish to exclude the air
from the sensitive salts enclosed within it. In the follow-
ing formulas which are given for the preparation of the
pyroxylins, one will produce an ordinary tough film, and

210 COLLODION EMULSIONS.

the otlier a faii-ly porous film, and consequently a rather
powdery pyroxylin.

The solvents of the pyroxylin should he as pure as
practicable to secure the maximum of sensitiveness.
There is, for instance, no doubt that when methlated
alcohol is used, there may be a lack of sensitiveness, and
even a production of fog. The ordinary methylated ether,
however, will be found, as a rule, to be sufficiently
pure.

CHAPTEE XXXIII.

PYROXYLIN.

The following formulse for the preparation of the various
kinds of pyroxylin will be useful to note. The first is
taken from "Instruction in Photography," and is re-
printed here as being convenient for reference. The
general directions given are those recommended by
Hardwich. Take —

Sulphuric acid (1-842) at 15" Cent. 18 fluid ounces

Nitric acid (1-4:56) 6 „ „

Water 4f „ „

Or,

Sulphuric acid (1-842) 18 fluid ounces

*Mtric acid (1-42) QX ,, ^^

Water 4J „ ^^

The water is first poured into a strong glazed porcelain
basin, the nitric acid next added, and lastly, the sulphuric
acid. The mixture is well stirred with a glass rod. The
temperature will now be found to be somewhere about
190°. It must be allowed to cool to 150°, and this tem-

* The nitric acid of the strength given in this formula is cheaper than
that of the first, and is a standard strength, hence it is recommended for
economy's sake to nse it.

212 PYROXYLIN.

perature must be maintained on a water Lath. A dozen
balls of cotton-wool, weighing about thirty grains (which
have previously been well washed in carbonate of soda
and thoroughly dried), should now be immersed separately
in the fluid with the aid of a glass spatula. Each ball
should be pressed separately against the side of the basin,
till it is evident that the acids have soaked into the fibre.
Care must be taken that each one is immersed at once.
Failing this, a different chemical combination takes place,
and nitrous fumes are given off, and the success of the
operation is vitiated. Immersing the dozen balls will take
about two minutes. The basin should after this be covered
up for about ten minutes.* At the expiration of this time
the whole of the cotton should be taken up between two
glass spatulas, and against the sides of the clean porce-
lain capsule as much of the acids as possible should be
squeezed out. The cotton should then be dashed into a
large quantity of water, and washed in running, or fre-
quent changes of, water for twenty-four hours. Finally,
when it shows no acid reaction to blue litmus paper, it i&
dried in the sun or on a water-bath.

The operation may be conjectured to be successful if
the cotton tear easily in the hand, and if the original
lumps cannot be easily separated. Should nothing but
fragments of the lumps be detected, it is probable (if the
acids used have been of the strength given above) that
the temperature has been allowed to fall. If dried, the
pyroxylin should, when pulled, break up into little bits,
and should not resemble the original cotton in texture.

The weight of good pyroxylin should be greater than
the original cotton by about 25 per cent.

If the acids used are too strong, the pyroxylin will be
mach heavier than this percentage, and will make a thick
glutinous collodion ; whereas, if the acids have been too

* This prevents the access of the air to the fluid, and prevents the absorp-
tion of oxygen, and consequent formation of the nitrous fumes.

PYROXYLIN. 213

diluted, it will probably weigh less than the original cotton,
and will yield a collodion adhering firmly to the plate,
and giving negatives of too great softness ; any small
particles of dust that may fall on the glass will form
transparent marks. The formula given steers between
the two extremes. There is a large proportion of sul-
phuric acid in the above solution of acids, and it is to this
that is probably due the tough film which the resulting
■collodion gives. In fact, the excess of sulphuric acid
partially " parchmentizes " the cotton.

The late Mr. G. W. Simpson described a modification
of Hardwich's formula, which has given excellent results
in our hands ; the mode of procedure is the same as that
described above. " As Hardwich's formula for the manu-
facture of pyroxlin is given, we may add a caution
derived from our own experience with it. In our practice,
we found it to contain too large a proportion of water,
and our experiments with it issued in something like fifty
per cent, of failures, the cotton dissolving almost entirely
in the acids. We may add a formula which we have
found to give an excellent sample of soluble cotton for
emulsion work, the collodion holding the particles of silver
salt well in suspension, and giving a homogeneous film,
adhering well to the glass. The formula we subjoin has
the advantage that the acids are readily obtainable in
commerce of the strength we mention, and are conse-
quently cheap. Six measured parts of sulphuric acid
1'840 (ordinary commercial oil of vitriol will serve), and
four measured parts of nitric acid 1'360. This is the
strength of acid commonly sold as a pure nitric acid. In
three measured ounces of the mixed acids, one drachm of
cotton wool should be immersed at a temperature of
150" Fah., using a water bath to maintain that tempera-
ture for ten minutes, when the cotton should be removed
and washed at once in a large quantity of water."

In the next formulfe the proportion of sulphuric acid is
-diminished, and in consequence we get a pyroxylin which

214 PYEOXYLIN.

is, if anything, deficient in tenacity. For dry plate
processes with the bath, however, it is excellent, and will
be found of great use in emulsion processes in which a
preservative is used. The formulae are those given by
Warnerke in a communication to the Photographic Society
of Great Britain made in 1876.

His modus operandi, based on a communication made
to him by Colonel Stuart Wortley, is the following : —
100 grains of the finest cotton-wool are put into a porce-
lain jar, and 30 grains of gelatine dissolved in the smallest
amount of hot water are added. By pressing it with a
wooden stick, all the cotton will be uniformly impregnated.
It is subsequently very thoroughly dried before the fire.

Nitric acid (sp. gr. 1*450) ... 4 fluid ounces
Water... ... ... ... 12-^ drachms

Sulphuric acid (sp. gr. 1'840) 6 fluid ounces

are mixed in the order named. An arrangement is pro-
vided to keep the temperature of the mixture uniformly
at 158° Fahr. The dried gelatinized cotton, weighing
now about 130 grains, is immersed in the mixed acids,
and left in twenty minutes. After the lapse of this time
the acids are pressed out, and the pyroxylin quickly
transferred to a large vessel of water. Washing and
drying follow. Colonel Stuart Wortley recommended
also a second mode. Gelatine, instead of being added to
the cotton, is dissolved in the water figuring in the formula
of the acids, and ordinary dry cotton immersed in the
mixture of gelatinized acids.

Mr. Wamerke states that before washing the gelatin-
ized emulsion a remarkable increase of intensity and sensi-
tiveness is obtained. After washing, the difierence is
less striking, but still sufficiently marked to prove the new
pyroxylin to be a very decided improvement.

Mr. Wamerke states that pyroxylin givmg extraordin-
ary density can be prepared from the raw hemp. Collo-
dion from hemp-pyroxylin is red in colour, and very fluid ;

PYROXYLIN. 215

but the insoluble deposit is very considerable ; it also
requires stronger acids. It is worth remarking that the
strength of acids must vary with different samples of
fibres, even in the case of different cottons. A very good
pyroxylin can be prepared from Whatman's hand-made
paper, instead of the cotton in.the above formida, which,
being sized with gelatine, offers a ready-made material,
suitable for making gelatinized pyroxylin."

The great difficulty in this formula is the easy solu-
bility of the cotton at the high temperature. A reduction
in the amount of water will prevent this. Pyroxylin from,
ungelatinized cotton can he prepared by the same formula^
and gives a powdery film. The writer disagrees with
Mr. Wamerke as to the desirability of this state of the
film for washed emulsion when used on rigid supports,
such as glass, but the limpidity given by it to the collo-
dion is very desirable in the case of a flexible support,
such as that with which Mr. Warnerke's name is asso-
ciated.

Mr. W. B. Bolton gave an excellent description of the
method to be adopted for making any pyroxylin suitable
for emulsion. He says :

" Pyroxylin possessing the requisite qualities is by no
means so easily obtained as the ordinary sort. Precipi-
tated pyroxylin forms at once, if properly made, even
from the cheapest materials, not only a perfect substitute
for the high-priced samples usually employed, but for
some purposes gives an absolutely superior result.

" We commenced with a sample of pyroxylin which is
sold at 16s. the pound ; it is very soluble, and gives
little or no residue, but is of little use for emulsion work.
Of this, 400 grains were dissolved in a mixture of 10 ounces
of methylated ether, s.g. "730, and 10 ounces of ordinary
methylated spirit, retailed at 5s. a gallon. The resulting
collodion, after standing for a couple of days, though very
thick, as might be expected, was tolerably clear, except
for the presence of a few floating specks and particles of

21 6 PYROXYLIN.

dust, wHch were removed by passing it through muslin.
This was poured into cold water, and the precipitate,
when washed and thoroughly dried, weighed 368 grains,
or exactly 8 per cent, less than the original cotton."

After stating that it is a wrong plan to pursue to pour
the collodion gently on the water, the writer continues :

" The proper course to follow, as laid down by M.
Chardon, is just the reverse of this ; the collodion is
poured into the water in a thin streara — preferably from
a height — and is stirred vigorously during the time of
pouring, and for a minute or two afterwards. By this
means it is broken up into innumerable drops, each of
which, immediately it comes into contact with the water,
is converted into a distinct spongy mass or flock, being
deprived almost instantaneously of its ether and alcohol.
The stirring is continued as long as the mass exhibits
any cohesive tendency, and when it feels harsh and firm
to the touch, it may be known that the removal of the
solvents is complete. The water is then changed, the
cotton passed through a cloth, and dried.

" Except in physical conditions, we cannot find, with a
given sample of cotton, that it is of much importance
whether the precipitation is performed in hot or cold
water."

In order to avoid waste in washing and drying, it will
be found convenient to employ a conical bag fixed upon
a hoop of thin cane. When the precipitation is complete,
the whole of the contents of the vessel are transferred to
the washing bag, and after passing two or three pints ot
water through to remove the last traces of ether and
alcohol, the mass of cotton is squeezed as dry as possible,
and may then be removed as a lump ; it is then broken
down with the fingers or a spatula upon a clean porcelain
dish, and dried at a gentle heat on a warm bath. When
quite dry, it should present the appearance of light flakes
of pure white, and easily reduced to powder. It dis-
solves as rapidly as ordinary pyroxylin, and, if carefully

P~XROXYLIKr. 217

prepared, gives at once a perfectly bright solution of a
faint yeUow tinge. It gives upon the glass a hard, smooth
film, non-contractile, and yet differing totally from the
so-called powdery films commonly spoken of in connec-
tion with dry plates.

In the same article, a reference is made to M. Blondeau's
analysis of precipitated cotton, in which it is stated that
8 per cent, of water is taken into combination. This
amount of water, if it exists in the cotton, must alter the
structure of the collodion in a marked way.

Be this as it may, precipitated cotton does give a very
fine film ; but we are inclined to think that part of the
effect is produced by the alcohol being eliminated from
it en masse, and carrying with it that constituent of the
pyroxylin which is soluble in the alcohol. This will be
seen to be the case in which a finished emulsion was
washed in alcohol ; the resulting film having much re-
semblance to that of M. Chardon's.

The amateur will probably find it most convenient
to purchase ordinary pyroxylin from some respectable
dealer, who is a manufacturer of good collodion, instead
of making it himself, for, of all processes connected with
photography, that of making pyroxylin is, perhaps, the
most unpleasant and hurtful to the health and clothes.
The stains on the latter from nitric acid or sulphuric acid
■can never be elirainated, unless the acid be immediately
neutralized, and sulphuric acid will rapidly eat through
any organic texture, unless it be either washed ilwrouglily ,
or an alkali be applied.

As regards the character of the solvents, there is little
to be said in regard to the ether. That of a specific
gravity of '730 is generally employed, and, if it be, an
alcohol of low specific gravity should be employed, such
as "812 ; whereas if the ether have a specific gravity of
•720, a specific gravity of "820 for the alcohol is allowable.

After the plain collodion (see next page) is mixed, it
should be allowed to settle. No matter what pyroxylin

218 PYKOXYLIN.

be employed, it will invariably be found that there is some
flocculent matter, too fine for filtering out, whicli, if not
got rid of, is one great cause of spots on emulsion plates,
and therefore every effort should be made to prevent its
finding its way into the emulsion. The collodion should,
therefore, be allowed to remain undisturbed for a week or
two, to allow these fine particles to deposit.

OHAPTEK XXXIV.

PREPARATION OF AN EMULSION.

It is unnecessary to enter into the history of the emulsion
processes ; bat it may not Tbe uninteresting to note that the
first published formula for a collodio-bromide emulsion
was by Messrs. Bolton and Sayce, in September, 1864.

Though not following an historical order, we have
thought it best to give the method of preparing an emul-
sion which can be followed in nearly all modifications of
the process ; and to make it clearer, a definite formula
has been made use of, giving an emulsion which is very
simple and clean working, and though not boasting any
extraordinary sensitiveness, is yet more sensitive than any
bath dry-plate process with which the writer is ac-
quainted.

The plain collodion* is made as follows : —

Alcohol -820 ... 10 ounces

Ether -730 20 ,,

Pyroxylin (ordinary) ... ... 400 grains

* If the plain collodion supplied by dealers be used, it must be recollected
that, as a rule, it contains about 5 grains of pyroxylin to the ounce after
the iodizer has been added. The formula may be taken to be as follows ; —

Alcohol 20 ounces

Ether 40 „

Pyroxylin 400 grains

The bromide and silver must be added according to the grains of pyroxylin,-
not according to the amotmt oj solvents in which it is dissolved.

220 PREPAEATION OF AN EMULSION.

We will suppose that -^re are going to prepare an emul-
sion which will make up to twenty ounces. When it is
evaporated, washed, and re-emulsified, each ounce of
washed emulsion should contain about 5 grains of pyroxy-
line, and, therefore, we must take one-fourth of the collo-
dion made tip as above (vide Note page 218), which will
be 7^ fluid ounces. It is proposed that each fluid ounce
-of re-dissolved emulsion shall contain about 15 grains of
silver bromide. The salt we propose to use is zinc bro-
mide, and we find that about 10 grains of this salt are
necessary for this purpose. To our 7^ ounces of collodion,
therefore, we must add at some time or another 200 grains
of this salt. Two portions of 100 grains each are weighed
out : one is dissolved in the smallest quantity possible of
alcohol, and 4 or 5 drops of concentrated nitric acid are
added to it to render innocuous any oxide or other im-
j)urity that may be present. This is then added to the
collodion. The other 100 grains are similarly dissolved,
but a larger proportion of nitric acid added, viz., 10 drops.
This is kept in a test-tube ready for use. We next require
300 grains of silver nitrate to saturate the zinc-bromide,
and to allow 3 grains in excess for each ounce of the con-
centrated collodion. As this will probably be about
11 ounces by the time the additions are made, 330 grains of
silver nitrate (which has previously been pounded up in an
agate mortar, or the crystals of which have been crushed
with a glass stopper on a thick glass plate) are weighed
out. This amount is then placed in a large test-tube,
with 5 dr. of water, and warmed : a perfect solution
ought to result. Ten drops of nitric acid are next added
to it. In another test-tube 1^ ounces of alcohol ("820 to
•830) are boiled, and poured upon the dissolved silver.
The two fluids may not mix at first, but by pouring them
from one test-tube to another this is readily accomplished.
The collodion is now placed in a glass jar, and a stirring-
rod placed ready to hand. It is usually insisted that the
subsequent operations should be conducted in the dark-

PREPAEATION OF AN EMULSION. 221

room. This exclusion of liglit is quite unnecessary (as-
the writer has practically proved;, owing to the presence
of the nitric acid, which renders the sub-bromide inert
as fast as it is formed by the action of light. The test-
tube containing the silver is noAV taken in the left hand,
and the stirring-rod in the right, and three-quarters ot
the silver nitrate solution is poured, drop by drop, into
the collodion, which is kept in brisk agitation by the glass
rod. The silver solution is then placed on one side, and
the dissolved bromide solution taken in the left hand. Alii
the latter is now added drop by drop, and then the re-
mainder of the silver solution in a similar manner. Some
of tlie silver salt is sure to be found crystallized on the
edge and sides of the test-tube. This is re-dissolved, as
before, in a little water and half an ounce of alcohol, and
added with the same precautions. If the above details
have been carefully carried out, the colour of a candle or
gas-flame, when viewed through the liquid which runs
down the inside of the glass jar after agitation, should
appear of a deep orange approaching to a ruby tint.
AVhen in this condition, it may be judged that it has
been rightly prepared. With the glass rod a drop or two-
of the emulsion should be dropped on to small strips of
glass, and examined by daylight for structure, &c. When
viewed through a window, the principal part of the light
transmitted should be orange. A little potassium cliromate
should be dropped on to the emulsion on the plate, and a
bright red colour will show that the silver is in excess,
which is what is required in our case. If this colouration
.be absent, it will indicate that the soluble bromide is in
excess, which, in some modifications of the same process,
is what may be desired. The emulsion must next be
decanted off into a bottle capable of containing at least
double the amount of fluid — -that is, at least 20 ounces —
and it should then be shaken for ten minutes. It may
now be put on one side for from sixteen to twenty-four
liours, when it will bo ready for the next operation.

222

PREPARATION OF AN EMULSION.

We will now give a slightly different method for mixing
the silver and the soluble bromide, which has been
adopted by some people, amongst others by Warnerke, to
whom the writer is much indebted for information on
various points.

A couple of corks, D and E (fig. 26), which should fit the
necks of the bottles A and B, are bored with holes just
wide enough to admit a glass tube, C, which has a diameter
of bore of about one-eighth of an inch. The whole of the
bromide is dissolved in half the amount of collodion used,
and placed in the bottle A, which (like B) should have
sufficient capacity to hold double the amount of emulsion
to be made up ; the cork, D, with the glass rod, C, should

next be fitted into it. Into the other bottle, B, the silver
nitrate solution is added to the collodion, sufficient alcohol
and water being used to keep it in thorough solution. The
bored cork, E, is then fitted in the neck, and the far end
of the glass tube deftly inserted, and the tops of the bottles
brought close together. The hands then grasp the necks,
and the contents are shaken up, when a little of B gradually
finds its way into A. The positions of the bottles are

PKEPAKATION OF AN EMULSION.

223

then reversed, and a little of the contents of A shaken
into B ; when each of the bottles seems to contain emulsion
equally dense, the whole of one bottle is gradually caused
to drop into the other, and by this means a perfect emulsion
is obtained. The emulsion may be made even more
rapidly by adopting the contrivance shown in fig. 27, in
which there are two tubes, one always acting as an inlet
for air, whilst through the other the collodion finds a
passage. In this case, narrow bored tubes are advisable,
certainly not greater than one-eighth of an inch.

"Now it has been said that in sixteen to twenty-four
hours the emulsion will be ready tor pouring out. This
statement is trae for the particular emulsion described,
but it is not necessarily true for emulsions when other
soluble bromides are employed. Thus we find that
Col. Wortley stated to the Photographic Society of Great
Britain, on 14th March, 1876, that the following is the
time necessary for emulsions made with the following
soluble bromides to ripen : —

Manganese

Cadmium

Strontium

Magnesium

Zinc

Cerium...

Potassium

Cinchonine

Sodium

Calcium

Ammonium

Uranium

Barium...

It will be noticed that Colonel Wortley gives zinc
emulsion ten and a-half hours, as the time for attaining
the maximum sensitiveness. The discrepancy is probably
due to the greater viscosity of the collodion employed in

n

hours

9

10

10

lOi

14

14

15

15i

17

m

17*

19'

224 PEEPARATION OF AN EMULSION.

the one case as compared with the other. The list, how-
ever, is useful as showing the comparative times that
should he allowed for ripening. We might here leave the
emulsion as ready for coating plates after proper dilution,
but we will further suppose that it is to be washed, a
modification introduced by Mr. W. B. Bolton, one of the
originators of the coUodio-bromide emulsion process.
The first step to be taken is to allow the solvents to
evaporate.

Evaporating the Solvents. — An emulsion generally may
be prepared in the afternoon of one day, well shaken
before leaving the laboratory, and on the next day, about
noon, the emulsion will be ready for drying. The mode
adopted by the writer is as follows : — The emulsion is
poured out into a flat dish, to a depth of a quarter of an
inch, and placed in a dark room, the temperature of the
latter being raised, if possible, to 70°. For the ten ounces
of emulsion made, a porcelain dish, about 14 by 12 by
three-quarters of an inch deep, is required.

After a short interval it will be found that a skin forms
on the surface of the collodion ; this is broken up with a
glass rod, and a fresh liquid sm-face given to it. Every
half hour the whole of the emulsion is thoroughly well
stirred up, till it begins to break into lumps, when it can
be left a short time, for the solvents still further to
evaporate. It is ready for the first washing when the
lumps require a little force to break them up — in other
words, when they arei about the same consistency as a
collodion film before dipping into the bath. The mass is
then removed to a glass beaker, and covered with distilled
water. At this point we have a good test as to whether
the evaporation of the solvents has been continued far
enough. If only a few of the lumps rise to the surface,
the evaporation has been sufficient ; if, on the other hand,
the majority float on the surface of the water, it has not
been continued long enough. The reason of this tendency
of the lumps to rise to the surface is due to the

PREPARATION OF AN EMULSION, 225

light specific gravity of the ether and alcohol, which,
CYen with the weight of the solid matter, is not sufficient
to counterbalance the specific gravity of the water.

This method of eliminating the solvents is, however,
wasteful, and, if preferred, resort may be had to
distillation ; but this method should not be adopted
unless all acid be omitted previous to distillation, since
boiling an emulsion in its presence produces a very
horny film, and nitrous ether is formed. The acid must
be applied in the first wash water. Let it be recollected
that where the bromide is not in excess, but lohere there is
an excess of silver nitrate, nitric acid, m' its equivalent, must
he added to the emulsion itself, or to the loash-water, at some
stage — the time of addition being dependent on the cir-
cumstances already explained. 'Ihe whole of the operations
up to the first ivashing may be carried on in the light. In
M. Chardon's process, as subsequently given (page 230), it
wiU be seen how this evaporation of the solvents, previous
to washing, may be dispensed with. It is hardly worth
while to repeat the method here, more particularly when,
in some respects, the above is really superior to it ; at
least, so the writer has found.

For the above quantity of emulsion, 1 drachm of nitric
acid, which will be ample to secure freedom from fog,
should be dropped into the dish, and distilled water added.
After a couple of hours the true washing may commence.

A method which we have found to give still better re-
sults, if the acid is omitted from the emulsion, is to wash
the peUicle twice or three times in water till nearly all
excess of silver is removed, and then to add 2 drachms of
hydrochloric acid to the next wash-water (which should
not be more than ten ounces), and then begin to wash
de novo. Mr. W. Bedford first recommended this plan.
Instead of the hydrochloric acid, a solution of bichro-
mate of potash, ten grains to the ounce, to which a pinch
ot common salt has been added, may be substi-
tuted. This is an excellent method, since any trace

226 PREPARATION OP AN EMULSION.

of bichromate is visible in the wash-water. The pinch
of salt prevents the formation of bichromate of silver.

To wash the emulsion, it may be placed in a jar or jam
pot, and be covered with water, where it can stand two or
three hours in the dark without detriment, when it should
be changed. The way in which the washing can be econo-
mically effected, as regards time, is at follows : — A piece
of course calico which has previously been washed in car-
bonate of soda, and then well rinsed, and dried, is spread
over the top of a second glass jar or large jam pot, and the
contents of the first thrown on to it. The calico acts as a
strainer, and the solid pellicle is left on it. The calico is
next taken up by the sides, and the contents are twisted up
in it, and as much as possible of the liquid then wrung out.
The calico is untwisted, and a bag formed by tying up the
ends, to holds the emulsion, which is shaken up and im-
mersed in fresh distilled water. After a quarter of an
hour the wringing operations are again proceeded with,
and this process repeated three or four times. The ex-
pelled water should now be tested for free silver nitrate
by a drop of hydrochloric acid. If it gives more than a
slight milkiness, such as is produced by adding silver
nitrate to water containing a grain of common salt to the
gallon, it must be washed till this maximum is attained.

Preparing the J^ellicle for Re-emulsifying. — A very im-
portant part of emulsion making is now to be touched
upon, viz., getting rid of the water held in the pellicular
mass.

To commence with, as much water as possible should
be squeezed out, and then we may proceed in one of these
ways.

1st. We may lay it out flat on a piece of blotting-paper,
and allow it to dry spontaneously. 2nd. We may put it
in a flat porcelain dish, and place it in a water bath, the
temperature of which can never exceed 150°, and thus
all moisture may be got rid of. In this proceeding the
very greatest care is necessary, as the emulsion is apt to

PREPARATION OF AN EMULSION. 227

become very hard indeed — so rauch so as to be scarcely-
soluble ; in addition to which, it is often apt to blacken
spontaneously if the temperature be at all high. The
third method is one which we can confidently recom-
mend for washed emulsion, being very simple, and
absolutely improving its qualities when re-dissolved.
This is to cover it with rectified spirit -820 after as much
water as possible has been squeezed out of it. In an
hour's time the excess is drained ofi", and the pellicle is
squeezed in the cotton rag as before. It is then once
more covered with the spirit, and left for half-an-hour,
when, after draining away the superfluous spirit, it is
ready for re-emulsifying. If it be desired to keep the
pellicle in a solid state, it will only be necessary to expose
it to the air for a few hours, when it will be found quite
dry.

It is instructive to examine the washings from the spirit.
It will be found that there is a certain small quantity of
silver bromide in suspension, which can be filtered out.
If the spirit be distilled over, a semi-opaque liquid residue
wiU be left, having a very high boiling point, a strong and
very disagreeable smell, and containing some organic salt
of silver, which discolours in the light. It may be said
that this organic compound is necessarv for density of
image ; but a trial of the emulsion washed in this way
will prove the contrary ; in addition to which, it will be
found much freer from spots than that washed and dried
by the first two methods indicated above.

There are some pyroxylins which it would be dangerous
to treat in this manner, since they are soluble, to a certain
extent, in absolute alcohol ; but it seems to the writer that
any such pyroxylins are to be avoided when washed
collodio-bromide emulsion is in question. If they are
employed, the old method of drying must be adopted.

The dried (or moist with alcohol) pellicle has next to
be dissolved in its proper proportions of solvents, which
are about 5 grains of pyroxylin to every ounce of the two

228 PREPARATION OF AN EMULSION.

when mixed. It is better to make it up first to the strength
of 10 grains of pyroxylin, and then to add the remaining
solvents, since the colour of the emulsion seems to be
better when a greater degree of viscidity is present when
the pellicle begins dissolving. In two or three hours the
whole of the silver bromide should be in suspension. It
will be found, however, that there is an improvement in
the quality of the film after the lapse of a couple of days,
or even more. A plate should be tried, before diluting
down the collodion with more ether and alcohol, in order
to test its flowing qualities, and to note the opacity of the
fihn.

In our own experience we like to be able to see the
outline of the flame of a gas jet through a film whilst
moist, but which, when dried, obstructs it. In this con-
dition the film is tough, requires no backing except for
special purposes, and is always capable of giving sufficient
density by alkaline development alone, without resort to
intensification.

Before taking into use, the emulsion should be filtered
through cotton-wool (see Chap. XVI.)

The exposure necessary for the washed emulsion already
described is very constant ; with a lens of aperture ^, and
in a fair light, thirty seconds will be found to be ample
when using the alkaline or ferrous oxalate developer.

CHAPTEE XXXV.

CANON BEECHEYS PROCESS— M. CHARDON S
PROCESS.

Canon Beechey's Process. — We have now to put on record
an unwashed collodion emulsion process, which is at once
simple and efficient, and the thanks of the photographic
public are due to Canon JbJeechey for its explicitness in
every detail. The following is the modus operandi : —

Take cadmium bromide (anhydrous) 400 grains
Alcohol (-805) 10 ounces

and allow the mixture to stand. Decant carefully, and
-add 80 minims of strong hydrochloric acid.

Take of the above solution... ... ^ ounce

Absolute ether (-720) 9 drachms

Pyroxyline (as above) ... 10 to 12 grains

To sensitize this, dissolve 40 grains of silver nitrate in an
ounce of alcohol ("820 sp. gr.) The best method of effect-
ing this is to pound up the silver nitrate in an agate
mortar, and to take only a quarter of the alcohol, and
boil it in a test-tube containing the silver salt. The
alcohol wiU become slightly brown (due, probably, to the
formation of a fulminate of silver), and should be de-
canted off into a bottle containing the collodion. The

230 M. chakdon's process.

remaining silver should he dissolved up in a similar
manner, the ounce of alcohol being just sufficient to effect
solution.

Between each addition of the silver nitrate the collodion
should be well shaken. When the final addition is made,
the emulsion should be very smooth, and rather thick.
When poured upon a strip of glass plate, it will appear
transparent by transmitted light, but after keeping
twenty-four hours (occasionally shaking the bottle con-
taining it in the interval) it ' ought to be very opaque and
creamy.

The plate is coated with a substratum, or edged (see
Chap. XIX.) by running a camel's-hair brush one-eighth
of an inch round the edges of the plates, with any of the
substrata given in the same chapter. The collodion, which
should have been shaken about half an hour* before, is
poured on it in the ordinary manner, and, when set, im-
mersed in a dish of distilled or rain water. When all
greasiness has disappeared, it is flooded with any of the
preservatives given in Chap. XLI. Canon Beechey recom-
mends the plate to be immersed in a dish containing beer
to which 1 grain per ounce of pyrogallic acid has been
added. The drying Is conducted in the usual manner.
The exposure may be taken to be about twice that which
is necessary for a wet plate. Between exposure and deve-
lopment the plate will keep fairly for a week, but after
that it seems to lose detail, and appears under-exposed.

M. Chardon^s Pi^ocess. — The following process was
awarded a prize by the French Photographic Society.
It does not differ much from the first process given, ex-
cept In the details of preparing the collodion.

In preparing the collodion for this process, M. Chardon
prefers the use of two kinds ot pyroxylin, both of which
have previously been precipitated from collodion into

* Canon Beechey recommends the bottle to be shaken immediately before
use, and the emulsion filtered.

M. chaedon's peocess. 231

water (see page 216). The oiie pyroxylin is prepared in
the manner given at page 211 ; the other, the high tempe-
rature cotton, prepared as at page 214. These are mixed
in the solvents to form collodion. A salted collodion is
made up as foUows : —

Alcohol ... ... ... ... 1 ounce

Ether ... ... ... ... 2 ounces

Double bromide of cadmium and

ammonium ... ... ... 14 grains

Zinc bromide ... ... ... 14 „

Precipitated pyroxylin, ordinary 7 ,,
Precipitated pyroxylin, high tem-
perature ... ... ... 28 ,,

A stock of this is made, and, when settled, decanted off
as required. It must not be filtered, as the evaporation
of the solvents is said to cause a change in the sensitive-
ness of the finished emulsion, though we doubt it. The
collodion is rendered sensitive in small quantities at a time.
The silver nitrate is finely powdered, the quantities
being as follows : —

The above salted collodion ... 1 ounce
Silver nitrate ... ... ... 6 '2 grains

Alcohol... ... ... ... Bounces

The ordinary means already described are employed for
forming the emulsion (see page 221). The emulsion is
vigorously shaken in a bottle, and put aside for thirty-six
hours to ripen. After this time has elapsed, about an
ounce of pure distilled water is placed in a glass beaker,
and a drachm of the emulsion poured into it ; after agi-
tating the mixture, it is filtered clear, which can be eiFected
by passing it once or twice through the filter paper. This
waste is tested for silver nitrate. A slight milkiness on
the addition of a chloride is all that is allowable. If it
shows no signs of free silver nitrate, more of the latter
salt dissolved in alcohol is added to the emulsion, just to
give the necessary milkiness. This emulsion thus formed

232 31. chaedon's process.

is next corrected by a collodion in which cohaltic chloride
is dissolved, made as follows : —

Alcohol 1 ounce

Ether ii ,,

Cobaltic chloride 60 grains

Pyroxylin ... ... ... 12 „

Of this he adds, about 2 drachms to each 10 ounces of
emulsion ; as before stated in this work (page 21), all
causes of fog are thus eliminated.

The novelty of M. Chardon's process is now to be ex-
plained. He takes the finished emulsion, and pours it
in a fine stream into a large quantity of water. After
stirring, the precipitated emulsion is filtered through a
cloth, is washed carefully (the method indicated at page 22
will answer), pressed between folds of blotting-paper,
and dried in the dark. This gives a flocculent powder of
a clear yellow colour. To prepare the finished emulsion,
the following is prepared . —

Ether

^ ounce

Alcohol...

1

2 11

Precipitated quinine ...

... 1 grain

The precipitated quinine can be made from the ordinary
sulphate of quinine by dissolving it in sulphuric acid,
and then adding ammonia. The precipitate thus formed
is employed.

The organic substance is first dissolved in the alcohol,
and, after filtering, the ether is added. To this amount
of solvents 17 grains of the dried powder is added. After
some hours, when all is in solution, the emulsion is filtered
through cotton-wool (see Chapter XL.) M. Chardon
states that the quinine gives porosity to the film ; but it
seems more probable that it acts like some other organic
matters — viz., prevents a tendency to fog.

The exposure for plates prepared by this process is
stated to be about double that required for a wet plate.

CHAITER XXXVL

COLLODION EMULSIONS TO WHICH PRESERVA-
TIVES ARE ADDED,

DawiorHs Process. — The next process which we shall
describe is one described by Dr. Dawson, in which an
" organifier " is added to the emulsion, and leads up to
the more complicated form recommended by Mr. Carey
Lea. We are indebted to the British Journal Almanac
for the formulae, which are as follows : —

Collodion.
Pyroxyline
Cadmium bromide
Ammonium bromide
Ether -725
Alcohol -810 ...

8 grains

2
1

11
ounce

In practice we have found no difference in result, if ether
of '730 be used, and alcohol of '812.

In our experience we find that the collodion should
be allowed to settle some days, and then be decanted
off. The pyroxyline employed may be that given at
page 21.

To sensitize this, a mixture is made of —

Silver nitrate ... ... ... 13 grains

Acetic acid ... ... ... 2 drops

Glycerine ... ... ... 1 drachm

Alcohol -830 4 drachms

234 COLLODION EMULSIONS.

These are dissolved in the usual manner, it being,
perhaps, the Letter plan to leave the glycerine out
till th& last minute. After emulsification it is allowed
to stand twenty-foiu- hours, and then 2 drops of hydro-
chloric acid are added to the above quantities. It is
allowed to rest for another twenty-four hours.

The emidsion is poured out into a dish of sufficient
capacity, in order for the solvents to evaporate, and in five
or six hours it is ready for further treatment. This con-
sists in covering the pellicular mass with water for an hour,
and, after pouring off, covering it for a similar time with —
Tannin ... ... ... ... 5 grains

Gallic acid ... ... ... 2 „

Acetic acid ... ... ... 2 drachms

Water (distilled) ... ... 1 ounce

The washing is now commenced in a manner similar tO'
that already described at page 225, till all traces of acid are
removed, which can be tested by litmus paper. When all
the water is wrung out, the emidsion is dried in a hot water
bath, or spread out in a warm room on blotting-paper.

The mode of eliminating all traces of water by alcohol
is not admissible in this case, as it would dissolve out the
tannic and gallic acid which may be left in the pellicle.

To re-dissolve the pellicle, equal quantities of ether and
alcohol are used, having the same specific gravity as that
given above. Dr. Dawson recommends that it be soaked
in the alcohol for twelve hours before adding the ether.

The development of the plates can be carried out by
the strong alkaline development.

Carey Leals Chlor-Iodo- Bromide Process. — In this pro-
cess we have silver iodide emulsified with bromide and
chloride, and, in some hands, it works well. The
following description will show how the emulsion is
prepared. The collodion is made thus —

Ether, -730 4 drachms

Alcohol, -805 4 „

Pyroxyline ... ... ... 8 grains

COLLODION EMULSIONS. 235

The cotton may be any of those given in Chap. XXXIV.

To CTery ounce of collodion the following are added : —
Dried cadmium bromide ... 9 grains
Ammonium bromide ... ... 2i „

Ammonium iodide ... ... 2 „

Directly before emulsifying, add —

Aqua-regia 2 drops

The emulsion, with an excess of silver, is formed by
adding 25 to 30 grains of silver nitrate ; and after an
hour's interval, 2 grains of cupric chloride or cobaltic
chloride ; 2 drops of hydrochloric acid may be substituted
for either of these, or for the aqua-regia.

The emulsion may at first appear flakey, but after the
addition of the chloride it is only necessary to shake well
and leave it for twelve hours. On again shaking, the
emulsion will be found perfect. It may be used before
drying, or after drying. In the former case, any of the
preservatives ordinarily used may be employed.

If it has to be dried, it is poured out into a dish, and
left till it is in a leathery condition on the surface, after
which a preservative is poured upon it. Any preserva-
tive will answer, but Mr. Lea recommends —

Water 6 ounces

Acetic acid ... ... ... ... 3 drachms

Solution of gum-arabic with sugar 4 ,,

Prepared albumen ... ... ... 1 ounce

Gallic acid (60 grains to 1 ounce of

alcohol) ... ... ... ... 4 drachms

Tannin (60 grains in 1 oz. of water) 2 ,,

The albumen is prepared by the addition of an equal
bulk of water to the white of one egg, and clarifying with
12 drops of acetic acid.

The gum and sugar solution is made by mixing half-
a-pound of gum-arabic and two ounces of sugar in 44
ounces of water, and adding 1^ drachms of carbolic acid.

236 COLLODION EMULSIONS.

The pellicvilar mass is then broken up, and it and the
preservative are transferred to a large glass jar and left
there twenty minutes. The preservative is then poured
oflf, and the washing takes place as given at page 225.

Instead of drying the emulsion, it may be poured
direct into the preservative, taking care that the latter is
more than four times the bulk of the former. The
washing in this case takes place by decantation in the
usual manner. This last method is stated to give the
most soluble pellicle. The pellicle is then dried in the
oven or water bath, and is re-emulsified by taking for
each three ounces of the original collodion —

Ether ... ... ... ... ... 1 ounce

Alcohol ... ... ... ... 1 „

Plain collodion (4 grains of pyroxy-

line to the ounce) ... ... ... 2 ounces

Shake well at intervals, and in a week it is ready for use.
The plate is coated in the ordinary manner, and dried.
The exposure is stated to be about equal to that of a wet
plate.

CHAPTEE XXXVIL

MR. H. COOPER'S COLLODIO" BROMIDE RELIABLE
DRY-PLATE PROCESS.

Me. Coopek's formula is as follows : —

" Prepare first a stock of plain collodion by dissolving
160 grains of ordinary pyroxylin* in six ounces of absolute
alcohol and ten ounces ether. Good methylated alcohol
will answer for these first solvents, as also ether s.g.
•730, purchasable at Is. 6d. per lb. Also make an alcho-
holic solution of zinc bromide, 80 grains to the ounce.
Even after filtering, this solution will throw down a
deposit upon keeping, and this must be carefully left un-
disturbed. To make 10 ounces of washed emulsion, take
5 ounces of the above collodion, and add to it one ounce
of the zinc bromide solution, and 20 minims of syrupy
lactate of ammonia.t Sensitize with 150 grains of silver
nitrate, dissolved first in 80 minims of water, and then in
3 ounces of strong alcohol. Boil together, and add it to
the bromised collodion at once. I attach importance to

* Mr. Coopei recommends tlie pyroxylin as prepared by Hopkin and
Williams, as answering the purpose.

t " Small experiments made since this paper was first written go to show
that a great gain in sensitiveness may be obtained by reducing the propor-
tion of plain collodion. I have tried three ounces, and even two ounces,
instead of the five, with the most encouraging results. 1 am indebted to a
leader in the British Journal for the suggestion."

238 cooper's collodio-bkosiide pkocess.

the addition of the boiling solution, so as to raise the
temperature of the mixture, and when only a small
quantity (such as the above) is made, I take the pre-
caution to wrap the bottle in a thick cloth to retain the
heat as long as possible. On examining the portions
just given, it will be seen that the silver nitrate is de-
cidedly in excess, and that the alcohol is used in larger
proportion than usual.

" Lactate of silver has long been a favourite addition of
mine to emulsions, and I am more than ever pleased
with its action. I must call attention to a curious effect
which is produced if the bromised collodion is allowed
to stand many minutes after the lactate is added, and
before the sensitizing. The collodion becomes quite
milky, and throws down a crystalline deposit. Jt is well
to add the lactate immediately before the silver, or even
to defer piitting it in until after the sensitizing. I cannot
pretend to say what chemical or physical effect occurs in
the ' lactised ' collodion : I merely mention the fact.

" The emulsion is ripe in about twenty-four hours ; but
I am disposed to think it an improvement to keep it for
a longer time, up to three days. At the expiration of the
ripening period, twenty minims of strongest nitric acid
are to be added, and the emulsion well shaken. I prefer
to add the acid just before the washing instead of at first.
I believe a better film is given by so doing.

" We are now faced with the question of how best to
wash the emulsion. Shall we pour it out and evaporate
the solvents, or precipitate it? From a lengthened
experience of both methods, I cannot recommend pre-
cipitation, except in cases where the finished emulsion is
to be used up within a month. It is now a generally
acknowledged fact that precipitated emulsions will not
keep well. But where large batches of plates can be
prepared at a time, and no waste occurs, I can speak to
the good qualities of the emulsion when precipitated by
mixing it with twice its bulk of the following organifier,

cooper's collodio-beomide process. 2'dd

and when the pellicle has fully separated and set, washing
for some time in water containing a little nitric acid
(half-ounce to one gallon), and finally in several changes
of pure water. The mixture —

Tannin ... ... ... ... 500 grains

Gallic acid 200 „

Grape sugar ... ... ... 200 ,,

Strong acetic acid ... ... 10 ounces

or a proportionately lesser quantity of glacial, to be dis-
solved in water, and make up to 100 ounces. This method
is expeditious. The alternative, and, I think, the better
plan, is to pour out the emulsion into a sufficiently large
dish (1 ounce to 25 square inches, or say 5 ounces in a
12 by 10 dish). Evaporate the solvents more thoroughly
than usual ; in fact, the pellicle may be allowed to get
almost dry. Wash first in water containing half an
ounce of nitric acid in one gallon of water, and then in
plain clean water for some considerable time. If the
water in use is hard, distilled water should be used at first
and lastly. Wash thoroughly. The extra drying of the
pellicle and the large proportion of alcohol it contained
will materially assist in shortening the time. When dry,
dissolve the above quantity of pellicle in 5 ounces of pure
absolute alcohol, and a like quantity of extra purified
methylated ether, s.g. "720. An emulsion prepared in
this manner with the lactate of ammonia will give excel-
lent negatives, without further preparation, -if the plates
are used at once ; but its subsequent treatment with alka-
line albumen gives the especial qualities for which I had
so greatly valued it. The plates are much quickened by
the after treatment. This particular emulsion has its
sensitiveness doubled, whilst some others are rendered
slower."

Mr. Cooper then describes gelatinizing the plates with
gelatine and chrome alum as given at page 115. He
says that small plates may have an edging only, but that
he prefers giving them the lull coating : —

240 cooper's collodio-beomide process.

" Coat with the emulsion. When well set, immerse in
water. I myself use a grooved box, well coated with
shellac, and when I have coated and immersed as many
plates as I intend to prepare, I cover up the box and
thoroughly ventilate the room, so as to get rid of all
fumes of alcohol and ether before proceeding further. I
see no reason why a tin box with removable grooved
pieces, similar to the one sent out by the Autotype Com-
pany for developing chromotypes, should not answer. Of
course it must be kept for the purpose alone.

" The plates are now to be flooded with the alkaline
albumen, or dipped in a bath of it. In either case the
albumen must be in contact with the film for at least a
minute. The plate is then to be thoroughly washed,
flowed with a preservative, drained, and dried. After
backing, it is ready for the camera. The albumen may
be prepared in bulk, either with whites of eggs, or with
the pure dried preparation. Of the latter, dissolve 60 grs.
in 3 ounces of water, and add 1 drachm of strongest
liquor ammonia "880. If white of egg be used, first pour
in a few minims of dilute acetic acid, and well stir. In
two or three hours strain, and to each ounce add two of
water and one drachm of liquor ammonia.

"Eorthe 'preservative' I have tried a host of sub-
stances, and find the simplest of all to be the best —
viz., a two-grain solution of gallic acid. For the sake of
constant uniformity and certainty, I was anxious to
discard from' my formulae all compounds of uncertain
chemical constitution, such as beer, or even tea and coffee,
or else I could, from my own experience, speak strongly
in favour of a decoction of tea, made by boiling 1 ounce
of compressed black tea in 4 ounces alcohol and 12 ounces
water. One ounce of this is diluted with 10 ounces of
water to form the final coating for the plate. It is of
importance that the plates should be thoroughly dried,
especially if intended for packing ; as although these plates
will stand exposure to a moist atmosphere better than

cooper's collodio-beomide peocess. 241

most others, any damp remaining in the films when they
are stored away will be a source of future trouble."

Mr. Cooper recommends a full exposure in the camera
for these plates. We have found that with a stop -2^, and
in an open landscape and good light, thirty seconds are
ample, but that three minutes may be given without .
detriment. Of the negatives produced by this process,
Mr. Cooper says : — -

" First, the quality of image is almost perfect, much
resembling that given by a really good coUodio-
albumen plate. Secondly, the films will keep for a lengthy
period without deterioration, both before and after
exposure. I exhibit a negative which was kept five
months before exposure, remaining for three months^ in
a dark slide, and carried about on long journeys, being
submitted to many variations of temperature and hygro-
scopic conditions of the atmosphere. After exposure and
before development it was kept five weeks. Other plates
have been kept three months after exposure. I give these
data, as many folks' ideas of a 'lengthy period' are
various. I have plates prepared early this year which I
am keeping on to test from time to time.

"In exposure, very great latitude is allowable — an
unspeakable boon to the photographer on a tour, with no
conveniences for developing a trial plate from time to
time."

CHAPTEE XXXVIII.

COLLODIO-BROMIDE EMULSION PREPARED IN
THE ALKALINE STATE AND WITH EXCESS
OF BROMIDE.

The writer, in some recent investigations, was led to the
conclusion that, theoretically, the loss of sensitiveness
due to using a collodio-bromide emulsion with an excess
of soluble bromide must be due to the want of a bromine
absorbent ; and that if, with an excess of soluble bromide,
we had the presence of such an absorbent, that then the
sensitiveness should be in a great measure restored.
When light causes the liberation of bromine from the
silver bromide (see page 9), and when a bromine absor-
bent, such as potassium nitrite, is present, we have the
following reaction : —

Bromide and '"^^ and Water give ^^1;?^-^ and ^^S^
2Br + KNO2 + H2O = 2HBr + KNO3

The hydrobromic acid liberated would have a tendency
to destroy the image ; hence it is desirable that a neutral
compound should be formed. This will be the case if an
alkaline carbonate be added, for then we have —

■„ . Potassium . Sodium „- ^ Sodium Potassium . Carbonic

Bromine ^j^t^^g and cajbonate 8'™ Bromide Nitrate ^^ Anhydride
2Br+ KNO2 + NajCOj = 2Na Br-|- KNO3 + CO^

This practically was proved to be the case. In making
a washed emulsion with excess of bromide, it will be

COLLODIO-BROMIDE EMULSION. 243

well, then, to add to every ten ounces of emulsion two
drachms of a saturated solution of potassium nitrite in
alcohol, and to apply to the film sodium carhonate in the
first wash water, and then to wash again. By this means
the retarding effect of any trace of soluble bromide left is
counteracted by the presence of the trace of potassium
nitrite and of sodium carbonate.

The following formulae will be found to form a very
excellent emulsion, giving very beautiful films, which, for
sensitiveness, are not behind those which are prepared
with excess of silver nitrate. It is based on the alteration
which is caused in the molecular structure of silver bro-
mide by the use of ammonia, as adopted for the gelatine
process. The ordinary collodion is formed as follows : —

Pyroxylin (high temperature) 25 grains
Alcohol ... ... ... ... 2 ounces

Ether 2 „

To this is added 100 grains of zinc bromide.

In order to emulsify this, 100 grains of silver nitrate
are dissolved in the smallest possible quantity of water,
made up to one ounce with alcohol, s.g. about "820, and
liquor ammonia added, drop by drop, till the oxide first
precipitated is re-dissolved. The emulsion is then formed
as given in Chap. XXXIV. It is immediately" placed in
a dish to evaporate, when it is at once washed till it
shows no alkaline, or a very faint trace of alkaline, re-
action. The water may be eliminated by the alcohol
plan, or by drying, as given in the same chapter.

The pellicle is then dissolved in 2^ ounces of alcohol
and 2^ ounces of ether. It will be noticed that the pro-
portion of pyroxylin to silver bromide is too small. Plain
collodion made as follows should therefore be judiciously
added, till a silver of good quality is obtained : —
Pyroxylin ordinary ... ... 50 grains

Ether -720 5 ounces

Alcohol -805 5 „

244 OOLLODIO-BKOMIDE EMULSION.

This must be added judiciously. It will probably be
found tliat as much as 5 ounces of this will have to be
added ; but a good deal depends on the quality of the
pyroxylin.

The emulsion should be orange when mixed, and also
after washing. It should be powdery to the touch when
a plate is coated with it. It will be found to be as rapid
as a wet plate, and if a preservative be used (see Chap.
XLI.) which will stand the emplojanent of undiluted
ferrous oxalate, it wiU be found, if rightly prepared, a good
deal more sensitive. The development takes place by
the alkaline method if preferred. An emulsion may be
made by the same formula as above, omitting the ammonia.
It will be found slower.

OHAPTEK XXXIX.

COLLODIO- ALBUMEN EMULSION.

The writer introduced to the photographic puhlic an
emulsion made with albumen, which proved to be very
sensitive, and some skilled photographers were pleased
with it. The process is given here, as it may, perhaps,
be used as a starting point from which other emulsions
may be satisfactorily deduced. In the hands of the writer
the images were inclined to be thin, but when chloride is
introduced, it is found that this lack of density vanishes to
a great extent, and leaves a very delicate and printable
image. The following is the mode of preparation : — 16
grains of ordinary cotton are dissolved in 6 drachms ot
ether ('TSO) and 4 of alcohol ("805), and the plain collodion
thus formed decanted. 20 grains of zinc bromide are
dissolved in a small quantity of alcohol, and enough bro-
mine water added to tinge the solution with a very pale
yeUow. This is added to the above amount of plain collo-
dion. For each halt ounce of the above, 1 grain of dried
albumen is taken and dissolved in the least possible
quantity of water, or 8 drops of the white of an egg
may be dropped into a drachm of alcohol, and thoroughly
stirred. Either of these solutions is then carefully
dropped into the coUodion (placed as usual in a jar), and
well stirred up. This should form an emulsion of albumen
in the collodion. Forty grains of silver nitrate are next
^dded in the way pointed out on page 33, after having

246 COLLODIO-ALBTJMEN EMULSION.

been dissolved in the smallest possible quantity of water
and boiling alcohol. A beautifully smooth emulsion
should result from this. Mr. Berkeley, who has tried this
emulsion, proceeds in a slightly different way ; he adds the
cotton to the ether, then adds the albumen, and finally
adds the amount of zinc bromide in the necessary amount
of alcohol.

The amount of silver nitrate added ensures that there is
an excess of at least two grains in each ounce of the
emulsion.

Instead of the emulsion being made entirely with zinc
bromide, greater density may be obtained by omitting four
grains of it, and adding four grains of calcium chloride.

The emulsion is next poured out into a dish, and the
ordinary manipulation carried out. After a couple of
washings, it may, however, advantageously be covered
with a weak solution of silver nitrate, and again washed
till the traces of silver are very faint.

The pellicle should be re-dissolved in equal quantities of
ether and alcohol, and finally there should be about seven
grains of the pyroxyline, as originally used, to each ounce
of the mixed solvents.

The emulsion, when finished, generally gives a tender
blue by transmitted light, and is seemingly transparent.
It may have a tendency ito curl off the plate on drying,
in which case the addition of a little ordinary washed
emulsion will correct it. It wiU develop with plain pyro-
gaUic acid, and can be intensified by pyrogaUic and citric
acid, with the addition of a few drops of silver nitrate solu-
tion ; or it can be developed by the alkaline developer, or
the ferrous oxalate developer, or the hydrosulphite deve-
loper. Some photographers have found a tendency in it
to form blisters when developing. This has not happened
to the writer when the developer was kept above GC* F.
In some hands this emulsion is extremely rapid — so much
so, as to require very considerably less exposure than an
ordinary wet plate.

CHAPTER XL.

PREPARATION OF THE PLATE.

When we require a glass plate to iise without a substra-
tum, we usually soak the plates in nitric acid and water,
and then wash under the tap, and carefully dry with a
cloth ; a cream of tripoli powder in alcohol is then ruhbed
over the plate and allowed to dry. When a plate is
required for use, the tripoli is rubbed off with a soft
cloth, and it is left unpolished ; a small piece of blotting-
paper is then folded up in the shape of a small spill, and
dipped in a solution of albumen in water (the strength is
immaterial), and the plate is given an edging by placing
the moistened end of the spill beneath the thumb of the
right hand, and drawing it round the edge of the plate.
By this means a " safe edge " is given to it. The amount
of fluid required is so small that the first edge may be
dry before the last is finished, and yet sufficient for the
purpose will be on the plate.

Some persons rub French chalk or talc over the surface
of the plate, and this will be found effective when using
washed emulsion, without giving an edging ; but we
honestly confess that where a preservative is used, this
is hardly sufficient. In our own experience a film will
adhere to the surface when it is only once wetted with

248

PREPARATION OF THE PLATE.

water, but not twice. In this case a substratum must be
employed to cause the necessary adhesion of the film to
the plate. The following answers : — •

Sheet gelatine ... ... 75 grains

Distilled water ... ... 60 ounces

Ammonia ... ... ... ^ ounce

Alcohol ... ... ... 1 „

The gelatine should be first softened in half the quantity
of water, and the remainder added in the boiling state,
which will dissolve it ; when cool the ammonia and alcohol
should be added, and it should be carefully filtered.

The substratum introduced by the late Mr. C. Hooper
may also be employed.

Albumen may also be used.

White of egg 1 ounce

Water 100 ounces

Ammonia ... ... 5 drops

50 grains of dried albumen may be substituted for the
white of egg. The albumen and water should be well
shaken together in a bottle for five minutes, and then be
filtered through fine filter-paper, taking care to avoid air-
bubbles.

A better formula, however, seems to be one due to
Mr. Ackland, and is thus described by Mr. W. Brooks : —

The whites of fresh eggs are collected, and to every
8 ounces, one ounce of water and 24 drops of glacial
acetic acid are added, by pouring it into the albumen
in a fine stream, and stirring evenly with a glass rod
for one or two minutes. The albumen should on no
account be beaten or whisked up, or the resulting prepara-
tion will be milky. It is allowed to rest one hour or more,
and is then strained through coarse muslin or cheese cloth.
To the strained albumen is added one drachm of the
strongest liquid ammonia ("880), when it can be put away
in corked bottles and kept for use.

PEEPAEATION OF THE PLATE. 249

To make a substratum, Mr. Brooks takes —

Prepared stock albumen ... 1 ounce

Water 1 pint

This is applied as above. For Dr. Vogel's substratum,
see page 115.

The cleaning of the plate is of much greater importance
when a substratum is used, than where it is omitted,
the great difficulty being to get an even film on the sur-
face ; it is impossible to get this if there be the least
repellent action between it and water. What the writer
recommends is, that the plates be soaked in nitric acid,
and be well rubbed with it by means of a pad of cotton
wool (freed from all resinous matter hy previous soaking in
a strong alkaline carbonate, and tJien thoroughly washed and
dried), and when the acid is washed away under the tap,
that it be followed by a solution of potash 20 grains,
alcohol ^ ounce, and water i ounce, also rubbed in with
a pad of wool. When water flows evenly over the sur-
face, the plate should be rinsed in distilled water, and,
after a short draining, the gelatine (except Dr. Vogel's,
see above) or albumen solution should be flowed over

Fig. 28.

it, and drained off immediately. A very thin substratum
will thus be given, which will dry rapidly, and be ad-
herent to every part of the surface. Another plan is
to use the Blanchard brush. A brush is made of swan's-

250

PEEPAEATION OF THE PLATE.

down calico, as follows : — A strip of glass, about six
inches long by two broad, should be procured, and round
one end should be attached, by thread or india-rubber
band, a double fold of swan's-down calico. This brush
should be dipped in the albumen, and the excess squeezed
out against the beaker. The plate, which should be dry,
should then be brushed smoothly down the surface in
parallel lines to within one-eighth of an inch of its edges,
set up to dry on blotting-paper, and protected from dust.
When dried (which should be done spontaneously), the
plate will be ready for the collodion. We have also
found that a squeegee covered over with swans'-down
calico, and damp with the substratum, is effective.

Some photographers recommend the use of india-rubber
for the substratum.

India-rubber 1 grain

Chloroform ... ... ... 1 ounce

Or,

India-rubber 1 grain

Benzole ... ... ... ... 1 ounce

These are flowed over the plate like collodion, the plate, of
course, being dry. Unless the solutions be very clear, and
free from all residue, a negative taken on a plate so coated
IS apt to show markings. There are, however, some
emulsions which seem to be totally independent of the
character of a substratum, and wiU not show these mark-
ings, even when the india-rubber solution is not bright.

Coating the Plate.- — When plates are to be coated, the
emulsion should be well shaken for three or four minutes,
and be then allowed to subside for ten minutes. The top
portion should then be filtered through washed cotton
wool.* The cotton wool should be placed in the neck of
a funnel, and not be too tightly pressed down ; and a

* Boiled in soda, and then thoroughly washed.

PKEPAEATION OF THE PLATE. 251

little strong alcohol passed through it to moisten it. The
first lot of" emulsion passing through the funnel should he
returned to the hottle, and filtered again. The amount
of emulsion required varies with the number and size of
the plates used. A trial plate is first coated to see if the
emulsion flows readily. If it appears to " drag " over
the surface, it should he diluted with a little ether and
alcohol (2 parts of the former to 1 of the latter). It will
be found that in coating a large plate the emulsion should
be thinner than lor a small plate. When it appears satis-
factory, the emulsion should once more be passed through
the filter. Coating the plates is next taken in hand.
The filtered emulsion is poured over the plate in the
usual manner, and the plate tilted up, and rocked to and
fro till the ridges and furrows, so often visible in these
plates, have disappeared. The surplus collodion should
be returned through the filter into another bottle, as by
so doing a fresh portion of the emulsion is used for each
plate coated, and there will be a consequent freedom
from specks due to any dust which may have fallen on a
plate previously coated. If this be a washed emulsion,
it should now be dried or treated with a preservative (see
Chap. XLI.) If it is to be dried, there is nothing so con-
venient as a hot air bath, such as used by chemists in
their laboratory. They can be obtained up to a size
which will take 8^ by 6^- plates. It is a good precaution
to line the inside with varnished paper, to prevent the
remote chance of any metallic specks depositing on the
plate during drying. If this be not at hand, the small
piece of apparatus recommended by Woodbury is very
effective. It consists of an iron tripod stand, such as
used in the laboratories, a flat sheet of cast iron, and a
spirit lamp when gas is not available. The iron plate is
placed on the iron tripod, and the spu'it lamp beneath it. Ct
is advisable to place a couple of pieces of blotting-paper
beneath the plate which is to be dried. By using the
blotting-paper the plate will be dried and heated uni-

252 PEEPAEATION OF THE PLATE.

formly througliout, which is not the case when it is
placed directly on the cast-iron plate, for curvature in
either wiU prevent the two surfaces coming in contact.
The heat should be so great that to touch the surface of
the blotting-paper is unpleasant to the fingers, and the
glass should be allowed to assume the same temperature.
It may be laid down as a maxim that the more rapid
the drying, the greater freedom there will be from all
spots.

Where a preservative is to be employed with a zoashed
emulsion, the plate must be washed with water till all
greasiness disappears, when it may be applied at once. If
an unwashed emulsion be used, the plate must be well
washed in distilled water, till all excess of haloid salt, if
that be in excess — or, as a ride, of the sUver nitrate, if that
be in excess — be thoroughly eliminated. The preserva-
tive may then be applied by flooding the film with it, or
by immersing the plate in a flat dish or dipping bath con-
taining it. When a plate is flooded with the preservative,
sufficient solution should be poured into a measure to
well cover the plate. It should then be poured evenly
over the film, and drained. A second portion of the pre-
servative should be applied, and worked over the plate for
a minute. After this it should be poured ofi", and the
plates set up to dry. The plates are in this case allowed
to dry spontaneously, but they are generally improved by
a final diy over the iron plate as directed above. If the
plates are dried in one of the drying cupboards described
in Chap. IV., they will be found to be free from markings,
and of better quality than if dried in an ordinary cup-
board.

In Chapter XLI. will be found a description of pre-
servatives which may be applied to washed emulsion with
success.

As a result of very numerous experiments, the writer
has unwillingly come to the conclusion that a washed
■emulsion without a preservative of some kind is a danger-

PREPARATION OF THE PLATE. 253

ous process In Avhich to place absolute trust. Films
which at first would give perfect negatives, will very
often show, when kept, spots which refuse to develop. An
interesting experiment is to take a plate freshly prepared,
and expose half of it to sunlight to darken it, and after
the lapse of a fortnight, to expose the other half. Though
the first part may show a perfectly uniform darkening of
the surface, the other half will, in all probability, show
the spots by their refusal to darken. A plate used with
a preservative, on the other hand, will blacken equally
after any length of keeping. The cause of these spots is
rather obscure, but we think we have traced them to a
quite unsuspected cause, which, if it prove correct,
wiU indicate another use of the preservative. It must
be remembered that the ordinary washed emulsion will
be free from the objection if the plates are prepared one
day, and exposed and developed within three or four
days. This lapse of time is often sufiicient for the
amateur.

Backing the Plate. — With some kinds of emulsion, more-
particularly if a gum or albumen preservative be used,
the films are very translucent, and the image is subject
to the well-known blurring due to light scattered by the
silver compound, and reflected from the back of the plate.
This defect is in a measure cured by applying some non-
actinic varnish to the back of the plate. This backing
may be made as follows : —

Powdered burnt sienna...

... 1 ounce

Gum ...

... 1 „

Glycerine

... 2 drachms

Water

... 10 ounces

The solution can be brushed on with a hog's bristle
brush. Ordinary printers' paper coated with gum-arabic,
stained with aurine or a blue absorbent dye, and fastened
on a plate, is as clean a method of backing a plate as
can be desired. Whichever backing is employed, it

254 PREPARATION OF THE PLATE.

should be removed previous to the development of the
plate, and it is often convenient to do so after the alcohol
has heen applied to the surface of the film, and before
"washing with water. The alcohol repels any water
contaiaing the soluble part of the backing, and thus pre-
vents staining of the image. A small tuft of cotton-wool
will remove the backing given above.

CHAPTEE XLI.

PSESERVATIVES USED WITH EMULSIONS.

Any emulsion, washed or unwashed, may be used with a
preservative, which ensures the plates being uniformly
sensitive, and also the absence of those troublesome spots
which refuse to develop. Colonel Wortley says that the
thorough washing of the film prevents the formation of
these spots ; and Mr. Woodbury never finds them when
he dries his plates rapidly and at a fairly high tempera-
ture. The emulsion used by Woodbury, however, contained
resin, and it may be due to this cause that he found the
absence of these enemies to emulsion work.

Beer Preservative. — The simplest preservative with
which we are acquainted is —

Beer ... ... ... ... 1 ounce

PyrogaUic acid ... ... ... 1 grain

After the plate is coated, it is washed till all greasiness
disappears, and the above is flowed on the fikn, and
allowed to remain on it for a minute. The beer solution
may then be drained ofi^, and the plate again washed, or
the final washing may be omitted, and the plate be
allowed to dry spontaneously. If, after the preservative
has been applied, the plate has to be washed, it should be
given a final rinse of distilled water.

256 PRESERVATIVES USED WITH EMULSIONS.

Mr. England recommends, after the plate witli tlie beer
preservative has been dried, that it should be washed and
given a final flooding with a pyrogallic acid solution, one
or two grains to the ounce of water. This procedure, he
says, immensely increases the rapidity ; it is rather more
trouble than the methods already given.

If the beer be left on the plate, and if the dimensions
of the latter be more than about five by seven, a substratum
(Chap. XVI.) should be used, as the films may have a
tendency to blister. It will be found, however, if, after
exposure, the plate be washed and be allowed to dry, and
then be treated with alcohol and water, and be developed,
that the film wiU adhere tenaciously to the plate, and
that no substratum will be requisite.

Mr. William Brooks, in the Photographic News,
described a modified method of applying the beer
preservative to washed emulsion plates.

The plate is coated in the usual manner, and when
properly set, it is, without washing, plunged into a bath
made as follows : —

Bitter ale... ... 1 ounce

Pyrogallic acid ... 1 grain

Sufficient of this is used to fill a dish to a depth of half-
an-inch. The ale should not be of the kind known as
sweet or mild, as both these contain too much saccharine
matter. The plate is left in the preservative till there is
no repellent action due to the ether and alcohol. It is then
taken out and dried spontaneously, a final warming, pre-
vious to storing, being given to it by means of a drying
oven or a hot water tin. The plates do not require back-
ing unless the emulsion be thin. The exposure necessary
must be ascertained by a trial plate.

Mr. Brooks states that he has kept plates prepared by
this formida five months before exposure, and about the
same time between exposure and development, and has
developed them without stain or speck.

PRESERVATIVES USED WITH EAIULSIONS. 257

The following preservatives may also be used with the
emulsion plates.

Carey LeoHs Preservative. — Mr. Carey Lea's " Litmus
Preservative " and tannin preservatives are as follow : — -

" Cover a quarter of a pound of good litmus with hot
water ; set a basin or plate over the bowl, and put in a
warm place for a day ; throw the paste upon a filter, and
pour on hot water till the filtrate amounts to a quart (the
filtration is slow) ; add a drachm of carbolic acid, and the
litmus solution keeps good indefinitely.

Litmus solution... ... ... 1 ounce

Water ... ... ... ... (Jounces

Gum-arabic ... ... ... 90 grains

Sugar (fine white) ... ... 90 „

Acetic acid (No. 8, or Beaufoy's) 25 minims

" The above quantity makes a convenient bath for a
^ by ^ plate.

" Throw the coUodio-bromized plate into a pan of water
until the greasy marks are gone, and then pass it into
this bath, where it should remain, with occasional agita-
tion, about ten minutes. The time is not important ; five
minutes will be sufficient : fifteen will do no harm."

The tannin preservative is as follows : —

Water ... ... ... ... 7J ounces

Gum arabic ... ... ... 90 grains

Sugar ... ... ... ... 90 „

Tannin ... ... ... ... 15 „

The washing of the plate is the same as above.

Regarding these two preservatives, Mr. Lea says :
the litmus gives the softest and most sensitive plates, but
needs an intenser cotton. The latter of the two pre-
servatives will work well with a wider range of pyroxy-
lin than the former, and give a brighter picture. The
tannin is the easiest to succeed with, but the litmus, when
well managed, undoubtedly gives the best negatives. In

258

PRESEKVATIVES USED WITH EMULSIONS.

^either case, the negatives are very beautiful ; better look-
ing or better printing negatives cannot be got with the
;wet process. The development may proceed by the strong
alkaline development (page 261), or by the process as
described by ilr. Cooper (page 237).

'Jhe Coffee Prcxervatii-e. — A coffee preservative is made
as follows : —

1. — Best coffee ...

White sugar

Boiling distilled or rain water
2. — (_rum-arabic

Sugar candy

Distilled water

^ oimce
90 grains

0^ ounces
90 grains
20 „

5^ ounces

When No. 1 is cooled, both solutions are filtered, and
the preservative applied by floating or by immersing the
washed plate in a flat dish containing the solution.

The plate will require a substratum unless the precau-
tion indicated above be observed.

'lannin Presei'vatlcc. — A simple preservative is made
with tannin as under : —

Tannin (pure) ..
Distilled water...

15 grains

1 ounce

The plate is washed, and the preservative applied as
above.

Albumen Beer
pared : —

1. — Dried albumen (or white of egg,
prepared as at page 79, 1 oz.).

Water

Liquor ammonia . . .
2. — Ordinary bitter beer
o. ^Ordinary bitter beer

Pyrogallic acid ...

The plate, after wasliing,

Pi-eserfatii:e. — The following are pre-

25 grains

1 ounce
\ drachm
1 ounce

1 ".
1 grain

flowed over with equal

PRESERVATIVES USED WITH EMULSIONS. 259

parts of 1 and 2, which are allowed to he in contact with
the film for one minute. It is then thoroughly washed,
and flowed over with No, 3, and set up to dry.

These plates are developed by any of the alkaline deve-
lopers given in the next chapter. Reducing the amount
of pyrogallic acid given to one-third will cause a thin
negative, which can be readily intensified by the ordinary
intensifier. This preservative gives great beauty and
delicacy to the negative, and subsequent intensification is
better than getting density by the alkaline developer
alone. The plates prepared with the albumen solution
are exceedingly rapid and safe.

A substratum is required for large plates.

Col. Worthy's Preservative is as follows, and he recom-
mends it as giving freedom from blisters often found with
gum preservatives.

The following stock solutions are prepared : —

No. 1. — Salicine, enough to make a saturated solu-
tion in distilled Avater.

No. 2.— Tannin

Distilled water

.. 60 grains
.. 1 ounce

No. 3. — Gallic acid

Alcohol

.. 48 grains
.. 1 ounce

To make the preservative, take

of—

No. 1

No. 2

No. 3

Sugar ...
Water ...

2 ounces
1 ounce

40 grains
7 ounces

This preservative may be used over and over again
with occasional filtering. The plates are best immersed
in it.

Red Gum Preservative. — The following alcoholic pre-
servative may be found useful : — Australian red gum, a
saturated solution, in equal parts of alcohol and water.

2B0 PRESERVATIVES USED WITH EMULSIONS.

The plate is washed, flooded with equal parts of alcohol
and water, and, after the preservative is floated on, it is
dried spontaneously. The gum must he removed hy
alcohol and water, and the development wiU take place
in the ordinary way. No substratum may he required.

Ch.iin Guiaemn Po'eservative. — This preservative is really
mixed with the emulsion itseK. It is prepared by making
a saturated solution of gum guiacum in alcohol -805,
One part of this to from 20 to 25 parts of the washed
emulsion are mixed, and the plate coated in the usual
manner. It is allowed to dry at a temperature of about
100° F., or else spontaneously. This is an excellent
addition to make to a horny coUodion.

The writer has tried the above preservatives, and has
therefore given them to the reader ; but there is no doubt
that almost any of the well-known preservatives might
have been applied with equal success.

CHAPTEE XLIL

DEVELOPMENT OF THE PLATE.

Foe emulsion work, an alkaline (or kindred) developer
of some kind is almost an essential, for though, faint detail
can be developed by pyrogallic acid alone in 7nost cases,
such a procedure entails a prolonged exposure.

The following are formulas for the alkaline developer
which the writer can recommend, having been in use by
him for several years past : —

(1). — Pyrogallic acid
Water

(2). — Potassium bromide
Water

(3). — Ammonia
Water

b grams
1 ounce

20 grains
1 ounce

1 part
32 parts

To develop, 2 parts by measure of (1), 2 parts of (2),
and 1 pajtof (3) are taken and well mixed in the deve-
loping cup. If an albumen or gum preservative be used.
No. 2 may be reduced to 1 part.

The developer given by Col. Wortley is as follows : —

(a). — Pyrogallic acid ... ... 96 grains

Methylated alcohol ... ... 1 ounce

262 DEVELOPMENT OF THE PLATE.

(b).

— Potassium bromide ...
Water distilled

... 120 grains
1 ounce

(«)•

— -Ammonitim carbonate

80 grains

AVater

1 ounce

Or,

(«)•■

— Liquor ammonia '880
Water

6 minims
1 ounce

By the last formula, 6 minims of («), 3 minims of (6),,
and three drachms of (c) are taken and mixed.
M. (.'bar don's developer is as foUo-vvs : —

1. — Ammoniam carbonate ... 10 grains

Potassium bromide ... ... 2 „

Water... ... ... ... 1 ounce

(Care must be taken that the carbonate is pure.)

2. — Pyrogallic acid ... ... ... 50 grains

Alcohol ... ... ... ... 1 ounce

To develop, the following proportions are taken : —

No. 1 ... ... ... ... 1 ounce

No. 2 10 to 15 minims

The image will appear very rapidly if the emulsion has
been properly prepared.

AVe will now Imagine that the plate has been exposed,
and that we are to develop the image. After taking the
plate out of the slide it is carefully dusted, and, if neces-
sary, a solution of equal parts of alcohol and water is
flowed over it to soften the film. It is then either washed
under the tap, if the water supply be of good quality, or
Is immersed In a dish of rain-water previously filtered
through charcoal. A¥hen all repellent action between
the spirit and water is obliterated, the mixed proportions
or solutions indicated above are carefully flowed over the
plate, and almost immediately poured back. The Image
ought to appear gradually and ^vlthout veil. If it shows

DEVELOPMENT OF THE PLATE. 263

iimvillingness to appear, a fresh solution sliould be made,
omitting half the bromide, and this will probably be
effected.

To develop a plate having a preservative, a little
thought should be taken as to the nature of the latter, as
has been indicated in the last paragraph. It is evidently
useless to waste alcohol if it is not soluble in it. In cases
where it is insoluble, the preliminary flooding with the
spirit should be omitted, and the soluble matter entirely
removed by water. Since the object of the alcohol was
to open the pores of the collodion, evidently the same
will be accomplished by removing the soluble matter
which fiUed them up.

Should there not be sufficient density, resort must be
had to the ordinary acid intensilier.

1. — Pyrogallic acid ... ... ... 2 grains

Citric acid ... ... ... 2 ,,

Water ... ... ... ... 1 ounce

And,
2. — Silver nitrate ... ... ... 20 grainy

^Vater ... ... ... ... 1 ounce

The plate must be well washed before using this.
Sufficient of No. 1 to cover this plate should be flowed
over it, and 4 or 5 drops of No. 2 dropped into the cup,
and the solution from off the plate returned on to it.
The intensification should then proceed till sufficient
density is secured.

The developer which Mr. Brooks recommended for his
process is as follows. It is an excellent formula, and, as
he gives some valuable hints about conducting develop-
ment, which apply to all processes alike, we give his
remarks in extenso : —

" After the plate has been exposed, take it on a pneu-
matic holder, and flow over it equal parts of alcohol and
water. I must here add a caution not to use the alcohol

264 DEVELOPMENT OF THE PLATE.

too strong, or it will attack the film unevenly, and cause
mottling, especially in the high-lights, as I am sure, from
past experience, this is one of the causes. It is not seen
so much in the half-tone, and scarcely at all in masses
of foliage, or where the subject is well broken up. If
mottling does occur, it is most at the thick end of the
plate. I do not know if this corresponds with the expe-
rience of other workers. If the alcohol is used without
diluting (say of s. g. of "825) the mottled markings are
very large, and as the alcohol is diluted with water, they
become smaller and smaller till they disappear altogether.
I generally allow it to soak well into the film for about two
minutes, of the strength mentioned above (halt water and
half alcohol). Methylated spirit answers every purpose,
providing that it is free from gum (if contaminated with
gum it turns milky on the addition of water). If a quan-
tity of plates are to be developed, I prefer to immerse
each plate in a tray containing the spirit, as it is then
done effectually. The plate is then taken and allowed to
soak in a dish of clean water, and rocked about until the
water flows evenly over the surface. Previous to apply-
ing the developer, flood the plate with the following : —

Stock albumen (page 79) ... 1 part
Water .., ... ... ... 4 parts

Allow this to soak well [into the film ; well rock the plate
to ensure even action ; not less than one minute must be
allowed for this part of the operation. The plate is then
slightly drained, and the alkaline developer applied, made
from the following stock solutions : —

P. — Pyrogallic acid (best) ... ... 96 grains

Absolute alcohol ... ... 1 ounce

A. — Sat. sol. ammonium carbonate ... 4 ounces
Potassium bromide ... ... 2 drachms

Water ... ... ... ... 8 ounces

A few drops of solution P for 9 by 8 plates (say 5 drops)?

DEVELOPMENT OF THE PLATE. 265

and 1 ounce of solution A are mixed in a perfectly clean
measure, and at once poured over the plate ; as soon as
it is covered it must be rocked vigorously for a few
seconds, so aR to make it blend with the albumen on the
plate ; and if the plate has been properly exposed the
image will at once make its appearance, gradually acquir-
ing intensity.

" After the developer has been on for some little time,
should it apparently cease in its action, drain it off, and
again apply a little of the prepared albumen solution for
about half a minute ; drain again, and apply the alkaline
developer as before ; the image will then, perhaps, rush
out very rapidly. This method can be repeated as often
a,s necessary ; but, as a rule, with a properly exposed plate,
one application of the albumen is sufficient. If more
density is required, a drop or two more of P solution can
be added. If too much pyrogallic is used, a very hard
negative is the result, so it must be used with judgment.
I have actually developed a 24 by 18 plate to full printing
■density with only half a grain of pyrogallic. The formula
given for solution A is given for work under normal con-
ditions. In the winter time the bromide can be reduced
one-half, and in very warm weather it can be increased.

" I have used the albumen as given above' for several
years, and the more I use it the more I like it, as it gives
an image so much like a good wet plate taken under the
best conditions.

" Should it be desirable, the intensity can be brought
up in the ordinary way before fixing with acid pyrogallic
and silver, same as for wet plates (see page 1.57.) The
plate must be well washed to free it from all traces of
ammonia, and before the silver is added to the acid pyro-
gallic it is first applied to the plate alone, which will
generally be sufficient to neutralize whatever may have
remained in the pores of the film."

Some prefer to develop their plates in a dish : indeed,
for ease of manipulation, a dish is highly desirable. Care

26(5 DEVEL0P3IEKT OF THE PLATE.

must be taken in this case that sufficient solution be taken
fully to cover the plates ; for an 8| by 6^ plate, and an
ordinary 10 by 8 porcelain dish, 4 ounces Avill be re-
quired.

The next developer, and which, for this process and
also the gelatino-bromide process, should become a
general favourite, is the ferrous oxalate developer.

The modes of preparing the ferrous oxalate solution
■will be found in Chapter XXIII. Our mode of procedure
with the developer is as follows : — If the saturated solu-
tion of the developer (made by dissolving ferrous oxalate-
in a saturated solution of potassium oxalate) be used, we
dilute it with half its bulk of water, and add to every
ounce 1 drachm of a solution of potassium bromide in
water (20 grains to 1 ounce), and apply this to the film
after washing, as described above. If the image appears
slowly, we add half the original quantity ot the ferrous
oxalate undiluted, and then, if the exposure be anywhere
near correct, this will bring up the requisite density.
Should more density be required, we intensify as given at
page 93.

Should the image refuse to come out even with the
stronger developer, one drop of a Tuth per cent, solution
of sodium hyposulphite to each ounce of developer will
have an accelerating eifeet (see page 152).

The exposure required for this developer seems to be
about two-thirds of that reqiiired for the alkaline deve-
loper given above, and is, therefore, a decided gain to the
]5liotographer.

There is a great charm in this developer, the plates
gaining intensity steadily, and withoirt any tendency of
being overdone, and the negatives give brilliant prints.

The ferrous-citro oxalate developer (see page 165) is-
also applicable for development. It works rather slower,
but can be used without the addition of any bromide.
The sodium hyposulphite may be used with it as Avith
the ferrous oxalate developer.

DEVELOPMENT OF THE PLATE.

267

A negative that is fuUy developed should show reduced
silver bromide next to the glass plate in the most opaque
parts ; so complete should this Ibe, that if the image be
dissolved away by nitric acid, we should have a positive
picture left behind formed of unalterable bromide, having
perfect gradation.

In the early days of emulsion making a weaker developer-
was made use of, and as for some plates it is still useful,
we insert it here for the guidance of students.

No. 1. — Pyrogallic acid ... ... 3 grains

Water .

1 ounce

(This will not keep long, but shou.ld be made when re-
quired.)

No. 1. — Ammonium carbonate ... 1^^ drachms

Water ... ... ... 1 ounce

No. 2.

Or,

No.

-Liquor ammonia
Water

•->. — Potassium bromide . . .
Water

No. 4. — ^Silver nitrate
Citric acid ...
Water

Nos. 2, 3, and 4 will keep infinitely.

The film should then be well washed under the tap. If
there be every reason to suppose that proper exposure
has been given, make a developing mixture in the fol-
lowing proportion : — •

1 part
12 parts

1 grain
1 ounce

20 grains
20 „
1 ounce

No. 1
No. 2
No. 3

1 drachm
1 drop

Sufficient should be taken to well cover the plate. Nos.

268 DEVELOPMENT OF THE PLATE.

2 and 3 should be first dropped into the developing cup,
and finally No. 1 is added. (The necessity of stirring is
prevented by this procedure.) Flood this over the plate.
The image, if everything be eii regie, should appear quickly,
and the developer should be worked over the plate till all
detail appears by reflected light. When this happens,
.another drop of No. 2 to each drachm should be dropped
into the measure, and the soltition poured back on to it as
before, and the intensification with the stronger ammoni-
acal solution proceeded with. The intensity will gradually
be increased, and it may happen that the requisite density
will be obtained. Should the density not be sufficient,
one drop of No. 4, with a drachm of No. 1, may be mixed,
and intensification takes place in the ordinary manner.
In the writer's experience, the colour and printing quali-
ties of all negatives by this process are improved by
even a slight application of the intensifier.

Should the negative flash out at once on the application
of the first developer, it is a sign of over-exposure of the
plate. The developer should immediately be returned to
the cup, and the plate washed. Two drops extra of No. 3
must be added to the developer, and the development pro-
ceeded with as before. The potassium bromide keeps
the shadows bright, and acts as a retarder ; so much has it
the latter qualification, that if a large quantity be added,
the plate will refuse to develop at all. It is better to fix
an over-exposed j)icture immediately the detail is all
-out, and intensify with pyrogallic acid and silver after-
wards.

If traces of the picture refuse to appear in three or four
seconds after an application of the primary developer,
a fresh developer should be made up similar to the above,
omitting the bromide of potassium. If the picture refuse
to appear satisfactorily when this course is adopted, the
plate is hopelessly under-exposed. When the detail is
well out, the intensification should be carried on as given
at page 263.

DEVELOPMENT OF THE PLATE. 269

Fixing Solution. — -The negative should be fixed with
potassium cyanide or sodium hyposulphite.

Potassium cyanide

... 25 grains

Water

1 ounce

. ^^■'

Sodium hyposulphite ...
Water

1 ounce
6 ounces

The first may be flowed over the plate, but a dipping
bath for the latter will be found advantageous for studio
work. There are some images which will not stand the
cyanide, and in rare instances some will not stand pro-
longed immersion in the hyposulphite ; it may be because
the metallic silver is in a very fine state of division. This
seems all the more probable since we know that in this
state it is attacked by the cyanide. When all the bromide
is dissolved from out of the film, the plate should be well
washed back and front. It is not amiss to give a dip in
a solution of alum, as used for gelatine plates, if hypo-
sulphite has been used, since it eifectually decomposes it.

The plate should be allowed to dry spontaneously, away
from dust, and it should then be varnished. Varnish
such as is used for wet plates should be procured and
applied, as given at page 161.

CHAPTER XLIIL

COLLODIO- CHLORIDE EMV'i.SION FOR
DEVELOPMENT.

Tn the previous processes it will be seen that silver bro-
mide forms the staple sensitive salt, though both iodide
and chloride have been introduced into the emulsion, but
in small quantities. The use of chloride by itself has, till
quite recently, been Inadmissible, on account of the diffi-
culty of producing a chemical developer suitable for it.
Dr. Eder and Captain Pizzighelli found that for gelatino-
chloridc plates, ferrous citrate in a weak form gave good
development. The developer was very weak, however, in
the form they gave, and the writer introduced the ferrous-
citro-oxalate form, which has proved suitable for collodio-
chloride plates.

There are two formula for collodio-chloride emulsions,
one with excess of silver, and the other with an excess of
chloride. For most purposes the latter is the one we pre-
fer, since it can be made and used in a quarter of an hour
when required. What is usually calli^d roUodio-chloride
is totally unfit for chemical development, and it is mis-
leading to class it under this denomination, since it has a
large proportion of citrate in its composition. To make
the collodio-chloride we proceed as follows : —

10

grains

5

5J

20

))

50

n

COLLODIO-CHLOKIDE EMULSION. 271

Weigh out the following —
Pyroxyline (any easily soluble sort)

J5 _ ;.' 3) ); j;

Calcium chloride ...

Silver nitrate

Dissolve the calcium chloride in i ounce of alcohol 'SOo,
"by warming over a spirit lamp. Place the 5 grains of
pyroxyline in 2-ounce bottle, and pour on it the alcohol
containing the calcium. After a couple of minutes add
■| ounce of ether, -when the cotton will dissolve.

Dissolve the 50 grains of silver nitrnte in a test-tube in
the smallest quantity of water, and add to it 1 ounce of
boiling alcohol '805, and mix. Previous to this the
10 grains of pyroxyline should have been placed in a four-
ounce bottle, and the alcohol containing the silver should
be poured on. Next add 1 ounce of ether, little by little,
with continuous shaking. The silver nitrate may very
probably partially crystallize out, but that is of very little
■consequence. Take the two bottles into the dark-room (a
room glazed for wet-plate work will answer perfectly), and
pour gradually the calcium chloride collodion into the silver
nitrate collodion — on no account vice versa. The resulting
emulsion, of course, is silver chloride in an extremely fine
state of division. A plate coated with it should show
a canary colour by transmitted skylight, and a thickish
iilm should make a gas flame appear ruby-coloured.
The emulsion may be washed in the usual way, if required
(see page 51) ; but, when washed, and used simply dried
after washing, it is, like other collodion emulsion prejiared
with an excess of haloid, rather insensitive. Before doing
anything with the emulsion, however, a plate should be
coated, washed under a tap, and placed in the dark slide.
The slide should be taken into white light, and half the
front pulled up for a second, and then closed. Ferrous-
citro-oxalate developer, as given at page 165, should
then be applied, and the result noted. A blackening of

272 COLLODIO-CHLOKIDE EMULSION.

the film may ensue. If correct on the application of the
developer, the film should not show any reduction of the
chloride, except on the exposed half of the plate. Should
blackening take place, nitric acid may be added ; but that
rather rots the film if kept too long in contact with the
emulsion, which would be the case if it is to remain un-
washed . A simpler plan is to add a soluble chloride which
would form a double chloride. Three or four drops of a
20-grain solution of cupric chloride (chloride of copper)
in alcohol should be added to the emulsion, and shaken
up, and immediately the fog disappears. Two or three
drops of gold tri-chloride, or of cobaltic chloride of a
similar strength as the copper chloride, would answer
equally as well.

So far as regards the making of the emulsion. The
next point is the preparation of the plates. As was said
before, it can be washed, but we really see no advantage
in so doing. Polished and edged plates (see page 77)
may be coated, washed, and then simply flooded once
over with —

Beer ... ... .. ... 5 ounces

Sugar (white) ... 1 moderate sized lump
Pyrogallic acid ... ... ... 5 grains

These, when dry, will be very sensitive, and put to shame
many a coUodio-bromide emulsion. Any of the preserva-
tives given in Chap. XLI. may also be used. To develop,
rinse, and then simply immerse them in a dish containing
the ferrous-citro-oxalate. In a short time the image will
begin to appear, and gradually gain strength. The
colour of the image is a beautiful ivory black, and admir-
ably suited for collodion transfers. If a warmer tint is
required, tone in a dish with —

Uranium nitrate... ... ... 10 grains

Ferricyanide of potassium ... 10 „
Water ... ... ... ... 10 ounces

COLLODIO-CHLOEIDE EMULSION. 273

The colour will rapidly warm, and would eventually
become a pretty chocolate colour.'

It will be noted that an emulsion prepared in this way
may be developed by the ferrous-citro-oxalate ivithout any
resfrainer.

They will also develop with : —

Hydrokinone ... ... ... 10 grains

Water ... ... ... ... 1 ounce

to every ounce of which are added 3 or 4 drops of a
saturated solution of carbonate of ammonia.

The emulsion may also be made with an excess of
silver nitrate, in which case, in the above formulas, seventy
grains of silver nitrate should be used. Fog may be
prevented by adding 2 or 3 drops of strong nitric acid to
the calcium chloride collodion, or it may be eliminated by
the use of bichromate of potash, or by hydrochloric acid,
or by cupric, cobaltic, or auric (gold) chlorides, after the
excess of silver has been washed away. In fact, the
same procedure should be adopted as in the collodio-
bromide process. The development of this emulsion is
carried on as above.

CoUodio-bromo-cJiloride Emulsion. — A very capital
emulsion is formed by mixing f part of an unwashed
coUodio-bromide emulsion with ^ part of an unwashed
coUodio-chloride emulsion. The same proportion of
washed emulsions may also be mixed with advantage.
The development of this emulsion is most advantageous
when an unrestrained developer such as the above is
used.

CH.\PTEE XLIV.

DEFECTS IN COLLODION EMULSION PLATES.

It is somevrliat difficult to name the especial detects
foimd in tlie emulsion dry plates, but we -n-ill endeavour
to point out tlie principal ones.

Misters in the film. — ^May be due to a preservative, more
particularly if it contain gummy matter. Thiis, with the
beer, or the gum-gallic or coftee preservatives, these may
make their appearance. The remedy has already been
given.

Black' spots ondevelopineut are usually due to dust being
allowed to settle on the film whilst drying ; decomposing
organic matter in fine particles is also a truitful source of
these annoyances.

Insensitive patches or spots on development have not yet
been tracked to an origm ; but if a preservative be em-
ployed, they will rarely be met with. They seem to be
due to impurities in tlie pyroxylin, since with certain
preparations they are altogether absent.

Crape markings in the film are usually due to the solvents
of the emulsion being too aqueous ; or tliey may be due
to the emulsion not having been shaken up shortly before
being used, or to the bromide being too coarse.

2hin transparent films with washed emulsion are usuallv
due to the last two caiises.

DEFECTS IN EMULSION PLATES. 275

Ihe mnulsion refusing to flow properly is due to deficiency
of solvents. This is frequently met with if the same
emulsion he used for coating many plates. It should be
■dUuted down with 1 part of alcohol (-812) to 2 of ether
■(•720).

Wlien the film tends to peel off the plate., the pyroxylin is
jjrobahly of too contractile and horny a nature, in which
■case the proper treatment is, to mix it with an emulsion
made with one of a more powdery character, or to mix a
little gum guiacum dissolved in alcohol with it.

Circular insensitive patches in the centre of the plates are
•sometimes met with in hot weather, when a pneumatic
plate-holder is used.

Ihe cause of fog has been pointed out in the first
chapter, and need scarcely be alluded to again. To
eliminate it in a washed emulsion, the careful addition of
■a few drops of a dilute solution of iodine in alcohol will
prove effective. With such an emulsion, when used
with a preservative, a dip in a 10 per cent, solution of
hydrochloric acid in water wiU eliminate all fog. In an
unwashed emulsion the addition of nitric acid will effect
a cure.

Flates which fog through having been exposed to light
may be rendered available for use by washing off any
preservative they may have on them, and immersing them
in a hock-coloured solution of potassium bichromate, or
by water faintly tinged with potassium permanganate, or
with a 10 per cejit. solution of hydroxyl or hydrochloric
•acid in water. After washing, a preservative may again
be applied.

Plates which fog under development, when the emulsion is
not in fault, must owe this defect to one of two causes :
1st, to the light of the developing room ; or, 2nd, to the
■developer. The first cause is easily tracked, as a plate
may be prepared and developed in almost absolute
■darkness without receiving any exposure to ordinary
light. If, after a short application of the developer,

276 DEFECTS IN EMULSION PLATES.

no fog is found, tlie light used during development is in
fault. If the plate fogs, the developer is wrong. _ In
this case, try making up fresh solutions, and using
more soluble bromide as a restrainer. With the ferrous
oxalate developer want of bromide is often the cause of

fog. . . ,

Drying marhings in a film are sometimes met with.
They generally form a sort of ripple marking near one
edge. They are usually found when impure water is
used for the final washing of a plate, and are absent when
a final rinsing with distilled water is given. With
plain washed emulsion these markings are never met
with unless the temperature of the drying oven is high.

J hick specks in aplate are usually due to the dried emul-
sion from the neck of the bottle mixing with the solution,
and finding a resting-place in the film.

CHAPTER XLV.

EMULSION PROCESSES FOR PRINTING.

Collodio-Citro-CMoride. — To prepare a citro- chloride
emulsion is not very easy at first sight, since the citrates
are very insoluble ia alcohol, and it is necessary to have
some such hody present in the collodion to form an
organic compound of silver to give vigour to the image.
It is very easy to do, however, hy a little artifice which
we have thought might be worth describing. Citrate of
ammonia is insoluble in alcohol, and therefore rather
difficult to introduce into an emulsion in the ordinary
manner ; but it can readily be introduced into collodion
by the following procedure. Take ten grains of pyroxy-
lin, and cover it with half an ounce of alcohol in which
20 grains of citric acid are dissolved, and then add 1 ounce
of fether. This forms collodion containing citric acid.
In order to get citrate of ammonia into the collodion in a
very fine state of emulsion, ammonia (gas) dissolved in
alcohol is added to the collodion. This is effected by
inserting a bent tube in a cork in a test tube which is a
quarter filled with liquor ammonia. Placing this in warm
water — in fact, nearly boiling water — the ammonia is
given off rapidly, and can be made to pass through al-
-cohol in another test tube. The alcohol absorbs the

278 COLLODION PROCESSES FOR PRINTING.

ammonia, and takes up a large proportion of gas, as those'
who use sal-volatile may be aware.

This ammoniacal alcohol is next added to the collodion
containing the citric acid, little by little, with shaking
and stirring, and sufficient is added till reddened litmus
paper shows a very slight trace of alkalinity. A very
fine emulsion of citrate of ammonia is thus formed, the
grain of which is indistinguishable by the naked eye,
and, like other emulsions when first mixed, is orange-
coloured when spread upon a glass plate. The emulsion
is again rendered slightly acid by the addition of a few
drops of a solution of citric acid in alcohol. If an emul-
sion of citrate of silver be required, there are two ways
of efi'ecting it — one by dissolving (say) 10 grains of silver
nitrate in the least possible quantity of water, to which
is added one drachm of alcohol, and gradually dropping
it into the collodion containing the citrate. It sometimes
happens that this gives a granular emulsion. If, how-
ever, the silver nitrate be coarsely powdered and added
to the emulsion, a very fine emulsion of citrate of silver
is produced by shaking. This may be washed in the
usual way, or may be precipitated by pouring in a fine
stream into water. Another method of forming the
citrate of silver is to pour out the emulsion of citrate of
ammonia into a flat dish, and, when well set, to cover it
with a solution of silver nitrate. It is then drained
from the silver, washed, and dried as usual. When re-
dissolved, the emulsified citrate of silver should be
excessively fine.

To prepare a coUodio-citro-chloride emulsion, two

Slans may be adopted : either to dissolve 20 grains of
ry calcium chloride in a small amount of alcohol, and
add it to the citrate of ammonia emulsion, and then to
add 80 grains of silver nitrate to it in the usual way.
What we prefer, however, is to make a coUodio-chloride
emulsion separately, and then to mix the citrate of silver
emulsion with it, according to taste.

COLLODION PKOCIJSSES FOB PRINTING. 279

To make a pure collodio-chloride emulsion, 1 dissolve
20 grains of calcium chloride in half-ounce of alcohol ;
add to it 5 grains of pyroxylin, and then Jounce of ether.
To 1 ounce of plain collodion made similarly, I add 60
grains of silver nitrate dissolved in the smallest quantity of
water, to which is added one drachm of warm alcohol.
This produces an emulsion of silver nitrate in the col-
lodion. To this the chlorized collodion is added drop hy
drop, with stirring or with shaking in a hottle, and a per-
fect emulsion of silver chloride should result. This can
be poured out to set in a dish as usual, and washed, dried,
and re-dissolved ; or can at once be poured out in a fine
stream into a large bulk of water, squeezed, soaked in
alcohol twice, wringing out in a cloth all excess of alcohol
each time. It can then be re-dissolved in the one ounce
of ether and one of alcohol, and should give a good
emulsion. The two emulsions may then be mixed
together as before stated. It is well to dissolve about
5 grains of silver nitrate in water and alcohol, and add
to the emulsion in order to increase the rapidity of
printing.

Any well-sized paper may be used with this collodion
emulsion, but we prefer the enamelled paper, such as
is used for collotype printing. The paper is turned up
round the edges for about ^ of an inch, to make a shallow
tray, and placed on a sheet of glass for steadiness. The
collodion emulsion is then poured on to the paper till
well covered, and all excess is drained off into the bottle.
It is then allowed to dry. It is now ready for printing,
which is done to a greater depth than for prints on
albumenized paper. After washing it may be toned by
the following : —

No. 1. — Ammonium sulphocyanate... 1^ ounce
Sodium hyposulphite ...45 grains

Sodium carbonate ... ... 15 »

Water 50 ounces

280 COLLODION PROCESSES EOR FEINTING.

No. 2. — Gold tri-chloride 30 grains

Chalk 1 teaspoonful

Water ... ... ... 50 ounces

Equal quantities of these are taken and mixed, and the
toning proceeds as usual. The prints ordinarily take
from two to ten minutes to tone. If a longer time be
required, add more gold till the desired effect is produced.
This toning bath can only be used once.

We have also found that a good tone may be given by
using the lime bath, or by the baths given at page 195.
These prints should be permanent, aijd possess a rare
beauty.

Gelatino-Citro- Chloride. — The writer has introduced a
process of printing by means of a citro-chloride in gela-
tine, which can be applied to paper and glass. The
method of preparation is as follows : —
1. — Sodium chloride
*Potassium citrate

Water

2. — Silver nitrate ...

Water

3. — Hard gelatine ...
Soft gelatine ...
Glycerine

Water

Nos. 3 and 2 are mixed together, and then an emulsion
formed by adding No. 1 in the usual way when forming
a gelatine emulsion. When set, the emulsion is squeezed
through canvas into cold water, and after allowing it to
remain in the water for ten minutes or a quarter of an
hour, dissolved up, with the addition of* about 3 drachms
of alcohol and 2 grains of chrome alum dissolved in
2 drachms of water. Plates or paper are then coated with
the femulsion, and printing takes place in the usual

* Tlje citrate may, be reduced to 20 'grains, and the silver nitrati ^ to
120 grains.

40

grains

40

w

1

ounce

150

grams

1

ounce

160

grams

160

n

1 drachm

H

; ounces

COLLODION PROCESSES FOK PRINTING. 281

manner. At first the emulsion may appear grainy ; if,
however, it be toiled for ten minutes, the grain disappears,
for the silver citrate is soluble in warm water. The
rapidity of printing by the boiling is certainly increased.
Plates, when coated, are rather transparent, and, prima
facie, a vigorous print might not be expected from them.
The rapidity of printing is very great ; it is more than
twice as rapid as ordinary albumenized paper. The
image prints of a violet tint by reflected light, and of a
rich chocolate colour by transmitted light. If fixed with-
out toning, the colour by transmitted and reflected light
is that of burnt sienna, and of great vigour and beauty.
Prints can be toned by any of the ordinary toning baths.
Borax and chloride of gold gives a pleasant tone ; the
sulpho-cyanide toning bath gives a black, rather ap-
proaching an inky tone. Platinum can be used to tone
the fixed print, but it has a great reducing action, and
there is a tendency for the whites to become yellowed to
a slight extent. No doubt endless variations in the
organic salts used might be made, but the citrate answers
well.

The prints should be well washed. It is believed that
they would not fade in the same way that albumen
prints are so prone to do, as the organic salt used is a
definite compound, and not one which is so complex and
uncertain as the albuminate of silver is. The liability to
fade is less with the above formula than with one which
has an excess of silver present. The potassium citrate is
in large excess ; hence no silver will attack the gelatine.
Of course this emulsion may be applied to opals or glass,
or it may be applied to paper as given in Chap. XXVII.
Mr. Ashman says the following gives a good tone : —
The following will be found capable of giving any tone
to the transparency or positive by reflected light, ranging
between warm brown and purple black : —

Ammonium sulphocyanate ... ... 1 drachm

Water ... ... ... ... 1 pint

Gold terchloride 1 grain

282 COLLODION PEOCESSES FOE FEINTING.

Upon adding the gold, it is converted into a sulpho-
cyanate, which will be seen to have a red colour. The
precipitate, however, dissolves in the excess of snlpho-
cyanate, and is then ready for use.

Washing before toning is dependent on the formulse
employed in making the emulsion ; in most cases it will
be found advisable. Toning action is first seen at the
edges, by the colour changing to a yellowish-brown ;
soon the whole print assumes a sepia tint, then purple,
and finally blue-black, the usual time occupied in these
changes being less than five minutes. The print should
then be transferred to another dish containing a plain
solution of ammonic sulphocyanate (2 drachms of the
salt in 1 pint of water), where it may remain five or ten
minates, after which it should be placed in weak hypo
1 — 10 until the soluble chloride is dissolved. Ammonium
sulphocyanate alone will be found to fix a plate or paper
print made with silver citro-chloride emulsion, but hypa
is cheaper and quicker. Should the plates or paper be
inclined to frill, place them in saturated chrome alum
solution after toning ; this in no way afi'ects the colour
or purity of the whites. Washing is the same as other
gelatine plates and silver prints.

Mr. Warnerke informs us that the paper or glass, when
heated, keeps whiter if there be free tartaric acid in the
emulsion, which we can well believe.

Unwashed Gelatino-Citro- Chloride Emulsion for Printing^
— At a meeting of the London and Provincial Photo-
graphic Association, Mr. A.L. Henderson described a modi-
fication of the above process : 16 grains of gelatine were
swelled in with cold water, and 2^ ounces of distilled
water were added. The gelatine was then dissolved by
the aid of heat, and 11|^ grains of sodium acetate added.
To the 42 grains of silver nitrate, dissolved in 1 ounce of
water, was next to be stirred in 5 grains of sodium
chloride and 7^ grains of sodium citrate, mixed together
in 1 ounce of water. Finally, the 1 ounce of gela-

COLLODION PROCESSES FOR PRINTING. 283

tine, swelled in water, was dissolved and added to the
emulsion thus formed, and then water added to make
up the bulk of 9 ounces. If the emulsion were required to
coat paper, he made up the hulk to half as much
again, or double. This emulsion would be used without
any washing.

Slow Collodion Emulsion Process for Transparencies. —
The following formula has met with approval for the
preparation of a collodion emulsion for transparencies, and
was one which we used for producing intense negatives :
50 grains of silver nitrate are dissolved in \ drachm of
water, and J ounce of boiling alcohol ('SOS) added.
This is poured on 10 grains of pyroxylin, and then 1
ounce of ether added to dissolve the cotton. The silver
very probably will precipitate in very fine grains, but
this is of no consequence. In another ^ ounce of alcohol,
40 grains of zinc bromide are dissolved, and this solution
is gradually added to the above collodion with shaking-
Such an emulsion will be found perfectly free from
mottling caused by excess of water, and wiU flow
smoothly. When a plate is coated it is washed, and any
preservative used (preferably beer), to which to every
■J pint a lump of sugar of the size of a large hazel nut is
added.

Slow Gelatine Emulsion. — Slow gelatine emulsion may
be prepared by the formula given in Chap. XXXVII., by
reducing the time of boiling to five minutes. If emulsi-
fication, as described in Chap. XXXVI., be accepted, it
win be found that after twelve hours it wiU be in a con-
dition to give a slow plate. Any emulsion may be made
slow by adding 10 grains of copper chloride to it after-
boiling. These slow plates give wonderful density.

CHAPTER XLVI.

PACKING PLATES.

Packing Gelatine Flates. — The method of packing
adopted by some dry-plate makers is an intolerable nuis-
ance. They make zig-zags of thick paper, which they
stuff between the ends of each plate, or pair of plates ;
and when a packet is unclosed and a plate taken out,
there is an endless bewilderment of paper and glass, each
out of place and hard to put right. Mr. England's plan
avoids this, and if the cardboard is smooth, no harm will
be done to the plates. He uses little frames of cardboard

7-^

Fig. 17,

to place between his plates, and they are just large enough
to be flush with their edges. Thus, for our sized plates
(Jk t)7 5), we cut strips of card SfV inches wide, 7 J inches
and an equal number of strips 5| inches long.

long.

PACKING PLATES. 285

Tough bank-post paper is gummed over with stiff gum,
and allowed to dry, and little squares of about half-inch
size cut out. A short piece and a long piece are laid
together, on a pair of lines ruled at right angles to one
another on a board, and when the square of gummed
paper is made to adhere beneath them, and then deftly
folded over, two sides of the required frame were made.
One more long, and one more short piece, similarly
treated, completed the frame. Four-sheet card is what
Mr. England recommends. When the strips are cut, we
make about thirty of these frames in an hour. The
plates are packed alternately back to back and face to
face, in the latter case a frame being placed between
them.

Our plates are packed in half-dozens, enclosed in twa
thicknesses of orange paper. The two packets are en-
closed in pieces of black varnished paper, and then placed!
in boxes.

Another plan which we have seen adopted appears tO'
be admirable for smallish sized plates, say up to 8^ by 6|.
Four small pieces of card about ^ inch by ^ inch are cut
for each alternate plate. After moistening one side, they
can be made to adhere to the margins of the plate, thus
spreading the two plates which are face to face, by an
interval of the thickness of the card ; and before placing
the plate in the slide, the strips are removed by a pen-
knife.

For large sized plates, we believe nothing better than
to place moderately stout orange packing paper cut to
the size of the plate between each pair. The orange
paper, as far as we have seen, has no deleterious effect on
the plates.

Boxes made of stiff millboard, and covered with orange
paper, are useful. The cover should cover both the top
and sides of the box. They should not be too small, but
be 1 inch longer and ^-inch wider, inside measurement,
than the plates. A depth of 1^ inches will then take one
dozen plates.

.286 PACKING PLATES.

Packing Collodion Emulsion Plates. — These plates are
even more difficult to pack than gelatine plates. Mr.
England's masks can be adopted. Dry plate boxes
with grooves are, however, what we prefer to all other
plans. The drawback to them is that they are rather
bulky.

Note-Book for Registemig Plates. — In making an expe-
dition during Avhich plates cannot be developed, or when
only some can, it is advisable to enter in a note-book all
details. We give an extract from a note-book, which
will show the form we recommend. It must be premised,
however, that each plate, besides bearing the number of
the batch, should also bear a distinctive number, which,
for convenience, may be written on the same label as
that indicating the batch, but using a red pencil instead
of blue.

When the slides are filled before starting, the columns
filled up are 4, 5, 6, 7, and the rest are filled up after ex-
posure and after development. By adopting this plan
a complete record of every plate exposed and developed
is obtained, and will be found of use in judging ex-
posures.

Eemarks.

Use of bromide
required in de-
veloping.

Detail in dark
trees of island
fairly out. -

Hypo, used in
developer.
Detail fair.

U3doiaA3(I

o o

O

•p9d0I9A8(I

CD~ CO*

CO_
so"

o"

1

t
n

River Arun,
looking to-
wards mill.

Lake near Ar-
undel, from
south.

CO

,-t

s

•amsodxa:

10 sec.

Inat.
3 -inch
opening

o

CO

•do^g

CO CO 1

( =^

■suai

1 i

JO isqimiH

00 -^ us (o .-< cq

•-I w -1 w CO CO

'laqnmii
la^atnc^isuag

CD CO CD CD OO CO
IM C^ !M CI .-1 rH

■nn^a

00 CO 00 00 M cq
C5 OS Oi O Q» 00

•8PTIS

CC '^ U3 CO t* CO

•WSii

a

Cloudy

1 1 *

■jnoH

2.30
S.IO

1 1 1

■BJ^a

00

00 '

18/6/81

Weights and Measures.

1 Sovereign weiglis

1 Shilling ,, ...

48 Pence „

HaK-penny and three-penny piece weigh
Florin and sixpence

Three pennies

4 half-crowns and 1 shilling

4 Florins, 4 half-crowns, 2 pennies

1 Half-penny = 1 inch in diameter

123-274 grains

87-273_ „
1 lb. avoirdupois

\ ounce

h „

1 „

2 ounces
4 „

AvoiKDTTPOis "Weight

27ji Grains . . .
16 Drachms
1 6 Ounces . . .

24 grains ...

20 pennyweights

12 ounces...

1 drachm (= 21^
1 ounce (= 437|
1 pound (= 7000

;rs.)>
„ )

Teot "Weight.
... 1 pennyweight (= 24 grains)
... 1 ounce (^ 480 ,,

... 1 pound (=5760 „

Old A-Poihecaeibs' "WEienx (superseded in 1864).

20 Grains ... 1 scruple (= 20 grains)

3 Scruples 1 drachm (= 60 ,, )

8 Drachms 1 ounce (= 480 ,, )■

12 Ounces 1 pound (= 5760 „ }

The New Apothecaries' Weight is the same as Avoirdupois.

LianiD Measttee.

60 Minims 1 drachm

8 Drachms 1 ounce =1-73 cub. ins. nearly

20 Ounces 1 pint =34-66 ,,, „

8 Pints 1 gallon=277-25 „ „

The Imp. Gallon is exactly 10 lbs. Avoir, of pure water ; the pint, IJ lbs.

Pliiid Measfee.

= 1 dessert spoonful
= 1 table ,,

1 Minim = 1 drop 2 Drs.

1 Drachm = 1 teaspoonful 4 „

Feench Measuees.
1 Gramme ... 15-432 grains
Kilogramme ... 1000 grammes (=2-2 lbs. Avoir, nearly)

1 Litre 35-216 ounces (fluid)

1 Cubic Centimetre (c.c.) ... 17 minims nearly
50 Cubic Centimetres ... 1 ounce 6 drachms 5 minims
1 Metre 39-37 inches

INDEX.

Aceto-GelatineEmulsioD, 169

Albumen Beer Preservative, 258

Alkaline Development of Gelatine
Plates, 134

Alkaline Development, Theory of,
14

Ammonia- Nitrate of Silver in Gela-
tine Emulsii 'ns, 93

Architectural Subjects, 129

Argentous Oxide, 6

Backing the Plate, 253
Beechey's Process, 229
Bennett's Gelatino-Bromide Pro-
cess, 81
Beer Preservative, 255
Black Spots oa Development, 274
Blisters on Gelatine Plates, 198, 274
Blocks of Sensitive Paper, 179
Boiling Gelatine Emulsions, 74, 97
Burnishing Prints, 195
Burton's Process, 91

Cadett's Shutter, 130

Camera, Exposure in, 180

Canvas for Squeezing Emulsion, 75

Chardon's Process, 229

Chemical Theory of the Photo-
graphic Image, 11

Chloride Paper, 194

Coating a Plate with Gelatine Emul-
sion, 118, 25ff

Coating Paper ■with Gelatine, 175

Coating Machine for Plates, 120
Coffee Preservative, 258
Cold Emulsification, 101
CoUodio-Albumen Emulsion, 245
Collodio-Bromide Emulsion, 242
Ccllodio-Bromo- Chloride Emulsion,

273
Cooper's Collodio-Bromide Process,

237
Collodio-Chloride Emulsion for

Development, 270
CoUodio-Citro-Chloride, 277
Collodion Emulsions, 207
Collodion, Preparation of, 218
Colour of Silver Bromide, 3
Cotesworth's Cold Emulsification,

104
Crape Markings in the PUm, 274
Cupboard Shelves, Level, 117
Cupric Chloride a Cure for Fog, 2ft
Cyanide of Silver Intensifier, 158

Dark Room and its Fittings, 30
Dark Koom, Illumination of, 41
Defects in Collodion Emulsion

Plates, 274
Defects in Gelatine Plates, 196
Density, Correct, of Image, 142
Developer, Alkaline, How Applied,

137
Developer, Wratten and Wain-

wright's, 146
Developer, Ferrous Citrate, 165

ccxc

Developer, Ferrous Citro Oxalate,

165
Developerj Hydroxylamine, 169
Developer, Nelson's, 146
Developers, Cowan's, for Gelatino-

Chloride Plates, 166
Development, Alkaline, 134
Development, Alkaline, Theory of,

U
Development, CoUodio-Chloride

Emulsion for, 270
Development, Ferrous Oxalate,

Theory of, 19
Development of the Plate, 261
Deyelopment, Practical, of a Gela*

tine Plate, 138
Development, Practical, with Fer-
rous Oxalate, 151
Digestion of Gelatine Emulsion

with Ammonia, 97
Drop Shutters, 133
Drying Cupboards, 33, 35, 37, 38,

39
Drying Gelatine Plates, 120
Drying Markings, 276
■ Drying Racks, 34
Dust Causing Pinholes, 206
Dustin'Slides, 126

Eder's Emulsions, 92
Edwards's Intensifier, 159
Emulsiaoation, Cold, 101, 102, 104
Emulsion, Aid to Gelatine, 169
Emulsion, Canvas for. Collodion,

207
Emulsion,. CoUodio- Albumen, 245
Emulsion, CoUodio-Bromide, 242
Emulsion, Cooking and Washing, 73
Emulsion, Dissolving Gelatine, 79
Emulsion, Fog in, 21
Emulsion Draining after Washing,

78
Emulsion, • Gelatino-Bromo-Iodide,

Preparation of, 69
Emulsion Mixing, England's Plan,

73
Emulsion Mixing by Spray Appa-
ratus, 71
Emulsion, Precipitation of Gela-
tine, by Spirit, 78

Emulsion, Preparation by Aqueous

Precipitation, 107
Emulsion, Preparation of, 219
Emulsions, Preservatives used with,

255
Examination of Slides, 127
Expansion of Gelatine, 66
Exposure of Gelatine Plates, 127

Ferrocyanide of Potassium in Deve-
loper, 145

Ferrous Citrate Developer, 165

Ferrous-Citro-Oxalate Developer,
166

Ferrous Oxalate Developer, 149

Ferrous Oxalate Developer and
Hyposulphite ot Soda, 152

Ferrous Oxalate, Eder's Form, 150

Ferrous Oxalate, Simple Form of,
149 ■

Ferrous Oxalate, Strong, 151

Ferrous Oxalate Development,
Theory of,. 19

Fixing Baths, 154

Films, Eastman's Negative, 188

Fixing Gelatine Negatives, 1 54

Fixing Solution, 269

Flow Properly, Emulsion Refusing
to, 276

Focussing the Picture, 128

Fog, Red, 199

Fog, Green, 199

Fog, General, -200

Fog in Emulsions, 21

Fogging of Plates, 275

Frilling, 19S

Gelatine, 62

Gelatine and Absorption of Water,

64
Gelatine Emulsions, 50
Gelatino-Bromide Papers, 173
Gelatino-Chloride Emulsion, 163
Gelatino-Citro-Chloride, 280
General Fog, 200
Geuter on Silver Sub-Chloride,
Green Fog, 199
Gum Guiacum Preservative, 260

Henderson's Cold Emulsification,
102

INDEX.

CCXCl

Holders for Sensitive Paper, 180
Hydrokinone Developer, 148
Hyposulphite m Developer, 20
Hyposulphite of Soda in Ferrous
Oxalate, 152

Image Flatness, 201

Image, Too Dense, 801

Insensitive Patches on Develop-
riient, 275, 274

Intensifier, Edwards's, 159

Intensifier, The Best, 158

Intensifier, Uranium, 159

Iriteasifiers, Mercury and Gelatine
Negatives, 157

Intensification of Eastman's Films,
191

Intensification of Gelatine Nega-
tives, 155

Intensification of Silver Gelatine
Negatives, 155

Iodide and Chloride in Emulsions,
58

Konarzewski's Emulsion, 172

Lanterns for Dark-Rooms, 46
Lea's, Carey, Preservative, 275
Levelling Shelf, 116

Mercury Intensifier, 158
Mbnckhoven's Gelatine Emulsion

Process, 111
Mosquito Netting, 75

Negative Paper, 185
Negative Paper, Double Surface, 187
Negative Tissue, 184
Nelson's Developer, 146
Nitric Acid a Cure for Fog, 27
Note-hook for Registering Plates,
"286

Oiling Eastman's Negative Films,

190
Over-ExpoBure and Under-

Exposure, 144, 145
Oxidizing Agents Cure for Fog, 27

Packing Collodion Emulsion Plates,

286
Packing Gelatine Plates, 284
Paget Prize Gelatine Emulsion, 84
Paper, Blocks of, 179
Paper, Gelatine -Bromide, 173
Paper, Gelatino-Bromide, Hints on

Coating, 177
Paper, Gelatino-Bromide, Develop-
ment of, 183
Paper, Gelatine -Chloride, 173
Paper, Holder for, 180
Paper Negatives, 185
Paper Positives, Development of,

192
Paper Positives, Chloride, 194
Papers, Negative, Exposure of, 179
Peeling of the Film off Plate, 275
Photographic Image, Construction

of, 5
Photographic Image, Chemical

Theory of, 11
Picture, Focussing the, 128
Pinholes, 205
Plate, Backing the, 253
Plate Coating Machine, 120
Plate, Coating the, 250,
Plate, Preparation of the, 247
Plates, Cleaning, 114 .
Plates, Washing, 118
Plates, Testing, 122
Platiuotye Intensifier, 160
Precipitation Method of Preparing

Emulsion, 107
Preservatives in Emulsions, 233,

265
Preliminary Considerations, 1
Printing, Emulsion Processs for,

277
Printing, Unwashed Gelatino-Citro-

Chloride for, 282
Pyroxylin, 210, 211
Pyroxylin, Bolton on, 214
Pyroxyliu, Hardwieb, 210
Pyroxylin, Simpson, 212
Pyroxylin,'Stuart Wortley's, 213
Pyroxylin, Warnerke's, 213

Red Fog, 199

Red Gum Preservative, 259

INBBX.

Eegistering Plates, Note-Book for,

286
Eetouching on Eastman's Plates, 191
Eeversed Action of Light, 131
EoUer Slide, 180

Scratches, Dark, on Negatives, 206

Shelf, LeveUing, 116

Shatter, Cadett's, ISO

Shutters, Drop, 133

SUver Bromide, Colour of, 3

Sensitiveness Hindered by Hard

Qelatine, 55
Sensitiveness Increased hy Keeping

a Gelatine Emulsion, 54
Sensitiveness in Gelatine Emulsions,

51
Sensitiveness, Eange of, 4
Sensitometer Scale, 123
Seusitometer, "Wamerke's, 122
Silver Sub -Chloride, 7
SUde, Eoller,180
Slides, Examination of, 127
Slow Gelatine Emulsion, 283
Soda, Carbonate of. Developer, 140,

147
Specks in Plate, 276
Spectrum, 8

Spectrum, Sensitiveness to, 4
Spiller's Hydroxylamine Developer,

167
Spots, Opaque, 5!03
Spots, Semi-transparent, 203
Spots, Dull, 204

Spots, Irregularly-shaped, 205
Spray Apparatus, 71
Stain on Gelatine Plates, 202
Starnes' Water Developer, 176
Stops in Focussing, 128
Substrata, 115

Testing Gelatine Plates for Bright-
ness, 124

Testing Gelatine Plates for Density,
124

Testing Gelatine Plates for Frilling,
125

Testing Plates, 122

Thin Transparent Films, 274

Tissue, Negative, 184

Transparencies, Slow Collodion
Emulsion Process for, 283

Unwashed Gelatino-Citro-Chloride

for Printing, 282
Uranium Intensifier, 159

Varnishing the Gelatine Negative,
161

Warnerke's Sensitometer, 122
Washing Emulsions, 77
Waxing Paper, 191
Weighing, 70

Wohler on Silver Sub-Bromide, 6
Wortley's (Col.) Preservative, 269
Wratten and Wainwright's Deve-
loper, 146

PHOTOGRAPHY MADE EASY

BY THE

PLATINOTYPE PROCESS

FOR

PERMANENT PRINTING

This process is equally adapted to either Amateur or Professional use, and
-enables the printing to be accomplished in one -third of the time usual with
albumenized paper, while the subsequent operations may be completed in a tithe of
time ; indeed , a picture may be printed and finished within the space of one liour.
The Papers are of various kinds, and may be either " rough " or " smooth," " black "
or "sepia," tinted.

Platiuotype produced more artistic pictures than any other method of Photo-
:graphic Printing.

Have been awarded in recognition of the great value of the process, .including
the Progress Mbdal of the Photographic Society of Great Britain ; also
■numerous medals for results at various Exhibitions at home and abroad.

HIGHEST AWARD

AT THE

International Inventions Bxliil)ition,
THE GOLD MEDAL

"FOR EXCELIENCE OF EESULTS IN PHOTOGRAPHIC PRINTING."

"Produced bz W. WILLIS' Invention,"

The Platinotype Process is used by many of the most distinguished Artists and
Photographers, both Professional and Amateur ; by many Engineers, and at
Works throughout the Country ; also by various Govenmient Departmects.

The Prospectus, with List of Papers, SfC, and other necessaries
for the process — which are few, simple, and inexpensive {say 24s., in-
cluding Paper) — may he had on application ; also INSTRUCTIONS.

THE PLATINOTYPE COMPANY,

29, Soutlianipton Eow, Higli Holborn, W-C.

Sole Manufacturers of the well-known Sulpho-Pyrogallol, the best Developer
■for Dry Plates. Packed, 2/10.

MABION & CO., 22 & 23, Soho Square, London, W.

MARION & CO.'S BRITANNIA DRY PLATEST

Important Notice. — Although the unpreoedented sale of Britannia Dry-
Plates may be said to be a sufficient guarantee and acknowledgement of their
superiority over all other Plates before the^Public, the Proprietors are convinced
that there are still many Professional and 'Amateur Photographers who have not
given due consideration to the advantages obtainable by the use of Britannia
Plates, and they beg to submit the annexed Prices for their careful attention, the
Plates being now of much superior quality to those of earlier manufacture.

Characteristics of the Plates. — Vigour of Image. Evenness of Kim.
Great Sensitiveness. Fineness of Texture. Freedom from Fog and FrilUng.
Clearness of Shadows and Edges. Cleanness and SimpUcity of Development.
Durability, Uniformity, and Cheapness.

Sizes. Per Gross.

Sizes.

Per Gross.

Sizes.

Per Gross

li in. square ... 12

6iX4i ...

... 40

9 X7 ...

... 90

2 „ ... 150

6|X45 ...

... 42.

8iX6i

... 102

3i „ ... 18

7ix4i ..,

... 51

10 X8 ...

... 126

4iX3i ... 18

8ix4i ...

... 54

12 XIO...

... 180

5 x4 27

74x5 ...

... 60

13 X8 ...

... 180

6iX3i 38

8iX6i ...

... 72 c

15 X12...

... 318 o.

E2CTRJ^ X.,A.Ii<3-B SIZES.

Sizes. Per Doz.

Sizes. Per Doz.

Sizes. Per Boz.

Si^es.

Per Doz.

17X11 ... 32

18X14 ... 40

20X16 ... 43

24X18

... 65 O-

17X14 ... 38

18X16 ... 41

23x15 ... 47 o'

MARION &- CO.'S

NEW SERIES OF BRITANNIA DRY PLATES.

EXTRA Rapid.

We have prepared the above in accordance with the pressing vrish of number-
less customers, who find the emulsion of the Britannia Plates superior to all other,
and who desire that the same superior quality may be supplied on a plate specially
prepared for Extra Rapid Work.

These " Extra Rapid " Plates vrill be found invaluable in the Studio, by
enabling the Operator to secure much more natural and pleasant-expressions, whilst;
for instantaneous effects out of doors' their utility is practically unsurpassable.
Please Note that these Plates are as Quieli as any in the Market.

Per Doz.

Per Doz.

Per Doz.

Per Doz

1\ in. sqr. i 6

5 X4

... 3 9

7-iX5

... 7 3

10X8

... IS

2 „ I 10

6iX4i

.- 5 3

8 X5

... 8 8

12x10

... 22 6

3i „ 23

64X41

•■• S 3

%^-x&^

... 10

15X12

... 33

4|x3^ 24

7^X44

... 6 5

9 X7

... 12

S GELATINO-CHLOHIDE PLATES.

MARION & CO,, Sole Proprietors.

The attention of Photographers and Attiateurs is respectfully solicited to these
tlates. In our opinion their use is likely to be very extensive, and a source of
considerable profit to the Profession.

Gelatino-Chloride Plates are printing plates for positives ; a good print can be-
obtained in 1 to 5 seconds in diffused daylight, and with gaslight in a proportion-
ately longer time.

No Transparencies have ever been produced finer in tone or richer in detail than
those by Cowan's Chloride Plates.

MAKION & CO,, 22 & 23, Sobo SoLuare, London, W.

WHAT DO THE PLATES SERVE FOR?

1. Portraiture and landscapes ; most lovely effects visible by transmitted light.

2. Lantern-slides and stereoscopic transparencies ; with full detail, and better
tone than by any other process.

3. Transparencies for enlargements ; full of detail, soft, vigorous, and equal in
all respects to the finest carbon positives, with this advantage — that they can be
produced in any light.

4- For reproduction of negatives, they are invaluable.

PerDoz. I PcrDoz. i PerDoz. Per Doz •

3iX3| ... 2 o I 6iX4| ... 56 8^X6^ ... 10 o 12 XlO ... 22 o
4^X3^ ... 2 6 7iX5 ... 76 9 X7 ... 12 o 13 X 8 ... 2?£o
5 X4 ... 40 8JX4i ... Sol lo XS ... 14 6

Any other sizes to order charged in the same proportion.

Samples of the Transparencies supplied : C.D.V., Is. ; Cabinet, 2s. ; and
Whole-Plate, 3s. each.
DEVELOPING SOLUTIONS.
Nos. I, 2, and 3, 10 oz. bottles, is. gd. ; 20 oz. bottles, 3s. each.
Iron Solution, ,, „ gd.; „ „ is. 3d. each.

N.B.— A'series of cheap Metal Gilt Kims, specially adapted 'for .Transparencies, made in all
sizes, and low in price. A series of cheap Metal Gilt Rims, specially adapted for Transparencies,
made in all sizes, and low in price.

MARION'S BRITANNIA ALPHA PAPER. .

A very rapid Printing Paper, by which prints can be obtained equal to Silver
Prints in the dark days of November by all exposure of ij to 4 seconds, also good
Prints obtained by exposure to Gaslight in 25 seconds.
1020 pieces of full Carte-de-visite size, in boxes ready for use

360

„ Cabinet size-

150

„ 81- X6i ..

108

„ 10 X 8 ..

72

„ 121 X 104 ••

48

„ 154x124..

20

24i., X 19 ..

20,

20

20

20

20

20

20

2

3 Rolls of 10 ft. 8 in. long by 9.i^ in. wide

One-third the above qualities can be had price 7/- per box.

MARION'S

BRITANNIA ARGENTIC BROMIDE PAPER.

A New Bromide Paper for Enlargements, &c., giving a superior tone to all other
Bromide Papers, and with a perfectly even coated surface fit for fuU printed
Prints as well as Vignettes.

A Box of 24 Sheets 12^ X lOJ 9 o

16 „ 15J X 12i 9 O

20 „ 24i X 19 27 o

A Roll of 10 ft. 8 ins. X 24J wide 9 o

MARION & CO.,

22 & 23, SOHO SQUARE,
LONDON, W,

A COMPLETE SYSTEM OF

FILM PH0T06RAPHY

p

CONSISTIKG OF

FLEXIBLE NEGATIVE PAPEE in packages of twenty-foup
sheets, cut to standard commercial . sizes, for exposure in our
Patent PILM CAEEIER (fig. 3) -in any ordinary dark slide.

FLEXIBLE NEGATIVE PAPEE, in Spools or EoUs, of 24 expo-
sures (fig. 2), for exposure in the EASTMAN-"WALKEE EOLL
HOLDEE (fig. 1), adaptable to existing Cameras.

Jlig 3.
FULL PAETICULAES ON APPLICATION TO—

THE EASTMAN DRY PLATE & FILM CO.,

13, SOHO SQUARE, LONDON, W.

POETEAIT & VIEW LENSES,

Unsurpassed for Brilliancy of Definition, Flatness of Field, and Depth of
Focus. Used by the leading Photographers throughout the World.

PORTRAIT LENSES.

IMPRO'fBD.

No. 3 for Portraits 6ix 4?
„ 3a „ Six 6J

10 X 8
18 X18
22 X18

£17 10
28 15
38
42 10
54

EAPID "CABIlfET."

No. 1 for Cabinets, Uft. distance 13

„ 2 „ 18ft. „ 17 10

„ 3 „ 20ft. ,, 19 10

EXTRA KAPID C.D.V.
Invaluable for Photographing Children.
No. 2a, IJin. focus, dia. 2im- — 13 10
„ 3a, 6 in. „ dia. 3|in. ... 25

QUICK-iCTING C.D.V,
No. 1 for Cards, Uft. distance... 5 15

„ 2 „ 16ft. 6 10

„ 3 „ 19ft. „ ... n 10

UNIVERSAL.
Por Portraits, Groups, &c.
Back

No.

1 ..

2 ..

3 ..

4 ..

5 ..

View
Size.

Group
Size.

fo. 1

3 X3

„ 2

4 X3

" 3

5 X4

.. *

nx4i

., 5

8 X5

„ 8

sjxej

„ '

9 x7

>. 8

10x8

„ 9

12x10

„ 10

13x11

., 11

15X12

>, 12

18X16

5 x4

Sin.

£3

7ix4J

4in.

3

5

8 x5

5in.

3

10

84x64

8in.

4

9 x7

7in.

5

10x8

Sin.

6

12x10

9rn.

7

13x11

lOin.

8

15x12

12in.

9

18x16

15in.

10

22x18

ISin.

12

25x21

21in.

15

Focus.

8ix6i ... 7ix4^.... SJin. .

10X8 ... SJXSJ ...lOJin. .

12x10 ... 10x8 ...13Jin. .

15X12 ... 12x10 ...lejin. .

18x16 ... 15X12 ...20 in. .

22x18 ... 18x16 ...24 in. .

25x21 ... 22x18 ...30 in. .

Price.

7 10

9
12 10
16 10
23
45
65

VIEW LENSES.

SYMMETEICAI..0
For Landscapes and Architecture.

4 x3

5 x4
7ix4i

8 X5
8Jx64

9 X7
10x8
12x10
13x11
15x12
18x16
22x20

RAPID SYMMETRICALS.*

For Groups, Views, Interiors, and Copying.

The most useful Lens for all Out-door

Photography.

Size o.£
View.
4x3
5x4
6x5
8x5

Six ei

9 X 7
10 X 8

12 xlO

13 Xll
li X12
18 Xl6
22 xlS
25 X22

* Furnished with Diaphragms on the Stan-
dard System recommended by the Photo-
graphic Society of Great Britain.

Size of ]

3quivalen

t.

Group.

Focus.

Price

... Stereo.' .

. 4iin. .

.£4

... 4x3 .

. 6 in. .

. 4 5

... 5x4 .

. 7iin. .

. 5 5

... 7iX 4i .

. 9 in. .

. 5 15

... 8X6 .

. lOiin..

. 6 10

... Six 6i .

. 12in. .

. 7 10

... S.Jx 6i .

. 14in.

.. 8 10

. 10 X 8 .

. 16in. .

.. 10 10

... 11 X 9 .

.. 18in.

.. 11 10

... 13 XU .

.. 20in. .

.. 14 10

... 15 Xl2 .

. 24in.

.. 18 10

... 18 X16 .

. 30in. .

.. 25

... 22 *X18 .

. 34in. .

. 30

Improved Expanding Bellows Cameras for Lenses of Long Focus.
AiPrA-RA-TTTS OF EVERY DBSOBIPTION-

CATALOeUMS ON APPLICATION.

ROSS & CO., Opticians,

112 (REMOVED FROM 164), NEW BOND STREET, LONDON, W.

Optical Works— BROOK STREET. lEstaHishedmO.I

F. W. VEREL X CO.'S

Gelatine Dry Plates.

To provide for the ever increasing demand tcr our Plates, we have found it
necessary to construct Larger Premises, and, having introduced machinery where
practicable, we are now in a position to- greatly increase out out-piit. To facilitate
working during the summer months, a Freezing Machine and other appliances have
been provided, which will secure uniformity in coating, and thus obviate a difficulty
generally experienced in the manufacture. .

Those who have not tried these Platea are respectfully requested to do so
before ordering for the season.

5 X4

6fX3J

6iX4i

6iX4f

7^X44

7 X5

Terms — Cash with Order only. Special Terms to Dealers and Large Consumers.

Our 60-times will be found invaluable for all Instantaneous work.

Sample Half-dozen Packet, any speed, J-plate, 12 stamps ; ^-plate, 27 stamps,

free.

EXCELSiORlNTENSIFIER

Above may now be had in Bottles at 1/6 and 2/6 ; per Parcel Post, 1/9 and 3/-

safely packed.

For general and LOCAL intensification this Preparation is unsurpassed.

GIVE IT A. TRIAL.

PRICE

LIST,

PER DOZEN.

10 and 30 times. 60 times.

LO and 30 times. 60 times.

a. d.

s. d.

s. d.

s. d.

.. I 6 .

..20

74X 6

• S •

. 6

•• 2 3 •

..30

8iX 6^

.60.

. 8

..32.

.. 3 6

9X7

• 76.

• 9

••3 4-

..40

10 X 8

. 10 6 .

. 12 6

..36.

.. .4 6

n X 9

. 13 .

• IS 6

••3 9-

••4 9

12 XIO

. 15 .

. 18

..40.

-SO

15 X12

. 26 6 .

. 30

AGENTS-

ALBION ALBUMENIZIN8 CO.,

96, Bath Street, Glasgow.
Messrs. MoGHIB 4 BOLTON,

47, West Nile Street, Glasgow.
Messrs. GEO. MASON & CO.,

180, Sauchiehall Street, Glasgow.
Mr. J. PALLOWMELD,

36, Lower Marsh, Lambeth, London, S.E.
Mr. JOHN J. ATKINSON,

Manchester Street, Liverpool.

Mr. J. M. SMITH, 13, High Ousegate, York.

Mr. P. HALL,

118, Grey Street, Newcastle-on-Tyne.
Mr. J. M. TUBNBULL,

Rose Street, Edinburgh.
Mr. W. HUME,

1, Lothian Street, Edinburgh.
Mr. B. LOWDON,

65. Reform Street, Dundee.
Mr. H. LESTER,

Bridge Street, Nuneaton.

F. W. VEREL

OATHCART, near

& CO.,

GUj ASGhOW,

Photographic Apparatus Manufacturer,

26, CALTHORPE STREET, GRAY'S INN ROAD,

LonsriDo:^.

TBIRTEEN PEIZE MEDALS have been awarded to G
and ChaiujilirjSox ^or Excellence of Design and

MARE'S Cameras

G. HARE'S NEW CAMERA.

Invented, and Introduced, June, 1882. The Best and most compact Camera ever Invented.

Since its introduction, this Camera
has received several important modifi-
S) cations in construction. It stands un-
rivalled for eleg'ance, lightness, and
general utility. It is specially adapted
for use with the Eastman-Walker Koll
Holder. A 6^x4^ Camera measures
■when closed 8x8x2i in., weighs only
3^1bs., and extends to 17in. The steady
and increasing demandf or this Camera
is the best proof of its popularity*
" Little need be said of Mr. George Harc*s well-known Patent Camera, except that it forms
the model upon which nearly all the others in the market are based." — Yide British Journal
of Phonography, August 28, 1885.

Size of
Plate.
5x4
6^X 4i
7^X 5

Square, with Re-
versible Holder.
£6
7 2 6

7 10

8 15

Brass

Binding.

£0 16

16

15

16

Size of
Plate.
lOx 8
12x10
15x12

Square, with Re-
versible Holder.

£9 16

11

13 5

Brass
Binding.
£0 18 a
10
10

These prices include one Double Slide.

Since this C.imera has been introduced, it has been awarded THREE SILVER
MEDALS : at Brussels International Photographic Exhibition, 1883 ; at the Eoyal Cornwall
Polytechnic Society, Falmouth; and at the International Inventions Exhibition, 1885. Also
Bronze Medal, Bristol International Exhibition, 1883^H1GHEST .AWARD.

O. Hare's IMPROVED PORTABLE BELLOWS CAMERA

lavented and Introduced 1878.

This Camera offers many advantages where a little extra weight and bulk is not objected to.
It is very solid and firm in construction, and especially suited for India and other trying climates.

IILITSTEATED PRICE LIST on application at the Manufactory—

Ill

I-
<

(Da

: a +-

■3^2

;« fc

a; 43 E-i .-03^

9 p4 ;

Ph e

PI

EM

1 .a

111

X
h

PL,
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George Houghton & Son,

PHOTOGRAPHIC WAREHOUSE,

S9, HIGH HOLBOBN, LONDON,

MANUFACTURERS OF

Cameras & all Kinds of Apparatus,

Dry Plates, Chemicals,

SENSITIZED PAPEE, MOUNTS, &c.,

PHOTOGRAPHIC STUDIOS,

PORTABLE DARK ROOMS, Xc,
DESIGNED, ERECTED, AND PITTED COMPLETE.,

ALL NECESSARY APPARATUS,

DRYING CUPBOARDS, &c.,

For tlie Manufacture of Grelatine
Dry Plates.

WETT FEICH LIST ON APPLICATION.

PAGET PRIZE PLATE COMPANY.

Thle Gelatine Dbt Plates issued by this Company and prepared under
the immediate Superintendanoe of Mr. "W. J. "WILSON, F.C.S.,

Winner of the JPrize of £50 offered hy Joseph Paget, Esq., and awarded ly The
FhotograpMc Society of Great Britain, for the best Dry Plate Process,

Still maintain the high reputation they have gained, and are in con-
stant demand by the leading Landscape and Portrait Photographers
in Great Britain and the Colonies.

Mk. W. D, Valentine (of Valentine and Sons, Landscape Photographers and
Publishers, of Dundee), writes as follows : —

"I have just tried the new lot of Extra Eapid Plates, and am much
pleased with them. I only ■vvish my operators had had them last year,
as the so-called Extra Eapid Plates we were then using were not to be
compared to yours."

. Mk. G. W. Wilson, (of G. W. Wilson and Co., Landscape Photographers and
Publishers, of Aberdeen) writes as follows : —

" I am sorry that I bothered this Summer with the plates of other
makers, but shall not do it again. "We have been trouile with frilling,
fog, thin edges, &o., &c., whilst with yours we are sure of what we
are doing."

Messrs. West and Son, who have taken the highest awards for their Yacht
pictures, write as follows ; —

" "We must really compliment you upon the last batch of Plates sent
us; they are better than ever."

Price Lists of the " Paget Prize Plates," and any information respecting tlteir use,
may he obtained by addressing —

TUB I/C.A.I>T-A.C3-EI?,,

PAGET PRIZE PLATE COMPANY,

EALING, LONDON, W.

N.B.— All Plates are now sent by the Company carriage free, to Pnoto-
graphers, te any Town in the United Kingdom.

UIIVEESITT OPTICAL WORKS,

81, TOTTENHAM COURT ROAD,

LoasriD03sr.

SEVEN GOLD MEDALS AWARDED.

In sulamitting the undermentioned list of Camera Lenses to the notice
of the Public, J . SWIFT & SON heg to state that they can con-
fidently guarantee them to he superior to any yet oSered by the trade,
in proof of which they will (on receipt of remittance or London refer-
ence) send sample for comparison with any others of English or
Foreign manufacture, feeling convinced that they are positively un-
equalled. The covering power of these Lenses, together with their
great flatness of field, sharpness of detail, combined with delicate
softness, is not approached by the Cameras of any other Optician, and
the Stops supplied with these Lenses are similar to those recommended
by the Photographic Society of Great Britain. Me. JAMES SWIFT
having had many years practical experience with the late Mr. Boss
(whose reputation as a maker of Camera Lenses is world-wide) is in a
position to justify the high character of the above Lenses, which he
trusts the scientific public will afford him opportunities of demon-
strating.

PORTABLE PARAGON CAMERA LENSES,

SPECIALLY CONSTRUCTED FOR LANDSCAPES, ARCHITECTURE,
AND COPYING.

Nos. ..

1

2

3

4

5

6

7

8

9

10

Focus ,.

. Sin.

4 in.

5 in.

6 m.

7 in.

Sin.

9 in.

10 in.

12 in.

15 in.

Plate ..,

. 3x3

4x3

5x4

7iXih

8x5

Six6i

9x7

10x8

12x10

13x11

Price ..

. £2 14/-

£2 18/-

£3 3/-

£3 12/-

£4 10/-

£5 8/-

£6 6/-

£7 4-

£8 2/.

£9

RAPID PARAGON CAMERA LENSES,

SPECIALLY CONSTRUCTED FOR PORTRAITS, GROUPS, INTERIORS,
AND INSTANTANEOUS WORK.

Views ... 3x3 4|x3i 5x4 6x5 8x5 8ix6J 9x7 10x8 12x10 13x11 15x12

Groups ... — Stereo. HxSi 5x4 7Jx44 8x5 84x6$ 9x7 10x8 12x10 13x11

Focus ,„ 3 in. 4i in. 6 in. 7J in. 9 in. lOJ in. 12 in. 14 in. 16 in. 18 in. 20 in.
Price ... £3 3/- £5 12/- £3 16/- £4 14/6 £5 3/6 £5 17/6 £6 15/- £7 13/- £? 9/- £10.7/- £13

Off the above prices 10 per cent, is allowed for cash.

^7^^^