Cyanogen is not an elementary body, like Chlorine or Iodine, but consists
of Carbon and Nitrogen united in a peculiar manner. Although a compound
substance, it reacts in the manner of an element, and is therefore
(like Ammonium, previously described) an exception to the usual laws of
chemistry. Many other bodies of a similar character are known.
Properties of Cyanide of Potassium.--These have been sufficiently
described at page 44, to which the reader is referred.
ETHER.
Symbol, C{4}H{5}O. Atomic weight, 37.
Ether is obtained by distilling a mixture of Sulphuric Acid and Alcohol.
If the formula of Alcohol (C{4}H{6}O{2}) be compared with that of Ether,
it will be seen to differ from it in the possession of an additional atom
of Hydrogen and of Oxygen: in the reaction the Sulphuric Acid removes
these elements in the form of water, and by so doing converts one atom
of Alcohol into an atom of Ether. The term Sulphuric applied to the
commercial Ether has reference only to the manner of its formation.
Properties of Ether.--The properties of Ether have been described to some
extent at pages 85 and 195. The following particulars however may be
added. It is neither acid nor alkaline to test-paper. Specific gravity, at
60°, about ·720. Boils at 98° Fahrenheit. The vapour is exceedingly dense,
and may be seen passing off from the liquid and falling to the ground:
hence the danger of pouring Ether from one bottle to another if a flame be
near at hand.
Ether does not mix with water in all proportions; if the two are shaken
together, after a short time the former rises and floats upon the surface.
In this way a mixture of Ether and Alcohol may be purified to some extent,
as in the common process of washing Ether. The water employed however
always retains a certain portion of Ether (about a tenth part of its
bulk), and acquires a strong ethereal odour; washed Ether also contains
water in small quantity.
Bromine and Iodine are both soluble in Ether, and gradually react upon and
decompose it.
The strong alkalies, such as Potash and Soda, also decompose Ether
slightly after a time, but not immediately. Exposed to air and light.
Ether is oxidized and acquires a peculiar odour (page 85).
Ether dissolves fatty and resinous substances readily, but inorganic salts
are mostly insoluble in this fluid. Hence it is that Iodide of Potassium
and other substances dissolved in Alcohol are precipitated to a certain
extent by the addition of Ether.
FLUORIDE OF POTASSIUM.
Symbol, KF. Atomic weight, 59.
_Preparation._--Fluoride of Potassium is formed by saturating Hydrofluoric
Acid with Potash, and evaporating to dryness in a platinum vessel.
Hydrofluoric Acid contains Fluorine combined with Hydrogen; it is a
powerfully acid and corrosive liquid, formed by decomposing Fluor Spar,
which is a Fluoride of Calcium, with strong Sulphuric Acid; the action
which takes place being precisely analogous to that involved in the
preparation of Hydrochloric Acid.
_Properties._--A deliquescent salt, occurring in small and imperfect
crystals. Very soluble in water: the solution acting upon glass in the
same manner as Hydrofluoric Acid.
FORMIC ACID.
Symbol, C{2}HO{3}. Atomic weight, 37.
This substance was originally discovered in the _red ant_ (_Formica
rufa_), but it is prepared on a large scale by distilling Starch with
Binoxide of Manganese and Sulphuric Acid.
_Properties._--The strength of commercial Formic Acid is uncertain, but
it is always more or less dilute. The strongest acid, as obtained by
distilling Formiate of Soda with Sulphuric Acid, is a fuming liquid with a
pungent odour, and containing only one atom of water. It inflames the skin
in the same manner as the sting of the ant.
Formic Acid reduces the Oxides of Gold, Silver, and Mercury to the
metallic state, and is itself oxidized into Carbonic Acid. The alkaline
formiates also possess the same properties.
GALLIC ACID.
Symbol, C{7}H{3}O{5} + H{3}O. Atomic weight, 94.
The chemistry of Gallic Acid is sufficiently described at page 27, to
which the reader is referred.
GELATINE.
Symbol, C{13}H{10}O{5}N{2}. Atomic weight, 156.
This is an organic substance somewhat analogous to Albumen, but differing
from it in properties. It is obtained by subjecting bones, hoofs, horns,
calves' feet, etc., to the action of boiling water. The jelly formed
on cooling is termed size, or, when dried and cut into slices, _glue_.
Gelatine, as it is sold in the shops, is a pure form of Glue. _Isinglass_
is gelatine prepared, chiefly in Russia, from the air-bladders of certain
species of sturgeon.
_Properties of Gelatine._--Gelatine softens and swells up in cold water,
but does not _dissolve_ until heated: the hot solution, on cooling, forms
a tremulous jelly. One ounce of cold water will retain about three grains
of Isinglass without gelatinizing; but much depends upon the temperature,
a few degrees greatly affecting the result.
When long boiled in water, and especially in presence of an acid, such
as the Sulphuric, Gelatine undergoes a peculiar modification, and the
Solution loses either partially or entirely its property of solidifying to
a jelly.
GLYCERINE.
Fatty bodies are resolved by treatment with an alkali into an Acid--which
combines with the alkali, forming a _soap_,--and Glycerine, remaining in
solution.
Pure Glycerine, as obtained by Price's patent process of distillation,
is a viscid liquid of sp. gr. about 1·23; miscible in all proportions
with water and Alcohol. It is peculiarly a neutral substance, exhibiting
no tendency to combine with acids or bases. It has little or no action
upon Nitrate of Silver in the dark, and reduces it very slowly even when
exposed to light.
GLYCYRRHIZINE.
Glycyrrhizine, obtained from the fresh root of Liquorice, is a substance
intermediate in properties between a sugar and a resin. Sparingly soluble
in water but very soluble in Alcohol. It precipitates strong solution of
Nitrate of Silver white, but the deposit becomes reddened by exposure
to light. Its preparation is described in the larger works on organic
chemistry.
GOLD, CHLORIDE OF.
Symbol, AuCl{3}. Atomic weight, 303.
This salt is formed by dissolving pure metallic Gold in Nitro-hydrochloric
Acid, and evaporating at a gentle heat. The solution affords deliquescent
crystals of a deep orange colour.
Chloride of Gold, in a state fit for Photographic use, may easily be
obtained by the following process:--Place a half-sovereign in any
convenient vessel, and pour on it half a drachm of Nitric Acid mixed with
two and a half drachms of Hydrochloric Acid and three drachms of water;
digest by a gentle heat, but do not _boil_ the acid, or much of the
Chlorine will be driven off in the form of gas. At the expiration of a few
hours add fresh Aqua-Regia in quantity the same as at first, which will
probably complete the solution, but if not, repeat the process a third
time.
Lastly, neutralize the liquid by adding Carbonate of Soda until all
effervescence ceases, and a green precipitate forms; this is _Carbonate
of Copper_, which must be allowed several hours to separate thoroughly.
The Chloride of Gold is thus freed from Copper and Silver, with which the
metallic Gold is alloyed in the standard coin of the realm. The solution
so prepared will be _alkaline_, and consequently prone to a reduction
of metallic Gold: a slight extra quantity of Hydrochloric acid should
therefore be added, sufficient to redden a piece of immersed litmus-paper.
The weight of a half-sovereign is about 61 grains, of which 56 grains are
pure Gold. This is equivalent to 86 grains of Chloride of Gold, which will
be the quantity contained in the solution.
The following process for preparing Chloride of Gold is more perfect than
the last:--Dissolve the Gold coin in Aqua-Regia as before; then boil with
excess of Hydrochloric Acid, to destroy the Nitric Acid,--dilute largely
with distilled water, and add a filtered aqueous solution of common
Sulphate of Iron (6 parts to 1 of Gold); collect the precipitated Gold,
which is now free from copper; redissolve in Aqua-Regia, and evaporate to
dryness on a water bath.
Avoid using _Ammonia_ to neutralize Chloride of Gold, as it would occasion
a deposit of "Fulminating Gold," the properties of which are described in
the next page.
_Properties of Chloride of Gold._--As sold in commerce it usually contains
excess of Hydrochloric Acid, and is then of a bright yellow colour; but
when neutral and somewhat concentrated, it is dark red (_Leo ruber_ of the
alchemists). It gives no precipitate with Carbonate of Soda unless heat
be applied; the free Hydrochloric Acid present forms, with the alkali.
Chloride of Sodium, which unites with the Chloride of Gold, and produces
a double salt, Chloride of Gold and Sodium, soluble in water.
Chloride of Gold is decomposed with precipitation of metallic Gold by
Charcoal, Sulphurous Acid, and many of the vegetable acids; also by
Protosulphate and Protonitrate of Iron. It tinges the cuticle of an
indelible purple tint. It is soluble in Alcohol and in Ether.
GOLD, FULMINATING.
This is a yellowish-brown substance, precipitated on adding Ammonia to a
strong solution of Chloride of Gold.
It may be dried carefully at 212°, but explodes violently on being heated
suddenly to about 290°. Friction also causes it to explode when dry; but
the moist powder may be rubbed or handled without danger. It is decomposed
by Sulphuretted Hydrogen.
Fulminating Gold is probably an Aurate of Ammonia, containing 2 atoms of
Ammonia to 1 atom of Peroxide of Gold.
GOLD, HYPOSULPHITE OF.
Symbol, AuO S{2}O{2}. Atomic weight, 253.
Hyposulphite of Gold is produced by the reaction of Chloride of Gold upon
Hyposulphite of Soda (see page 133).
The salt sold in commerce as Sel d'or is a double Hyposulphite of Gold and
Soda, containing one atom of the former salt to three of the latter, with
four atoms of water of crystallization. It is formed by adding one part of
Chloride of Gold, in solution, to three parts of Hyposulphite of Soda, and
precipitating the resulting salt by Alcohol: the Chloride of Gold must be
added to the Hyposulphite of Soda, and not the Soda salt to the Gold (see
page 250).
Properties.--Hyposulphite of Gold is unstable and cannot exist in an
isolated state, quickly passing into Sulphur, Sulphuric Acid, and metallic
Gold. When combined with excess of Hyposulphite of Soda in the form of Sel
d'or, it is more permanent.
Sel d'or occurs crystallized in fine needles, which are very soluble in
water. The commercial article is often impure, containing little else than
Hyposulphite of Soda, with a trace of Gold. It may be analyzed by adding
a few drops of strong Nitric Acid (free from Chlorine), diluting with
water, and afterwards collecting and igniting the yellow powder, which is
metallic Gold.
GRAPE SUGAR.
Symbol, C{24}H{28}O{28}. Atomic weight, 396.
This modification of Sugar, often termed _Granular Sugar_, or _Glucose_,
exists abundantly in the juice of grapes and in many other varieties of
fruit. It forms the saccharine concretion found in honey, raisins, dried
figs, etc. It may be produced artificially by the action of fermenting
principles and of dilute mineral acids, upon Starch.
_Properties._--Grape Sugar crystallizes slowly and with difficulty from
a concentrated aqueous solution, in small hemispherical nodules, which
are hard, and feel gritty between the teeth. It is much less sweet to the
taste than Cane Sugar, and not so soluble in water (1 part dissolves in
1-1/2 of cold water).
Grape Sugar tends to absorb Oxygen, and hence it possesses the property of
decomposing the salts of the noble metals, and reducing them by degrees
to the metallic state, even without the aid of light. _Cane_ Sugar does
not possess these properties to an equal extent, and hence it is readily
distinguished from the other variety. The product of the action of Grape
Sugar upon Nitrate of Silver appears to be a very low form of Oxide of
Silver combined with organic matter.
HONEY.
This substance contains two distinct kinds of Sugar, Grape Sugar, and an
uncrystallizable substance analogous to, or identical with, the Treacle
found associated with common Sugar in the cane-juice. The agreeable
taste of Honey probably depends upon the latter, but its reducing power
on metallic oxides is due to the former. Pure Grape Sugar can readily
be obtained from inspissated Honey, by treating it with Alcohol, which
dissolves out the syrup, but leaves the crystalline portion.
Much of the commercial article is adulterated, and, for Photographic use,
the Virgin Honey should be obtained direct from the comb.
HYDROCHLORIC ACID.
Symbol, HCl. Atomic weight, 37.
Hydrochloric Acid is a volatile gas, which may be liberated from most of
the salts termed Chlorides by the action of Sulphuric Acid. The acid, by
its superior affinities, removes the base; thus,--
NaCl + HO SO{3} = NaO SO{3} + HCl.
Properties.--Abundantly soluble in water, forming the liquid Hydrochloric
or Muriatic Acid of commerce. The most concentrated solution of
Hydrochloric Acid has a sp. gr. 1·2, and contains about 40 per cent, of
gas; that commonly sold is somewhat weaker, sp. gr. 1·14 = 28 per cent,
real acid.
Pure Hydrochloric Acid is colourless, and fumes in the air. The yellow
colour of the commercial acid depends upon the presence of traces of
Perchloride of Iron, or of organic matter; commercial Muriatic Acid also
often contains a portion of free Chlorine and of Sulphuric Acid.
HYDRIODIC ACID.
Symbol, HI. Atomic weight, 127.
This is a gaseous compound of Hydrogen and Iodine, corresponding in
composition to the Hydrochloric Acid. It cannot however, from its
instability, be obtained in the same manner, since, on distilling
an Iodide with Sulphuric Acid, the Hydriodic Acid first formed is
subsequently decomposed into Iodine and Hydrogen. An aqueous solution of
Hydriodic Acid is easily prepared by adding Iodine to water containing
Sulphuretted Hydrogen gas; a decomposition takes place, and Sulphur is set
free: thus, HS + I = HI + s.
Properties.--Hydriodic Acid is very soluble in water, yielding a strongly
acid liquid. The solution, colourless at first, soon becomes brown from
decomposition, and liberation of free Iodine. It may be restored to its
original condition by adding solution of Sulphuretted Hydrogen.
HYDROSULPHURIC ACID.
Symbol, HS. Atomic weight, 17.
This substance, also known as Sulphuretted Hydrogen, is a gaseous compound
of Sulphur and Hydrogen, analogous in composition to the Hydrochloric and
Hydriodic Acid. It is usually prepared by the action of dilute Sulphuric
Acid upon Sulphuret of Iron, as described at page 373; the decomposition
being similar to that involved in the preparation of the Hydrogen acids
generally:--
FeS + HO SO{3} = FeO SO{3} + HS.
Properties.--Cold water absorbs three times its bulk of Hydrosulphuric
Acid, and acquires the peculiar putrid odour and poisonous qualities
of the gas. The solution is faintly acid to test-paper, and becomes
opalescent on keeping, from gradual separation of Sulphur. It is
decomposed by Nitric Acid, and also by Chlorine and Iodine. It
precipitates Silver from its solutions in the form of black Sulphuret
of Silver; also Copper, Mercury, Lead, etc.; but Iron and other metals
of that class are not affected, if the liquid contains free acid.
Hydrosulphuric Acid is constantly employed in the chemical laboratory for
these and other purposes.
HYDROSULPHATE OF AMMONIA.
Symbol, NH{4}S HS. Atomic weight, 51.
The liquid known by this name, and formed on passing Sulphuretted Hydrogen
gas into Ammonia, is a double Sulphuret of Hydrogen and Ammonium. In the
preparation, the passage of the gas is to be continued until the solution
gives no precipitate with Sulphate of Magnesia, and smells strongly of
Hydrosulphuric Acid.
_Properties._--Colourless at first, but afterwards changes to yellow,
from liberation and subsequent solution of Sulphur. Becomes milky on the
addition of any acid. Precipitates, in the form of Sulphuret, all the
metals which are affected by Sulphuretted Hydrogen, and, in addition,
those of the class to which Iron, Zinc, and Manganese belong.
Hydrosulphate of Ammonia is employed in Photography to darken the Negative
image, and also in the preparation of Iodide of Ammonium, the separation
of Silver from Hyposulphite solutions, etc.
HYPOSULPHITE OF SODA.
Symbol, NaO S{2}O{2} + 5 HO. Atomic weight, 125.
The chemistry of Hyposulphurous Acid and the Hyposulphite of Soda has been
sufficiently described at pages 43, 129, and 137 of the present Work. The
crystallized salt includes five atoms of water of crystallization.
HYPOSULPHITE OF GOLD. _See_ Gold, Hyposulphite of.
HYPOSULPHITE OF SILVER. _See_ Silver, Hyposulphite of.
ICELAND MOSS.
_Cetraria Islandica._--A species of Lichen found in Iceland and the
mountainous parts of Europe; when boiled in water, it first swells up, and
then yields a substance which gelatinizes on cooling.
It contains Lichen Starch, a bitter principle soluble in Alcohol, termed
"Cetrarine," and common Starch; traces of Gallic Acid and Bitartrate of
Potash are also present.
IODINE.
Symbol, I. Atomic weight, 126.
Iodine is chiefly prepared at Glasgow, from _kelp_, which is the fused
ash obtained on burning seaweeds. The waters of the ocean contain minute
quantities of the Iodides of Sodium and Magnesium, which are separated and
stored up by the growing tissues of the marine plant.
In the preparation, the mother-liquor of kelp is evaporated to dryness
and distilled with Sulphuric Acid; the Hydriodic Acid first liberated is
decomposed by the high temperature, and fumes of Iodine condense in the
form of opaque crystals.
_Properties._--Iodine has a bluish-black colour and metallic lustre; it
stains the skin yellow, and has a pungent smell, like diluted Chlorine.
It is extremely volatile when moist, boils at 350°, and produces dense
violet-coloured fumes, which condense in brilliant plates. Specific
gravity 4·946. Iodine is very sparingly soluble in water, 1 part requiring
7000 parts for perfect solution; even this minute quantity however
tinges the liquid of a brown colour. Alcohol and Ether dissolve it more
abundantly, forming dark-brown solutions. Iodine also dissolves freely in
solutions of the alkaline Iodides, such as the Iodide of Potassium, of
Sodium, and of Ammonium.
_Chemical Properties._--Iodine belongs to the Chlorine group of elements,
characterized by forming acids with Hydrogen, and combining extensively
with the metals (see Chlorine). They are however comparatively indifferent
to Oxygen, and also to each other. The Iodides of the alkalies and
alkaline earths are soluble in water; also those of Iron, Zinc, Cadmium,
etc. The Iodides of Lead, Silver, and Mercury are nearly or quite
insoluble.
Iodine possesses the property of forming a compound of a deep blue colour
with Starch. In using this as a test, it is necessary first to liberate
the Iodine (if in combination) by means of Chlorine, or Nitric Acids
saturated with Peroxide of Nitrogen. The presence of Alcohol or Ether
interferes to a certain extent with the result.
IODIDE OF AMMONIUM.
Symbol, NH{4}I. Atomic weight, 144.
The preparation and properties of this salt are described at page 198, to
which the reader is referred.
IODIDE OF CADMIUM.
Symbol, CdI. Atomic weight, 182.
See page 199, for the preparation and properties of this salt.
IODIDE OF IRON.
Symbol, FeI. Atomic weight, 154.
Iodide of Iron is prepared by digesting an excess of Iron filings with
solution of Iodine in Alcohol. It is very soluble in water and Alcohol,
but the solution rapidly absorbs Oxygen and deposits Peroxide of Iron;
hence the importance of preserving it in contact with metallic Iron, with
which the separated Iodine may recombine. By very careful evaporation,
hydrated crystals of Proto-iodide may be obtained, but the composition of
the solid salt usually sold under that name cannot be depended on.
The _Periodide_ of Iron, corresponding to the _Perchloride_, has not been
examined, and it is doubtful if any such compound exists.
IODIDE OF POTASSIUM.
Symbol, KI. Atomic weight, 166.
This salt is usually formed by dissolving Iodine in solution of Potash
until it begins to acquire a brown colour; a mixture of Iodide of
Potassium and _Iodate of Potash_ (KO IO{5}) is thus formed; but by
evaporation and heating to redness, the latter salt parts with its Oxygen,
and is converted into Iodide of Potassium.
_Properties._--It forms cubic and prismatic crystals, which should be
hard, and _very slightly or not at all deliquescent_. Soluble in less than
an equal weight of water at 6O°; it is also soluble in Alcohol, but not
in Ether. The proportion of Iodide of Potassium contained in a saturated
alcoholic solution, varies with the strength of the spirit:--with common
Spirits of Wine, sp. gr. ·836, it would be about 8 grains to the drachm;
with Alcohol rectified from Carbonate of Potash, sp. gr. ·823, 4 or 5
grains; with absolute Alcohol, 1 to 2 grains. The solution of Iodide
of Potassium is instantly coloured brown by free Chlorine; also very
rapidly by Peroxide of Nitrogen (page 86); ordinary acids however act less
quickly, Hydriodic Acid being first formed, and subsequently decomposing
spontaneously.
The impurities of commercial Iodide of Potassium, with the means to be
adopted for their removal, are fully given at page 197.
IODIDE OF SILVER. _See_ Silver, Iodide of.
IODOFORM.
The composition of this substance is analogous to that of Chloroform,
Iodine being substituted for Chlorine. It is obtained on boiling together
Iodine, Carbonate of Potash, and Alcohol.
Iodoform occurs in yellow nacrous crystals, which have a saffron-like
odour. It is insoluble in water, but soluble in spirit.
IRON, PROTOSULPHATE OF.
Symbol, FeO SO{3} + 7 HO. Atomic weight, 139.
The properties of this salt, and of the two salifiable Oxides of Iron, are
described at page 29. It dissolves in rather more than an equal weight of
cold water, or in less of boiling water.
Aqueous solution of Sulphate of Iron absorbs the Binoxide of Nitrogen,
acquiring a deep olive-brown colour: as this gaseous Binoxide is itself a
reducing agent, the liquid so formed has been proposed as a more energetic
developer than the Sulphate of Iron alone (?).
IRON, PROTONITRATE OF.
Symbol, FeO NO{3} + 7 HO. Atomic weight, 153.
This salt, by careful evaporation _in vacuo_ over Sulphuric Acid, forms
transparent crystals, of a light green colour, and containing 7 atoms
of water, like the Protosulphate. It is exceedingly unstable, and soon
becomes red from decomposition, unless preserved from contact with air.
The preparation of solution of Protonitrate of Iron for developing
Collodion Positives, is given at page 206.
IRON, PERCHLORIDE OF.
Symbol, Fe{2}Cl{3}. Atomic weight, 164.
There are two Chlorides of Iron, corresponding in composition to the
Protoxide and the Sesquioxide respectively. The Protochloride is very
soluble in water, forming a green solution, which precipitates a dirty
white Protoxide on the addition of an alkali. The Perchloride, on the
other hand, is dark brown, and gives a foxy-red precipitate with alkalies.
_Properties._--Perchloride of Iron may be obtained in the solid form by
heating Iron wire in excess of Chlorine; it condenses in the shape of
brilliant and iridescent brown crystals, which are volatile, and dissolve
in water, the solution being acid to test-paper. It is also soluble in
Alcohol, forming the Tinctura Ferri Sesquichloridi of the Pharmacopœia.
Commercial Perchloride of Iron ordinarily contains an excess of
Hydrochloric Acid.
LITMUS.
Litmus is a vegetable substance prepared from various _lichens_, which are
principally collected on rocks adjoining the sea. The colouring matter is
extracted by a peculiar process, and afterwards made up into a paste with
chalk, plaster of Paris, etc.
Litmus occurs in commerce in the form of small cubes of a fine violet
colour. In using it for the preparation of test-papers, it is digested
in hot water, and sheets of porous paper are soaked in the blue liquid
so formed. The red papers are prepared at first in the same manner, but
afterwards placed in water which has been rendered faintly acid with
Sulphuric or Hydrochloric Acid.
MERCURY, BICHLORIDE OF.
Symbol, HgCl{2}. Atomic weight, 274.
This salt, also called Corrosive Sublimate, and sometimes _Chloride of
Mercury_ (the atomic weight of Mercury being halved), may be formed by
heating Mercury in excess of Chlorine, or more economically, by subliming
a mixture of Persulphate of Mercury and Chloride of Sodium.
_Properties._--A very corrosive and poisonous salt, usually sold in
semi-transparent, crystalline masses, or in the state of powder. Soluble
in 16 parts of cold, and in 3 of hot water; more abundantly so in Alcohol,
and also in Ether. The solubility in water may be increased by the
addition of free Hydrochloric Acid, or of Chloride of Ammonium.
The Protochloride of Mercury is an insoluble white powder, commonly known
under the name of _Calomel_.
METHYLIC ALCOHOL.
This liquid, known also by the names of _wood naphtha_ and _pyroxylic
spirit_, is one of the volatile products of the destructive distillation
of wood. It is very volatile and limpid, with a pungent odour.
By a recent excise regulation, ordinary Spirit mixed with ten per cent, of
wood naphtha is sold free of duty, under the name of "Methylated Spirit."
MILK.
The Milk of herbivorous animals contains three principal
constituents--Fatty matter, Caseine, and Sugar; in addition to these,
small quantities of the Chloride of Potassium, and of Phosphates of Lime
and Magnesia, are present.
The fatty matter is contained in small cells, and forms the greater part
of the cream which rises to the surface of the milk on standing; hence
shimmed milk is to be preferred for Photographic use.
The second constituent, Caseine, is an organic principle somewhat
analogous to Albumen in composition and properties. Its aqueous solution
however does not, like Albumen, _coagulate_ on boiling, unless _an acid_
be present, which probably removes a small portion of alkali with which
the Caseine was previously combined. The substance termed "rennet," which
is the dried stomach of the calf, possesses the property of coagulating
Caseine, but the exact mode of its action is unknown. Sherry-wine is also
commonly employed to curdle Milk; but brandy and other spirituous liquids,
when free from acid and astringent matter, have no effect.
In all these cases a portion of the Caseine usually remains in a soluble
form in the _whey_; but when the Milk is coagulated by the addition of
acids, the quantity so left is very small, and hence the use of the
rennet is to be preferred, since the presence of Caseine facilitates the
reduction of the sensitive Silver salts.
Caseine combines with Oxide of Silver in the same manner as Albumen,
forming a white coagulum, which becomes _brick-red_ on exposure to light.
Sugar of Milk, the third principal constituent, differs from both
cane and grape sugar; it may be obtained by evaporating _whey_ until
crystallization begins to take place. It is hard and gritty, and only
slightly sweet; slowly soluble, without forming a syrup, in about two and
a half parts of boiling, and six of cold water. It does not ferment and
form Alcohol on the addition of yeast, like grape sugar, but by the action
of _decomposing animal matter_ is converted into Lactic Acid.
When skimmed Milk is exposed to the air for some hours, it gradually
becomes _sour_, from Lactic Acid formed in this way; and if then heated to
ebullition, the Caseine coagulates very perfectly.
NITRIC ACID.
Symbol, NO{5}. Atomic weight, 54.
Nitric Acid, or _Aqua-fortis_, is prepared by adding Sulphuric Acid to
Nitrate of Potash, and distilling the mixture in a retort. Sulphate
of Potash and free Nitric Acid are formed, the latter of which, being
volatile, distils over in combination with one atom of water previously
united with the Sulphuric Acid.
_Properties._--Anhydrous Nitric Acid is a solid substance, white and
crystalline, but it cannot be prepared except by an expensive and
complicated process.
The concentrated _liquid_ Nitric Acid contains 1 atom of water, and has
a sp. gr. of about 1·5; if perfectly pure, it is colourless, but usually
it has a slight yellow tint, from partial decomposition into Peroxide of
Nitrogen: it fumes strongly in the air.
The strength of commercial Nitric Acid is subject to much variation. An
acid of sp. gr. 1·42, containing about 4 atoms of water, is commonly
met with. If the specific gravity is much lower than this (less than
1·36), it will scarcely be adapted for the preparation of Pyroxyline.
The yellow _Nitrous Acid_, so called, is a strong Nitric Acid partially
saturated with the brown vapours of Peroxide of Nitrogen; it has a high
specific gravity, but this is somewhat deceptive, being caused in part by
the presence of the Peroxide. On mixing with Sulphuric Acid, the colour
disappears, a compound being formed which has been termed a _Sulphate of
Nitrous Acid_.
In the Appendix a Table is given which exhibits the quantity of real
anhydrous Nitric Acid contained in samples of different densities.
_Chemical Properties._--Nitric Acid is a powerful oxidizing agent (see
page 13); it dissolves all the common metals, with the exception of Gold
and Platinum. Animal substances, such as the cuticle, nails, etc., are
tinged of a permanent yellow colour, and deeply corroded by a prolonged
application. Nitric Acid forms a numerous class of salts, _all of which
are soluble in water_. Hence its presence cannot be determined by any
precipitating reagent, in the same manner as that of Hydrochloric and
Sulphuric Acid.
_Impurities of Commercial Nitric Acid._--These are principally Chlorine
and Sulphuric Acid; also Peroxide of Nitrogen, which tinges the acid
yellow, as already described. Chlorine is detected by diluting the acid
with an equal bulk of distilled water, and adding a few drops of Nitrate
of Silver,--a _milkiness_, which, is Chloride of Silver in suspension,
indicates the presence of Chlorine. In testing for Sulphuric Acid, dilute
the Nitric Acid as before, and drop in _a single drop_ of solution of
Chloride of Barium; if Sulphuric Acid be present, an insoluble precipitate
of Sulphate of Baryta will be formed.
NITROUS ACID. _See_ Silver, Nitrite of.
NITRATE OF POTASH.
Symbol, KO NO{5}. Atomic weight, 102.
This salt, also termed _Nitre_, or _Saltpetre_, is an abundant natural
product, found effloresced upon the soil in certain parts of the East
Indies. It is also produced artificially in what are called Nitre-beds.
The properties of Nitrate of Potash are described as far as necessary at
page 190.
NITRATE OF BARYTA.
Symbol, BaO NO{5}. Atomic weight, 131.
Nitrate of Baryta forms octahedral crystals, which are anhydrous. It is
considerably less soluble than the Chloride of Barium, requiring 12 parts
of cold and 4 of boiling water for solution. It may be substituted for the
Nitrate of Lead in the preparation of Protonitrate of Iron.
NITRATE OF LEAD.
Symbol, PbO NO{5}. Atomic weight, 166.
Nitrate of Lead is obtained by dissolving the metal, or the Oxide of Lead,
in _excess_ of Nitric Acid, diluted with 2 parts of water. It crystallizes
on evaporation in white anhydrous tetrahedra and octahedra, which are
hard, and decrepitate on being heated; they are soluble in 8 parts of
water at 60°.
Nitrate of Lead forms with Sulphuric Acid, or soluble Sulphates, a white
precipitate, which is the insoluble Sulphate of Lead. The _Iodide_ of Lead
is also very sparingly soluble in water.
NITRATE OF SILVER, _See_ Silver, Nitrate or.
NITRO-GLUCOSE.
When 3 fluid ounces of cold Nitro-Sulphuric Acid, consisting of 2 ounces
of Oil of Vitriol and 1 ounce of highly concentrated Nitric Acid, are
mixed with 1 ounce of finely powdered Cane Sugar, there is formed at first
a thin, transparent, pasty mass. If it is stirred with a glass rod for a
few minutes without interruption, the paste coagulates as it were, and
separates from the liquid as a thick tenacious mass, aggregating into
lumps, which can easily be removed from the acid mixture.
This substance has a very acid and intensely bitter taste. Kneaded in
warm water until the latter no longer reddens litmus-paper, it acquires a
silver colour and a beautiful silky lustre. It may be used in Photography
to confer intensity upon newly mixed Collodion; but is inferior to
Glycyrrhizine employed for the same purpose.
NITRO-HYDROCHLORIC ACID.
Symbol, NO{4} + Cl.
This liquid is the Aqua-Regia of the old alchemists. It is produced by
mixing Nitric and Hydrochloric Acids: the Oxygen contained in the former
combines with the Hydrogen of the latter, forming water and liberating
Chlorine, thus:--
NO{5} + HCl = NO{4} + HO + Cl.
The presence of free Chlorine confers on the mixture the power of
dissolving Gold and Platinum, which neither of the two acids possesses
separately. In preparing Aqua-Regia it is usual to mix one part, by
measure, of Nitric Acid with four of Hydrochloric Acid, and to dilute
with an equal bulk of water. The application of a gentle heat assists the
solution of the metal; but if the temperature rises to the boiling point,
a violent effervescence and escape of Chlorine takes place.
NITRO-SULPHURIC ACID.
For the chemistry of this acid liquid, see page 77.
OXYGEN.
Symbol, O. Atomic weight, 8.
Oxygen gas may be obtained by heating Nitrate of Potash to redness, but in
this case it is contaminated with a portion of Nitrogen. The salt termed
Chlorate of Potash (the composition of which is closely analogous to that
of the Nitrate, Chlorine being substituted for Nitrogen) yields abundance
of pure Oxygen gas on the application of heat, leaving behind Chloride of
Potassium.
_Chemical Properties._--Oxygen combines eagerly with many of the chemical
elements, forming Oxides. This chemical affinity however is not well
seen when the elementary body is exposed to the action of _Oxygen in the
gaseous form_. It is the _nascent_ Oxygen which acts most powerfully as
an oxidizer. By nascent Oxygen is meant Oxygen on the point of separation
from other elementary atoms with which it was previously associated; it
may then be considered to be in the liquid form, and hence it comes more
perfectly into contact with the particles of the body to be oxidized.
Illustrations of the superior chemical energy of nascent Oxygen are
numerous, but none perhaps are more striking than the mild and gradual
oxidizing influence exerted by atmospheric air, as compared with the
violent action of Nitric Acid and bodies of that class which contain
Oxygen loosely combined.
OXYMEL.
This syrup of Honey and Vinegar is prepared as follows. Take of
Honey 1 pound.
Acid, Acetic, fortiss. (Beaufoy's Acid) 11 drachms.
Water 13 drachms.
Stand the pot containing the Honey in boiling water until a scum rises
to the surface, which is to be removed two or three times. Then add the
Acetic Acid and water, and skim once more if required. Allow to cool, and
it will be fit for use.
POTASH.
Symbol, KO + HO. Atomic weight, 57.
Potash is obtained by separating the Carbonic Acid from Carbonate of
Potash by means of Caustic Lime. Lime is a more feeble base than Potash,
but the Carbonate of Lime, being _insoluble_ in water, is at once formed
on adding Milk of Lime to a solution of Carbonate of Potash (see page 314).
_Properties._--Usually met with in the form of solid lumps, or in
cylindrical sticks, which are formed by melting the Potash and running it
into a mould. It always contains one atom of water, which cannot be driven
off by the application of heat.
Potash is soluble almost to any extent in water, much heat being evolved.
The solution is powerfully alkaline (p. 308), and acts rapidly upon the
skin; it dissolves fatty and resinous bodies, converting them into soaps.
Solution of Potash absorbs Carbonic Acid quickly from the air, and should
therefore be preserved in stoppered bottles; the glass stoppers must be
wiped occasionally, in order to prevent them from becoming immovably
fixed by the solvent action of the Potash upon the Silica of the glass.
The Liquor Potassæ of the London Pharmacopœia has a sp. gr. of 1·063, and
contains about 5 per cent, of real Potash. It is usually contaminated
with _Carbonate_ of Potash, which causes it to effervesce on the addition
of acids; also, to a less extent, with Sulphate of Potash, Chloride of
Potassium, Silica, etc.
POTASH, CARBONATE OF.
Symbol, KO CO{2}. Atomic weight, 70.
The impure Carbonate of Potash, termed _Pearlash_, is obtained from the
ashes of wood and vegetable matter, in the same manner as Carbonate of
Soda is prepared from the ashes of seaweeds. Salts of Potash and of Soda
appear essential to vegetation, and are absorbed and approximated by
the living tissues of the plant. They exist in the vegetable structure,
combined with organic acids in the form of salts, like the Oxalate,
Tartrate, etc., which, when burned are converted into Carbonates.
_Properties._--The Pearlash of commerce contains large and variable
quantities of Chloride of Potassium, Sulphate of Potash, etc. A purer
Carbonate is sold, which is free from Sulphates, and with only a trace of
Chlorides. Carbonate of Potash is a strongly alkaline salt, deliquescent,
and soluble in twice its weight of cold water; insoluble in Alcohol, and
employed to deprive it of water (see page 196).
PYROGALLIC ACID.
Symbol, C{8}H{4}O{4} (Stenhouse). Atomic weight, 84.
The chemistry of Pyrogallic Acid has been described at page 28.
SEL D'OR. _See_ Gold, Hyposulphite of.
SILVER.
Symbol, Ag. Atomic weight, 108.
This metal, the _Luna_ or _Diana_ of the alchemists, is found native in
Peru and Mexico; it occurs also in the form of Sulphuret of Silver.
When pure it has a sp. gr. of 10·5, and is very malleable and ductile;
melts at a bright red heat. Silver does not oxidize in the air, but
when exposed to an impure atmosphere containing traces of Sulphuretted
Hydrogen, it is slowly tarnished from formation of Sulphuret of Silver. It
dissolves in Sulphuric Acid, but the best solvent is Nitric Acid.
The standard coin of the realm is an alloy of Silver and Copper,
containing about one-eleventh of the latter metal.
To prepare pure Nitrate of Silver from it, dissolve in Nitric Acid and
evaporate until crystals are obtained. Then wash the crystals with a
little dilute Nitric Acid, redissolve them in water, and crystallize by
evaporation a second time. Lastly, fuse the product at a moderate heat, in
order to expel the last traces of Nitric and Nitrous Acids.
SILVER, AMMONIO-NITRATE OF.
Crystallized Nitrate of Silver absorbs Ammoniacal gas rapidly, with
production of heat sufficient to fuse the resulting compound, which
is white, and consists of 100 parts of the Nitrate + 29·5 of Ammonia.
The compound however which Photographers employ under the name of
Ammonio-Nitrate of Silver may be viewed more simply as a solution of the
Oxide of Silver in Ammonia, without reference to the Nitrate of Ammonia
necessarily produced in the reaction.
Very strong Ammonia, in acting upon Oxide of Silver, converts it
into a black powder, termed _Fulminating Silver_, which possesses the
most dangerous explosive properties. Its composition is uncertain. In
preparing Ammonio-Nitrate of Silver by the common process, the Oxide
first precipitated occasionally leaves a little black powder behind, on
re-solution; this does not appear however, according to the observations
of the Author, to be Fulminating Silver.
In sensitizing salted paper by the Ammonio-Nitrate of Silver, _free
Ammonia_ is necessarily formed. Thus--
Chloride of Ammonium + Oxide of Silver in Ammonia
= Chloride of Silver + Ammonia + Water.
SILVER, OXIDE OF.
Symbol, AgO. Atomic weight, 116.
This compound has already been described in Part I., page 17.
SILVER, CHLORIDE OF.
Symbol, AgCl. Atomic weight, 144.
The preparation and properties of Chloride of Silver are given in Part I.
page 14.
SILVER, BROMIDE OF.
Symbol, AgBr. Atomic weight, 186.
See Part I. page 17.
SILVER, CITRATE OF. _See_ Citric Acid.
SILVER, IODIDE OF.
Symbol, AgI. Atomic weight, 234.
See Part I. page 16.
SILVER, FLUORIDE OF.
Symbol, AgF. Atomic weight, 127.
This compound differs from those last described in being soluble in
water. The dry salt fuses on being heated, and is reduced by a higher
temperature, or by exposure to light.
SILVER, SULPHURET OF.
Symbol, AgS. Atomic weight, 124.
This compound is formed by the action of Sulphur upon metallic Silver,
or of Sulphuretted Hydrogen or Hydrosulphate of Ammonia upon the Silver
salts; the decomposition of Hyposulphite of Silver also furnishes the
black Sulphuret.
Sulphuret of Silver is insoluble in water, and nearly so in those
substances which dissolve the Chloride, Bromide, and Iodide, such as
Ammonia, Hyposulphites, Cyanides, etc.; but it dissolves in Nitric Acid,
being converted into soluble Sulphate and Nitrate of Silver. (For a
further account of the properties of the Sulphuret of Silver, see page
146.)
SILVER, NITRATE OF.
Symbol, AgO NO{5}. Atomic weight, 170.
The preparation and properties of this salt have been explained at pages
12 and 362.
SILVER, NITRITE OF.
Symbol, AgO NO{3}. Atomic weight, 154.
Nitrite of Silver is a compound of Nitrous Acid, or NO{3}, with Oxide of
Silver. It is formed by heating Nitrate of Silver, so as to drive off a
portion of its Oxygen, or more conveniently, by mixing Nitrate of Silver
and Nitrite of Potash in equal parts, fusing strongly, and dissolving in a
small quantity of boiling water: on cooling, the Nitrite crystallizes out,
and may be purified by pressing in blotting-paper. Mr. Hadow describes
an economical method of preparing Nitrite of Silver in quantity, viz. by
heating 1 part of Starch in 8 of Nitric Acid of 1·25 specific gravity,
and conducting the evolved gases into a solution of pure Carbonate of
Soda until effervescence has ceased. The Nitrite of Soda thus formed is
afterwards added to Nitrate of Silver in the usual way.
_Properties._--Nitrite of Silver is soluble in 120 parts of cold water;
easily soluble in boiling water, and crystallizes, on cooling, in long
slender needles. It has a certain degree of affinity for Oxygen, and tends
to pass into the condition of Nitrate of Silver; but it is probable that
its Photographic properties depend more upon a decomposition of the salt
and liberation of Nitrous Acid.
_Properties of Nitrous Acid._--This substance possesses very feeble
acid properties, its salts being decomposed even by Acetic Acid. It is
an unstable body, and splits up, in contact with water, into Binoxide
of Nitrogen and Nitric Acid. The Peroxide of Nitrogen, NO{4}, is also
decomposed by water, and yields the same products.
SILVER, ACETATE OF.
Symbol, AgO (C{4}H{3}O{3}). Atomic weight, 167.
This is a difficultly soluble salt, deposited in lamellar crystals when
an Acetate is added to a strong solution of Nitrate of Silver. If _Acetic
Acid_ be used in place of an Acetate, the Acetate of Silver does not fall
so readily, since the Nitric Acid which would then be liberated impedes
the decomposition. Its properties have been sufficiently described at page
89.
SILVER, HYPOSULPHITE OF.
Symbol, AgO S{2}O{2}. Atomic weight, 164.
This salt is fully described in Part I. page 129. For the properties of
the soluble double salt of Hyposulphite of Silver and Hyposulphite of
Soda, see page 43.
SUGAR OF MILK. _See_ Milk.
SULPHURETTED HYDROGEN. _See_ Hydrosulphuric Acid.
SULPHURIC ACID.
Symbol, SO{3}. Atomic weight, 40.
Sulphuric Acid may be formed by oxidizing Sulphur with boiling Nitric
Acid; but this plan would be too expensive to be adopted on a large
scale. The commercial process for the manufacture of Sulphuric Acid is
exceedingly ingenious and beautiful, but it involves reactions which are
too complicated to admit of a superficial explanation. The Sulphur is
first burnt into gaseous Sulphurous Acid (SO{2}), and then by the agency
of Binoxide of Nitrogen gas, an additional atom of Oxygen is imparted from
the atmosphere, so as to convert the SO{2} into SO{3}, or Sulphuric Acid.
_Properties._--Anhydrous Sulphuric Acid is a white crystalline solid. The
strongest liquid acid always contains one atom of water, which is closely
associated with it, and cannot be driven off by the application of heat.
This _mono-hydrated_ Sulphuric Acid, represented by the formula HO SO{3},
is a dense fluid, having a specific gravity of about 1·845; boils at
620°, and distils without decomposition. It is not volatile at common
temperatures, and therefore does not _fume_ in the same manner as Nitric
or Hydrochloric Acid. The concentrated acid maybe cooled down even to
zero without solidifying; but a weaker compound, containing twice the
quantity of water, and termed _glacial_ Sulphuric Acid, crystallizes at
40° Fahr. Sulphuric Acid is intensely acid and caustic, but it does not
destroy the skin or dissolve metals so readily as Nitric Acid. It has an
energetic attraction for water, and when the two are mixed, condensation
ensues, and much heat is evolved; four parts of acid and one of water
produce a temperature equal to that of boiling water. Mixed with aqueous
Nitric Acid, it forms the compound know a as Nitro-Sulphuric Acid.
Sulphuric Acid possesses intense chemical powers, and displaces the
greater number of ordinary acids from their salts. It _chars_ organic
substances, by removing the elements of water, and converts Alcohol into
Ether in a similar manner. The _strength_ of a given sample of Sulphuric
Acid may be calculated, nearly, from its specific gravity, and a Table is
given by Dr. Ure for that purpose. (See Appendix.)
_Impurities of Commercial Sulphuric Acid._--The liquid acid sold as Oil
of Vitriol is tolerably constant in composition, and seems to be as well
adapted for Photographic use as the _pure_ Sulphuric Acid, which is far
more expensive. The specific gravity should be about 1·836 at 60°. If
a drop, evaporated upon Platinum-foil, gives a fixed residue, probably
Bisulphate of Potash is present. A milkiness, on dilution, indicates
Sulphate of Lead (see page 186).
_Test for Sulphuric Acid._--If the presence of Sulphuric Acid, or a
soluble Sulphate, be suspected in any liquid, it is tested for by adding a
few drops of dilute solution of Chloride of Barium, or Nitrate of Baryta.
A white precipitate, _insoluble in Nitric Acid_, indicates Sulphuric Acid.
If the liquid to be tested is very acid, from Nitric or Hydrochloric Acid,
it must be largely diluted before testing, or a crystalline precipitate
will form, caused by the sparing solubility of the Chloride of Barium
itself in acid solutions.
SULPHUROUS ACID.
Symbol, SO{2}. Atomic weight, 32.
This is a gaseous compound, formed by burning Sulphur in atmospheric air
or Oxygen gas: also by heating Oil of Vitriol in contact with metallic
Copper, or with Charcoal.
When an acid of any kind is added to Hyposulphite of Soda, Sulphurous Acid
is formed as a product of the decomposition of Hyposulphurous Acid, but it
afterwards disappears from the liquid by a secondary reaction, resulting
in the production of Trithionate and Tetrathionate of Soda.
_Properties._--Sulphurous Acid possesses a peculiar and suffocating odour,
familiar to all in the fumes of burning Sulphur. It is a feeble acid, and
escapes with effervescence, like Carbonic Acid, when its salts are treated
with Oil of Vitriol. It is soluble in water.
TETRATHIONIC ACID.
Symbol, S{4}O{5}. Atomic weight, 104.
The chemistry of the Polythionic Acids and their salts will be found
described in the First Part of this Work, page 157.
WATER.
Symbol, HO. Atomic weight, 9.
Water is an Oxide of Hydrogen, containing single atoms of each of the
gases.
_Distilled water_ is water which has been vaporized and again condensed;
by this means it is freed from earthy and saline impurities, which, not
being volatile, are left in the body of the retort. _Pure_ distilled water
leaves no residue on evaporation, and should remain perfectly clear on the
addition of Nitrate of Silver, _even when exposed to the light_; it should
also be neutral to test-paper.
The condensed water of steam-boilers sold as distilled water is apt to be
contaminated with oily and empyreumatic matter, which discolours Nitrate
of Silver, and is therefore injurious.
_Rain-water_, having undergone a natural process of distillation, is
free from inorganic salts, but it usually contains a minute portion of
_Ammonia_, which gives it an alkaline reaction to test-paper. It is very
good for Photographic purposes if collected in clean vessels, but when
taken from a common rain-water tank should always be examined, and if much
organic matter be present, tingeing it of a brown colour and imparting an
unpleasant smell, it must be rejected.
_Spring_ or _River_ water, commonly known as "hard water," usually
contains Sulphate of Lime, and Carbonate of Lime dissolved in Carbonic
Acid; also Chloride of Sodium in greater or less quantity. On boiling
the water, the Carbonic Acid gas is evolved, and the greater part of
the Carbonate of Lime (if any is present) deposits, forming an earthy
incrustation on the boiler.
In testing water for Sulphates and Chlorides, acidify a portion with a few
drops of _pure_ Nitric Acid, free from Chlorine (if this is not at hand,
use pure Acetic Acid); then divide it into two parts, and add to the first
a _dilute_ solution of Chloride of Barium, and to the second, Nitrate of
Silver,--a milkiness indicates the presence of Sulphates in the first case
or of Chlorides in the second. The _Photographic Nitrate Bath_ cannot be
used as a test, since the Iodide of Silver it contains is precipitated
on dilution, giving a milkiness which might be mistaken for Chloride of
Silver.
Common hard water can often be used for making a Nitrate Bath when nothing
better is at hand. The Chlorides it contains are precipitated by the
Nitrate of Silver, leaving soluble _Nitrates_ in solution, which are not
injurious. The Carbonate of Lime, if any is present, neutralizes free
Nitric Acid, rendering the Bath alkaline in the same manner as Carbonate
of Soda. (See page 89.) Sulphate of Lime, usually present in well water,
is said to exercise a retarding action upon the sensitive Silver Salts,
but on this point the writer is unable to give certain information.
Hard water is not often sufficiently pure for the developing fluids. The
Chloride of Sodium it contains decomposes the Nitrate of Silver upon
the film, and the image cannot be brought out perfectly. The _New River
water_, however, supplied to many parts of London, is almost free from
Chlorides, and answers very well. In other cases a few drops of Nitrate of
Silver solution may be added, to separate the Chlorine, taking care not to
use a large excess.
APPENDIX.
QUANTITATIVE TESTING OF SOLUTIONS OF NITRATE OF SILVER.
The amount of Nitrate of Silver contained in solutions of that salt may be
estimated with sufficient delicacy for ordinary Photographic operations by
the following simple process.
Take the _pure_ crystallized Chloride of Sodium, and either dry it
strongly or fuse it at a moderate heat, in order to drive off any water
which may be retained between the interstices of the crystals; then
dissolve in distilled water, in the proportion of 8-1/2 grains to 6 fluid
ounces.
In this way, a standard solution of salt is formed, each drachm of
which (containing slightly more than one-sixth of a grain of salt) will
precipitate exactly half a grain of Nitrate of Silver.
In order to use it, measure out accurately one drachm of the Bath in a
minim measure and place it in a two-ounce stoppered phial, taking care to
rinse out the measure with a drachm of distilled water, which is to be
added to the former; then pour in the salt solution, in the proportion
of a drachm for every 4 grains of Nitrate _known to be present_ in an
ounce of the Bath which is to be tested; shake the contents of the
bottle briskly, until the white curds have perfectly separated, and the
supernatant liquid is clear and colourless; then add fresh portions of the
standard solution, by 30 minims at a time, with constant shaking. When the
last addition causes no _milkiness_, read off the total number of drachms
employed (the last half-drachm being subtracted), and multiply that
number by 4 for the weight in grains of the Nitrate of Silver present in
an ounce of the Bath.
In this manner the strength of the Bath is indicated within two grains to
the ounce, or even to a single grain if the last additions of standard
salt-solution be made in portions of 15, instead of 30 minims.
Supposing the Bath to be tested is thought to contain about 35 grains of
Nitrate to the ounce, it will be convenient to begin by adding to the
measured drachm, 7 _drachms_ of the standard solution; afterwards, as
the milkiness and precipitation become less marked, the process must be
carried on more cautiously, and the bottle shaken violently for several
minutes, in order to obtain a clear solution. A few drops of Nitric Acid
added to the Nitrate of Silver facilitate the deposition of the Chloride;
but care must be taken that the sample of Nitric Acid employed is pure and
free from Chlorine, the presence of which would cause an error.
RECOVERY OF SILVER FROM WASTE SOLUTIONS,--FROM THE BLACK DEPOSIT OF
HYPO-BATHS, ETC.
The manner of separating metallic Silver from waste solutions varies
according to the presence or absence of alkaline Hyposulphites and
Cyanides.
a. _Separation of metallic Silver from old Nitrate Baths._--The Silver
contained in solutions of the Nitrate, Acetate, etc. may easily be
precipitated by suspending a strip of sheet Copper in the liquid; the
action is completed in two or three days, the whole of the Nitric Acid and
Oxygen passing to the Copper, and forming a blue solution of the Nitrate
of Copper. The metallic Silver however, separated in this manner, always
contains a portion of Copper, and gives a blue solution when dissolved in
Nitric Acid.
A better process is to commence by precipitating the Silver entirely in
the form of _Chloride of Silver_, by adding common Salt until no further
milkiness can be produced. If the liquid is well stirred, the Chloride of
Silver sinks to the bottom, and may be washed by repeatedly filling the
vessel with common water, and pouring off the upper clear portion when
the clots have again settled down. The Chloride of Silver thus formed may
afterwards be reduced to metallic Silver by a process which will presently
be described (p. 374).
b. _Separation of Silver from solutions containing alkaline Hyposulphites,
Cyanides, or Iodides._--In this case the Silver cannot be precipitated by
adding Chloride of Sodium, since the Chloride of Silver is soluble in such
liquids. It is necessary therefore to use the Sulphuretted Hydrogen, or
the Hydrosulphate of Ammonia, and to separate the Silver in the form of
Sulphuret.
Sulphuretted Hydrogen gas is readily prepared, by fitting a cork and
flexible tubing to the neck of a pint bottle, and having introduced
Sulphuret of Iron (sold by operative chemists for the purpose), about as
much as will stand in the palm of the hand, pouring upon it 1-1/2 fluid
ounce of Oil of Vitriol diluted with 10 ounces of water. The gas is
generated gradually without the application of heat, and must be allowed
to bubble up through the liquid from which the Silver is to be separated.
The smell of Sulphuretted Hydrogen being offensive, and highly poisonous
if inhaled in a concentrated form, the operation must be carried on in the
open air, or in a place where the fumes may escape without doing injury.
When the liquid begins to acquire a strong and persistent odour of
Sulphuretted Hydrogen, the precipitation of Sulphuret is completed. The
black mass must then be collected upon a filter, and washed by pouring
water over it, until the liquid which runs through gives little or no
precipitate with a drop of Nitrate of Silver.
The Silver may also be separated in the form of Sulphuret from old
Hypo-Baths, by adding Oil of Vitriol in quantity sufficient to decompose
the Hyposulphite of Soda; and burning off the free Sulphur from the brown
deposit.
Conversion of Sulphuret of Silver into metallic Silver.--The black
Sulphuret of Silver may be reduced to the state of metal by roasting and
subsequent fusion with Carbonate of Soda; but it is more convenient, in
operating on a small scale, to proceed in the following manner:--first
convert the Sulphuret into Nitrate of Silver, by boiling with Nitric Acid
diluted with two parts of water; when all evolution of red fumes has
ceased, the liquid may be diluted, allowed to cool, and filtered from
the insoluble portion, which consists principally of Sulphur, but also
contains a mixture of Chloride and Sulphuret of Silver, unless the Nitric
Acid employed was free from Chlorine; this precipitate may be heated, in
order to volatilize the Sulphur, and then digested with Hyposulphite of
Soda, or added to the Hypo-Bath.
The solution of Nitrate of Silver obtained by dissolving Sulphuret of
Silver, is always strongly acid with Nitric Acid, and also contains
_Sulphate_ of Silver. It may be crystallized by evaporation; but unless
the quantity of material operated on is large, it will be better to
precipitate the Silver in the form of Chloride, by adding common Salt, as
already recommended.
REDUCTION OF CHLORIDE OF SILVER TO THE METALLIC STATE.
The Chloride of Silver is first to be carefully washed, by filling up
the vessel which contains it, many times with water, and pouring off the
liquid, or drawing it off close with a siphon. It may then be dried at a
gentle heat, and fused with twice its weight of dry Carbonate of Potash,
or better still, with a mixture of the Carbonates of Potash and Soda.
The process for reducing Chloride of Silver in the moist way, by metallic
Zinc and Sulphuric Acid, is more economical and less troublesome than
that just given; it is conducted as follows:--The Chloride, after having
been well washed as before, is placed in a large flat dish, and a bar
of metallic Zinc laid in contact with it. A small quantity of Oil of
Vitriol, diluted with four parts of water, is then added, until a slight
effervescence of Hydrogen gas is seen to take place. The vessel is set
aside for two or three days, and is not to be disturbed, either by
stirring or by moving the bar. The reduction begins with the Chloride
immediately in contact with the Zinc, and radiates in all directions. When
the whole mass has become of a grey colour, the bar is to be carefully
removed and the adhering Silver washed off with a stream of water; the
Zinc usually presents a honeycombed appearance, with irregularities upon
the surface, which however are not metallic Silver;--they consist only of
Zinc or of Oxide of Zinc.
In order to ensure the purity of the Silver, a fresh addition of Sulphuric
Acid must be made, after the Zinc bar has been removed, and the digestion
continued for several hours, in order to dissolve any fragments of
metallic Zinc which may have been inadvertently detached. The grey powder
must be repeatedly washed, first with Sulphuric Acid and water (this is
necessary to dissolve a portion of an insoluble Salt of Zinc, probably
an oxychloride) and then with water alone, until the liquid runs away
_neutral_, and gives no precipitate with Carbonate of Soda; it may
then be fused into a button, to burn off organic matter if present, and
subsequently converted into Nitrate of Silver by boiling with Nitric Acid
diluted with two parts of water.
In reducing Chloride of Silver precipitated from old Nitrate Baths
_containing Iodide of Silver_, the grey metallic powder is sometimes
contaminated with unreduced Iodide of Silver, which dissolves in
the solution of Nitrate of Silver formed on treating the mass with
Nitric Acid. To avoid this, wash the purified Silver with solution of
Hyposulphite of Soda, and then again with water.
MODE OF TAKING THE SPECIFIC GRAVITY OF LIQUIDS.
Instruments are sold, termed "Hydrometers," which indicate specific
gravity by the extent to which a glass bulb containing air, and properly
balanced, rises or sinks, in the liquid; but a more exact process, and one
equally simple, is by the use of the specific gravity bottle.
These bottles are made to contain exactly 1000 grains of distilled water,
and with each is sold _a brass weight_, which counterbalances it when
filled with pure water.
In taking the specific gravity of a liquid, fill the bottle quite full
and insert the stopper, which being pierced through by a fine capillary
tube allows the excess to escape. Then, having wiped the bottle quite dry,
place it in the scale-pan, and ascertain the number of grains required to
produce equilibrium; this number added to, or subtracted from, _unity_
(the assumed specific gravity of water), will give the density of the
liquid.
Thus, to take examples, supposing the bottle filled with _rectified
Ether_ to require 250 grains to enable it to counterbalance the brass
weight,--then 1· _minus_ ·250, or ·750, is the specific gravity; but in
the case of _Oil of Vitriol_ the bottle, when full, will be heavier than
the counterpoise by perhaps 836 grains; therefore 1· _plus_ ·836, _id est_
1·836, is the density of the sample examined.
Sometimes the bottle is made to hold only 500 grains of distilled water,
in place of 1000; in this case the number of grains to be added or
subtracted must be multiplied by 2.
In taking specific gravities, observe that the temperature be within a few
degrees of 60° Fahrenheit (if higher or lower, immerse the bottle in warm
or cold water); and wash out the bottle thoroughly with water each time
after use.
ON FILTRATION AND WASHING PRECIPITATES.
In preparing filters, cut the paper into squares of a sufficient size,
and fold each square neatly upon itself, first into a half-square, and
then again, at right angles, into a quarter-square;--round off the corners
with a pair of scissors, and open out the filter into a conical form, when
it will be found to drop exactly into the funnel, and to be uniformly
supported throughout.
Before pouring in the liquid, always moisten the filter with distilled
water, in order to expand the fibres; if this precaution be neglected,
the pores are apt to become choked in filtering liquids which contain
finely divided matter in suspension. The solution to be filtered may be
poured gently down a glass rod, held in the left hand (_a silver spoon_
may be used, in case of necessity, for Nitrate Baths, and all liquids not
containing Nitric or Hydrochloric Acid), and directed against the side of
the funnel, near to the upper part. If it does not immediately run clear,
it will usually do so on returning it into the filter and allowing it to
pass through a second time.
_Mode of Washing Precipitates._--Collect the precipitate upon a filter and
drain off as much of the mother-liquor as possible; then pour in distilled
water by small portions at a time, allowing each to percolate through the
deposit before adding a fresh quantity. When the water passes through
perfectly pure, the washing is complete; in testing it, a single drop
may be laid upon a strip of glass and allowed to evaporate spontaneously
in a warm place, or the proper chemical reagents may be applied, and the
washing continued until no impurity can be detected. Thus, for example,
in washing the Sulphuret of Silver precipitated from a Hypo-Bath by means
of Hydrosulphate of Ammonia, the process will be completed when the water
which runs through causes no deposit with a drop of Nitrate of Silver
solution.
ON THE USE OF TEST-PAPERS.
The nature of the colouring matter which is employed in the preparation of
litmus-paper has already been described at page 353.
In testing for the alkalies and basic oxides generally, the blue
litmus-paper which has been reddened by an acid may be used, or, in place
of it, the _turmeric_-paper. Turmeric is a yellow vegetable substance
which possesses the property of becoming brown when treated with an
alkali; it is however less sensitive than the reddened litmus, and is
scarcely affected by the weaker bases, such as Oxide of Silver.
In using test-papers, observe the following precautions:--they should be
kept in a dark place, and protected from the action of the air, or they
soon become purple from Carbonic Acid, always present in the atmosphere
in small quantity. By immersion in water containing about one drop of
Liquor Potassæ or Ammoniæ, or a grain of Carbonate of Soda to four
ounces, the blue colour is restored. As the quantities which are tested
for in Photography are often infinitesimally small, it is essential that
the litmus-paper should be in good condition; and test-papers prepared
with porous paper will be found to show the colour better than those
upon glazed or strongly-sized paper. The mode of employing the paper is
as follows:--Place a small strip in the liquid to be examined: if it
becomes at once _bright red_, a strong acid is present; but if it changes
_slowly to a wine-red_ tint, a weak acid, such as Acetic or Carbonic, is
indicated. In the case of the Photographic Nitrate Bath faintly acidified
with Acetic Acid, a purple colour only may be expected, and a decided red
colour would suggest the presence of Nitric Acid. In the Hypo fixing and
toning Bath which has acquired acidity, the litmus-paper will perhaps
redden in about three or four minutes.
Blue litmus-papers may be changed to the red papers used for alkalies by
soaking in water acidified with Sulphuric Acid, one drop to half a pint;
or by holding for an instant near the mouth of a bottle containing Glacial
Acetic Acid. In examining a Nitrate Bath for alkalinity by means of the
reddened litmus-paper, at least five or ten minutes should be allowed for
the action, since the change of colour from red to blue takes place very
slowly.
REMOVAL OF SILVER STAINS FROM THE HANDS, LINEN, ETC.
The black stains upon the hands caused by Nitrate of Silver, may readily
be removed by moistening them and rubbing with a lump of Cyanide of
Potassium. As this salt however is highly poisonous, many may prefer the
following plan:--Wet the spot with a saturated solution of Iodide of
Potassium, and afterwards with Nitric Acid (the strong Nitric Acid acts
upon the skin and turns it yellow, it must therefore be diluted with two
parts of water before use); then wash with solution of Hyposulphite of
Soda.
Stains upon white linen may be easily removed by brushing them with a
solution of Iodine in Iodide of Potassium, and afterwards washing with
water and soaking in Hyposulphite of Soda, or Cyanide of Potassium, until
the yellow Iodide of Silver is dissolved out; the Bichloride of Mercury
(neutral solution) also answers well in many cases, changing the dark spot
to white (p. 151).
A TABLE SHOWING THE QUANTITY OF ANHYDROUS ACID IN DILUTE SULPHURIC ACID OF
DIFFERENT SPECIFIC GRAVITIES. (URE.)
+---------+------------++---------+------------++---------+------------+
| |Real Acid || |Real Acid || |Real Acid |
|Specific | in 100 ||Specific | in 100 ||Specific | in 100 |
|Gravity. |parts of the||Gravity. |parts of the||Gravity. |parts of the|
| | Liquid. || | Liquid. || | Liquid. |
+---------+------------++---------+------------++---------+------------+
| 1·8485 | 81·54 || 1·8115 | 73·39 || 1·7120 | 65·23 |
| 1·8475 | 80·72 || 1·8043 | 72·57 || 1·6993 | 64·42 |
| 1·8460 | 79·90 || 1·7962 | 71·75 || 1·6870 | 63·60 |
| 1·8439 | 79·09 || 1·7870 | 70·94 || 1·6750 | 62·78 |
| 1·8410 | 78·28 || 1·7774 | 70·12 || 1·6630 | 61·97 |
| 1·8376 | 77·46 || 1·7673 | 69·31 || 1·6520 | 61·15 |
| 1·8336 | 76·65 || 1·7570 | 68·49 || 1·6415 | 60·34 |
| 1·8290 | 75·83 || 1·7465 | 67·68 || 1·6321 | 59·52 |
| 1·8233 | 75·02 || 1·7360 | 66·86 || 1·6204 | 58·71 |
| 1·8179 | 74·20 || 1·7245 | 66·05 || 1·6090 | 57·89 |
+---------+------------++---------+------------++---------+------------+
A TABLE SHOWING THE QUANTITY OF ANHYDROUS ACID IN THE LIQUID NITRIC ACID
OF DIFFERENT SPECIFIC GRAVITIES. (URE.)
+---------+------------++---------+------------++---------+------------+
| |Real Acid || |Real Acid || |Real Acid |
|Specific | in 100 ||Specific | in 100 ||Specific | in 100 |
|Gravity. |parts of the||Gravity. |parts of the||Gravity. |parts of the|
| | Liquid. || | Liquid. || | Liquid. |
+---------+------------++---------+------------++---------+------------+
| 1·5000 | 79·700 || 1·4640 | 69·339 || 1·4147 | 58·978 |
| 1·4980 | 78·903 || 1·4600 | 68·542 || 1·4107 | 58·181 |
| 1·4960 | 78·106 || 1·4570 | 67·745 || 1·4065 | 57·384 |
| 1·4940 | 77·309 || 1·4530 | 66·948 || 1·4023 | 56·587 |
| 1·4910 | 76·512 || 1·4500 | 66·155 || 1·3978 | 55·790 |
| 1·4880 | 75·715 || 1·4460 | 65·354 || 1·3945 | 54·993 |
| 1·4850 | 74·918 || 1·4424 | 64·557 || 1·3882 | 54·196 |
| 1·4820 | 74·121 || 1·4385 | 63·760 || 1·3833 | 53·399 |
| 1·4790 | 73·324 || 1·4346 | 62·963 || 1·3783 | 52·602 |
| 1·4760 | 72·527 || 1·4306 | 62·166 || 1·3732 | 51·805 |
| 1·4730 | 71·730 || 1·4269 | 61·369 || 1·3681 | 51·068 |
| 1·4700 | 70·933 || 1·4228 | 60·572 || 1·3630 | 50·211 |
| 1·4670 | 70·136 || 1·4189 | 59·775 || 1·3579 | 49·414 |
+---------+------------++---------+------------++---------+------------+
WEIGHTS AND MEASURES.
_Troy, or Apothecaries' Weight._
1 Pound = 12 Ounces. 1 Ounce = 8 Drachms. 1 Drachm
= 3 Scruples. 1 Scruple = 20 Grains. (1 Ounce Troy = 480
Grains, or 1 Ounce Avoirdupois _plus_ 42·5 grains.)
_Avoirdupois Weight._
1 Pound = 16 Ounces. 1 Ounce = 16 Drachms. 1 Drachm
= 27·343 grains. (1 Ounce Avoirdupois = 437·5 grains.) (1 Pound
Avoirdupois = 7000 Grains, or 1 Pound Troy _plus_ 2-1/2 Troy Ounces
_plus_ 40 grains.)
_Imperial Measure._
1 Gallon = 8 Pints. 1 Pint = 20 Ounces. 1 Ounce = 8
Drachms. 1 Drachm = 60 Minims. (A Wine Pint of water
measures 16 Ounces, and _weighs_ a Pound.)
An Imperial Gallon of water _weighs_ 10 Pounds Avoirdupois, or
70,000 Grains. An Imperial Pint of water _weighs_ 1-1/4 Pound Avoirdupois.
A fluid Ounce of water _weighs_ 1 Ounce Avoirdupois, or
437·5 Grains. A Drachm of water _weighs_ 54·7 Grains.
_French Measures of Weight._
1 Kilogramme = 1000 Grammes = something less than 2-1/4 Pounds
Avoirdupois.
1 Gramme = 10 Decigrammes--100 Centigrammes = 1000
Milligrammes = 15·433 English Grains.
A Gramme of water _measures_ 17 English Minims, nearly.
1000 Grammes of water _measure_ 35-1/4 English fluid Ounces.
_French Measures of Volume._
1 Litre = 13 Decilitres = 100 Centilitres = 1000 Millilitres =
35-1/4 English fluid Ounces.
1 Litre = 1 Cubic Decimetre = 1000 Cubic Centimetres.
1 Cubic Centimetre = 17 English Minims.
A Litre of water _weighs_ a Kilogramme, or something less than
2-1/4 Pounds Avoirdupois. A Cubic Centimetre of water _weighs_ a
Gramme.
INDEX.[56]
[56] The preparation and properties of the Chemicals used in Photography
will be found in the Alphabetical List commencing at page 327.
Aberration, chromatic, 54;
spherical, 56.
Accelerating agents, their mode of action in Collodion explained, 95.
Acetate of Silver, its preparation and formula, 365;
its formation in Nitrate Bath explained, 89;
ensures absence of free Nitric Acid, 116;
tends slightly to favour fogging and spots, 104;
contra-indicated for glass Positives, 111.
Acetic Acid, properties and mode of testing purity of, 327;
useful in preventing fogging, 104;
in rendering the development slow and even, 99;
does not coagulate Albumen, 329;
a good commercial form of acid, 212;
Acetic Acid essential in Calotype, waxed paper, and Albumen
processes, 177;
also in printing paper Positives by development, 260.
Aceto-Nitrate of Silver, term explained, 177.
Achromatic Lenses, their construction explained, 55;
the visual and chemical foci often coincident in, 60.
Acids, nature of, 308.
Actinism, explained, 61;
importance of distinguishing Actinic from visual rays, 62;
mode of finding Actinic focus, 229.
Affinity, chemical, 312.
Albumen, its chemistry, 328;
forms a compound with oxide of Silver, 20;
used in Positive printing to produce a fine surface layer, 122;
to increase sensitiveness, 125;
affects the colour of the prints, 127;
protects the image from oxidation, 150;
putrifies when exposed to moisture, 155;
discolours the Nitrate Bath, 245.
Albumen negative process, its invention, 10;
theory of, 180;
Collodio-Albumen process of M. Taupenot, 294.
Albuminized paper, formula for, 241;
slow in fixing, 131;
not well adapted for toning by Sel d'or, 269;
good for stereoscopic subjects and small portraits, 249;
cannot be sensitized with Ammonio-Nitrate of Silver, 246.
Alcohol, its chemistry, 330;
sometimes too dilute for making Collodion, 84;
mode of rectifying, 196;
must not contain impurities, 96;
effects of adding to Collodion, 84, 96;
to developer, 205.
Alkalies, nature of, 308.
Alkalinity of Nitrate Bath, explained, 88;
the evils it produces, 104;
how to test for it, 377;
how to remove it, 277.
Amber varnish, 226.
Ammonia, preparation and properties, 331;
its use in fixing, 42;
Mr. Shadbolt's formula for, 271;
its action upon Chloride of Gold, 343;
effect of concentrated Ammonia upon Oxide of Silver, 362.
Ammonio-Nitrate of Silver, its chemistry, 262;
used in Positive printing to increase sensitiveness, 125;
to give black tones, 127;
cannot be used with Albumen, 246;
increases permanency of print, 169;
old Nitrate Baths not easily convertible into Ammonio-Nitrate, 248;
mode of preparing, 247;
best applied to the paper by brush or rod, 248;
Oxide of Silver in Nitrate of Ammonia, a useful substitute for it, 249.
Ammonio-Nitrate paper, formula for, 246;
a more simple formula, but less sensitive than the last, 258.
Atomic theory explained, 322.
Bath for fixing and toning Positives. _See_ Fixing and toning Bath.
Bichloride of Mercury, whitening action on glass Positives
explained, 113;
solution for, 207;
used to intensify Negatives, 118;
bleaches paper prints, 151;
should not be added to paste used in mounting prints, 164;
removes Silver stains, 377.
Binocular vision, phenomena of, explained, 66.
Blackening Negatives, 37, 117.
Black tones, mode of obtaining, in paper Positives, 168, 246.
Bromide of Silver, its preparation and properties, 17;
its superior sensibility to coloured light, 63;
less acted on by white light than Chloride, 19;
less sensitive to invisible image than Iodide, 25;
employment in Collodion, 101;
found useful in Photographing by artificial light, 66;
diagram of chemical spectrum on, 64.
Bromo-Iodide of Silver, 173.
Brushes, mode of applying Silver solutions by, 248.
Calotype process, theory of, 176.
Camera, its first invention, 7;
theory of its construction, 54;
mode of testing accuracy of, 229;
cause of the image being inverted, 53;
the term "flatness of field" explained, 54;
best position of the Camera for portraits, 220;
for architectural subjects, 231;
a funnel-shaped tube placed in front of the lens, 229;
stereoscopic Camera, 234;
microscope Camera, 236.
Causes of failure in Collodion process, 276.
Chemical affinity, illustrations of, 312.
Chemical elements, 306.
Chemical focus, directions for finding, 229;
shorter than visual in non achromatic lenses, 60;
longer than visual in microscopic objectives, 237;
varies slightly with the nature of the light, 238.
Chemical spectrum, 61.
Chemicals, Photographic, Vocabulary of, 327.
Chloride of Silver, its preparation and properties, 14;
more sensitive to white light than Bromide or Iodide, 19;
less sensitive to invisible image, 24;
its blackening by light explained, 20, 141;
accelerated by excess of Nitrate, 19;
by organic matter, 20, 142;
experiments illustrating darkening of papers prepared with, 21;
simple explanation of the mode of preparing sensitive papers with, 22;
agents which dissolve it, 42;
mode of reducing it to metallic state. 374.
Chloride of Gold, its preparation and properties, 342;
action of Ammonia upon it, 343;
use of an alkaline solution of, for toning, 132, 271;
compounds formed on adding it to Hyposulphite of Soda, 133;
mode of preparing the fixing and toning Bath with, 250;
the Sel d'or Bath with, 267.
Chromatic aberration, 54.
Citric Acid, forms a red compound with Suboxide of Silver, 21, 338;
used in printing to give purple tones, 128;
formula for preparing paper with, 246.
Cleaning glass plates, theory of, 39;
details of, 213.
Collodion, its discovery, 10;
chemistry of Pyroxyline, 75;
physical effect of Ether and Alcohol in, 83;
of water in, 85;
glutinosity of, 83;
coloration of iodized, explained, 85;
sensitiveness and intensity affected by the change, 97, 99;
details of manufacture of Collodion, 185;
Positive Collodion, theory of, 108;
formula for, 201;
Negative Collodion, theory of, 113;
formula for, 208;
Collodion for copying engravings, 231;
for keeping processes, 298;
for hot climates, 210;
for working by artificial light, 238;
to remove the brown colour from Collodion, 86.
Collodion film, the proper time for immersing it in the Bath, 219;
a thin film often good for direct Positives, 109;
a thicker film for Negatives, 113;
cause of the film falling away from the glass, 83, 293;
spots and markings on, 281;
conditions which affect its sensitiveness to light, 92;
causes influencing its behaviour with the developer, 98;
mode of preserving sensitiveness of film, 289.
Collodio-Albumen process, theory of, 181;
practical details of, 294.
Colours, their nature explained, 47;
their chemical action on sensitive film, 64;
their photographic action assisted by reflection of white light, 66.
Combination, laws of, 307.
Conjugate foci, explained, 52, 272.
Crookes, Mr., remarks upon chemical spectrum, 63;
upon waxed paper process, 180;
preservative process for Collodion films, 289.
Curvature of luminous image formed by lens, explained, 53.
Cyanide of Potassium, its fixing action explained, 44;
preparation of solution of, 207;
used to remove stains, 377.
Daguerreotype, its invention, 8;
theory of the process, 171.
Development of invisible image, explanation of, 34-40;
second, or intensifying stage explained, 37;
details of developing glass Positives and Negatives, 221-223;
development of paper Positives, 259;
conditions which increase or diminish rapidity of development, 98;
irregularities of development, 103.
Developers, their preparation and properties, 26;
comparative strength of, 98;
theory of, for Positives, 111;
for Negatives, 117;
formulæ for Positive developers, 205;
for Negative, 211.
Diagrams, mode of copying, 232.
Diaphragms for lenses. _See_ Stops.
Double decomposition, illustrated, 14;
explained, 314.
Dry Collodion process, 298.
Elementary bodies, table of, 306;
combination of, 307.
Engravings, mode of copying, 231;
often yield dark-coloured prints, 255.
Equivalent proportions, 320.
Ether, properties of, 339;
purification of, for Photography, 195;
must be kept in a dark place, 196;
should not be distilled from residues of old Collodion, 96.
Experiments, illustrating action of Light upon Chloride of Silver, 21;
illustrating formation and development of invisible images, 25;
illustrating photographic action of coloured light, 62.
Exposure in the Camera, rules for Positives, 221;
for Negatives, 225;
for preserved Collodion plates, 292;
for microscopic photographs, 238;
effects of under and over-exposing, 35;
exposure required in Calotype process, 177;
in waxed paper, 180;
in Albumen negative process, 181;
in dry Collodion process, 301;
in Taupenot's process, 297.
Fading of Positives, explained at length, 160;
Author's researches on, 153.
Film, sensitive. _See_ Collodion film.
Filters, mode of cutting, 376.
Fixing, theory of, 41;
of paper prints explained, 128;
solution for fixing glass Positives and Negatives, 212;
manipulatory details of fixing, 225;
fixing paper Positives with Ammonia, 271.
Fixing and toning Bath, its preparation, 250;
conditions which favour or retard its action, 135;
certain states of the Bath injurious to the proofs, 136;
importance of keeping it in an active condition, 168;
must not be employed immediately after mixing, 251;
must not be allowed to become acid by constant use, 168;
theory of the gradual change of properties it undergoes, 156.
Foci, actinic and luminous, 60;
actinic, mode of finding, 229;
variation between them in microscopic objectives, 237.
Focussing the object, 220.
Fogging, theory of, 103;
mode of detecting causes of, 276.
Formulæ for solutions required in Collodion process, 201;
for papers used in Positive printing, 241;
want of correspondence between, 257.
Gallic Acid, its preparation and properties, 27;
used in paper processes, 178;
becomes mouldy by keeping, 261.
formula for developing paper Positives with, 261.
Gallo-Nitrate of Silver, 177;
discolours rapidly when developing dishes are not clean, 179.
Gelatine, its properties, 341;
forms a compound with an Oxide of Silver, 21;
employed in dry Collodion process, 299;
modified form of, 302;
affects the colour in printing processes, 128;
used in Positive printing to form an even surface layer, 126;
as a cement to mount Photographs, 257.
Glass plates, rules for cleaning, 39;
details of cleaning, 213;
mode of coating with Collodion, 215;
with Albumen, 180.
Glutinous Collodion, explained, 83.
Glycyrrhizine, its nature, 342;
its action in Collodion, 114;
formula for solution of, 209.
Gold, Chloride of. _See_ Chloride of Gold.
Gold salts, their use in Photographic printing explained, 131;
in the Daguerreotype process, 175.
Gradation of tone, in Collodion Photographs, affected by the density of
the film, 109, 113;
by use of Glycyrrhizine, 115.
Gradation of tone, in paper Positives, conditions affecting it in prints
obtained by direct exposure, 123;
in Positives printed by development, 266.
Hadow, Mr., researches on Collodion, 77;
formula for making Pyroxyline, 187.
Heliography, invented by M. Niépce, 7.
Historical sketch of Photography, 6.
Honey keeping process, 289.
Hunt, Mr., introduces Protosalts of Iron in developing, 111.
Hypo Bath. _See_ Fixing and Toning Bath.
Hyposulphite of Silver, its peculiar changes in colour, 129;
the sweet compound which it forms with Hyposulphite of Soda, 44.
Hyposulphite of Soda, preparation and properties, 43;
theory of its fixing action, 43;
blackens Nitrate of Silver, 129;
causes a milkiness with acids, 137;
its decomposition by constant use in fixing, 138;
the salts it forms with Chloride of Gold, 133;
its conversion into sulphuretting Tetrathionate by Iodine and
Perchloride of Iron, 139;
test for presence of, 169.
Iceland moss, its use in Positive printing, 128;
formula for preparing paper with, 245.
Imperfections in Collodion Negatives, 282;
in Positives, 284;
in paper Positives, 285.
Intensity, explanation of term, 92;
mode of increasing in Negatives, 99, 114;
effect of Acetate of Silver upon, 116;
of Nitrite of Silver upon, 102;
mode of diminishing, in glass Positives, 109, 110;
conditions affecting intensity in paper Positives, 123;
in developed paper Positives, 266.
Invisible images, theory of formation of, 34;
development of, 36;
experiments illustrating, 25.
Iodate, how formed in Collodion film, 94;
produces insensitiveness, 198.
Iodide of Ammonium, preparation of, 198;
not fitted for iodizing Collodion required to be kept long, 210.
Iodide of Iron, an accelerator to Collodion, 116.
Iodide of Potassium and Silver, properties of, 42;
mode of iodizing Calotype papers by, 177.
Iodide of Potassium, tests of purity of, 197;
extent of solubility in Alcohol, 351;
dissolves Iodide of Silver, 42.
Iodide of Silver, its preparation and properties, 16;
unaffected by direct action of light, 19;
highly sensitive to invisible image, 24;
hypothesis of formation of latent image on, 34;
possibility of its reduction by Pyrogallic Acid shown, 33;
excess of Nitrate of Silver essential to its blackening by
developer, 36;
diagrams of chemical spectrum on, 61, 64;
fixing agents for, 42;
its solubility in the Nitrate Bath, 86;
retards the action of Hypo fixing and toning Bath, 136;
superior permanency of developed prints on, 167;
details of Negative printing process on, 263.
Iodine, in Collodion, diminishes sensitiveness, 94;
forms Nitric Acid and Iodate in the Bath, 94;
often useful in Positive Collodion, 110;
in Negative Collodion, if fogging occurs, 105;
mode of removing from Collodion, 86.
Iodized Collodion. See Collodion.
Kaolin, properties of, 335;
used to decolorize Nitrate Baths, 91;
importance of purifying it before use, 245.
Landscape Photography, with preserved Collodion plates, 288.
Latent image. See Invisible image.
Laws of substitution explained, 78.
Le Grey, M,, his toning process with Chloride of Gold, 132;
his waxed paper Negative process, 178.
Lenses, various forms of, 51;
foci of, 52;
formation of images by, 53;
use of stops, 58;
portrait, 59;
chemical foci of, 60;
chromatic aberration of, 54;
spherical aberration of, 56;
simple directions for using lenses, 227;
for finding chemical focus, 229.
Light; its action upon Silver Salts, 19;
experiments illustrating, 21;
formation of invisible images by, 24;
its alternating action upon Daguerreotype plate, 39;
its compound nature, 46;
photographic action of coloured light, 60;
refraction of light, 49.
Llewellyn, Mr., his Oxymel process, 291.
Manipulations of Collodion process, 213;
of Photographic printing, 251;
of toning by Sel d'or, 267.
Manuscripts, mode of copying, 231.
Markings on Collodion Pictures, 281.
Measures and Weights, 379.
Microscopic Photography, 235.
Moser, M. Ludwig, his researches on the development of invisible
images, 37.
Mounting Positive Prints, substances which should be avoided in,
155, 164;
details of, 257.
Negative processes for printing Positives, 259, 263.
Negatives, definition of, 106;
Collodion Negatives, theory of production of, 113;
Calotype, 176;
waxed paper, 178;
Albumen, 180;
Collodio-Albumen (Taupenot), 181;
mode of developing Collodion Negatives, 37, 117, 223;
of converting Positives into, 117;
formula for solutions for Negatives, 208;
the Collodion best adapted for Negatives, 114;
spots and markings upon Negatives, 282;
decomposition of Pyroxyline a cause of fading of, 166.
Nitrate of Silver, preparation and properties of, 12;
preparation of from standard coin of realm, 362;
often contains free Nitric Acid, 13;
when very strongly fused, contains Nitrite
(_see_ Nitrite of Silver), 14;
not acted on by light, 18;
its reduction by Pyrogallic Acid explained, 31;
the melted Nitrate more certain in its action, 13, 101;
its presence essential in developing the image, 36, 98;
increases sensitiveness of Collodion plate, 92;
dissolves Iodide of Silver, 86;
discoloured by Albumen, 245, 329;
forms a compound with Honey, 289;
with various other organic bodies, 21;
very little acted on by Glycerine, 342;
mode of recovering the Silver from, 372.
Nitrate Bath, mode of preparing for glass Positives, 110, 203;
for Collodion Negatives, 116, 211;
its power of dissolving Iodide of Silver, its occasional acidity and
alkalinity explained, 86;
the mode in which Acetate of Silver may be formed in it, 89;
a list of the substances by which it is decomposed, 90;
changes by use, 91;
effect of these changes on sensitiveness, 97;
on intensity, 102;
care required to prevent it from yielding foggy pictures, 104;
a caution against the too frequent addition of alkali, 204;
quantitative testing of the Bath, 371.
Nitrite of Silver, adds to rapidity of development, 102;
tends slightly to produce fogging, 104;
solarizes the high lights, 111.
Nitric Acid, its preparation and properties, 355;
its oxidizing powers, 12;
impairs sensitiveness of Collodion film, 93;
lessens rapidity of development, 98;
tends to prevent fogging, 104;
sometimes usefully employed for glass Positives, 110;
contra-indicated for Negatives, 116;
its accumulation in the Nitrate Bath explained, 94;
mode of removing it, 90;
cannot exist in contact with Acetate of Silver, 116;
produces stains on cloth, 215;
mode of determining the strength of Commercial Nitric Acid, 186;
table of strength of Nitric Acid of different densities, 378.
Nitro-Sulphuric Acid, explained, 77;
process for making by mixed acids, 186;
by Oil of Vitriol and Nitre, 190;
should not be used cold, 83.
Nomenclature, chemical, 315.
Norris, Dr., his dry Collodion process, 298.
Notation, chemical, 318.
Organic bodies, chemistry of, 324.
Oxide of Silver, preparation and properties, 17;
dissolves in the Nitrate Bath, rendering it alkaline, 88;
properties of its solution in Ammonia, 362;
preparation of ditto, 247;
its solution in Nitrate of Ammonia used in Photography, 249.
Oxymel, keeping process, 291;
preparation of Oxymel, 360.
Paper, Photographic, selection of, 240;
peculiarity of English papers, 241.
Paper, sensitive, for printing. _See_ Sensitive Paper.
Perchloride of Iron, preparation of toning Bath with, 160.
Permanence of Positives, mode of testing, 169.
Photographic image, chemical composition of, 140;
action of destructive tests on, 145.
Photographic properties of Salts of Silver, 18;
of Iodide of Silver upon Collodion, 74.
Photographic researches by the Author, 140.
Photography, historical sketch of, 6;
the term explained, 61.
Portrait lenses, theory of their construction, 59;
rules for their use, 227;
mode of finding chemical focus, 229.
Portraits, drapery for, 66;
directions for taking, 220;
the position of the Camera, and other points of importance, 228;
the time of exposure, 221.
Positive printing, on Albuminized paper, formulæ for, 241;
on plain paper, formulæ for, 245;
on Ammonio-Nitrate paper, formula for, 246, 258;
by development, formulæ for, 259;
manipulatory details of printing, fixing, toning, washing, and
mounting, 251;
process of toning by Sel d'or, theory of, 134;
practice of, 267;
reasons for the want of correspondence between different formulæ, 257;
use of Chloride of Gold in toning, 132, 271;
theory of the preparation of the sensitive paper for Positives, 122;
theory of the process of fixing, 129;
of toning by Gold, 132;
the Author's researches, 140;
rationale of the printing process, 120;
composition of the image, 140;
fading of Positive prints, 160;
destructive action of Sulphur on, 145;
of oxidizing agents on, 148;
of Chlorine, acids, boiling water, etc., on, 151;
of combustion of coal-gas on, 153;
effect of damp air on, 153;
theory of mode of washing Positives, 162;
comparative permanency of prints, 166;
mode of testing permanency, 169.
Positives, definition of, 106;
Collodion Positives, theory of production of, 108;
formulæ for solutions for, 201;
development of, 111, 221;
Collodion and Nitrate Bath best adapted for, 109;
mode of whitening by Bichloride of Mercury, 112;
solution for whitening, 207;
mode of backing up, 226;
spots and markings on, 284;
mode of printing Positives on Collodion, 272.
Positives, enlarged, mode of printing, 272.
Practice of Collodion process, 183.
Preservative processes for Collodion plates, 289.
Printing, Photographic, theory of, 120;
practical details of, 240.
Prism, refraction of light by, 51;
diagram of formation of spectrum by, 47;
explained, 54.
Prismatic spectrum, 47, 61.
Protonitrate of Iron, preparation of, 206;
a feeble developer when free from excess of Sulphate of Iron, 98;
theory of its mode of action, and rules for its use, 112;
cannot be prepared in quantity by adding Nitrate of Potash to Sulphate
of Iron, 314;
sometimes requires the addition of Nitrate of Silver, 206.
Protosulphate of Iron, its preparation and properties, 29;
its characteristics as a developer for Collodion Positives, 111;
not well adapted for developing Collodion Negatives, 117;
preparation of the solution for Positives, 205;
mode of applying it to the plate, 221;
to remove iron stains on glass, 215.
Pyrogallic Acid, its preparation and properties, 28;
solution for developing glass Positives, 205;
for Negatives, 211;
cannot be used without Acetic Acid, 105;
less adapted for developing paper pictures, 178;
requires addition of Nitric Acid when used for Positives, 111;
superior to Sulphate of Iron for developing Negatives, 117, 144;
mode of obviating the brown discoloration of developing solutions, 212.
Pyroxyline, its nature and properties, 75;
preparation of, by Mr. Hadow's formula, 186;
by a rule-of-thumb mixture of the acids, 188;
by the Oil of Vitriol and Nitre process, 190;
details of immersing, washing, and drying, 191;
the glutinous variety produced by cold acids, 83;
recapitulation of the effects of varying the strength of the acid
mixture, 193;
spontaneous decomposition of Pyroxyline, 166.
Reduction of metallic oxides by developers, theory of, 26;
of Silver salts by developers, theory of, 30;
practical details of reducing Silver compounds to metallic state, 372.
Salts nature of, 310.
Salts of Silver, their preparation and properties, 12;
their Photographic action, 18;
theory of their reduction by developer, 30;
directions for obtaining metal from, 372.
Sel d'or, toning process by, its theory, 134;
its practical details, 267;
its advantages, 271;
gives permanent prints, 167.
Sensitiveness, term explained, 92;
conditions favourable to, 97.
Sensitiveness of Collodion film, causes influencing, 92;
superior sensitiveness partially explained, 74;
preservation of sensitive film, 288.
Sensitive paper, theory of preparation of, 22, 122;
its darkening by light described, 123;
preparation of Albuminized paper, 241;
of plain paper, 245;
of Ammonio-Nitrate paper, 246, 258;
of paper for Negative processes, 259;
causes which affect the sensitiveness of Positive paper, 123;
which alter the colour of the image, 126;
spots and markings on, 285;
a large excess of Nitrate of Silver essential, 124;
the paper should not be kept too long, 130, 286.
Serum of Milk, preparation of, 262, 355;
used in Negative printing process, 262.
Shadbolt, Mr., his Honey keeping process, 289;
employs artificial light in Micro-Photography, 237.
Silver, properties of, 362;
estimation of, in Nitrate Baths, 371;
recovery from waste solutions, 372;
reduction from Chloride, 374;
stains, removal of, 377.
Size, mode of removing, from paper Positives, 255.
Solar spectrum, 47, 61.
Soluble paper. _See_ Pyroxyline.
Specific gravity of liquids, mode of finding, 375.
Spherical aberration, 56.
Spirits of Wine, preparation and properties, 330;
not always sufficiently strong for Collodion, 84;
mode of rectifying, 196;
sometimes contaminated with, fusel oil, 96.
Spots on Collodion plates, 279;
on paper Positives, 285;
on prints obtained by development, 266;
on preserved Collodion plates, 293.
Stains, Silver, removal of, 377.
Stereoscope, invention of, 67;
theory of, 68;
Wheatstone's, 69;
Brewster's, 70.
Stereoscopic Photographs, rules for taking, 71;
practical details of, 232.
Stops, theory of use of, 57;
simple mode of making, 228;
position of the stop often important, 230.
Strength of acids, tables of, 378.
Subchloride of Silver, its preparation and properties, 15;
decomposed by fixing agents, 141.
Suboxide of Silver, its properties, 18;
forms compounds with organic matters. Citric Acid, Albumen, etc., 21.
Substitution, laws of, explained, 78.
Sulphate of Iron. _See_ Protosulphate of Iron.
Sulphate of Quinine, absorption of chemical rays by, 65.
Sulphuric Acid, table of strength of, 378.
Sutton, Mr., theory of Sel d'or toning process, 134;
practical details of, 267;
Negative printing process, 262;
preparation of Serum of Milk for, 355.
Symbols, use of, 318.
Syruped Collodion film, 289.
Talbot, Mr., his discoveries, 9;
theory of Calotype process, 176.
Taupenot, M., his Collodio-Albumen process, 181;
practical details of, 294.
Temperature, its effect upon development of Collodion film, 102;
upon fogging, 105;
upon keeping Collodion, 210;
upon action of fixing Bath for paper Positives, 130;
upon Hypo toning Bath, 136.
Test-papers, use of, 376.
Toning Bath for Positives, with Sel d'or, 134, 267;
with Hyposulphite and Gold, _see_ Fixing and Toning Bath;
with Chloride of Iron and Hyposulphite, 160.
Toning of Positives, term defined, 121;
may injure the stability of the proof, 154;
points to be kept in view to avoid fading, 167;
manipulatory details of, 253;
by Sel d'or, 267.
Transparencies, mode of printing, 273.
Varnishes for Collodion Photographs, 226.
View Lenses, directions for using, 230.
Vocabulary of Photographic chemicals, 327.
Washing Positive prints, rules for, 162;
details of, 255.
Waxed paper process, theory of, 178.
Weights and Measures, table of, 379.
PRINTED BY JOHN EDWARD TAYLOR, LITTLE QUEEN STREET, LINCOLN'S INN FIELDS.
* * * * *
Transcriber Note
Minor typos have been corrected. Images moved to prevent splitting
paragraphs.