_Obs._ The above are kept in small decanters, and used to flavour water,
grog, liqueurs, &c., instead of sugar or capillaire; also to perfume the
breath. Other flavoured syrups, for the same purposes, are prepared in a
similar manner.
=HU'MIC ACID.= _Syn._ ULMIC ACID. See HUMUS.
=HUMULIN.= The name given to a beautiful extract or essence of hops, made
as follows:--
A concentrated tincture of hops is prepared by percolation with rectified
spirit; the same hops are then exhausted with water; the spirit is removed
from the tincture by careful distillation, and the upper aqueous portion
is skimmed off, and added to the infusion, which latter is then evaporated
to the consistence of a soft extract; the oleo-resinous residuum of the
tincture is next added, and well mixed in; after which the whole is put
into pots and carefully tied over for sale. The product possesses all the
fragrant, tonic, and bitter qualities of the hop in a highly condensed
form. See HOPS, LUPULIN, &c.
=HU'MUS.= _Syn._ ULMIN. When wood, or woody fibre, is exposed to the joint
action of air and moisture, it suffers eremacausis or decay, and crumbles
down into a dark-brown or black powder commonly called 'mould,' and to
which chemists have given the name of 'humus.' In this state it exists in
fertile soils, in which it is derived from the decay of plants. A powder
of similar composition is produced by the action of powerful chemical
reagents on sugar, lignin, &c. When acted upon by dilute boiling solution
of caustic potassa, this substance yields a deep-brown solution, from
which acids precipitate a flocculent brown substance generally called
'ulmic' or 'humic acid.' Both bodies require further investigation, as
they are supposed to vary exceedingly in composition.
=HUNGER.= The peculiar sensation arising from the want of food. When
severe, it increases to actual pain, the coats of the stomach are acted on
by its own juices, the respiration becomes less frequent, the circulation
languid, and there is a general diminution of the heat of the body and of
the secretions. The return of hunger is accelerated by exercise and
labour, and by the exposure of the body to a low temperature. Long fasting
is injurious, more particularly to the young and the debilitated. See
APPETITE, NUTRITION, &c.
=HUS'BANDRY.= The business of the farmer; by some the term is restricted
to the joint operations of farming and gardening on the small scale. It is
also sometimes used synonymously with agriculture.
=HY'ACINTH.= In _botany_, the English name for the genus _Hyacinthus_.
There are numerous varieties of the garden hyacinth, all very beautiful.
The bulbs are largely imported from Holland, and are often grown in water
contained in suitable glass vessels (hyacinth glasses). In _mineralogy_,
the term is applied to crystallised yellow or brown zircon. See GEMS.
=HYDRAC'IDS.= _Syn._ HYDROGEN ACIDS. A name formerly given to those acids
which do not contain oxygen, as hydrochloric, &c. It is still occasionally
employed.
=HY'DRAGOGUES.= _Syn._ HYDRAGOGA, L. Medicines which cause the removal of
water from any of the cavities of the body. Many cathartics, as gamboge,
jalap, &c., are classed under this head.
=HYDRAS'TIN.= The name given to a concentrated remedy much employed by the
medical eclectics of America.
_Prep._ Treat the powdered root of golden-seal (_Hydrastis Canadensis_)
with cold water by percolation; acidulate the infusion with hydrochloric
acid; collect the precipitate on a filter; then dry it, dissolve the dried
mass in alcohol, filter, and set aside to crystallise.
_Prop._ Yellow, acicular crystals, insoluble in cold alcohol, ether, and
water.--_Dose_, 3 to 5 gr., 3 to 6 times a day; as a tonic in dyspepsia,
inflammation of the stomach, &c.--_Obs._ According to the most recent
investigations, hydrastin contains berberine, and another alkaline called
hydrastia or hydrastina.
=HYDRASTIS CANADENSIS.= _Syn._ The GOLDEN SEAL. This is a small herbaceous
perennial North American plant, belonging to the natural order,
_Ranunculaceæ_. The rhizome, which is the officinal part, though yellow in
the recent root, becomes of a dark yellowish-brown by age. It contains
albumen, starch, fatty matter, resin, yellow colouring matter, sugar,
lignin, and various salts; also a peculiar nitrogenous crystallisable
substance, to which Dr Durand, the discoverer, proposed the provisional
name of hydrastin, which substance will be found described below. The root
of the golden-seal, as well as the alkaloids obtainable from it, are
largely used in American medical practice, and are stated to possess
valuable tonic, aperient, diuretic, and deobstruent powers. They have been
employed in dyspepsia, jaundice, and functional disorders of the liver.
They are also regarded as one of the best substitutes for quinine in
intermittents.
Golden seal has been given in the form of infusion, decoction, tincture,
and extract, and the fluid extract is now officinal in the United States'
Pharmacop[oe]ia.
=HY'DRATES.= Compounds of hydroxyl (HO) with other bodies, _e.g._
KHO--hydrate of potassium. The term hydrate is also given to chemical
combinations of water (H_{2}O) with other substances, _e.g._
C_{2}HCl_{3}O.H_{2}O--hydrate of chloral.
=HY'DRIDE.= A compound of hydrogen with another radical, _e.g._ hydride of
methyl--CH_{3}H.
=HYDRIO'DATE.= A name formerly given to the salts now termed iodides. See
IODIDES.
=HYDRIO'DIC ACID.= _Syn._ IODHYDRIC ACID; ACIDUM HYDRIODICUM, L. An acid
compound of iodine and hydrogen. See IODINE.
_Prep._ 1. By heating iodine in hydrogen, the volume of the gas becomes
doubled, and a colourless acid gas is produced; it is, however, never
prepared for use by this means. 2. Place 10 parts of potassic iodide in a
small retort with 5 parts of water, and add 20 of iodide; then drop in
cautiously one part of phosphorus, cut into small fragments, and apply a
gentle heat. The gas will be given off abundantly and may be collected, by
displacement, in dry bottles.
A solution of hydriodic acid may be prepared by suspending iodine in
water, and passing a current of sulphuretted hydrogen through the mixture
until the brown colour of the iodine disappears; sulphur is deposited in
abundance, and hydriodic acid formed.
=HYDRO'BENZANIDE.= White crystalline mass, obtained from oil of bitter
almonds by treatment with ammonia.
=HYDROBRO'MIC ACID.= See BROMIDE.
=Hydrobromic Acid.= (HBr.) _Syn._ HYDRIC BROMIDE, HYDROGEN BROMIDE.
_Prep._ This very powerfully acid gaseous body may be prepared as
follows:--1. By decomposing bromide of potassium with a concentrated
solution of phosphoric acid. 2. By decomposing bromide of phosphorus by
means of a small quantity of water.
Hydrobromic acid gas is colourless and non-inflammable; it extinguishes
flame. It is extremely irritating to the lungs when breathed. It is very
soluble in water.
=HYDROBRO'MIDE.= _Syn._ BROMIDE (which _see_).
=HYDROCAR'BON.= A compound of carbon and hydrogen. The hydrocarbons
constitute a most important series of organic compounds.
=HYDROCHLORIC ACID.= (HCl = 36·5.) _Syn._ MURIATIC ACID, HYDRIC CHLORIDE,
HYDROGEN CHLORIDE. This important gaseous compound was discovered by
Priestly in 1772. In nature it is given off with other gases from active
volcanoes, and is occasionally to be met with in the springs and rivers of
volcanic districts. When hydrogen and chlorine are mixed in equal volumes,
they are without action upon each other if kept in the dark, but if
exposed to direct sunlight, chemical combination, accompanied by a loud
explosion, instantly takes place between them, the result of their union
being the colourless gaseous, intensely sour hydrochloric acid. If,
instead of bright sunshine, the mixed gases are exposed to diffused
daylight, chemical union also ensues between them, but the process is then
a slow and gradual one; the passage through them, however, of the electric
spark, or the application of a lighted match or taper instantly causes
their explosion and combination.
One volume of chlorine unites with one volume of hydrogen, forming two
volumes of hydrochloric acid; no condensation occurs in the act of union.
Hydrochloric acid may also be formed by transmitting moist chlorine
through a red-hot porcelain tube; oxygen being at the same time liberated.
_Prep._ Hydrochloric acid, save for the purposes of illustrative
experiment, is never obtained by any of the above processes. An easy mode
of procuring it, when required for laboratory use, is to heat the ordinary
aqueous solution of the acid in a flask, and to collect the gas, which is
given off by displacement. It may also be readily got by introducing
pieces of common salt (which should have been previously fused in a
crucible at a red-heat and allowed to cool) into a glass retort, and
pouring over them about twice their weight of oil of vitriol. The
hydrochloric acid, which escapes very abundantly, must be collected either
by displacement or over mercury.
_Prop._ Hydrochloric acid is a colourless gas, very acid to the taste, and
irritating to the eyes; and induces coughing even if breathed in small
quantities, or when largely diluted. It is very destructive to vegetation,
on which account the soda manufacturer is compelled by law to condense and
thus prevent the escape of its fumes. It has a specific gravity of 1·261.
When subjected to a pressure of 40 atmospheres at 50° F., it becomes a
colourless fluid capable of dissolving bitumen, and having a specific
gravity of 1·27. It has never been frozen. Hydrochloric acid neither
burns, nor supports combustion. The white fumes which it forms when
exposed to the air, are due to its condensing the atmospheric moisture,
and thus giving rise to a body less volatile than water. This gas is
greedily and instantly absorbed by water. A fragment of ice placed in a
jar of the gas absorbs it, and becomes immediately dissolved.
=Hydrochloric Acid, Solution of.= The hydrochloric acid of commerce is a
solution of the above gas in water. When exposed to the air it emits grey
fumes. Water at 40° F. absorbs about 480 times its bulk of hydrochloric
acid, increasing in volume about one third in doing so, acquiring a
density of 1·2109, and then containing nearly forty-three per cent. of the
acid.
_Strength of Solution of Hydrochloric Acid, 77° Fahr._ (E. DAVY.)
---------------------------------------------------
|Hydrochloric| |Hydrochloric
Sp. Gravity.| acid in |Sp. Gravity.| acid in
| 100 parts. | | 100 parts.
-------------------------|-------------------------
1·21 | 42·43 | 1·10 | 20·20
1·20 | 40·40 | 1·09 | 18·18
1·19 | 38·38 | 1·08 | 16·16
1·18 | 36·36 | 1·07 | 14·14
1·17 | 34·34 | 1·06 | 12·12
1·16 | 32·32 | 1·05 | 10·10
1·15 | 30·30 | 1·04 | 8·08
1·14 | 28·28 | 1·03 | 6·06
1·13 | 26·26 | 1·02 | 4·04
1·12 | 24·24 | 1·01 | 2·02
1·11 | 22·22 | |
---------------------------------------------------
In the laboratory, solution of hydrochloric acid is in constant use. It
may be easily prepared from chloride of sodium and sulphuric acid. The
retort should be connected with a couple of Woulfe's bottles; into the
first of which a small quantity of water should be poured, to detain any
impurities mechanically carried over with the gas; the second bottle
should contain four parts of water, and should be placed in a vessel of
cold water, as the gas in becoming condensed, disengages a large amount of
heat. The gas comes off and is absorbed readily by the water upon applying
a gentle heat to the retort.
It is by this last method that solution of hydrochloric acid is obtained
in such enormous quantities[347] for the various purposes in which it is
used, in the arts and manufactures.
[Footnote 347: In South Lancashire alone, more than 1000 tons of
hydrochloric acid in solution are made weekly.]
Hydrochloric acid is, in fact, a by-product in the manufacture of
carbonate of soda, and is generated during the first stage of the
operation, known as the salt-cake process, which consists in the
decomposition of salt by sulphuric acid, and is accomplished in a furnace
called the salt-cake furnace.
The hydrochloric acid gas which is given off escapes from the furnace
through a flue with the products of combustion into high brick towers
filled with coke or stones, over which a stream of water trickles down,
the whole of the acid vapours are thus condensed, the smoke passing off by
a chimney connected with the towers. The diluted acid solution thus formed
is concentrated by the aid of the apparatus shown in section in figs. 1,
2, and 3.
This apparatus consists of several cast-iron cylinders, 57 feet long by 27
feet in diameter, closed in the same manner as gas retorts, by lids luted
with clay. One of the lids has an opening _o_, into which is fitted the
stoneware or leaden pipe _a_, conveying the hydrochloric acid to the
condensing apparatus. The other, or posterior lid, is also provided with
an opening _d_, through which is passed the tube of a leaden funnel, so
that after the retort is filled with salt sulphuric acid may be poured in.
The construction of the furnace in which two retorts are usually placed,
permits the flame of the fire at O to play round the cylinders before
reaching the flue leading to the chimney F. B is an arch over the furnace.
The first stage of the operation consists in filling each cylinder with
330 lbs. of salt. The lids or covers are then luted on, and the fire is
kindled. The requisite quantity of strong sulphuric acid is next poured
into the retort, and the funnel having been withdrawn from D, the hole is
covered by a clay plug.
[Illustration: FIG. 1.]
As soon as the reaction is over, the 396 lbs. of sulphate of soda produced
are removed, and the operation repeated.
The condensation apparatus 1 and 3 is composed of rows of Woulfe's
bottles, partly filled with water, care being taken to place the first
pairs of these bottles in a tank of cold water.
The condensation of the last portions of hydrochloric acid gas is effected
either by the aid of the coke columns, or in leaden chambers, into which
fine jets of cold water are injected on all sides.
"A saturated solution of hydrochloric acid in water has the specific
gravity of 1·21; and when heated in a retort, loses at first hydrochloric
acid gas, but after a time an aqueous acid distils over, at the ordinary
atmospheric pressure, containing 20·22 per cent. of hydrochloric acid, and
boiling constantly at 110° C. If the distillation be conducted under
diminished pressure, the liquid boils at a lower temperature, and attains
a composition which is different for each boiling point; hence the dilute
acids thus obtained by boiling the solution of hydrochloric acid gas in
water, cannot be considered as definite compounds of hydrochloric acid and
water."[348]
[Footnote 348: Roscoe and Dittmar.]
[Illustration: FIG. 2.]
[Illustration: FIG. 3.]
Commercial hydrochloric acid is usually of a yellow colour owing to its
being contaminated with iron. It also very frequently contains sodium,
arsenic, sulphuric and sulphurous acids, and free chlorine.
Pure aqueous solution of hydrochloric acid should leave no residue upon
evaporation; it should give no precipitation of ferric oxide when
saturated with ammonia, sulphuretted hydrogen should cause no turbidity in
it; if diluted with three or four times its volume of water, and chloride
of barium be added, no white cloud or precipitate should form in the
mixture; nor should the acid, if pure, discolour a fluid made faintly blue
with iodide of starch.
Hydrochloric acid is largely consumed in the manufacture of chlorine, sal
ammoniac, chloride antimony, glue, phosphorus, in the preparation of
carbonic acid for the manufacture of artificial mineral waters, in
beet-root sugar works, hydro-metallurgy, and alone, or mixed with nitric
acid, for dissolving various metals.[349] See ACIDS, EFFECTS OF VEGETATION
ON, CHLORINE.
[Footnote 349: Wagner.]
=HYDROCHLORIC ETHER.= (C_{2}H_{5}Cl.) _Syn._ ETHYL CHLORIDE, CHLORIDE OF
ETHYL. This ether may be obtained either by saturating alcohol with
hydrochloric acid gas, and then distilling at a gentle heat, or by
distilling a mixture of three parts of oil of vitriol, two of alcohol, and
four of fused chloride of sodium; the retort is in either case connected
with a tubulated receiver, surrounded by water at a temperature of about
68° Fahr., in which most of the alcohol and water which pass over during
the operation become condensed, whilst the ether escapes in the form of
vapour through a bent tube, which is inserted into the tubulure of the
receiver, and passes to the bottom of a flask kept cool with ice. The
liquid which is condensed in the flask must be rectified from calcic
chloride.
Hydrochloric ether is a colourless liquid, having a specific gravity at
32° Fahr. of 0·921, and a boiling point of 51·9° Fahr. The specific
gravity of its vapour is 2·219. It has an ethereal, penetrating, somewhat
garlicky odour. It is sparingly soluble in water, but readily so in
alcohol. These solutions fail to give a precipitate with argentic nitrate.
=HYDROCYANIC ACID.= (HCN HCy.) _Syn._ PRUSSIC ACID, HYDRIC CYANIDE,
CYANHYDRIC ACID. Hydrocyanic acid was discovered by Scheele; but its
nature and chemical properties were first investigated by Gay-Lussac.
_Sources._ This acid is found in water distilled from the kernels of the
apricot, the peach, the plum, and cherry, the leaves of the laurel, and
some other shrubs. The kernels of the bitter almond also yield it by
distillation, mixed with an essential oil. The juice of the tapioca plant
(the _Jatropha manihot_) likewise contains it. Many nitrogenous
substances, when submitted to destructive distillation, also evolve
hydrocyanic acid. Crystallised ammonic formiate subjected to heat in a
retort yields a vapour which, passed through a red-hot tube, decomposes
into this acid and water. Another method by which it may be obtained,
consists in sending a current of dry sulphuretted hydrogen gas through a
long tube filled with cyanide of mercury; and very recently it has been
obtained by the direct combination of nitrogen and acetylene gas, by
adding one volume of the former to two of the latter, and passing a series
of electric sparks through the mixture, the gases combining without
condensation. Lastly, it is yielded when a metallic cyanide or
ferrocyanide is decomposed by an acid, this latter being the means by
which it is invariably procured.
1. ANHYDROUS HYDROCYANIC ACID may be prepared by Wöhler's plan, which is
as follows:--A crude potassium cyanide is prepared by fusing eight parts
of the dried potassium ferrocyanide with three of potassium carbonate and
one of charcoal.
The fused mass is treated with six times its weight of water in a
well-closed vessel; the clear liquid is decanted from the iron, which it
is the object of this operation to separate, and is poured into a retort:
sulphuric acid, diluted with an equal weight of water, is gradually added
in the proportion of one part of oil of vitriol to two parts of the
cyanide. At first the distillation proceeds spontaneously from the heat
developed by the admixture of sulphuric acid with the water. In order to
condense the acid, the products are made to pass through a long U-shaped
tube, immersed in cold water and filled with calcic chloride, with the
exception of the first fourth of the tube, which contains fragments of the
crude potassium cyanide; to the bent tube is attached a second delivery
tube, which passes to the bottom of a bottle cooled with ice and salt. The
calcic chloride in the syphon tube retains the moisture, and the potassic
cyanide any sulphuric acid that might chance to pass over, whilst the
hydrocyanic acid collects in the anhydrous state in the cooled receiver.
Trautwein recommends it to be prepared by the dehydration of the strong
aqueous acid, by means of fused and pulverised chloride of calcium.[350]
[Footnote 350: The details of this process are given in 'Watt's Chemical
Dictionary.']
[asterism] The observance of the greatest care and caution are necessary
in the preparation of this most potent poison. The operation is most
safely performed in winter. The apparatus should be so arranged as to
allow of any vapours given off being carried from the operator by a brisk
current of air.
_Prop._ At ordinary temperatures anhydrous hydrocyanic acid is a
colourless liquid, having a specific gravity of 0·7058 at 44·6° Fahr. It
is very inflammable, burning with a violet flame resembling that of
cyanogen, but somewhat whiter in colour. It is soluble in all proportions
in water, the resulting mixture being lighter than that fluid, and
miscible with alcohol. It is very feebly acid; potassic cyanide always
having an alkaline reaction. Red oxide of mercury is readily dissolved by
it, and when added to a solution of argentic nitrate it precipitates white
flocculi of cyanide of silver. Anhydrous hydrocyanic acid is an extremely
volatile liquid; if a drop be let fall on a glass plate, part of it
becomes frozen by the cold produced by its own evaporation.