_Obs._ This is a very fine, permanent green pigment. "A great deal of
needless alarm has been excited about its supposed deleterious effects. It
is extensively employed for staining wall-papers, and persons inhabiting
rooms thus papered are said to have had their health seriously deranged by
the arsenical fumes evolved from it. Now, it is utterly impossible that
arsenic could volatilise from such a compound at ordinary temperatures; it
does not decompose at any temperature below redness." (Watts.) [It is,
however, probable that the air of such apartments is sometimes charged
with the poisonous pigment through its becoming mechanically detached from
the paper. To breathe an atmosphere so impregnated would be dangerous. The
use of papers coloured with Scheele's green, especially of the kind called
'flock,' should, therefore, be carefully avoided.--ED.]
=Verd'igris.= See COPPER (Acetates) and VERDIGRIS.
=Green, Verd'iter.= This is essentially a mixture of oxide and carbonate
of copper in uncertain proportions, with chalk. Factitious green bice and
mountain green have a like composition. See VERDITER.
=Green, Verona.= The mineral called green earth.
=Green, Vienna.= The same as Schweinfurt green.
=GREEN SICKNESS.= See CHLOROSIS.
=GREEK FIRE.= This compound, so much used in ancient warfare, is believed
to have had naphtha for its chief ingredient. According to some
authorities, it was a mixture of asphalt, nitre, and sulphur.
=GREGORY'S SALT.= The crude hydrochlorate of morphia, prepared by
Gregory's process. It is a double hydrochlorate of morphia and codeia.
=GRINDELIA ROBUSTA.= A perennial plant belonging to the natural order
_Compositæ_; a native of California, in which state it is largely used
against poisoning by the "poison oak" (the _Rhus toxicodendron_). Of late
years it is said to have been in American medical practice used with
excellent effect in asthma and kindred diseases. Dr Q. C. Smith, writing
to the 'Pacific Medical and Surgical Journal' for April, 1875, states one
patient to whom pills made of the solid extract were administered, had
suffered from severe and frequent attacks of asthma since childhood, and
had found no relief from various remedies. Dr Smith gave his patient the
extract of the grindelia in pills of three grains each, one three times a
day for two or three days, then a pill at bedtime only, for eight or ten
days longer. Under this mode of treatment the attacks are said to have
been much less severe, and less frequent; the patient not only gaining in
strength and general health in the meantime, but having experienced an
immunity from attack for four months. The parts of the plant used are the
selected leaves and tops.
=GRIND'ING.= The operation of reducing substances to powder by attrition
or friction. In the laboratory, the term is chiefly applied to powdering
by means of a mill or by mechanical power, in opposition to simple
pounding or trituration in a mortar or with a slab and muller. All the
principal powders, paints, &c., sold by the druggist, drysalter, and
colourman, are reduced in the drug or colour mill. Recently machinery has
even been applied to the common mortar. An ingenious and very useful
contrivance of this kind is the 'mechanical mortar' of Mr H. Goodhall, of
Derby.
=GRIND'STONES. (Artificial).= Washed siliceous sand, 3 or 4 parts;
shell-lac, 1 part; melt together, and form the mass into the proper shape
whilst warm, with strong pressure. The fineness of the sand must depend on
the work the stone is intended for. The same composition is formed upon
pieces of wood, as corn rubbers, and for the purpose of sharpening knives,
and cutting stones, shells, &c. See EMERY.
=GROATS.= _Syn._ GRITS; GRUTELLUM, AVENA DECORTICATA, AVENÆ SEMINA, AVENA
(Ph. L.), L. Common oats, deprived of their exterior integuments or husks.
This is generally effected in a mill, which, at the same time, cuts them
into two or three pieces. When crushed flat, they are denominated EMBDEN
GROATS.
=GROUT.= Mortar reduced to a thin paste with water, used to fill up the
joints of masonry and brickwork. A finer kind is used to 'finish off' the
best ceilings.
=GRUEL.= _Syn._ OATMEAL GRUEL, WATER G.; DECOCTUM AVENÆ, L. Oatmeal or
groats boiled with water to a proper consistence, and strained. It is
variously flavoured to suit the palate; but the addition of a little white
sugar, and finely powdered Jamaica ginger, with or without a glass of
wine, is the least likely to offend the stomach. Nutmegs, cinnamon, &c.,
frequently disagree with invalids. Sometimes milk or butter is added.
Embden groats require less boiling than the common groats. Of oatmeal, the
Scotch is commonly said to be the best.
The following directions for making gruel from oatmeal are given by Dr A.
T. Thomson: "Oatmeal, 2 oz.; cold water, 1-1/2 pint; rub the meal in a
basin, with the back of a spoon, in some of the water, pouring off the
fluid after the grosser particles have subsided, but whilst the milkiness
remains; repeat this with fresh water, unite the washings, and boil until
a soft, thick mucilage is formed."
=GUA'IACIN.= _Syn._ GUAIACIC ACID, PURE GUAIACUM RESIN. A substance having
the nature of an acid, discovered by Trommsdorff in the wood and bark of
_Guaiacum officinale_.
_Prep._ The tincture of guaiacum is treated with hydrate of lime, and the
guaiacate of lime thus formed is decomposed with dilute sulphuric acid; it
is purified by dissolving it in alcohol.
_Prop., &c._ Insoluble in water; soluble in alcohol and ether; it unites
with the caustic alkalies, forming alkaline guaiacates (guaiacum soaps);
air and light turn it green; gluten, mucilage of gum Arabic, &c., turn it
blue; nitric acid and chlorine turn it successively green, blue, and
brown; tincture of guaiacin, added to hydrocyanic acid and sulphate of
copper, produces an intense blue colour. (Pagenstecher.) A delicate
photographic paper may be formed by washing unsized paper with an
alcoholic solution of guaiacum resin, and afterwards with one of neutral
acetate of lead. (Johnston.)
=GUA'IACUM.= _Syn._ GUAIAC, GUM GUAIACUM, GUAIACUM RESIN; GUAIACUM (Ph.
L.), (GUAIAC RESIN, GUAIACA RESINA, B. P.). The resin prepared by means of
fire from the wood of _Guaiacum officinale_, by natural exudation, by
incision, or by heat. (B. P.) This substance is often adulterated. When
pure, its "fresh fracture is red, slowly passing to green; the tincture
slowly strikes a lively blue colour on the inner surface of a thin paring
of raw potato." (B. P.) Adulteration with resin may be generally
discovered by the odour evolved when the guaiacum is heated. An alcoholic
tincture of guaiacum, rendered milky with water, recovers its transparency
on the addition of caustic potassa in excess; but this is not the case
when resin is present.
Guaiacum is stimulant, sudorific, and alterative.--_Dose_, 10 to 30 gr.,
either in powder or pills; in chronic rheumatism, gout, obstinate chronic
skin disease, scrofula, syphilis, &c. It forms the active ingredient of
the once celebrated 'CHELSEA PENSIONER,' and the 'GOUT SPECIFIC' of Mr
Emerigon. The latter was made by digesting 2 oz. of guaiacum resin in 48
fl. oz. of rum, for seven or eight days. The dose of this was a
table-spoonful every morning, fasting, for a twelvemonth. Its other
properties are similar to those of GUAIACIN, but are less marked. Sp. gr.
1·20 to 1·22.
=Guaiacum Wood.= _Syn._ LIGNUM VITÆ, GUAIACI LIGNUM (Ph. L.), L. The wood
of _Guaiacum officinale_. This is employed under the form of shavings,
raspings, and sawdust, in decoctions only. See DECOCTION and BALSAM.
=GUA'NO.= _Syn._ HUANHO, Peruv. This substance, now so extensively used in
agriculture, is the partially decomposed excrement of certain aquatic
birds, chiefly the common penguin, which congregate in countless numbers
on the barren and uninhabited islets and rocks on the western coasts of
South America and the coasts of Africa. It abounds in ammonia and the
phosphates, and is undoubtedly the richest natural manure known. Under
judicious application the increase of the crops of grain, turnips,
potatoes, and grass consequent upon its use is said to be about 33%.
"Guano is peculiarly adapted to horticultural and floricultural
improvement, by its relative cleanliness and facility of application."
(Ure.)
"According to Denham Smith,[339] South American guano, as imported,
presents itself in three distinct states, the three varieties being not
unfrequently mixed together in the same bag; the first variety is damp and
pulverulent; the second exists as large concretions, presenting various
aspects when broken; the third is heavy and crystalline, and is termed
'stone' by the labourers. These three varieties differ widely in
composition, as the following comprehensive analysis, by Smith, will
show:--
[Footnote 339: 'Proceedings of the Chem. Soc.,' vol. ii.]
+--------------------------------------------------------------+
| _Soluble in Water._ |
+-----------------------------+------------+---------+---------+
| | I. | II. | III. |
| |Pulverulent.|Concrete.| Saline. |
| +------------+---------+---------+
|Water | 222·00 | 250·00 | 97·00 |
|Chloride of ammonium | 25·50 | -- | 30·30 |
|Sulphate of potash | 80·00 | -- | -- |
| " soda | traces | 258·44 | 191·77 |
|Oxalate of ammonia | 74·00 | 93·90 | -- |
| " soda | -- | -- | 105·63 |
|Phosphate of ammonia | 63·30 | 61·24 | -- |
| " potash | -- | 77·32 | 49·47 |
| " soda | 1·20 | -- | 3·60 |
|Chloride of sodium | -- | 29·22 | 286·31 |
| " potassium | -- | -- | 41·63 |
|Organic matter | 15·00 | 6·68 | 25·53 |
|Urate of ammonia | 154·18 | -- | -- |
|Uric acid | 25·16 | -- | -- |
|Ammonia phosphate of magnesia| 5·64 | 7·84 | 1·33 |
|Animal matter | 11·80 | 8·60 | 7·56 |
| |
| _Insoluble in Water._ |
+-----------------------------+------------+---------+---------+
| | I. | II. | III. |
| |Pulverulent.|Concrete.| Saline. |
| +------------+---------+---------+
|Oxalate of lime | 25·60 | 109·58 | -- |
|Phosphate of lime | 199·30 | 62·70 | 132·23 |
| " magnesia | 20·30 | 8·74 | 25·80 |
|Oxide of iron | -- | -- | 1·56 |
|Humus and organic matters | 60·92 | 8·00 | 18·36 |
|Sand | 15·60 | 7·20 | 4·20 |
|Loss | ·50 | 10·54 | 7·78 |
| +------------+---------+---------+
| | 1000·00 | 1000·00 | 1000·00 |
+-----------------------------+------------+---------+---------+
"Several of the South American guano beds are now exhausted, but new
varieties are constantly being introduced; and although the qualities are
continually varying, guanos, on the whole, may be divided into two
classes, the one characterised by the abundance of ammonia, the other by
that of phosphates, the Peruvian and Angamos being characteristic of the
former, and the Saldanha Bay and Bolivian of the latter. In selecting a
guano, the following points (Anderson) ought to be attended to by the
farmer:--
"1st. The guano should be light coloured and dry, colouring very slightly
when squeezed together, and not gritty.
"2nd. It should not have too powerful an ammoniacal smell, and should
contain lumps which, when broken, appear of a paler colour than the
powder.
"3rd. A bushel should not weigh more than from 56 to 60 pounds.
"These characters are, however, imitated with great skill, so that they
cannot be implicitly relied upon, and they are applicable to Peruvian
guano only."[340]
[Footnote 340: The above particulars are from an elaborate paper by Dr H.
M. Noad, in the 'Chemist and Druggist,' vol. ii.]
_Purity, Adulteration._ Guano, owing to its high price, is very commonly
adulterated, or is in an advanced stage of decomposition when sold. Much
of what is vended under the name is altogether a fictitious article. These
artificial mixtures are made to look so like genuine guano, that the mere
practical man, who goes only by their appearance, is very often deceived
by them, and, owing to the failure of his crops in consequence, is led to
distrust the efficacy of guano as a manure. A sample of pretended guano
examined by Johnstone was found to contain, in the state in which it was
sold, more than half its weight of gypsum, the rest being peat or coal
ashes, with a little common salt, crude sulphate of ammonia, and either
dried urine or the refuse of the glue manufactories, to give it a smell.
"I could not satisfy myself that it contained a particle of real
guano."[341] Vessels which sail hence for the guano stations are now very
commonly ballasted with rough gypsum or plaster of Paris. This substance
is mixed with the guano as it is loaded, and enables the importers to
deliver from the vessel a "nice-looking, light-coloured article."
Purchasers of guano are very desirous of having it delivered from the
vessel, as they believe they thus obtain it pure. The favourite material
for the adulteration of guano, at the present moment, is a variety of
umber, which is brought from Anglesea in large quantities. The rate of
admixture is said to be about 15 cwt. of umber to about 5 cwt. of Peruvian
guano, from which an excellent-looking article is manufactured, which is
sold under the name of 'African guano.'
[Footnote 341: 'Elem. of Agric. Chem.']
Pure guano has a pale-brown colour, a more or less offensive odour, and
the average sp. gr. of 1·63 to 1·64. If the sp. gr. exceed 1·75, it is
either damaged or adulterated; and if it is less than 1·62, it contains an
undue quantity of moisture. The best is neutral to test-paper, and
sometimes has even an acid reaction; but that of commerce has generally an
alkaline reaction, owing to the presence of free ammonia, and, in
consequence, turns turmeric paper brown, and gives white fumes when a
glass rod dipped in hydrochloric acid is held over it. Triturated with
quicksilver or caustic potassa, good guano evolves a powerful odour of
ammonia; digested in water, fully one half of it is dissolved; dried by
the heat of boiling water, it does not lose more than from 7 to 9% in
weight; and burned upon a red-hot shovel, it leaves a white ash, not a red
or dark-coloured one. (See directions for selecting guano given _above_,
also _below_.)
_Analysis_ or _assay_. The quantitative analysis of guano, so as to
exhibit the names and proportions of all its numerous component
substances, is an extremely tedious and difficult matter in the hands of
persons unaccustomed to chemical manipulations. As, however, its value to
the agriculturist depends chiefly on its richness in ammonia, potassa, and
phosphoric acid, the analysis of guano for practical purposes may be
reduced to an assay for these articles. Indeed, the presence of ammonia
(the most valuable of them), in the proper quantity, may be fairly taken
as evidence of the presence of the rest. The following methods of testing
guano are both simple and accurate, and are so arranged as to permit its
per-centage richness in one or more of its leading constituents to be
determined without much trouble or expense.
1. _a._ 100 gr. of the sample for examination (fairly selected) are
crushed to a powder, and placed on a small, weighed, and perfectly dry
paper filter, and then desiccated, by exposure for 2 or 3 hours to the
heat of boiling water. The loss in weight, taken in grains, after
deducting 9, indicates the quantity per cent. of water or moisture which
the sample contains in excess of that present in good or pure guano.[342]
[Footnote 342: According to Dr Noad, the proportion of water in genuine
guanos ranges from 7 to 20%.]
_b._ The paper filter, with its contents, is next suspended for some time
over concentrated sulphuric acid (oil of vitriol) contained in a
wide-mouthed bottle or jar, by means of a thread attached to the cork or
stopper, care being taken to exclude the external air. The exposure in
this way is continued until the guano ceases to diminish in weight, which
is ascertained by weighing it at intervals after the first 3 or 4 hours.
When this point is arrived at, the filter and its contents are very
carefully weighed. The difference between its present weight and its
original weight (before the desiccation in _a_), taken in grains, gives
the gross quantity of water per cent.
_c._ The dried guano from _b_ is next placed in a weighed, smooth crucible
or capsule, and exposed to a low red heat until all the organic matter is
completely destroyed, and the whole is reduced to a white ash, which is
weighed as soon as it has become cold. This weight, in grains, gives the
gross weight per cent. of non-volatile matter (fixed alkaline and earthy
chlorides, phosphates, and sulphates); the total loss of weight by
combustion denotes the gross per-centage of combustible and volatile
matter (urea, uric acid, ammoniacal salts, and organic matter). The latter
should not be less than 55 to 60%.
[Illustration]
2. _a._ A second 100 gr. of the guano, selected as before, is distilled
along with about 75 gr. of fresh-slaked quicklime, and a little water, in
a small matrass connected with a tubular, triple bulb-condenser,
containing cold distilled water, and immersed in a basin of ice-cold
water. (See _engr._) The condenser is charged by plunging one of its
extremities into the water, and sucking at the other, until the liquid
reaches the level indicated in the margin. A very gentle heat only,
cautiously increased, need be employed. After the process is over, the
strength of the solution of ammonia found in the condenser is tested,
either by taking its density in a small specific-gravity bottle, or by
determining its saturating power in the manner described under
ALKALIMETRY. This furnishes the per-centage of ready formed ammonia
sufficiently accurate for all ordinary purposes, provided proper care is
taken.
When extreme accuracy is required, the condenser is charged with a weighed
quantity of dilute hydrochloric acid of a known strength, instead of
water, and after the process is over, this is tested as before. The
quantity of ammoniacal test-liquor (see ALKALIMETRY) now taken to saturate
it, deducted from what it would have taken before the exposure in the
condenser, gives the per-centage sought.
[Illustration]
Another method, giving very accurate results, is to use a rather strong
hydrochloric acid (sp. gr. about 1·13) for the condenser; after the
operation is over, the contents of the latter are poured into a glass or
porcelain capsule, a solution of bichloride of platinum is added, in
excess, and the whole is then gently evaporated to dryness; the residuum
is rubbed to powder, and exhausted with a mixture of two measures of
alcohol and one measure of ether; the undissolved portion is next dried at
a heat not exceeding 212° Fahr., and weighed. The weight, in grains, of
the ammonia chloride of platinum thus obtained, multiplied by ·0763, gives
the per-centage of ready-formed ammonia, as before. When hydrochloric acid
is used for the condenser, a simple U-tube and beaker glass may be
employed, if a bulb-condenser is not at hand. (See _engr._) The advantages
resulting from the use of acid instead of water for the condenser is, that
with the former no ammonia can possibly escape being absorbed, whilst
little care is required to keep the condenser cool.
[Illustration]
_b._ 25 gr. of the guano are next weighed, and after being slightly
moistened with a little dilute hydrochloric acid, are thoroughly dried by
the heat of boiling water; the dried sample is then mixed in a warm
unglazed porcelain mortar with 10 times its weight of a mixture of 2 parts
of quicklime to 1 part of hydrate of soda (both quite dry). This mixture
is introduced into a combustion tube of hard Bohemian glass, about 16 or
18 inches long, and 3/4 of an inch in diameter (see _engr._) The mortar is
rubbed out with a little of the soda-lime mixture, which is also
introduced into the tube with that already put there; a little plug of
ignited asbestos is then loosely placed over the whole, and the tube is
immediately connected with a tubular bulb-condenser, containing moderately
strong hydrochloric acid, great care being taken that the joints are made
air-tight, which may be determined by the operator sucking a few bubbles
out of the apparatus. If, after suction, the liquid remains at a higher
level in the furthest bulb (_b_), it is a sign that the connection is
sound. This being done, heat is applied to the combustion-tube, by means
of spirit-lamps; or, more conveniently, by means of the furnace now
usually employed in organic analysis (see _engr._) The tube is next
gradually surrounded with red-hot charcoal, by shifting by degrees the
screen (_c_), and adding more charcoal, so as to gradually expel the
ammonia. The disengagement of gas should take place uninterruptedly, but
not too rapidly, in order that the acid may not ascend into the
combustion-tube and spoil the experiment. The non-condensable volatile
matters which pass off furnish a key to the progress of the operation. The
heat is at length increased to a full red. When gas ceases to be evolved,
and the mixture in the tube has become quite white, the experiment is at
an end. The point (_a_) of the combustion-tube is broken off, and the
ammonia which remains in the tube is expelled by sucking gently at the
extremity (_b_) of the bulb-condenser. The latter is then disconnected
with the apparatus, and emptied into a glass or porcelain capsule, in
order to be tested, as directed under 2, _a_. The quantity of ammonia, in
grains, thus found, multiplied by 4, gives the WHOLE QUANTITY of AMMONIA
per cent., both actual and potential, producible from the sample of guano
examined.
[Illustration]
_c._ The quantity of ready-formed ammonia (see 2, _a_) deducted from the
quantity last found (see 2, _b_) gives the quantity of LATENT or POTENTIAL
AMMONIA that will be slowly developed by the decomposition of the guano
in the soil, and become available for the food of plants. This is the most
valuable product of this substance as a manure, and can only be obtained
in quantity from well-preserved, dry guano.
3. _a._ A third quantity of 100 gr. of the guano, selected as before, is
triturated and digested for some time with 12 times its weight of hot
distilled water, and the whole being thrown on a filter, the undissolved
portion is washed with a little warm distilled water; the solution and
'washings' are then mixed together, and acidulated with nitric acid; a
solution of pernitrate of iron is next added, and afterwards solution of
ammonia, in excess; the liquid is next heated for a short time, and the
bulky reddish-brown precipitate is collected, washed with hot water,
dried, ignited, and weighed. The weight, in grains, less the weight of the
peroxide of iron in the pernitrate consumed, gives the weight of
PHOSPHORIC ACID present in the soluble phosphates contained in the sample.
The pernitrate of iron is made by direct solution in hot strong nitric
acid, of twice as much pure iron wire as there is phosphoric acid
suspected to be present in the liquid. A slight excess will not alter the
result. The number of grains of metallic iron used to form the solution,
multiplied by 1·4286, gives the weight of the peroxide of iron which is to
be deducted from the gross weight of the precipitate.
_b._ The filtrate and 'washings' left from 3 _a_ are mixed, and treated
with a little oxalate of ammonia to throw down any lime, and then
carefully evaporated to dryness and ignited; the residuum of the ignition,
when cold, after being carefully weighed, is treated with the smallest
portion of water that will dissolve it; the solution is acidified with
hydrochloric acid, and a solution of bichloride of platinum added, in
excess; some strong alcohol is next poured in, the precipitate carefully
collected on a filter, washed with rectified spirit, dried at 212° Fahr.,
and weighed. The weight, in grains, multiplied by ·1940, gives the
per-centage of POTASSA sought.
_c._ The weight of the potassa multiplied by 1·852, and deducted from the
weight of the ignited residuum in 3 _b_ already found (see _above_), gives
the quantity of CHLORIDE OF SODIUM or COMMON SALT (nearly).
4. _a._ The insoluble residuum from 3 _a_, dried, and ignited, or the ash
from 1 _c_, is digested for 10 or 12 hours in 600 times its weight of
water (to which a little common salt or sal-ammoniac may be added), after
which the whole is thrown upon a filter; a solution of chloride of barium
is then added to the filtrate as long as a precipitate (if any) forms; the
latter is collected, washed, dried, ignited, and weighed. The weight, in
grains, multiplied by ·5843, denotes the quantity of GYPSUM or SULPHATE OF
LIME which has been used to adulterate the sample.
_b._ The insoluble residuum last left on the filter is digested for some
time in warm dilute hydrochloric acid; the whole is then thrown upon a
filter, and the undissolved portion (SILICA or SAND, with, perhaps, a
trace of ALUMINA) is washed, dried, ignited, and weighed. It should not
weigh more than 3 to 3-1/2 gr. (3 to 3-1/2%).
_c._ The filtrate and 'washings' from _b_ are next mixed together; the
mixed liquid is acidified with dilute sulphuric acid and heated until all
the hydrochloric acid is expelled, and the whole reduced to a soft pasty
mass; rectified spirit is now poured in, and after active stirring for
some time, the mixture is thrown on a filter, and the solid portion washed
with a little more rectified spirit; it is then dried, ignited, and
weighed. The weight, in grains, multiplied by ·7650, gives the quantity of
PHOSPHATE OF LIME per cent. required.
_d._ The filtrate from _c_ is diluted with water, and after being boiled
for a few minutes, ammonia is added in slight excess, followed by a
solution of sulphate of magnesia (previously mixed with as much
sal-ammoniac as will prevent ammonia producing a precipitate in it),
slowly dropped in as long as it disturbs the liquor; the whole is now
allowed to rest for 10 or 12 hours, when the precipitate is collected on a
filter, and washed with water alkalised with ammonia, as long as the
filtering liquid is rendered turbid by chloride of barium; it is next
dried, submitted to intense ignition for some time in a covered platinum
crucible, and, when cold, carefully weighed. The weight, in grains,
multiplied by ·6429, indicates the per-centage of PHOSPHORIC ACID in the
insoluble phosphates (phosphates of lime, magnesia, &c.) in the sample
examined.
5. A fourth 100 gr, of guano is weighed, and exhausted by trituration and
digestion with hot water (see 3 _a_); the solution is evaporated to
dryness by a gentle heat, and the residuum of the evaporation, after being
weighed, is powdered and enclosed in a stout phial with 8 times its volume
of alcohol, sp. gr. ·825 (63 o. p.); the plant is next securely corked and
guarded, and exposed for some time, with agitation, to the heat of 212°
Fahr., the whole is then allowed to cool, the contents of the phial
filtered, the undissolved portion washed with hot alcohol, and both the
filtrate and the 'washings' gently evaporated to dryness, and weighed.
This gives the richness of the sample in UREA, one of the most valuable
constituents of the best guano. Its presence is "a certain proof of its
entire soundness." (Ure.)
6. _a._ Another 100 gr. of the guano is taken, and, after being exhausted
with water, is dried at 212° Fahr., and weighed; it is then digested with
heat in 20 times its weight of borax-water (containing 1% of borax), or in
a solution of caustic potassa, and after a time the whole is thrown on a
weighed filter, washed with a little cold distilled water, dried by a heat
not higher than that of boiling water, and again carefully weighed. The
loss, in grains, indicates the proportion per cent. of URIC ACID.
The accuracy of the result may be verified by adding dilute hydrochloric
acid, in slight excess, to the filtrate, collecting the bulky, crystalline
precipitate of uric acid which forms, washing it carefully with a little
rectified spirit, drying it, and weighing it, as before. This weight,
which in general is a very little under that denoted above, is the more
accurate of the two. The precipitate is shown to be uric acid by its
assuming a rich crimson colour when treated with a little nitric acid,
which turns to a rich purple (_murexide_) when it is moistened with
ammonia water.
_b._ The quantity of uric acid last obtained, multiplied by 1·1012, gives
the per-centage of URATE OF AMMONIA.
_Obs._ Amongst the numerous constituents of guano, none are so valuable in
an agricultural point of view as the three substances referred to in the
last two sections. Indeed, almost all the ammonia furnished by this
substance to the soil, after the latter, manured with it, has been exposed
to the air and rain, is derived from the slow decomposition of urea, or
urate of ammonia. It is these substances from which the store of latent,
or, as Dr Ure terms it, potential ammonia, is derived. The ammonia
existing in the guano under the form of carbonate, or of soluble salts
(ready formed ammonia), is either soon dissipated in air or is washed away
by heavy rains, and, therefore, forms the least valuable and durable
portion of this manure. It may be even added artificially, a matter almost
impossible with the former. An assay, therefore, for the latent ammonia,
or the urea, or the urate of ammonia, any one of them singly, at once
furnishes us, as we have already hinted, with evidence of the quality of
the guano examined, without the expense and trouble of a complete analysis
of this substance. Urea and uric acid are only to be found in the very
best samples of guano, and their presence is a positive proof of entire
soundness and superior quality. The other valuable portions of guano are
potassa and phosphoric acid (phosphate of lime chiefly); the rest are of
little importance. (See 2 _c_, _above_.)
=GUARANA= (Grimault & Co., Paris). 12 migrain powders, each weighing 1·75
grammes, consisting of guarana, but perhaps also containing an admixture
of cocoa seeds, neither prepared nor roasted. (Hager.)
=GUARANA'.= _Syn._ PAULLINIA, BRAZILIAN COCOA. An alimentary and medicinal
substance prepared from the seeds of _Paullinia sorbilis_, a Brazilian
tree. The dried seeds, deprived of their aril, are pounded and kneaded
into a mass, which is afterwards made into oblong or rounded cakes
(GUARANA BREAD). These cakes are used as we use chocolate--mixed with
water and sugar, and drank as a beverage. In Brazil this beverage is
largely consumed, both on account of its nutritive qualities, and for its
stomachic, febrifugal, and aphrodisiac effects. See CHOCOLATE, &c., also
_below_.
=GUARANINE'.= A crystalline substance discovered by M. Martius in guarana.
It appears to be identical with caffeine, the active principle of coffee
and tea.
=GUD'GEON.= The _Cyprinus gobeo_ (Linn.), a small fresh-water fish, common
almost everywhere. The white is considered the best. It was formerly used
in medicine.
=GUM.= _Syn._ GUMMI, L. The general term for an important class of
vegetable products. Gums are more or less soluble in cold water, but
insoluble in alcohol, ether, and oils. They are obtained from certain
plants in amorphous masses; most of them exude spontaneously, or on
puncturing the bark. The most perfect type of this class is the substance
called GUM ARABIC, or GUM ACACIA. The gums are employed as demulcents in
medicines, and are used as cements, and for giving stiffness and gloss to
textile fabrics. Among the vulgar the term is often incorrectly applied to
the resins and gum resins.
=Gum Acacia.= _Syn._ GUM ARABIC; ACACIÆ GUMMI (B. P.); G. ARABICUM, G.
ACACIA, ACACIA (Ph. L.), L. "From various species" (of _Acacia_) "yielding
gum" (Ph. L. & E.), chiefly _Acacia arabica_ and _A. vera_. "Whitish or
yellowish, transparent or cracked on the surface, and opaque; brittle; it
dissolves freely in water." (Ph. L.) It is scentless, and may be bleached
by exposure to the sun and air, at the temperature of boiling water. Sp.
gr. 1·355. (Ure.) The pure soluble principle of gum Arabic is termed
ARABIN (which _see_). BARBARY or MOROCCO GUM, GUM SENEGAL, and EAST INDIA
GUM, are inferior commercial varieties of the same substance from other
species of _Acacia_ (see _below_).
Powdered gum Arabic (PULVIS ACACIÆ) is frequently adulterated with flour
or farina, or with Senegal or other inferior gums. The first may be
detected by agitating a little of the powder with cold water; the pure gum
dissolves rapidly, whilst the starch or flour falls to the bottom of the
vessel. Or, a little of the powder may be mixed with boiling water, and
when cold, tested with tincture of iodine; if it contains starch or flour,
the paste will assume a blue colour. If it contains cherry-tree gum or
tragacanth, it will be only partly soluble in cold water, and the paste
will be partly coloured, and more or less interspersed with gelatinous
clots.
For the detection of dextrin in gum Arabic Hager finds that when some of
the adulterated article is placed in a glass dish, with vertical sides,
and a solution of ferric chloride, density 1·48, diluted with an equal
volume of water, is poured over it until the grains are just covered, in
the course of a minute or so that particles of gum Arabic will adhere to
the bottom of the vessel, whilst the grains of dextrin do not.
Much of the white gum Arabic of the shops is formed by bleaching gum
Senegal, by what is called 'Picciotto's process.' The gum is dissolved in
water, and sulphurous acid gas passed through the solution. The liquid is
afterwards boiled to expel the sulphurous acid, a little of which,
however, still remains behind. To obtain the gum in a still whiter state,
carbonate of baryta is added, and after agitation the mixture is filtered;
it is afterwards shaken with gelatinous alumina, again filtered, and
evaporated. The product (BLEACHED GUM) is very white, but lacks the
peculiar toughness and adhesiveness of the best gum acacia.
=Gum, Barbary.= _Syn._ MOROCCO GUM. An inferior product, consisting of a
mixture of several Acacia gums. It is exported from Mogador.
=Gum, Bassora.= A solution of yellowish gum brought from the neighbourhood
of Bassora. It differs from most gums in being nearly insoluble in water.
The plant yielding it is believed to be a species of _Mimosa_. It contains
the principle BASSORIN, which also exists in gum tragacanth.
=Gum, Bleached.= See GUM ARABIC (_above_).
=Gum, Brit'ish.= _Syn._ DEXTRIN, STARCH GUM. Starch converted by the
action of acids, diastase, or heat, into a soluble substance resembling
gum.
_Prep._ 1. Malt (crushed small), 1 lb.; warm water, 2 galls.; mix, heat
the whole to 145° Fahr., add of potato starch 5 lbs., raise the heat to
160° or 165° Fahr., and mash for about 25 minutes, or until the liquid
becomes thin and clear; it must then be instantly run off, and raised to
the boiling point to prevent the formation of sugar; after boiling for 3
or 4 minutes the whole must be filtered, and evaporated to dryness by a
steam heat.
2. By exposing dry potato starch, in a stove, to a heat of about 400°
Fahr. Yellow and inferior.
3. (M. Payen.) Dry starch, 1 ton, is moistened uniformly with concentrated
nitric acid, 4-1/2 lbs. (diluted with), water, q. s., and the paste or
dough is made up into small bricks or loaves, and dried in a stove; it is
next reduced to coarse powder, and exposed in a stove-room for some time
to a current of air at 160° to 165° Fahr.; it is next ground, sifted, and
exposed, as before, to a heat of about 228° Fahr.; it is, lastly, ground,
and passed through the 'bolting machine.' Very white and superior. This
process has been patented in France by M. Henzé.
4. (Pinel.) Water, 100 galls., nitric acid, 1/2 gall., and hydrochloric
acid, 1/2 pint, are mixed together, and so much potato starch is mixed as
will form a thin paste; in two hours the liquid is drained off, and the
solid matter is made up into lumps, which are dried by a gentle heat in a
stove-room; they are next coarsely pulverised, and the powder is exposed
on three successive days to the respective temperatures of 100°, 150°, and
190° Fahr.; the whole is then sifted, and, lastly, exposed to a heat
ranging from 300° to 350° Fahr. Darker coloured than the last. To give it
the appearance of gum Arabic, it is made into a paste with water
containing 1% of nitric acid, and after being spread on copper plates in
layers 3/4 to 1 inch thick, it is exposed to a stove heat ranging from
240° to 300° Fahr.
_Prop., &c._ White; insipid; transparent; friable; soluble in cold water,
and in dilute spirit; insoluble in alcohol and ether; its solution yields
a precipitate with acetate of lead. Iodine commonly turns commercial
dextrin blue, but does not affect the colour of pure dextrin. It is
distinguished from ordinary gum by its right-handed polarization of light,
and by yielding oxalic but not mucic acid, when treated with nitric acid.
Dextrin is nutritive, emollient, and agglutinant. In France it is largely
employed by the pastry-cooks and confectioners, and in medicine as a
substitute for gum. The French surgeons also commonly employ it as a
'stiffening' for the splints used for fractured limbs. In this country it
is chiefly used as a fine dressing for muslins, silk, and other textile
fabrics, and in calico printing. Recently it has been made up into
tear-like masses, and sold for gum Arabic, to which, however, it is vastly
inferior as an agglutinant. See DEXTRIN.
=Gum, Cherry-tree.= _Syn._ FRUIT-TREE GUM, PLUM-TREE G.; GUMMI CERASI, G.
PRUNI, L. An exudation from the stems of cherry, plum, and some other of
the _Rosaceæ_. It is only partly soluble in water. It contains CERASIN
(which _see_).
=Gum, East India.= This product, which consists of inferior kinds of gum
acacia, is chiefly exported from Bombay, having been previously conveyed
there from the coast of Arabia. It varies greatly in quality. Some samples
are quite unfitted for making gum-water.
=Gum, Insoluble.= See BASSORA GUM, CHERRY-TREE GUM, and GUM TRAGACANTH.
=Gum, Seed.= _Syn._ GUMMI SEMINUM, L. A species of soluble gum extracted
from the seed of the flax (linseed), quince, &c.
=Gum, Senegal.= This product, which is largely exported from Portendie,
Sierra Leone, and the French settlements on the Senegal, ranks next in
quality to gum acacia, and for many purposes, as calico-printing for
instance, it answers equally well. The transparent and light-coloured
pieces are frequently picked out and sold as gum Arabic.
=Gum Trag'acanth.= _Syn._ TRAGACANTH, GUM DRAGON; GUMMI TRAGACANTHA, G.
DRACONIS, TRAGACANTHA (Ph. L.), L. The gummy exudation of the _Astragalus
verus_, hardened by the air. When digested in water, it swells
considerably, a portion is dissolved, and the whole combines to form a
thick mucilage. It is totally soluble in boiling water, when some change
is supposed to take place in it; a great portion, however, afterwards
separates. Sp. gr. 1·384. It is chiefly employed in calico-printing, and
by shoemakers and lozenge-makers; by the latter to give toughness to the
saccharine mass.
Powdered tragacanth is often adulterated with flour of starch, and not
unfrequently with the commoner varieties of gum Arabic. According to M.
Planche, a mixture of pulverised tragacanth and gum Arabic forms, with
water, a thinner mucilage than the same quantity of either of these gums
alone. This fraud may be detected as follows:--Make a mucilage of the
suspected gum, and add thereto a few drops (2 or 3 to the dr.) of
alcoholic tincture of guaiacum, taking care to stir it all the while. If
the sample contains any gum Arabic, the mixture, in the course of a few
minutes, assumes a fine blue colour, whilst it does not change colour if
the gum tragacanth is pure, 5% of gum arabic can be thus detected. When
the quantity is very small, one to four hours may elapse before the colour
is developed. Starch and flour are detected in the manner noticed under
GUM ARABIC.
=Gum, Turkey.= Various qualities of gum acacia are sold under this name.
=GUM RES'INS.= _Syn._ GUMMI RESINÆ, L. Vegetable products in which the
properties of gum and resin are combined. They are partly soluble in
water, and partly in alcohol. Many of them form a species of emulsion when
triturated with the former fluid. The principal gum resins are AMMONIACUM,
ASSAF[OE]TIDA, BDELLIUM, GALBANUM, GAMBOGE, MYRRH, OLIBANUM, OPOPONAX,
SAGAPENUM, and SCAMMONY.
=GUN BAR'RELS.= See BROWNING.
=GUN COT'TON.= See PYROXYLIN.
=GUN MET'AL.= An alloy containing 90·5% of copper and 9·5% of tin, used
for casting pieces of ordnance (erroneously termed 'brass guns'), also
those parts of machinery which are subjected to considerable friction. See
ALLOYS, BRONZE, STEREO-METAL, &c.
=GUN'POWDER.= This substance is a mechanical mixture of saltpetre,
charcoal, and sulphur. It is seldom prepared on the small scale.
_Prep._ The saltpetre having been trebly refined, by boiling, skimming,
filtering, and crystallising, is melted into cakes, which are then brushed
to remove any adhering grit or dirt, broken into pieces with a mallet,
ground to a fine powder in a mill, and sifted through a fine bolting sieve
of brass wire. The charcoal is that of the alder or willow, and is
carefully burnt, as already described, and is then reduced to powder. The
sulphur is refined by distillation, and ground to the same fineness as the
charcoal and saltpetre. The ingredients are weighed out in the proper
proportions, and mixed together in a machine consisting of a wooden drum,
having a shaft passing through its centre, to which numerous 'flyers' in
the shape of knife-blades are attached, the drum and flyers revolving in a
contrary direction. When mixed, the charge is carried to the
'incorporating mill,' where it is ground under vertical iron
'mill-stones,' with a small quantity of distilled water, until the
ingredients are thoroughly incorporated. The product of this operation is
then pressed into a hard cake, which is next broken into pieces,
granulated by means of sieves, and after being 'glazed' by friction, and
the dust separated, is dried, with proper precautions, in a stove heated
to about 130° by steam pipes.
The proportions of saltpetre, charcoal, and sulphur, used for different
kinds of powder, differ very slightly. In 'sporting powders' the
proportion of saltpetre is generally from 1 to 3% greater than in the
Government powders. In 'miners' powders' it is about 10% less, an excess
of sulphur being used. The following are the proportions adopted by
European powers:
Saltpetre. Charcoal. Sulphur.
England 75 15 10
France 75 12·5 12·5
Austria 75 15 10
Prussia 75 13·5 11·5
Russia 73·78 13·59 12·63
Spain 76·47 10·78 12·75
Sweden 76 15 9
(Capt. Jervis-White Jervis.)
_Obs._ The quality of gunpowder is best estimated by actual trial of its
power and cleanliness in use. It should be dry, hard, and free from dust;
the grains should be of a uniform size, and glossy, and the colour a
dark-grey or brownish-grey, not perfectly black. A very little placed on a
piece of paper and fired should instantly explode with a flash, and
neither leave an appreciable residue on the paper nor burn it. Dried by
the heat of boiling water, or in vacuo, it should not lose more than 1/2
to 1% of its weight. Damp powder rapidly 'fouls' the gun. Gunpowder,
containing more than 7% of water, does not recover its strength by simply
drying it. The sp. gr. ranges between 1·795 and 1·800.
Karolyi succeeded in analysing the gases of gunpowder which had been fired
in conditions closely resembling those which occur in artillery practice.
For this purpose he enclosed a charge of powder in an iron cylinder of
such strength that it just burst when the powder was fired by means of the
electric spark. This charged cylinder was suspended in a hollow spherical
bomb, from which the air was exhausted before firing.
After the explosion had been produced, the gases and the solid residue of
the powder were submitted to analysis. The results obtained were the
following:[343]
[Footnote 343: 'Phil. Mag.,' 1863.]