Oscar Oldberg.

Inorganic general, medical and pharmaceutical chemistry, theoretical and practical; a text-book and laboratory manual, containing theoretical, descriptive, and technological chemistry; online

. (page 21 of 49)
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translucent pieces, free from white pulverulent bicarbonate.

To make a preparation such as the Pharmacopoeia intends,
the diluted acid should be cold in order that the free carbonic
acid which is formed may dissolve in sufficient quantity in the
liquid. The presence of this carbonic acid renders it imprac-
ticable to determine the point of neutralization by means of test-
paper; but the preparation, as made, is slightly acid. The solu-
tion should have a pure acidulous saline taste, or the saline
taste modified only by that of the carbonic acid ; a slight excess
of acetic acid is desirable ; but any excess of alkali is objectionable.
Even when neutral the solution gives an acid reaction to litmus
paper owing to the carbonic acid.

When the ammonium carbonate dissolves in the acetic acid the
temperature is lowered, on account of the liberation of carbonic
acid gas. This fall of the temperature of the liquid is advantage-
ous, as it aids the solution of another portion of the gas.

In some pharmacopoeias ammonia water is used instead of
ammonium carbonate. In this case the temperature rises. Test-
paper can be used to ascertain the reaction when this method
is followed, but it is directed that the solution shall be, not
neutral, but slightly acid.

The preparation must not be filtered as that would expel nearly
all the carbonic acid.



268 AMMONIUM CITRATE.

AMMONIUM CITRATE SOLUTION.

LIQUOR AMMONII CITRATIS.

A solution of ammonium citrate each ml of which contains
0.50 Gm of (H 4 N) 3 C 6 H 5 O 7 is often employed in clearing cer-
tain liquids containing iron compounds and liable to become
cloudy or to form precipitates. Small additions of such a solu-
tion to the preparations known as "beef, wine and iron" and
elixirs containing phosphate or pyrophosphate of iron associated
with organic substances prevent the formation -of certain pre-
cipitates containing iron, or dissolve them when formed. Such
a solution may also be advantageously employed in the prepara-
tion of soluble phosphate and pyrophosphate of iron.

It is prepared as follows :

Citric acid . 500 Gm

Stronger ammonia water (28% of H 3 N) . . 430 ml
Distilled water.

Dissolve the acid in the ammonia water. Neutralize perfectly
by adding as much ammonia water as may be required. Then
add enough distilled water to make the whole measure 1,250 ml.

Solution of Di-ammoniutn-Hydrogen Citrate,

may be prepared by adding 250 Gm of citric acid to 1,250 ml
of the solution of normal ammonium citrate just described and
then diluting with enough distilled water to make the whole
measure 1,800 ml.

Each ml of this solution contains 0.50 Gm of di-ammonium-
hydrogen citrate (H 4 N) 2 HC 6 H 5 O 7 .

This solution is frequently used in the preparation of the
soluble phosphate and pyrophosphate of iron.

AMMONIUM BENZOATE.

AMMONII BENZOAS.

H 4 NC 7 H 5 2 =i 39 .

Benzoic acid 20 parts

Distilled water 40 parts

Water of ammonia, sufficient.



AMMONIUM BICARBONATE. 269

Dissolve the benzoic acid in 33 parts of water of ammonia
previously diluted with the water. Evaporate over a water-bath
by gentle heat, adding a little more ammonia water from time to
time, if necessary to keep the alkali in constant excess, so as to
prevent the formation of acid ammonium benzoate, which is less
soluble. When reduced to 50 parts set aside to crystallize. Col-
lect and dry the crystals. The mother liquor will yield more
crystals after evaporation, keeping the ammonia slightly in ex-
cess as before.

Reaction. HC 7 H 5 O 2 +H 4 NOH=H 4 NC 7 H 5 O 2 +H 2 O.

Description. White, thin, lamellar crystals, odorless or having
a faint odor of benzoic acid; soluble in 5 or 6 parts of cold
water, 1.2 parts of boiling water, 30 parts of alcohol, 7.6 parts
boiling alcohol, or 8 parts of glycerin.

Should be kept in tightly closed bottles.

AMMONIUM BICARBONATE.

AMMONII BICARBONAS. .

H 4 NHC0 3 = 79.

Stronger ammonia water (28% of H 3 N), any desired quantity.

Carbon dioxide.

Conduct a stream of carbon dioxide into the stronger am-
monia water contained in a flask keeping the flask and contents
cool with running water. Continue the current of CO 2 until the
gas is no longer absorbed. The salt crystallizes from the solu-
tion. Separate the crystals by turning the contents of the flask
into a funnel provided with a strainer or perforated diaphragm;
drain well, and dry them over sulphuric acid.

Keep the product in a tightly closed bottle in a cool place.

Reaction. H 4 NOH+CO 2 =H 4 NHCO 3 .

Notes. Erdmann recommends putting the concentrated am-
monia water in a small flask closed by a stopper bearing a short
glass tube extending down nearly to the surface of the liquid
but not dipping into it. The carbon dioxide is to be conducted
into the flask through that tube. Normal ammonium carbonate



27O AMMONIUM BROMIDE.

is first precipitated but redissolves. After the liquid has stood
for some time under the pressure of the gas, the bicarbonate is
separated. When no more crystals are formed a stratum of
alcohol cautiously laid over the mother liquor will cause the
deposition of an additional crop. The salt may best be preserved
in glass tubes filled with carbon dioxide and sealed.

Another Method.

Dissolve ouc the ammonium carbonate from powdered ordi-
nary ammonium carbonate by macerating it with twice its weight
of alcohol for a few minutes. After separating the alcoholic
solution of the carbonate, wash the undissolved ammonium bi-
carbonate with another portion of alcohol, using the same quan-
tity as before. Expose the product to the air until the alcohol
has evaporated, and then bottle it.

The carbonate may also be removed by macerating the ordi-
nary ammonium carbonate for two hours with twice its weight
of water.

Description. Colorless crystals, or a white crystalline powder
of ammoniacal taste and faintly ammoniacal odor (or nearly
odorless if quite dry). Soluble in 5.5 parts of water at 15.
Insoluble in alcohol.

AMMONIUM BROMIDE.

AMMONII BROMIDUM.

H 4 NBr= 9 8.

Iron wire 4 parts

Bromine 12 parts

Ammonia water 25 parts

Distilled water.

Put the iron wire into a flask, add 50 parts of warm (not
hot) water, and then gradually add 9 parts of bromine. Put a
loose plug of cotton into the neck of the flask, and shake gently
from time to time until a greenish liquid is obtained having no
odor of bromine. Filter this solution of ferrous bromide, add
the remainder of the bromine to the filtrate and shake gently
so that a uniform solution may be obtained.



AMMONIUM BROMIDE. 271

Pour this solution into the ammonia water previously diluted
with 50 parts of distilled water. Shake well. Heat the mix-
ture over the water-bath for half an hour. Then filter. When
the liquid has passed through the filter, wash the residue upon 'it
with some hot distilled water, letting the washings run into the
filtered solution.

Evaporate the liquid in a porcelain dish until a pellicle begins
to be formed. Then stir the contents with a glass rod while
continuing the evaporation until a granular salt remains. Should
this not be perfectly white or colorless, redissolve it in its own
weight of boiling distilled water, add a sufficient quantity of am-
monia water to render the solution slightly alkaline to test-paper,
boil the liquid a few minutes, filter it, and evaporate the filtrate
to dryness as before.

Reaction.

2Fe+2Br 2 =2FeBr 2 ; then 3FeBr,-f Br 2 =FeBr 2 .2FeBr 3 ; then
FeBr 2 .2FeBr 3 +8H 4 NOH=8H 4 NBr+FeO.Fe 2 O 3 +4H 2 O.

Description. Colorless, transparent crystals, or a white crys-
talline granular salt, odorless, of pungent saline taste. Soluble
in 1.50 parts of water, and in 30 parts of alcohol at 15 C. ;
in 0.7 parts of boiling water, and in 15 parts of boiling alcohol.

Another Method.

Bromine 25 parts

Ammonia water.

Water.

Hydrogen sulphide.

Shake 200 parts of water with 5 parts of bromine. Conduct
a stream of hydrogen sulphide into the liquid. When the liquid
is no longer rendered turbid by the hydrogen sulphide, add an-
other 5 parts of bromine, and again direct hydrogen sulphide
into the liquid until the red color disappears. Repeat the addi-
tion of bromine, 5 parts at a time, and the treatment with hy-
drogen sulphide until all of the bromine has been used and con-
verted into hydrobromic acid by the current of hydrogen sul-
phide.

Filter out the sulphur and heat the filtrate to expel the excess



AMMONIUM CARBONATE.

of hydrogen sulphide from the liquid. When filter paper moist-
ened with a solution of lead acetate is no longer blackened by
the liquid, filter again. Supersaturate the filtrate with am-
monia (about 60 parts will be required).

Evaporate the solution of ammonium bromide until salt be-
gins to separate. Then add a little more ammonia, after which
continue the evaporation to dryness, stirring constantly.

Reaction.

Br 2 +H 2 S=2HBr+S; then
HBr+H 4 NOH=H 4 NBr+H 2 O.



AMMONIUM CARBAMATE.

AMMONII CAR13AMAS.

H 4 N(H 2 NCO 2 )=;8.

Dissolve the ammonium carbamate from powdered ordinary
ammonium carbonate with strong alcohol and evaporate the al-
coholic solution to dryness by the aid of very moderate heat (not
exceeding 25).

Description. A white powder readily soluble in water and in
alcohol.

AMMONIUM CARBONATE OFFICINAL.

AMMONII CARBON AS OFFICINALIS.

(Hartshorn Salt.)
Approximately H 4 NHCO 3 .H 4 NH 2 NCO 2 =i57.

This is a somewhat variable mixture of ammonium-hydrogen
carbonate and ammonium carbamate.

It is manufactured on a large scale by heating a mixture of am-
monium sulphate (or ammonium chloride) and calcium carbonate,
when the so-called ammonium carbonate sublimes and is con-
densed.



AMMONIUM CARBONATE. 273

Description. Hard, colorless or white, translucent (nearly
transparent in thinner fragments), having, when quite hard and
not effloresced, but a faint ammoniacal odor if not confined in a
closed vessel. When exposed to the air it becomes covered with
a white efflorescence, and finally converted into porous lumps
or white powder. Confined in a closed vessel the salt causes the
vessel to be filled with vapor of a strongly ammoniacal odor.
The taste is sharp and saline.

It is slowly but completely soluble in from 4 to 5 parts of
water at 15. Hot water decomposes it.

Alcohol dissolves' out the carbamate, leaving the acid ammonium
carbonate as a pulverulent residue.

The reaction of ammonium carbonate is strongly alkaline.

Only hard, translucent pieces of ammonium carbonate should
be used for pharmaceutical purposes. Pieces covered with a
white coating may be scraped, and the hard translucent interior
used. When porous and white throughout, the salt should be
used only in the production of ammonium salts in cases where
the result is not affected by the condition of the ammonium car-
bonate.

This substance must be kept in tightly closed bottles in a cool
place.

AMMONIUM CARBONATE TRUE.

AMMONII CARBONAS VERUS.

(Normal or Neutral Ammonium Carbonate.)
(H 4 N) 2 C0 3 .H 2 0=u 4 .

Ordinary ammonium carbonate 157 parts

Stronger ammonia water 63 parts

Distilled water 8 parts

Digest them together for two days in a closed wide-mouthed
bottle at from 20 to 25. The whole contents form a solid
crystalline mass, which constitutes the di-ammonium carbonate.

Keep the product in a tightly closed bottle in a cool place.

Another Method.
Dissolve eight parts of the ordinary ammonium carbonate in

Vol. 1118



274 AMMONIUM CHLORIDE.

nine parts of warm ammonia water (containing 10 per cent of
H 3 N) in a closed bottle. Cool the solution so that crystals may
be formed. Collect and drain the crystals quickly and press
them gently between cloths or bibulous paper. Bottle at once.

Reaction.

H 4 NHCO 3 .H 4 NH 2 NCO 2 +H 4 NOH= 2 ( H 4 N ) 2 CO 3 .

Description. Colorless crystals of ammoniacal odor and taste ;
soluble in their own weight of water at 15.

AMMONIUM CHLORIDE PURIFIED.

AMMONII CHLORIDUM PURIFICATUM.

H 4 NC1=53. 4 .

The impurities liable to be present in crude "sal ammoniac" or
crude, commercial ammonium chloride are the chlorides and sul-
phates of iron and of calcium. The iron compounds may be
both ferrous and ferric, but are usually ferrous. Of the im-
purities mentioned the most common is ferrous chloride. This
does not discolor the ammonium chloride until the sal ammoniac
is exposed to the air so that the ferrous salt is oxidized to ferric.

The sal ammoniac should be tested for ferrous salt, ferric salt,
sulphates and calcium, with test solutions of potassium ferri-
cyanide, potassium ferrocyanide, barium chloride, and am-
monium carbonate or oxalate, successively, in the usual way.
Should all of the impurities named be present, they may be re-
moved as follows :

Dissolve the impure ammonium chloride in about twice its
weight of water, or less. Heat the solution to boiling. Filter.
Add solution of barium chloride in small quantities to the hot
filtrate and stir well. As soon as a further addition of barium
chloride no longer causes turbidity in a filtered test-portion of the
liquid, add a solution of ammonium carbonate or oxalate to com-
pletely precipitate the calcium and the excess of barium. Filter.
Then add to the filtrate about 25 ml of strong chlorine water for
each kilogram of ammonium chloride in solution. Boil for
twenty or thirty minutes. Then add enough ammonia water to



AMMONIUM CHLORIDE. 275

render the liquid alkaline and to impart an ammoniacal odor to it.
Filter again. Evaporate the filtrate to i.io sp. w. and then
set it aside to crystallize, or evaporate nearly to dryness and dry
the granulated salt perfectly in the usual way.

When salts of organic bases are present in the crude sal am-
moniac made from gas liquor they should be destroyed by boiling
100 parts of the crude product with 125 parts of water and 15
parts of concentrated nitric acid until no more acid vapors are
evolved. The residue may then be treated as before described
to remove the chlorides and sulphates of calcium and iron.

Should ferrous chloride be found to be the only impurity pres-
ent, treat the solution of the impure ammonium chloride with
chlorine water and ammonia as described. Should the product
be not entirely free from iron after one treatment, repeat the
addition of chlorine water, boil again, add ammonia in excess as
before and again granulate or crystallize the product.

When ferric chloride is the only impurity the process of purifi-
cation is simple :

Crude ammonium chloride 20 parts

Water 30 parts

Ammonia water ( 10% ) i part

Dissolve the ammonium chloride in the water heated to boiling.
Add the ammonia water. Continue the boiling for a few minutes.
Filter. Evaporate to granulation. Dry the product thoroughly.

Pure Ammonium Chloride

may be readily made from pure diluted hydrochloric acid and pure
ammonia water:

Diluted hydrochloric acid (10% of HC1) 2 parts

Ammonia water (10% of H 3 N) I part

Add the ammonia water gradually to the acid, stirring well.
Evaporate to granulation or crystallization, and dry the product.

Reaction. H 3 N+HC1=H 4 NC1.

Description. Pure ammonium chloride is a colorless crystalline,
or a white, granular salt ; odorless, taste saline, cooling. Soluble



276 AMMONIUM IODIDE.

in 3 parts of water of 15, and in its own weight of boiling water.
Nearly insoluble in alcohol. Reaction neutral. Volatilises with-
out residue when strongly heated.



AMMONIUM IODIDE.

AMMONII IODIDUM.

H 4 NI= 144.50.

Potassium iodide 6 parts

Ammonium sulphate 4 parts.

Alcohol 2 parts

Distilled water 12 parts

Dissolve the salts, each in 6 parts of distilled water ; filter the
solutions; mix them; evaporate the filtrate to about 15 parts;
set the liquid aside in a cool place for about twelve hours; add
the alcohol to the solution and set the mixture in an ice-water
bath until cooled down to 5 ; separate and reject the crystals of
potassium sulphate, which are now separated, and add a little
ammonia to the clear solution and evaporate it to dryness.

Put the product in a dry bottle, which must be tightly closed,
and kept in a dark place.

Reaction. 2KI+(H 4 N) 2 SO 4 = 2H 4 NI+K 2 SO 4 .

Notes. The alcohol is added to facilitate the separation of the
potassium sulphate, which is insoluble in diluted alcohol, while
the ammonium iodide is soluble. The solution may, after standing
twelve hours, be cooled to 5 on an ice-water bath before the alco-
hol is added, the clear solution then separated from the crystals
of potassium sulphate by throwing the whole into a cooled glass
funnel having a loose plug of moist cotton placed in its throat.
The filtrate may then be evaporated to dryness, and the ammon-
ium iodide extracted from the dry salt-mass by means of warm
alcohol, which will leave the potassium sulphate undissolved. The
alcoholic solution of ammonium iodide may then be allowed to
evaporate until the dry salt is obtained. The yield of ammonium
iodide from 6 parts of potassium iodide should be about 5.33 parts,
which is soluble in 50 parts of warm alcohol.



AMMONIUM NITRATE. 277

Description. A white crystalline powder, without odor, and
having a sharp saline taste. Very hygroscopic. Soluble at 15
in two-thirds of its own weight of water and in 9 parts of alcohol ;
in half its weight of boiling water and in 3.7 parts of boiling
alcohol.

The salt is very unstable, soon turning yellow or even brown,
and acquiring an odor of iodine. The free iodine by which the
product is discolored may be removed by washing the salt with
ether and then rapidly drying the white salt; or a concentrated
aqueous solution may be made of the salt and enough ammonium
sulphide solution added to render the liquid colorless, after which
it is filtered and evaporated to dryness.

AMMONIUM NITRATE.

AMMONII NITRAS.

H 4 NNO 3 =8o.

Nitric acid (68% ) 10 volumes

Ammonia water (10% H 3 N) 7 volumes

Distilled water.

Dilute the nitric acid with 10 volumes of distilled water. Place
the ammonia water in a large porcelain dish, and add to it, gradu-
ally, the diluted nitric acid, stirring well. When all of the acid
has been added, test the reaction of the liquid on litmus paper.
If not distinctly (though faintly) alkaline, make it so by the
addition of sufficient ammonia water. Filter the solution if not
perfectly clear. Evaporate the filtrate until it acquires the den-
sity of 1.25 while still hot. Then set it aside to cool that crystals
may be formed. Collect and dry the crystals.

Additional crops of crystals may be obtained from the mother
liquor by further evaporation.

Keep the product in dry, well closed bottles.

Reaction. H 4 NOH+HNO 8 =H 4 NNO 8 +H 2 O.

Notes. If fused ammonium nitrate is desired instead of crys-
tals, the salt should be fused at a temperature not exceeding
166 C. and should be kept at that temperature until it ceases
to give off watery vapor.

During the evaporation of a solution of ammonium nitrate it



278 AMMONIUM OXALATE.

happens that the liquid gradually acquires an acid reaction ; this
should be corrected by the addition of enough ammonia to restore
a slightly alkaline reaction before the liquid is set aside to crys-
tallize.

Description. Long, colorless, prismatic crystals, or a fused
white mass. Odorless. Taste sharp and bitter. Hygroscopic.
Soluble at 15 in half its weight of water or in 20 parts of alcohol ;
very soluble in boiling water, and in 3 parts of boiling alcohol.



AMMONIUM OXALATE.

AMMONII OXALAS.

(H 4 N) 2 C 2 O 4 .H 2 O=i42.

Oxalic acid 100 Gm

Boiling distilled water 800 ml

Ammonium carbonate, sufficient.

Dissolve the acid in the water, neutralize with ammonium car-
bonate, raising the temperature, at the end of the neutralization,
to the boiling point ; filter while hot, and set aside to cool and
crystallize.

Reaction. 2(H 4 NHCO 3 .H 4 NH 2 NCO 2 )+3H 2 C 2 O 4

= 3 (H 4 N) 2 C 2 4 +2H 2 0+ 4 C0 2 .

Notes. About 83 Gm of ammonium carbonate will be required
to saturate 100 Gm of oxalic acid. Instead of 83 Gm of ammon-
ium carbonate, the corresponding quantity (270 ml) of ammonia
water (10 per cent) may be used. The solution should be ren-
dered exactly neutral to test-paper, filtered while hot, and set
aside to cool slowly. When the solution is dilute and the cooling
and crystallization slow, very handsome needle-shaped crystals
may be obtained. By evaporating the mother liquor and again
crystallizing, additional crops of the salt are recovered.

Description. This salt crystallizes in rhombic prisms, easily
soluble in water.



AMMONIUM PHOSPHATE. 279

AMMONIUM PHOSPHATE.

AMMONII PHOSPHAS.

(H 4 N) 2 HP0 4 =I 3 2.

Prepared by adding strong ammonia solution to diluted phos-
phoric acid until a slightly alkaline reaction on test-paper is pro-
duced. The solution is then evaporated, the alkaline reaction
being maintained by adding a little more ammonia from time to
time, as required. The crystals formed upon allowing the solu-
tion to cool are collected and quickly dried on bibulous paper
placed upon a porous tile.

Ammonium phosphate must be kept in well-stoppered bottles.

Description. Transparent, colorless prisms, inodorous, of a
somewhat alkaline saline taste. Readily soluble in water ; insoluble
in alcohol.

AMMONIUM SULPHATE.

AMMONII SULPHAS.

(H 4 N) 2 S0 4 =i 3 2.

Ammonia water . 2 volumes

Diluted sulphuric acid 5 volumes

Add the acid gradually to the ammonia water, stirring the
liquid. Should the solution not be alkaline in its reaction on test-
paper, add enough additional ammonia water to render it alkaline.
Filter. Evaporate to crystallization. During the evaporation test
the liquid from time to time with litmus paper, and add more
ammonia if necessary to prevent the solution from acquiring an
acid reaction, or to render it alkaline again should it become acid
by the loss of ammonia.

Reaction. 2H 4 NOH+H 2 SO 4 =(H 4 N) 2 SO 4 +H 2 O.

Description. Colorless and odorless crystals, soluble in 1.33
parts of water at 15.



28<D AMMONIUM VALERATE.

AMMONIUM VALERATE.

AMMONII VALERIANAS.

NH 4 C 5 H 9 O 2 =ii9.

Prepared by saturating valeric acid with dry ammonia gas,
usually generated from a mixture of equal parts of ammonium
chloride and lime. The heat produced by the chemical union keeps
the salt in a liquid condition, and on cooling the valerate crystal-
lizes. The salt cannot be crystallized from an aqueous solution.

A solution of ammonium valerate may be readily prepared by
dissolving 102 Gm of valeric acid in 61 Gm of stronger water of
ammonia; if diluted with distilled water until it measures 238
milliliters, each ml of this solution will contain 0.50 Gm of the
salt.

Neutral ammonium valerate easily parts with ammonia and be-
comes acid ; in solution it is to be carefully neutralized with am-
monia water.

Description. Colorless crystalline plates, soluble in water and
alcohol, and having the odor of the acid. They should volatilize
completely.

ANTIMONY CHLORIDE.

ANTIMONI CHLORIDUM.

SbCl 3 =226.5.

Antimonous oxide 3 parts

Hydrochloric acid (32% of HC1) 8 parts

Heat gently together in a porcelain dish, stirring well, until the
acid ceases to dissolve any more of the oxide. Then raise the
temperature slowly to the boiling point and continue boiling until
a drop of the liquid deposits crystals on cooling. Then pour the
liquid into a retort provided with a thermometer in the tubulure
and distill, heating the retort in a sand bath. The distillate at
first consists of hydrochloric acid, which is to be collected separ-
ately. As soon as the boiling point rises to 200 and a drop of the
distillate solidifies on a cold surface, change the receiver and con-



ANTIMONY CHLORIDE. 28l

tinue the distillation. The distillate now passing over is antimony
trichloride.

Reaction. Sb 2 O 3 +6HCl=:2SbCl3+3H 2 O.

Description. A white or yellowish-white soft solid or semi-
solid. Very deliquescent. Decomposes when brought in contact
with water. Soluble in alcohol without decomposition. It can
be dissolved in water containing hydrochloric acid, citric acid, or
tartaric acid. It is also soluble in glycerin.

Antimony Chloride Solution.

LIQUOR ANTIMONI CHLORIDI.

A solution of SbCl 3 in water containing hydrochloric acid.

Purified antimonous sulphide, in extremely

fine powder 100 Gm

Hydrochloric acid (35% of HC1) 530 Gm

Put the acid in a flask of one cubic-decimeter's capacity. Heat
it to about 50. Add the antimonous sulphide, in very fine powder,
gradually to avoid too copious evolution of hydrogen sulphide.
Shake well. Apply heat, first gently, then gradually raising the
temperature to the boiling point of the liquid. Boil for half an



Online LibraryOscar OldbergInorganic general, medical and pharmaceutical chemistry, theoretical and practical; a text-book and laboratory manual, containing theoretical, descriptive, and technological chemistry; → online text (page 21 of 49)