Chlorine disengaged 1 atom. 4·5 17·82
Sulphate of soda 1 -- 9·0 35·64
Proto-sulphate of manganese 1 -- 9·5 37·62
Water 2 -- 2·25 8·92
----- ------
25·25 100·00
These proportions are, however, very different from those employed, by
many, nay I believe by all manufacturers; and they ought to be so, on
account of the impurity of their oxide of manganese. Yet making
allowance for this, I am afraid that many of them commit great errors in
the relative quantities of their materials.
From the preceding computation, it is evident that 1 ton of salt with 1
ton of the above native oxide of manganese properly treated, would yield
0·59 of a ton of chlorine, which would impregnate 1·41 tons of slaked
lime, producing 2 tons of bleaching-powder, stronger than the average of
the commercial specimens; or allowing for a little loss, which is
unavoidable, would afford 2 tons of ordinary powder, with a little more
slaked lime.
[Illustration: 287 288]
_Fig._ 287. represents a retort of lead, well adapted to the evolution
of chlorine from the mixture of salt, manganese, and sulphuric acid, or
from manganese and muriatic acid. The interior vessel is cast in lead,
and it has round its bottom part a cast-iron steam case. The salt and
manganese are introduced by the aperture C, and the sulphuric acid by
the syphon funnel F. The contact of these three substances is
continually renewed by the agitator or stirrer B, which consists of
wrought or cast iron sheathed with lead. _e_ is the gas discharge pipe.
The residuums are drawn off by the bottom discharge pipe G. The heating
case receives its steam by the pipe _h_.
The chlorine gas _fig._ 288. is conveyed from the retort B into the
chamber I, by the tube E E E. This chamber is divided into four
compartments, to receive the gas disengaged from four retorts, like the
above. The bottom of it is covered with a stratum three or four inches
thick of quicklime, newly slaked and sifted, which is stirred about
from time to time, by the rakes L L L L. When the saturation is
sufficient, the chloride of lime is taken out by the doors K K K K. The
size of this apparatus allows 2 cwt. of manganese, and its equivalent
quantity of salt and sulphuric acid, or of muriatic acid, to be
introduced at once into the retort. D is the handle of the agitator.
The same form of retort will suit perfectly well to prepare chlorine for
making liquid chloride of lime, which is preferred by many bleachers and
calico-printers who have conveniences for preparing it themselves. The
most concentrated solutions of the dry chloride of lime do not mark more
than 6° B. (sp. grav. 1·04), and discolour only 50 volumes of Gay
Lussac’s solution of indigo, whilst the chloride made in the humid way
marks from 8° to 9° B. (about 1·060), and discolours 80 volumes of the
same solution.
In the chloride of lime apparatus, most generally used by the skilful
calico-printers of Mulhausen, the mixture of muriatic acid and manganese
is put into glass globes, with long necks, heated upon a sand-bath. The
chlorine is conveyed by glass tubes into a cylindrical stone cistern,
containing milk of lime. The furnace of the sand baths is made of cast
iron, and has brick partitions, to give each retort its own fire. The
smoke of all these fires goes off by a flue into sheet iron pipes. The
cistern is made of siliceous sandstone. Its cover is of wood, coated
with a resinous cement; and it fits at its edges into grooves cut in the
stone. A wheel serves to agitate the liquid continually; its paddles
being kept at two inches distance from the sides of the cistern. The
milk of lime is introduced by a funnel, and the chloride is drawn off by
a discharge pipe. I think the lead retort and agitator used in this
country greatly preferable to the experimental laboratory plan described
above. In all such apparatus we should avoid giving any pressure to the
tubes or vessels, and should not therefore dip the extremities of the
gas pipes beneath the surface of the liquid, but rather facilitate the
combination of the chlorine and the lime, by enlarging the surfaces of
contact and by agitating. Intermediate vessels containing water, or the
chemical cascade of M. Clement, are very useful for absorbing any
muriatic acid which may be disengaged along with the chlorine, and
thereby preventing the needless formation of muriate of lime in the
chambers or cisterns of impregnation.
When the solution of the chloride of lime is mixed with hydrate of lime,
it bears, without decomposing, a pretty high temperature, provided it be
not too long continued; it may even, in certain cases, be raised to near
the boiling point without suffering a marked loss of its discolouring
power; but when the chloride is deprived of that excess of lime, it is
decomposed in a short time, even at a heat of 110° F.
When chlorine is admitted to milk of lime, it infallibly produces some
muriate of lime; but the quantity is kept at a _minimum_ by constantly
presenting an excess of lime to the gas with the agitator, and by
keeping the temperature as low as possible. Hence the influx of gas
should not be so rapid as to generate much heat. An automatic agitator,
moved by steam or water power, is therefore much better than one driven
by the hand of the operator, who is apt to intermit his labours. If the
liquor becomes hot at the end of the process, it should be immediately
drawn off into large stone bottles, and cooled. The rose-colour, which
sometimes supervenes, is due to a minute quantity of manganese. The
strongest liquid chloride of lime that can be prepared will not
discolour more than 80 times its volume of Gay Lussac’s indigo test.
On acting upon cotton cloth with a concentrated solution of chloride of
lime, at from 110° to 120° F., pure carbonic acid gas is disengaged, and
the texture of the cloth is injured. Here the hydrogen of the water and
the cotton being seized by the chlorine, the liberated oxygen combines
with the carbon to form carbonic acid. In the discharge troughs where
printed calicoes are passed through strong solutions of chloride of
lime, stalactitic crusts of carbonate of lime come to be formed in this
way.
The _chlorometre_ of Gay Lussac consists of a test solution of indigo
and a graduated tube. One part of the best indigo, passed through a silk
sieve, is to be dissolved in nine parts of concentrated sulphuric acid,
by the aid of a water-bath heat applied for six hours. The sulphate of
indigo is now to be diffused through such a body of water that one
volume of chlorine gas shall discolour exactly ten times its volume of
this dilute solution. The test liquor should be protected from the
agency of light.
Mr. Crum, of Thorniebank, near Glasgow, has lately modified Dr. Dalton’s
copperas test for chloride of lime, and made it convenient to the
practical man. The Doctor justly considered that the more chlorine any
bleaching powder contains, the more of the green sulphate of iron will
it convert into the red sulphate, so that we have only to add successive
portions of the chloride to a given weight of the dissolved copperas,
and note the point at which all the iron gets peroxidized. See
BLEACHING.
[Illustration: 289]
Besides the method of analysis already quoted from my memoir on the
manufacture of the chloride of lime, another occurred to me long ago,
which I often practised as an easy and expeditious test. Chlorine
decomposes ammonia. If therefore water of ammonia, faintly tinged with
litmus, be added slowly to a solution of a given weight of chloride of
lime, the colour will continue to disappear till the chlorine be all
neutralized by the reaction of the hydrogen of the ammonia. The quantity
of liquid ammonia of a certain strength requisite to neutralize in this
way, a certain volume, say, one cubic inch, or a thousand grain measures
of chlorine gas, may be assumed as the standard of such a chlorometer.
As chlorine or chloride of lime, when mixed with water of ammonia,
causes the disengagement of azote, the quantity of this gas evolved may
also be made the foundation of an accurate and convenient chlorometer.
The two substances should be mixed over mercury, in a graduated syphon
tube. The shut end A and the open end B are both graduated to one scale;
for example, to hundredths of a cubic inch, or to grain or 10 grain
measures. The tube is to be filled with mercury, and then 10 measures of
it are to be displaced at the open end, by inserting a wooden plug. This
space, being filled with the solution of chloride of lime, is to be
turned up into the shut end by covering the open end with the finger,
and inverting the tube; a few drops of water may be sent through to wash
the mercury. The ammonia being now let up, will cause a reaction, and
evolve a quantity of azote, equivalent to the chlorine present. The
action may be quickened by holding the sealed end of the tube obliquely
over a lamp heat. The mercury is protected from the chlorine by the
ammonia; and should any notion be entertained of such an action, the
ammonia may be let up first. I have made innumerable researches over
mercury with a detached apparatus of that kind, which combines precision
with rapidity of result. It was by a similar mercurial syphon that I
analyzed the carbonates, as described in the first edition of my
Dictionary of Chemistry, twenty-one years ago.
M. Gay Lussac takes, as the basis of his indigo chlorometer, the fact,
that one pound of pure crystallized peroxide of manganese is capable of
affording, with muriatic acid, 0·7964 parts of a pound of chlorine; or
one kilogramme yields 251-1/4 litres; that is, one pound yields 251-1/4
pound measures. Hence 3·98 grammes of that manganese are capable of
affording 1000 gramme measures, or 1 litre of chlorine; or, in round
numbers, 4 grains will yield 1000 grain measures. This quantity of gas,
being received into that volume of milk of lime, constitutes therefore
Gay Lussac’s primary standard. The small retort in which the manganese
and muriatic acid are put, ought to be heated to ebullition, to
discharge every particle of chlorine. To prevent the manganese, in this
experiment, from sticking to the bottom in a cake, it has been proposed
to mix it previously with a little plumbago. See CHLOROMETRY.
For preparing the chlorides of potash and soda, the same apparatus may
be employed as for the liquid chloride of lime. The alkaline solutions
should be weak, containing not more than a pound to the gallon of water.
Potash liquor saturated with chlorine, is much employed at Paris for
whitening linen, under the name of the water of Javelle, the place where
it was first made as a manufacture. One hundred parts of chlorine are
said to saturate 133 parts of pure potash, and 195 of the carbonate; but
the latter should not be used for preparing the bleaching fluid, as the
carbonic acid resists the combination of the chlorine. A chloride of
carbonate of soda has been lately recommended as a disinfecting
substance against contagious miasmata or _fomites_. One hundred parts of
chlorine will saturate 150 of the dry carbonate, and 405 of the
crystallized. M. Payen prepares this medicinal chloride by adding 138
parts of carbonate of soda to a liquid, consisting of water 1800,
chloride of lime 100, at 98° of strength, by Gay Lussac’s standard. The
chloride of lime is to be dissolved, and the sediment well washed; the
carbonate of soda, dissolved by heat, is to be poured into the solution,
the precipitate allowed to subside, the clear fluid decanted, and the
solid matter washed upon a filter. The collected solutions are neutral
chloride of soda. Sixty-two parts of the carbonate of soda are then to
be dissolved in the remainder of the water, and added to the
preparation; the whole being thus filtered, a limpid liquor is obtained,
indicating 5° by the hydrometer of Baumé.
The chloride of magnesia was long ago proposed by Sir H. Davy for
bleaching linen, as being preferable to chloride of lime, because the
resulting muriate of magnesia was not injurious to the fibre of cloth,
as muriate of lime may be, under certain circumstances. I prepared a
quantity of chloride of magnesia, by exposing a hydrate of that earth in
the chlorine chamber of a large manufactory of chloride of lime at
Glasgow, and obtained a compound possessed of considerable discolouring
powers; but I found that the chlorine was so feebly saturated by the
base, that it destroyed the colours of fast-dyed calicoes as readily as
chlorine gas or chlorine water did, and was therefore dangerous for
common bleaching, and destructive in clearing the grounds of printed
goods, which is one of the most valuable applications of the calcareous
and alkaline chlorides. The occasion of my making these experiments was
the importation of a considerable quantity of magnesite, or native
atomic carbonate of magnesia, from the district of Madras, by an
enterprising friend of mine. Encouraged by the encomiums bestowed on the
chloride of magnesia by many chemical writers, he expected to have
benefited both the country and himself, by bringing home the earthy base
of that compound, at a moderate price; but was disappointed to his cost.
Dr. Thomson is of opinion that the bleaching compound of lime and
chlorine is not a chloride of lime, but a combination of chlorous acid
with lime and of chlorine with calcium; consisting in its most
concentrated state of
3 atoms of chloride of calcium = 21
1 atom of chlorite of lime = 11
---
32
---
So that about one third of the weight is chlorite of lime, to which
alone the bleaching powers of the substance are owing. He admits a fact,
rather inconsistent with this opinion, that bleaching powder does not
attract moisture from the atmosphere with nearly so much rapidity as
might be expected from a mixture containing two thirds of its weight of
so deliquescent a salt as muriate of lime; unless this indeed be
prevented by the chloride and chlorite being united into a double salt,
which is a mere conjecture without either proof or analogy. And further,
when dilute sulphuric or muriatic acid is poured upon bleaching powder,
a profusion of chlorine is given out immediately, which he also admits
to be inconsistent with the notion of its being a mixture of chloride of
calcium and chlorite of lime, for no such evolution takes place when the
above acids are mixed with solutions of chloride of calcium and chlorate
of potash. Though I am of opinion that bleaching powder is simply a
chloride of lime, in which the lime corresponds to the water in the
aqueous chlorine, yet I cannot see the truth or appositeness of his last
reason, because chlorine is certainly given out when chlorate of potash
is acted upon by dilute muriatic acid, as any man may prove by adding to
a mixture of these two substances a vegetable colour; for it will be
speedily blanched. Dr. Thomson considers the chloride which is at
present made in Mr. Tennant’s great factory, as containing one atom of
chlorine associated with one atom of lime, or, taking his numbers, as
consisting of
Hydrate of lime 4·625
Chlorine 4·5
Or nearly equal weights of the chlorine and the base; indicating a
surprising degree of excellence in the preparation. The average
commercial samples of bleaching powder from different factories which I
examined some years ago, did not possess nearly that strength; but
varied in their quantity of chlorine from 20 to 28 per cent. In my
synthetic experiments related above, the greatest quantity of chlorine
that would combine with the atomic hydrate of lime, was in the
proportion of 130 to 200; but there is no doubt that if the lime
contains additional water, it will condense more gas. I have never seen
a chloride of lime of the strength mentioned by Dr. Thomson, and I
should think there must be some fallacy in his statements. I have
recorded in the paper above quoted an experiment which proves that with
additional moisture, a chloride of lime may be obtained of the following
composition:--
Chlorine 39·5
Lime 39·9
Water 20·6
-----
100·0
-----
In the article BLEACHING, of the Encyclopædia Britannica, Dr. Thomson
deduces from a test trial of Mr. Crum, that the best bleaching powder is
a compound of 1 atom chlorite of lime = 11, 3 atoms chloride of calcium
= 21, and 8 atoms of water = 9. “But,” adds he, “in general the whole
lime is not accurately saturated with chlorine. Accordingly, when the
bleaching powder is dissolved in water a small residue almost always
remains undissolved. Unless the powder be fresh made, a portion of
chlorite is always converted into chloride of calcium. It is probable
therefore that the best bleaching powder, as it comes into the hands of
the bleachers, consists of
1 atom chlorite of lime 11
3 atoms chloride of calcium 21
6 atoms water 6·75
Impurity 2·25
-----
41·00
-----
“If we consider the bleaching powder as a compound of chlorine and lime,
our mode of calculating will not be altered. Instead of 1 atom chlorite
of lime, and 3 atoms chloride of calcium, we shall have 4 atoms chloride
of lime, 6 atoms water, and 2·25 of impurity as before.” In such
ambiguity does this able chemist place this interesting compound, for
theoretical reasons, of which I cannot see the value. Surely there is no
difficulty in conceiving chlorine to exercise a direct attractive force
towards the hydrate of lime, as it is known to do towards each of its
elementary constituents, the oxygen and the calcium. Such refinements as
the preceding tend merely to mystify a plain matter. Even the chlorous
acid here brought into play to form the ideal chlorite, is by his own
admission a hypothetical being. “When chlorate of potash” says Dr.
Thomson, “is mixed with sulphuric acid, and made into small balls the
size of a pea, if we expose these balls to a heat somewhat lower than
that of boiling water, a bright yellowish green gas separates, which may
be received over mercury. Its smell is peculiar and aromatic. Water
absorbs at least seven times its volume of it. It destroys vegetable
blues. Its constituents are,
1 volume chlorine 2·5 or 4·5
2 volumes oxygen 2·222 or 4.
Thus this compound consists in weight of chlorine 4·5, oxygen 4 = 8·5.
It has been called _quarteroxide of chlorine_, but it is more probably a
_teroxide_. It has been supposed by some to possess acid properties, and
has therefore been called _chlorous acid_. But this is only as yet a
hypothesis.”
Surely this by the Doctor’s own showing is very slender authority for
renouncing our long-received doctrines concerning the constitution of
bleaching powder. I shall conclude by remarking that the ultra-atomists
are now in a dilemma about this substance; M. Welter, and many French
chemists calling it a sub-chloride, of 1 atom of chlorine to 2 atoms of
lime, and Dr. Thomson showing that Mr. Tennant, the greatest and best
manufacturer of it, has produced it in the state of a chloride, or 1
atom of each. The fact is, in chloride of lime, as in water of ammonia,
alcohol, and muriatic acid, there is no _sufficient reason_ for definite
proportion in any term short of saturation, and therefore we shall find
_that_ chloride in every gradation of strength from 1 per cent. of
chlorine up to 40 per cent.--the strongest which I succeeded in
preparing, though I passed a constant stream of chlorine in great excess
over a pure hydrate of lime for upwards of 24 hours, with frequent
renewal of the surface; indeed, till it refused to absorb any more gas,
as indicated by its remaining stationary in weight.
CHLOROMETRY; _Chlorometrie_, is the name given by the French to the
process for testing the decolouring power of any combination of
chlorine, but especially of the commercial articles, the chlorides of
lime, potash, and soda. M. Gay Lussac proposed many years ago the
following _graduated_ method of applying indigo to this purpose. As
indigo varies much in its dyeing quality, and of consequence in the
proportion of chlorine required for its decoloration, he assumes as the
unity of blanching power, one litre of chlorine gas, measured at the
mean pressure of 29·6 inches, and at the temperature of melting ice.
This volume of gas, when combined with a determinate quantity of water,
is employed to test the standard solution of indigo. For this purpose a
solution in sulphuric acid of any sample of indigo is taken, and diluted
with water to such a degree that 10 measures of it, in a graduated tube,
are decoloured by that one measure of combined chlorine gas. Each
measure of indigo solution so destroyed is called a degree, and this
measure being divided into five parts, the real test of chlorine is
given to fiftieths, which is sufficiently nice. For the standard of the
assays, a chloride of lime as pure and fully saturated as possible is
taken, and dissolved in such a quantity of water, that the solution
shall contain, or be equivalent to, one volume of chlorine gas.
Calculation proves that this condition is exactly fulfilled by
dissolving 4938 grammes of the said chloride in half a litre of water;
or in English measures, 5 gr. very nearly in 500 grain measures of
water. This solution, which serves for a type, indicates 10° in the
assay, or proof; that is to say, each single volume destroys the colour
of 10 volumes of the dilute indigo solution. It may be remarked, that a
greater degree of precision is in general attainable with a weak
solution of chlorine or a chloride, for example at 4° or 5°, than with
one much stronger; consequently if, after a preliminary trial, the
standard considerably exceeds 10°, a given volume of water must be added
to the solution, and then the above proof must be taken. If the volume
of water added was double, the number of degrees afterwards found must
be tripled, to obtain the true title of the chloride. It is, however, to
be observed that the degree of decoloration varies with the time taken
in making the mixture; the more slowly the chlorine is added to the
indigo, the less of it escapes into the atmosphere, and the more
effective it becomes in destroying the colour. The best mode of
obtaining comparable results, is to pour suddenly into the test quantity
of chlorine the whole volume of the indigo solution likely to be
decoloured; but it is requisite to find approximately beforehand, what
quantity of indigo-blue will probably be destroyed. When it comes to the
verge of destruction, it is green; but yellowish-brown when entirely
decomposed.
I have tried the indigo test in many ways, but never could confide in
it. The sulphuric solution of indigo is very liable to change by
keeping, and thus to lead to erroneous results. The method of testing
the chlorides by green sulphate of iron, described under bleaching, is
in my opinion preferable to the above.
M. Gay Lussac has recently proposed another proof of chlorine, founded
on the same principle as that by green vitriol, namely, the quantity of
it requisite to raise a metallic substance from a lower to a higher
stage of oxidizement. He now prescribes as the preferable plan of
chlorometry, to pour very slowly from a graduated glass tube, a
standard solution of the chloride, to be tested upon a determinate
quantity of arsenious acid dissolved in muriatic acid, till the whole
arsenious be converted into the arsenic acid. The value of the chloride
is greater the less of it is required to produce this effect. It is easy
to recognize, by a few drops of solution of indigo, the instant when all
the arsenious acid has disappeared; for then the blue tint is
immediately effaced, and cannot be restored by the addition of a fresh
drop of the indigo solution.
In graduating the arsenical chlorometer, M. Gay Lussac takes for his
unity the decolouring power of one volume of chlorine at 32° Fahr., and
divides it into 100 parts. Suppose that we prepare a solution of
chlorine containing its own volume of the gas, and an arsenious
solution, such, that under a like volume, the two solutions shall
reciprocally destroy each other. Let us call the first, the normal
solution of chlorine, and the second, the normal arsenious solution. We
shall fix at 10 grammes the weight of chloride of lime subjected to
trial; and dissolve it in water, so that the total volume of the
solution shall be a litre (1000 grammes measure), including the
sediment. If we take a constant volume of this solution, 10 centimetres
cube (10 gramme measures), for example, divided into 100 equal parts,
and pour into it gradually the arsenious solution (measured by like
portions), till the chlorine be destroyed, the bleaching power will be
proportional to the number of portions of the arsenious solution, which
the chloride shall have required. If the chloride has destroyed 100
portions of the arsenious solution, its title will be 100; if it has
destroyed 80 portions, its title will be 80, &c. and so forth.
On pouring the acidulous arsenious solution into the chloride of lime,
this will become very acid; the chlorine will be emitted abundantly, and
the proof will be quite incorrect. If, on the contrary, we pour the
solution of the chloride of lime into the arsenious solution, this evil
will not occur, since the chlorine will always find plenty of arsenious
acid to act upon, whatever be the dilution of the one or the other; but
in this case, the standard of the chlorine is not given directly, as it
is in the inverse ratio of the number of portions which are required to
destroy the measures of the arsenious solution. If 50 portions of the
chloride have been required, the proof will be 100 × 100/50 = 200°; if
200 have been required, the proof will be 100 × 100/200 = 50°, &c. This
evil is not, however, very serious, since we have merely to consult a
table, in which we can find the proof corresponding to each volume of
the chloride employed for destroying the constant measure of the
arsenious solution. The arsenious solution should be slightly tinged
with sulphate of indigo, so as to show, by the disappearance of the
colour, the precise point or instant of its saturation with chlorine,
that is, its conversion into arsenic acid. If the arsenious acid be
pure, the normal solution may be made directly by dissolving 4·439
grammes of it in muriatic acid (free from sulphurous acid), and diluting
the solution till it occupies one litre, or 1000 grammes measure.
_Annales de Chimie et Physique_, LX. 225.
CHOCOLATE. Is an alimentary preparation of very ancient use in Mexico,
from which country it was introduced into Europe by the Spaniards in the
year 1520, and by them long kept a secret from the rest of the world.
Linnæus was so fond of it, that he gave the specific name, _theobroma_,
food of the gods, to the cacao tree which produced it. The cacao-beans
lie in a fruit somewhat like a cucumber, about 5 inches long and 3-1/2
thick, which contains from 20 to 30 beans, arranged in 5 regular rows
with partitions between, and which are surrounded with a rose-coloured
spongy substance, like that of water-melons. There are fruits, however,
so large as to contain from 40 to 50 beans. Those grown in the West
India islands, Berbice and Demerara, are much smaller, and have only
from 6 to 15; their development being less perfect than in South
America. After the maturation of the fruit, when their green colour has
changed to a dark yellow, they are plucked, opened, their beans cleared
of the marrowy substance, and spread out to dry in the air. Like
almonds, they are covered with a thin skin or husk. In the West Indies
they are immediately packed up for the market when they are dried; but
in the Caraccas they are subjected to a species of slight fermentation,
by putting them into tubs or chests, covering them with boards or
stones, and turning them over every morning, to equalize the operation.
They emit a good deal of moisture, lose the natural bitterness and
acrimony of their taste by this process, as well as some of their
weight. Instead of wooden tubs, pits or trenches dug in the ground are
sometimes had recourse to for curing the beans; an operation called
_earthing_ (_terrer_). They are lastly exposed to the sun, and dried.
The latter kind are reckoned the best; being larger, rougher, of a
darker brown colour, and, when roasted, throw off their husk readily,
and split into several irregular fragments; they have an agreeable mild
bitterish taste, without acrimony. The Guiana and West India sorts are
smaller, flatter, smoother-skinned, lighter coloured, more sharp and
bitter to the taste. They answer best for the extraction of the butter
of cacao, but afford a less aromatic and agreeable chocolate. According
to Lampadius, the kernels of the West India cacao beans contain, in 100
parts, besides water, 53·1 of fat or oil, 16·7 of an albuminous brown
matter, which contains all the aroma of the bean, 10·91 of starch, 7-3/4
of gum or mucilage, 0·9 of lignine, and 2·01 of a reddish dye stuff
somewhat akin to the pigment of cochineal. The husks form 12 per cent.
of the weight of the beans; they contain no fat, but, besides lignine,
or woody fibre, which constitutes half their weight, they yield a light
brown mucilaginous extract by boiling in water. The fatty matter is of
the consistence of tallow, white, of a mild agreeable taste, called
butter of cacao, and not apt to turn rancid by keeping. It melts only at
122° Fahr., and should, therefore, make tolerable candles. It is soluble
in boiling alcohol, but precipitates in the cold. It is obtained by
exposing the beans to strong pressure in canvass bags, after they have
been steamed or soaked in boiling water for some time. From 5 to 6
ounces of butter may be thus obtained from a pound of cacao. It has a
reddish tinge when first expressed, but it becomes white by boiling with
water.
The beans, being freed from all spoiled and mouldy portions, are to be
gently roasted over a fire in an iron cylinder, with holes in its ends
for allowing the vapours to escape; the apparatus being similar to a
coffee-roaster. When the aroma begins to be well developed, the roasting
is known to be finished; and the beans must be turned out, cooled, and
freed by fanning and sifting from their husks. The kernels are then to
be converted into a paste, either by trituration in a mortar heated to
130° F., or by the following ingenious and powerful machine. The
chocolate paste has usually in France a little vanilla incorporated with
it, and a considerable quantity of sugar, which varies from one third of
its weight to equal parts. For a pound and a half of cacao, one pod of
vanilla is sufficient. Chocolate paste improves in its flavour by
keeping, and should therefore be made in large quantities at a time. But
the roasted beans soon lose their aroma, if exposed to the air.
[Illustration: 290]
_Fig._ 290. represents the chocolate mill. Upon the sole A, made of
marble, six conical rollers B B, are made to run by the revolution of
the upright axis or shaft _q_, driven by the agency of the fly wheel E
and bevel wheels I K. The sole A rests upon a strong iron plate, which
is heated by a small stove, introduced at the door H. The wooden frame
work F, forms a ledge, a few inches high, round the marble slab, to
confine the cocoa in the act of trituration. C is the hopper of the mill
through which the roasted beans are introduced to the action of the
rollers, passing first into the flat vessel D to be thence evenly
distributed. After the cacao has received the first trituration, the
paste is returned upon the slab, in order to be mixed with the proper
quantity of sugar, and vanilla, previously sliced and ground up with a
little hard sugar. When the chocolate is sufficiently worked, and while
it is thin with the heat and trituration, it must be put carefully into
the proper moulds. If introduced too warm, it will be apt to become damp
and dull on the surface; and, if too cold, it will not take the proper
form. It must be previously well kneaded with the hands to ensure the
expulsion of every air bubble.
In Barcelona, chocolate mills on this construction are very common, but
they are turned by a horse-gin set to work in the under story,
corresponding to H in the above figure. The shaft G is, in this case,
extended down through the marble slab, and is surrounded at its centre
with a hoop to prevent the paste coming into contact with it. Each of
these horse-mills turns out about ten pounds of fine chocolate in the
hour, from a slab two feet seven inches in diameter.
Chocolate is flavoured with cinnamon and cloves, in several countries,
instead of the more expensive vanilla. In roasting the beans the heat
should be at first very slow, to give time to the humidity to escape; a
quick fire hardens the surface, and injures the process. In putting the
paste into the tin plate, or other moulds, it must be well shaken down
to insure its filling up all the cavities, and giving the sharp and
polished impression so much admired by connoisseurs. Chocolate is
sometimes adulterated with starch; in which case it will form a pasty
consistenced mass when treated with boiling water. The harder the slab
upon which the beans are triturated, the better; and hence porphyry is
far preferable to marble. The grinding rollers of the mill should be
made of iron, and kept very clean.
CHROMATES, saline compounds of chromic acid with the bases. See
CHROMIUM.
CHROMIC ACID; see CHROMIUM.
CHROMIUM. The only ore of this metal, which occurs in sufficient
abundance for the purposes of art, is the octohedral chrome-ore,
commonly called chromate of iron, though it is rather a compound of the
oxides of chromium and iron. The fracture of this mineral is uneven; its
lustre imperfect metallic; its colour between iron-black and
brownish-black, and its streak brown. Its specific gravity, in the
purest state, rises to 4·5; but the usual chrome-ore found in the market
varies from 3 to 4. According to Klaproth, this ore consists of oxide of
chromium, 43; protoxide of iron, 34·7; alumina, 20·3; and silica, 2; but
Vauquelin’s analysis of another specimen gave as above, respectively,
55·5, 33, 6, and 2. It is infusible before the blowpipe; but it acts
upon the magnetic needle, after having been exposed to the reducing
smoky flame. It is entirely soluble in borax, at a high blowpipe heat,
and imparts to it a beautiful green colour.
Chrome-ore is found at the Bare Hills, near Baltimore, in Maryland; in
the Shetland isles, Unst and Fetlar; the department of Var, in France,
in small quantity; and near Portsoy, in Banffshire; as also in Silesia
and Bohemia.
The chief application of this ore is to the production of chromate of
potash, from which salt the various other preparations of this metal
used in the arts are obtained. The ore, freed, as well as possible, from
its gangue, is reduced to a fine powder, by being ground in a mill under
ponderous edge-wheels, and sifted. It is then mixed with one third or
one half its weight of coarsely bruised nitre, and exposed to a powerful
heat, for several hours, on a reverberatory hearth, where it is stirred
about occasionally. In the large manufactories of this country, the
ignition of the above mixture in pots is laid aside, as too operose and
expensive. The calcined matter is raked out, and lixiviated with water.
The bright yellow solution is then evaporated briskly, and the chromate
of potash falls down in the form of a granular salt, which is lifted out
from time to time from the bottom with a large ladle, perforated with
small holes, and thrown into a draining-box. This saline powder may be
formed into regular crystals of neutral chromate of potash, by solution
in water and slow evaporation; or it may be converted into a more
beautiful crystalline body, the bichromate of potash, by treating its
concentrated solution with nitric, muriatic, sulphuric, or acetic acid,
or, indeed, any acid exercising a stronger affinity for the second atom
of the potash than the chromic acid does.
Bichromate of potash, by evaporation of the above solution, and slow
cooling, may be obtained in the form of square tables, with bevelled
edges, or flat four-sided prisms. They are permanent in the air, have a
metallic and bitter taste, and dissolve in about one tenth of their
weight of water, at 60° F.; but in one half of their weight of boiling
water. They consist of chromic acid 13, potash 6; or, in 100 parts, 68·4
+ 31·6. This salt is much employed in calico-printing and in dyeing;
which see.
Chromate of lead, the chrome-yellow of the painter, is a rich pigment of
various shades, from deep orange to the palest canary yellow. It is made
by adding a limpid solution of the neutral chromate (the above granular
salt), to a solution, equally limpid, of acetate or nitrate of lead. A
precipitate falls, which must be well washed, and carefully dried out of
the reach of any sulphuretted vapours. A lighter shade of yellow is
obtained by mixing some solution of alum, or sulphuric acid, with the
chromate, before pouring it into the solution of lead; and an orange
tint is to be procured by the addition of subacetate of lead, in any
desired proportion.
For the production of chromate of potash from chrome ore, various other
processes have been recommended. The following formulæ, which have been
verified in practice, will prove useful to the manufacturers of this
important article:--
I. Two parts of chrome ore, containing about 50 per cent. of
protoxide of chromium:
One part of saltpetre.
II. Four parts of chrome ore, containing 34 per cent. of protoxide of
chromium.
Two parts of potashes.
One part of saltpetre.
III. Four parts of chrome ore, -- 34 --
Two of potashes.
Four tenths of a part of peroxide of manganese.
IV. Three parts of chrome ore.
Four parts of saltpetre.
Two parts of argal.
Some manufacturers have contrived to effect the conversion of the oxide
into an acid, and of course to form the chromate of potash, by the
agency of potash alone, in a calcining furnace, or in earthen pots fired
in a pottery kiln.
After lixiviating the calcined mixtures with water, if the solution be a
tolerably pure chromate of potash, its value may be inferred, from its
specific gravity, by the following table:--
At specific gravity 1·28 it contains about 50 per cent. of the salt.
1·21 33
1·18 25
1·15 20
1·12 16
1·11 14
1·10 12
In making the red bichromate of potash from these solutions of the
yellow salt, nitric acid was at first chiefly used; but, in consequence
of its relatively high price, sulphuric, muriatic or acetic acid has
been frequently substituted upon the great scale.
There is another application of chrome which merits some notice here;
that of its green oxide to dyeing and painting on porcelain. This oxide
may be prepared by decomposing, with heat, the chromate of mercury, a
salt made by adding to nitrate of protoxide of mercury, chromate of
potash, in equivalent proportions. This chromate has a fine cinnabar
red, when pure; and, at a dull red heat, parts with a portion of its
oxygen and its mercurial oxide. From M. Dulong’s experiments it would
appear, that the purest chromate of mercury is not the best adapted for
preparing the oxide of chrome to be used in porcelain painting. He
thinks it ought to contain a little oxide of manganese and chromate of
potash, to afford a green colour of a fine tint, especially for pieces
that are to receive a powerful heat. Pure oxide of chrome preserves its
colour well enough in a muffle furnace; but, under a stronger fire, it
takes a dead-leaf colour.
The green oxide of chrome has come so extensively into use as an enamel
colour for porcelain, that a fuller account of the best modes of
manufacturing it must prove acceptable to many of my readers.
That oxide, in combination with water, called the hydrate, may be
economically prepared by boiling chromate of potash, dissolved in water,
with half its weight of flowers of sulphur, till the resulting green
precipitate ceases to increase, which may be easily ascertained by
filtering a little of the mixture. The addition of some potash
accelerates the operation. This consists in combining the sulphur with
the oxygen of the chromic acid, so as to form sulphuric acid, which
unites with the potash of the chromate into sulphate of potash, while
the chrome oxide becomes a hydrate. An extra quantity of potash
facilitates the deoxidizement of the chromic acid by the formation of
hyposulphite and sulphuret of potash, both of which have a strong
attraction for oxygen. For this purpose the clear lixivium of the
chromate of potash is sufficiently pure, though it should hold some
alumina and silica in solution, as it generally does. The hydrate may be
freed from particles of sulphur by heating dilute sulphuric acid upon
it, which dissolves it; after which it may be precipitated, in the state
of a carbonate, by carbonate of potash, not added in excess.
By calcining a mixture of bichromate of potash and sulphur in a
crucible, chromic acid is also decomposed, and a hydrated oxide may be
obtained; the sulphur being partly converted into sulphuret of
potassium, and partly into sulphuric acid (at the expense of the chromic
acid), which combines with the rest of the potash into a sulphate. By
careful lixiviation, these two new compounds may be washed away, and the
chrome green may be freed from the remaining sulphur, by a slight heat.
Liebig and Wöhler have lately contrived a process for producing a
subchromate of lead of a beautiful vermillion hue. Into saltpetre,
brought to fusion in a crucible at a gentle heat, pure chrome yellow is
to be thrown by small portions at a time. A strong ebullition takes
place at each addition, and the mass becomes black, and continues so
while it is hot. The chrome yellow is to be added till little of the
saltpetre remains undecomposed, care being taken not to overheat the
crucible, lest the colour of the mixture should become brown. Having
allowed it to settle for a few minutes, during which the dense basic
salt falls to the bottom, the fluid part, consisting of chromate of
potash and saltpetre, is to be poured off, and it can be employed again
in preparing chrome yellow. The mass remaining in the crucible is to be
washed with water, and the chrome red being separated from the other
matters, is to be dried after proper edulcoration. It is essential for
the beauty of the colour, that the saline solution should not stand long
over the red powder, because the colour is thus apt to become of a dull
orange hue. The fine crystalline powder subsides so quickly to the
bottom after every ablution, that the above precaution may be easily
observed.
As _Chromic Acid_ will probably ere long become an object of interest to
the calico printer, I shall describe here the best method of preparing
it. To 100 parts of yellow chromate of potash, add 136 of nitrate of
barytes, each in solution. A precipitate of the yellow chromate of
barytes falls, which being washed and dried would amount to 130 parts.
But while still moist it is to be dissolved in water by the intervention
of a little nitric acid, and then decomposed by the addition of the
requisite quantity of sulphuric acid, whereby the barytes is separated,
and the chromic acid remains associated with the nitric acid, from which
it can be freed by evaporation to dryness. On re-dissolving the chromic
acid residuum in water, filtering and evaporating to a proper degree, 50
parts of chromic acid may be obtained in crystals.
This acid may also be obtained from chromate of lime, formed by mixing
chromate of potash and muriate of lime; washing the insoluble chromate
of lime which precipitates, and decomposing it by the equivalent
quantity of oxalic acid, or for ordinary purposes even sulphuric acid
may be employed.
Chromic acid is obtained in quadrangular crystals, of a deep red colour;
it has a very acrid and styptic taste. It reddens powerfully litmus
paper. It is deliquescent in the air. When heated to redness, it emits
oxygen and passes into the deutoxide. When a little of it is fused along
with vitreous borax, the compound assumes an emerald green colour.
As chromic acid parts with its last dose of oxygen very easily, it is
capable in certain styles of calico printing of becoming a valuable
substitute for chlorine where this more powerful substance would not
from peculiar circumstances be admissible. For this ingenious
application, the arts are indebted to that truly scientific
manufacturer, M. Daniel Kœchlin, of Mulhouse. He discovered that
whenever chromate of potash has its acid set free by its being mixed
with tartaric or oxalic acid, or a neutral vegetable substance, (starch
or sugar for example), and a mineral acid, a very lively action is
produced, with disengagement of heat, and of several gases. The result
of this decomposition is the active reagent, chromic acid, possessing
valuable properties to the printer. Watery solutions of chromate of
potash and tartaric acid being mixed, an effervescence is produced which
has the power of destroying vegetable colours. But this power lasts no
longer than the effervescence. The mineral acids react upon the chromate
of potash only when vegetable colouring matter, gum, starch, or a
vegetable acid are present, to determine the disengagement of gas.
During this curious change carbonic acid is evolved; and when it takes
place in a retort, there is condensed in the receiver a colourless
liquid, slightly acid, exhaling somewhat of the smell of vinegar, and
containing a little empyreumatic oil. This liquid heated with the
nitrates of mercury or silver reduces these metals. On these principles
M. Kœchlin discharged indigo blue by passing the cloth through a
solution of chromate of potash, and printing nitric acid thickened with
gum upon certain spots. It is probable that the employment of chromic
acid would supersede the necessity of having recourse in many cases to
the more corrosive chlorine.
The following directions have been given for the preparation of a _blue
oxide_ of chrome. The concentrated alkaline solution of chromate of
potash is to be saturated with weak sulphuric acid, and then to every 8
lbs. is to be added 1 lb. of common salt, and half-a-pound of
concentrated sulphuric acid; the liquid will now acquire a green colour.
To be certain that the yellow colour is totally destroyed, a small
quantity of the liquor is to have potash added to it, and filtered; if
the fluid is still yellow, a fresh portion of salt and of sulphuric acid
is to be added: the fluid is then to be evaporated to dryness,
redissolved, and filtered; the oxide of chrome is finally to be
precipitated by caustic potash. It will be of a greenish-blue colour,
and being washed, must be collected upon a filter.
_Chromate of Potash, adulteration of, to detect._ The chromate of potash
has the power of combining with other salts up to a certain extent
without any very sensible change in its form and appearance; and hence
it has been sent into the market falsified by very considerable
quantities of sulphate and muriate of potash, the presence of which has
often escaped observation, to the great loss of the dyers who use it so
extensively. The following test process has been devised by M. Zuber, of
Mulhouse. Add a large excess of tartaric acid to the chromate in
question, which will decompose it, and produce in a few minutes a deep
amethyst colour. The supernatant liquor will, if the chromate be pure,
afford now no precipitate with the nitrates of barytes or silver; whence
the absence of the sulphates and muriates may be inferred. We must,
however, use dilute solutions of the chromate and acid, lest bitartrate
of potash be precipitated, which will take place if less than 60 parts
of water be employed. Nor must we test the liquid till the
decomposition be complete, and till the colour verge rather towards the
green than the yellow. Eight parts of tartaric acid should be added to
one of chromate to obtain a sure and rapid result. If nitrate of potash
(saltpetre) is the adulterating ingredient, it may be detected by
throwing it on burning coals, when deflagration will ensue. The green
colour is a certain mark of the transformation of the chromic acid
partially into the chrome oxide; which is effected equally by the
sulphurous acid and sulphuretted hydrogen. Here this metallic acid is
disoxygenated by the tartaric, as has been long known. The tests which I
should prefer, are the nitrates of silver and baryta, having previously
added so much nitric acid to the solution of the suspected chromate, as
to prevent the precipitation of the chromate of silver or baryta. The
smallest adulteration by sulphates or muriates will thus be detected.
CINNABAR; the native red sulphuret of mercury. It occurs sometimes
crystallized in rhomboids; has a specific gravity varying from 6·7 to
8·2; a flat conchoidal fracture; is fine grained; opaque; has an
adamantine lustre, and a colour passing from cochineal to ruby red. The
fibrous and earthy cinnabar has a scarlet hue. It is met with
disseminated in smaller or larger lumps in veins, which are surrounded
by a black clay, and is associated with native quicksilver, amalgam with
iron-ore, lead-glance, blende, copper-ore, gold, &c. Its principal
localities are Almaden in Spain, Idria in the Schiefergebirge, Kremnitz
and Schemnitz in Hungary; in Saxony, Bavaria, Bohemia, Nassau, China,
Japan, Mexico, Columbia, Peru. It consists of two primes of sulphur, =
32·240, combined with one of mercury, = 202,863; or in 100 parts of 12·7
sulphur + 87·3 mercury. It is the most prolific ore of this metal; and
is easily smelted by exposing a mixture of it with iron or lime to a red
heat in retorts. Factitious cinnabar is called in commerce VERMILLION,
which see, as also MERCURY.
CINNAMON. (_Cannelle_, Fr.; _Zimmt_, Germ.) Is the inner bark of the
_laurus cinnamomum_, a handsome-looking tree, which grows naturally to
the height of 18 or 20 feet, in Java, Sumatra, Ceylon, and other islands
in the East Indian seas. It has been transplanted to the Antilles,
particularly Guadaloupe and Martinique, as well as Cayenne, but there it
produces a bark of very inferior value to the Oriental.
Cinnamon is gathered twice a year, but not till after the tree has
attained to a certain age and maturity. The young twigs yield a bark of
better quality than the larger branches. The first and chief harvest
takes place from April to August; the second, from November to January.
After having selected the proper trees, all the branches more than three
years old are cut off; the epidermis is first removed with a two-edged
pruning knife, then a longitudinal incision is made through the whole
extent of the bark, and lastly, with the bluntest part of the knife, the
true bark is carefully stripped off in one piece. All these pieces of
bark are collected, the smaller ones are laid within the larger, and in
this state they are exposed to the sun, whereby in the progress of
drying, they become rolled into the shape of a quill. These convoluted
pieces are formed into oblong bundles of 20 or 30 lbs. weight, which are
placed in warehouses, sorted and covered with mats. Good cinnamon should
be as thin as paper, have its peculiar aromatic taste, without burning
the tongue, and leave a sweetish flavour in the mouth. The broken bits
of cinnamon are used in Ceylon for procuring the essential oil by
distillation. 445,367 lbs. of cinnamon were imported into this kingdom
in 1835, of which 16,604 only were retained for internal consumption.
CITRIC ACID. (_Acide citrique_, Fr.; _Citronensäure_, Germ.) Scheele
first procured this acid in its pure state from lemon juice, by the
following process. The juice put into a large tub, is to be saturated
with dry chalk in fine powder, noting carefully the quantity employed.
The citrate of lime which precipitates being freed from the supernatant
foul liquor, is to be well washed with repeated affusion and decantation
of water. For every 10 pounds of chalk employed, nine and a half pounds
of sulphuric acid, diluted with six times its weight of water, are to be
poured while warm upon the citrate of lime, and well mixed with it. At
the end of twelve hours, or even sooner, the citrate will be all
decomposed, dilute citric acid will float above, and sulphate of lime
will be found at the bottom. The acid being drawn off, the calcareous
sulphate must be thrown on a canvass filter, drained, and then washed
with water to abstract the whole acid.
The citric acid thus obtained may be evaporated in leaden pans, over a
naked fire till it acquires the specific gravity 1·13; after which it
must be transferred into another vessel, evaporated by a steam or water
bath till it assumes a syrupy aspect, when a pellicle appears first in
patches, and then over the whole surface. This point must be watched
with great circumspection, for if it be passed, the whole acid runs a
risk of being spoiled by carbonization. The steam or hot water must be
instantly withdrawn, and the concentrated acid put into a crystallizing
vessel in a dry, but not very cold apartment. At the end of four days,
the crystallization will be complete. The crystals must be drained,
re-dissolved in a small portion of water, the solution set aside to
settle its impurities, then decanted, re-evaporated, and
re-crystallized. A third or fourth crystallization may be necessary to
obtain a colourless acid.
If any citrate of lime be left undecomposed by the sulphuric acid, it
will dissolve in the citric acid, and obstruct its crystallization, and
hence it will be safer to use the slightest excess of sulphuric acid,
than to leave any citrate undecomposed. There should not however be any
great excess of sulphuric acid. If there be, it is easily detected by
nitrate of barytes, but not by the acetate of lead as prescribed by some
chemical authors; because the citrate of lead is not very soluble in the
nitric acid, and might thus be confounded with the sulphate, whereas
citrate of barytes is perfectly soluble in that test acid. Sometimes a
little nitric acid is added with advantage to the solution of the
coloured crystals, with the effect of whitening them.
Twenty gallons of good lemon juice will afford fully ten pounds of white
crystals of citric acid.
Attempts were made both in the West Indies and Sicily, to convert the
lime and lemon juice into citrate of lime, but they seem to have failed
through the difficulty of drying the citrate for shipment.
The crystals of citric acid are oblique prisms with four faces,
terminated by dihedral summits, inclined at acute angles. Their specific
gravity is 1·617. They are unalterable in the air. When heated, they
melt in their water of crystallization; and at a higher heat, they are
decomposed. They contain 18 per cent. of water, of which one half may be
separated in a dry atmosphere, at about 100° F., when the crystals fall
into a white powder.
Citric acid in crystals is composed by my analysis of carbon, 35·8,
oxygen 59·7, and hydrogen 45; results which differ very little from
those of Dr. Prout, subsequently obtained. I found its atomic weight to
be 8·375, compared to oxygen 1,000. I cannot account for Berzelius’s
statements relative to the composition of this acid.
Citric acid in somewhat crude crystals is employed with much advantage
in calico-printing. If adulterated with tartaric acid, the fraud may be
detected by adding potash to the solution of the acid, which will
occasion a precipitate of cream of tartar.
CIVET. (_Civette_, Fr.; _Zibeth_, Germ.) This substance approaches in
smell to musk and ambergris; it has a pale yellow colour, a somewhat
acrid taste, a consistence like that of honey, and a very strong
aromatic odour. It is the product of two small quadrupeds of the genus
_viverra_ (_v. zibetha_ and _v. civetta_), of which the one inhabits
Africa, the other Asia. They are reared with tenderness, especially in
Abyssinia. The civet is contained in a sac, situated between the anus
and the parts of generation, in either sex. The animal frees itself from
an excess of this secretion by a contractile movement which it exercises
upon the sac, when the civet issues in a vermicular form, and is
carefully collected. The negroes are accustomed to increase the
secretion by irritating the animal; and likewise introduce a little
butter, or other grease, by the natural slit in the bag, which mixes
with the odoriferous substance, and increases its weight. It is employed
only in perfumery.
According to M. Boutron-Chalard, it contains a volatile oil, to which it
owes its smell, some free ammonia, resin, fat, an extractiform matter,
and mucus. It affords, by calcination, an ash, in which there are some
carbonate and sulphate of potash, phosphate of lime, and oxide of iron.
CLAY (_Argile_, Fr.; _Thon_, Germ.) is a mixture of the two simple
earths, alumina and silica, generally tinged with iron. Lime, magnesia,
with some other colouring metallic oxides, are occasionally present in
small quantities in certain natural clays.
The different varieties of clay possess the following common
characters:--
1. They are readily diffusible through water, and are capable of forming
with it a plastic ductile mass, which may be kneaded by hand into any
shape. This plasticity exists, however, in very different degrees in the
different clays.
2. They concrete into a hard mass upon being dried, and assume, upon
exposure to the heat of ignition, a degree of hardness sometimes so
great as to give sparks by collision with hardened steel. In this state
they are no longer plastic with water, even when pulverised. Tolerably
pure clays, though infusible in the furnace, become readily so by the
admixture of lime, iron, manganese, &c.
3. All clays, even when previously freed from moisture, shrink in the
fire in virtue of the reciprocal affinity of their particles; they are
very absorbent of water in their dry state, and adhere strongly to the
tongue.
4. Ochrey, impure clays emit a disagreeable earthy smell when breathed
upon.