_Ores of manganese._--There are two principal ores of this metal which
occur in great masses; the peroxide and the hydrated oxide; the first of
which is frequently found in primitive formations.
1. _Metalloide oxide of manganese_; _pyrolusite_, or gray manganese ore;
has a metallic lustre, a steel gray colour, and affords a black powder.
Spec. grav. 4·85. Scratches calc-spar. It effervesces briskly with borax
at the blow-pipe, in consequence of the disengagement of oxygen gas.
This is the most common ore of manganese, and a very valuable one, being
the substance mostly employed in the manufacture of chloride of lime and
of flint-glass. It is the peroxide. Great quantities are found near
Tavistock, in Devonshire, and Launceston, in Cornwall.
2. _Braunite_, is a dark brown substance, of a glassy metallic lustre,
affording a brown powder. Spec. grav. 4·8. It scratches felspar; but is
scratched by quartz. Infusible at the blow-pipe, and effervesces but
slightly when fused with glass of borax. It is the deutoxide. It gives
out at a red heat only 3 per cent. of oxygen.
3. _Manganite_, or hydroxide of manganese; is brownish-black or
iron-black, powder brown, with somewhat of a metallic lustre. Spec.
grav. 4·3. Scratches fluor spar; affords water by calcination in a glass
tube; infusible at the blow-pipe; and effervesces slightly when fused
with glass of borax. It consists of about 90 of deutoxide, and 10 of
water.
4. _Haussmanite_, _black braunstein_; is brownish-black, affords a
reddish-brown powder. Spec. grav. 4·7; scratches fluor spar; infusible
at the blow-pipe; does not effervesce when fused with borax. It is a
deutoxide. This is a rare mineral, and of no value to the arts.
5. _Barytic oxide of manganese_; _fibrous wad_. It is a combination of
deutoxide and peroxide, with some baryta.
6. _Manganese blende_, or sulphuret of manganese; has a metallic aspect;
is black, or dark steel gray; spec. grav. 3·95; has no cleavage; cannot
be cut; infusible, but affords after being roasted distinct evidence of
manganese, by giving a violet tinge to soda at the blow-pipe. Soluble in
nitric acid; solution yields a white precipitate with the ferro-cyanide
of potassium. It consists of sulphur 53·65; manganese 66·35.
7. _Carbonate of manganese_; _dialogite_. Spec. grav. 3·4; affords a
green frit by fusion with carbonate of soda; is soluble with some
effervescence in nitric acid; solution when freed from iron by succinate
of ammonia, gives a white precipitate, with ferrocyanide of potassium.
It consists of 28 carbonic acid, 56 protoxide of manganese, 5·4 of lime,
4·5 protoxide of iron, and 0·8 magnesia.
8. _Hydrosilicate of manganese_; is a black metallic looking substance,
which yields a yellowish-brown powder, and water by calcination; is
acted upon by muriatic acid, but affords no chlorine. It consists of
silica 25; protoxide of manganese 60; water 13.
9. _Ferriferous phosphate of manganese_, is brown or black. Spec. grav.
3·6; scratches fluor; affords by calcination a very little of an acid
water which corrodes glass; very fusible at the blow-pipe into a black
metalloid magnetic bead; is acted upon by nitric acid: solution lets
fall a blue precipitate with ferrocyanide of potassium; which tested by
soda is shown to be manganese. It consists of phosphoric acid 32·78;
protoxide of iron 31·90; protoxide of manganese 32·60; phosphate of lime
3·2. Another phosphate called _hureaulite_, contains 38 of phosphoric
acid; 11·10 of protoxide of iron; 32·85 of protoxide of manganese, and
18 of water.
_Black wad_, is the old English name of the hydrated peroxide of
manganese. It occurs in various imitative shapes, in froth-like coatings
upon other minerals, as also massive. Some varieties possess imperfect
metallic lustre. The external colour is brown of various shades, and
similar in the streak, only shining. It is opaque, very sectile, soils
and writes. Its specific gravity is about 3·7. Mixed with linseed oil
into a dough, black wad forms a mass that spontaneously inflames. A
variety from the Hartz, analyzed by Klaproth, afforded peroxide of
manganese 68; oxide of iron 6·5; water 17·5; carbon 1; barytes and
silica 9. The localities of black wad are particularly Cornwall and
Devonshire, the Hartz, and Piedmont. I have analyzed many varieties of
the black wad sold to the manufacturers of bleaching salt, and flint
glass, and have found few of them so rich in peroxide of manganese as
the above. Very generally they contained no less than 25 _per cent._ of
oxide of iron, 8 or 9 of silica, about 7 of water, and the remainder
amounting to only 60 _per cent._ of the peroxide.
M. Gay Lussac has proposed to determine the commercial value of
manganese ore, by the quantity of chlorine which it affords when treated
with liquid muriatic acid. He places the manganese powder in a small
retort or matras, pours over it the acid, and the chlorine being
disengaged with the aid of a gentle heat, is transmitted into a vessel
containing milk of lime or potash water. This liquor is thereafter
poured into a dilute solution of sulphate of indigo; and the quantity
of chlorine is inferred from the quantity of the blue solution which is
decoloured. I pass the chlorine into test solution of indigo.
The manufacturer of flint glass uses a small proportion of the black
manganese ore, to correct the green tinge which his glass is apt to
derive from the iron present in the sand he employs. To him it is of
great consequence to get a native manganese containing as little iron
oxide as possible; since in fact the colour or limpidity of his product
will depend altogether upon that circumstance.
Sulphate of manganese has been of late years introduced into calico
printing, to give a chocolate or bronze impression. It is easily formed
by heating the black oxide, mixed with a little ground coal, with
sulphuric acid. See CALICO PRINTING.
The peroxide of manganese is used also in the formation of glass pastes,
and in making the black enamel of pottery. See OXALIC ACID.
MANGLE. (_Calandre_, Fr.; _Mangel_, Germ.) This is a well known machine
for smoothing table cloths, table napkins, as well as linen and cotton
furniture. As usually made, it consists of an oblong rectangular wooden
chest, filled with stones, which load it to the degree of pressure that
it should exercise upon the two cylinders on which it rests, and which,
by rolling backwards and forwards over the linen spread upon a polished
table underneath, render it smooth and level. The moving wheel, being
furnished with teeth upon both surfaces of its periphery, and having a
notch cut out at one part, allows a pinion, uniformly driven in one
direction, to act alternately upon its outside and inside, so as to
cause the reciprocating motion of the chest. This elegant and much
admired English invention, called the mangle-wheel, has been introduced
with great advantage into the machinery of the textile manufactures.
Mr. Warcup, of Dartford, obtained a patent several years ago for a
mangle, in which the linen, being rolled round a cylinder revolving in
stationary bearings, is pressed downwards by heavy weights hung upon its
axes, against a curved bed, made to slide to and fro, or traverse from
right to left, and left to right, alternately.
Mr. Hubie, of York, patented in June, 1832, another form of mangle,
consisting of three rollers, placed one above another in a vertical
frame, the axle of the upper roller being pressed downwards by a
powerful spring. The articles intended to be smoothed are introduced
into the machine by passing them under the middle roller, which is made
to revolve by means of a fly wheel; the pinion upon whose axis works in
a large toothed wheel fixed to the shaft of the same roller. The linen,
&c. is lapped as usual in protecting cloths. This machine is merely a
small CALENDER.
MANIOC, is the Indian name of the nutritious matter of the shrub
_jatropha manihot_, from which _cassava_ and _tapioca_ are made in the
West Indies.
MANNA, is the concrete saccharine juice of the _Fraxinus ornus_, a tree
much cultivated in Sicily and Calabria. It is now little used, and that
only in medicine.
MARBLE. This title embraces such of the primitive, transition, and purer
compact limestones of secondary formation, as may be quarried in solid
blocks without fissures, and are susceptible of a fine polished surface.
The finer the white, or more beautifully variegated the colours of the
stone, the more valuable, _ceteris paribus_, is the marble. Its general
characters are the following:--
Marble effervesces with acids; affords quicklime by calcination; has a
conchoidal scaly fracture; is translucent only on the very edges; is
easily scratched by the knife; has a spec. grav. of 2·7; admits of being
sawn into slabs; and receives a brilliant polish. These qualities occur
united in only three principal varieties of limestone; in the saccharoid
limestone, so called from its fine granular texture resembling that of
loaf sugar, and which constitutes modern statuary marble, like that of
Carrara; 2. in the foliated limestone, consisting of a multitude of
small facets formed of little plates applied to one another in every
possible direction, constituting the antique statuary marble, like that
of Paros; 3. in many of the transition and carboniferous, or
_encrinitic_ limestones, subordinate to the coal formation.
The saccharoid and lamellar, or statuary marbles, belong entirely to
primitive and transition districts. The greater part of the
close-grained coloured marbles belong also to the same geological
localities; and become so rare in the secondary limestone formations,
that immense tracts of these occur without a single bed sufficiently
entire and compact to constitute a workable marble. The limestone lying
between the calcareo-siliceous sands and gritstone of the under oolite,
and which is called Forest marble in England, being susceptible of a
tolerable polish, and variegated with imbedded shells, has sometimes
been worked into ornamental slabs in Oxfordshire, where it occurs in the
neighbourhood of Whichwood forest; but this case can hardly be
considered as an exception to the general rule. To constitute a
profitable marble-quarry, there must be a large extent of homogeneous
limestone, and a facility of transporting the blocks after they are dug.
On examining these natural advantages of the beds of Carrara marble, we
may readily understand how the statuary marbles discovered in the
Pyrenees, Savoy, Corsica, &c. have never been able to come into
competition with it in the market. In fact, the two sides of the valley
of Carrara may be regarded as mountains of statuary marble of the finest
quality.
Gypseous alabaster may be readily distinguished from marbles, because it
does not effervesce with acids, and is soft enough to be scratched by
the nail; stalagmitic alabaster is somewhat harder than marble,
translucent, and variegated with regular stripes or undulations.
Some granular marbles are flexible in thin slabs, or, at least, become
so by being dried at the fire; which shews, as Dolomieu suspected, that
this property arises from a diminution of the attractive force among the
particles, by the loss of the moisture.
The various tints of ornamental marbles generally proceed from oxides of
iron; but the blue and green tints are sometimes caused by minute
particles of hornblende, as in the slate-blue variety called Turchino,
and in some green marbles of Germany. The black marbles are coloured by
charcoal, mixed occasionally with sulphur and bitumen; when they
constitute stinkstone.
Brard divides marbles, according to their localities, into classes, each
of which contains eight subdivisions:--