M O D 
M O L 
face is tlicn to be first covered with fine fluid 
plaster, beginning at the upper part of the 
forehead, and spreading it over the eyes, 
which are to be kept close, that the plaster ; 
may not come in contact with the glebe ; yet. j 
not closed so strongly as to cause any uuna- | 
tural wrinkles. Cover then the nose and 
ears, plugging first up the meatus auditorii 
With cotton, and the nostrils with a small 
quantity of tow rolled up, of a proper size to 
exclude the plaster. During the time that 
the nose is thus stopped, the person is to 
breathe through the mouth: in this state the 
fluid plaster is to be brought down low 
enough to cover the upper lip, observing to 
leave the rolls of tow projecting out of the 
plaster. When the operation is thus far car- 
ried on, the plaster must be suffered to hard- 
en ; after which the tow may be withdrawn, 
and the nostrils left free and open for breath- 
ing. The mouth is then to be closed in its 
natural position, and the plaster brought 
down to the extremity of the chin. Begin 
then to cover that part of the breast which 
is to be represented, and spread the plaster 
to the outsides of the arms and upwards, in 
such a manner as to meet and join that which 
i; previously laid on the face: when the 
whole of the mass has acquired its due hard- 
ness, it is to be cautiously lifted, without 
breaking or giving pain to the person. After 
the mould is constructed, it must be sea- 
soned iii the manner already directed ; and 
when tire mould is cast, it is to be separated 
from the model by means of a small mallet 
and chisel. The eyes, which are necessarily 
.shown closed, are to be carved, so that the 
eye-lids may be represented in an elevated 
{ josture; the nostrils hollowed out, and the 
rack part of the head, from which, on ac- 
count of the hair, no mould can be taken, 
must be finished according to the skill of the 
artist. The edges of the model are then to 
be neatly smoothed off, and the bust fixed on 
its pedestal. 
MODULATION, in music, the art of 
conducting harmony, in composition, or ex- 
temporary performance, through those keys 
and modes which have a due relation to the 
fundamental, or original key- Though 
every piece, as is well known, has its princi- 
pal or governing key, yet, for the sake of 
contrast and relief, it is not only allowable 
but necessary to pass from key to key, and 
from mode to mode; to assume different 
sharps or flats, and lead the ear through 
those transitions of tone and harmony which 
interest the feelings and delight the ear. 
But though in grand compositions there is no 
quality of a greater importance than that of 
a masterly modulation, it is not easy to lay 
down rules for its accomplishment. Some- 
times a gradual and almost insensible evolu- 
tion of harmony is requisite to the composer’s 
object; at other times, a bol l and sudden 
change can alone produce the necessary 
effect. 
MODULE. See Architecture. 
MODUS DECIMANDI, in law, is 
where money, land, or other valuable con- 
sideration, has been given, timeout of mind, 
to the minister or parson of any certain 
place, in the room of tithes. A clergyman 
may sue in a spiritual court for a modus de- 
ciniundi ; yet if the modus is denied there, 
or a custom is to be tried, the trial thereof 
Belongs to the courts of common law. When 
MOL 
lands are converted to other uses, as in the 
case of hay-ground turned into tillage, the 
modus may be discharged, and the tithes 
paid again in kind. 
MOERH1NGIA, mossy chickweed, in 
botany, a genus of the octandria digynia class 
of plants, the flower of which is composed of 
four short, undivided petals ; and its fruit is a 
subglobose capsule, with one cell, in which 
are contained numerous roundish seeds. 
There is one species. 
MOLE. See Zalpa. 
MOLLUGO, African chickweed; a ge- 
nus of the tryginia order, in the triandria 
class of plants; and in the natural method 
ranking under the 22il order, caryophyllei. 
The calyx is pentnphyllous; there is no co- 
rolla; the capsule is trilocular, and trivalved. 
There are six species, annuals of the Gape, 
and of the E. and \V. Indies. 
MOLUCCELLA, in botany, a genus of 
the didynamia-gymnospermia class of plants, 
the flower of which ismonopetalous and labi- 
ated; the upper lip being entire, and the 
lower one trilid : the seeds are turbinated, 
and contained in the bottom of the cup. 
One annual species. 
M Q LY BD ATS . These salts, composed 
of molybdic acid combined with the alkalies 
and earths, were formed by Scheele; but 
their properties are still almost completely 
unknown. The supermolybdat of potass 
alone has been described with some detail. It 
is formed by detonating one part of sulphu- 
ret of molybdenum and three parts of nitre 
in a crucible. By dissolving the reddish 
mass which remains after this operation, and 
filtering, a solution of sulphat of potass and 
molybdat of potass is obtained. By evapo- 
rating the solution, the sulphat of potass is 
separated; when sulphuric acid isdroptinto 
the remaining liquid, supermolybdat of po- 
tass is precipitated. This salt is soluble in 
water. Its solution chrystallizes by evapora- 
tion in small rhomboida'l plates inserted into 
each other. They are bright, and have a 
metallic taste. When exposed to the blow- 
pipe upon charcoal, they melt without swell- 
ing, and are converted into situ globules, 
which are quickly absorbed by the charcoal. 
When melted with a mixture of phosphat of 
soda and of ammonia (or microcosmic salt), 
they communicate a green tinge. Hot wa- 
ter dissolves them completely, and prussiat 
of potass occasions in this solution a reddish 
brown precipitate. When a solution of mu- 
riat of tin is poured upon them, they acquire 
a blue colour. 
MOLYBDENUM. The Greek word 
/«.oXt>0§cc(vix, and its Latin translation plum- 
bago, seem to have been employed by the 
antients to denote various oxides of lead; but 
by trie moderns they were applied indiscri- 
minately to all substances possessed of the 
following properties: light, friable, and soft, 
of a -dark colour and greasy feel, and which 
leave a stain upon the lingers. Scheele first 
examined these minerals with attention. He 
found that two very different substances had 
been confounded together. To one of these, 
which is composed of carbon and iron, he 
appropriated the word plumbago ; the other 
he called molybdena. 
Molybdena is composed of scaly particles 
adhering slightly to each other. Its colour 
is blucish, very much resembling that of lead. 
E e 2 
21 if 1 
Scheele analysed it in 1778, and obtained 
sulphur and a whitish powder, which pos- 
sessed the properties of an acid, and which, 
therefore, he called add of molybdena. 
Bergman suspected this acid, from its pro- 
perties, to be a metallic oxide; and at his 
request, iiielm, in 1782, undertook tire la- 
boiious course ©f experiments by which he 
succeeded in obtaining a metal from this 
acid. His method ’was to form it into a 
paste with linseed oil, and then to apply a 
very strong heat. This process he repeated 
several times successively. To the metal 
which he obtained he gave the name of mo- 
lybdenum. The experiments of Scheele 
were afterwards repeated by Pelletier, Ilse- 
' man, and Ileyer; and not only fully con- 
firmed, but discovered many new facts, and 
the metallic nature of moiybdic acid was put 
beyond a doubt: though, in consequence of 
the very violent heat necessary to fuse mo- 
lybdenum, only very minute grains of it have 
been hitherto obtained in the state of a me- 
tal. Still more lately, Mr. Hatchett has pub- 
lished a very valuable set of experiments, 
which throw much new light upon the nature 
of this metal. 
Molybdenum is externally of a whitish* 
yellow colour, but its fracture is a whitish 
grey. Hitherto it lias only been procured i* 
small grains, agglutinated together in brittle 
masses. Its specific gravity is 7.500. It is 
almost infusible in our fires. 
When exposed to heat in an open vessel, 
it gradually combines with oxygen, and is 
converted into a white oxide, which is vola- 
tilized in small brilliant needle-form crystals. 
This oxide, having the properties of an acid, 
is known by the name of molybdic acid. 
From the experiments of Mr. Hatchet, it 
follows that molybdenum is capable of com- 
bining with four different proportions of ox\ - 
gen, and of forming four oxides; namely, 1. 
'The black; 2. The blue; 3. The green, to 
which Mr. Hatchet has given the name of 
molybdous acid; and, 4. The yellow or 
white, or the molybdic acid. 
1. The protoxide, or black oxide, may be 
obtained by mixing molybdic acid with 
charcoal powder in a crucible, and applying 
heat. A black mass remains, which is the 
black oxide. It seems to contain only a very 
minute quantity of oxygen, 
2. The blue oxide may be obtained by 
the same process not carried so far: it is 
formed also whenever a plate of tin is 
plunged into a solution of molybdic acid. 
3. The peroxide, or molybdic acid, is 
obtained by distilling six parts of diluted ni- 
tric acid repeatedly off native molymbdena 
m powder. A white mass is left behind, 
composed of sulphuric and molybdic acids. 
A little pure water washes away the sul- 
phuric acid, anil molybdic acid remains be- 
hind. This acid has at first a white colour ; 
but when melted and sublimed, it becomes 
yellow. 
Molybdenum combines readily with sul- 
phur; and the compound has exactly the 
properties of molybdena, the substance which 
Scheele decompounded. Molymbdena is 
therefore sulphuret of molybdenum. The 
reason that Scheeie obtained from it mo- 
lybdic acid was, that the melal combined 
with oxygen during his process. Sulphuret 
of molybdenum may be formed also by dis- 
