PRE 
applies as in the first case. When a neutral 
salt is employed as a precipitant, the sub- 
stance which falls is always a compound. 
It is composed of one of the ingredients of 
the precipitating salt united to one ingre- 
dient of salt in solution. Such salts alone 
can be employed as are known to form in- 
soluble compounds with the acid or base 
which we wish to throw down. In these 
cases the separation is complete, when the 
new salt formed is completely insoluble. 
Neutral salts perform the oflrce of precipi- 
tants in general much more readily and 
completely than pure bases or acids. Thus 
the alkaline carbonates throw down the 
earths much more effectually than the pure 
alkalies, and sulphate of soda separates 
barytes much more rapidly than pure sul- 
phuric acid. This superiority is owing partly 
to the combined action of the acid and base, 
and partly to the comparatively weak action 
of a neutral salt upon the precipitate, when 
compared to that of an acid or alkali. For 
the precipitation takes place, not because 
the salts are insoluble in water, but because 
tliey are insoluble in the particular solution 
in which the precipitate appears. N ow if 
this solution happens to be capable of dis- 
solving any particular salt, tliat salt will not 
precipitate, even though it be insoluble in 
water. Hence the reason why precipitates 
so often disappear, when there is present in 
the solution an excess of acid, of alkali, &c. 
PRECONTRACT of marriage, in the 
civil law, avoided the marriage' ; but by the 
statute 2 George I. c. 23, called the mar- 
riage act, it is declared, that it shall not be 
allowed, nor shall any contract of marriage 
be enforced in the ecclesiastical courts. Tlie 
only remedy upon breach of a promise of 
marriage is by action for damages at com- 
mon law. 
PREDIAL tithes, those which are paid 
of things arising and growing from the 
ground only, as corn, hay, fruit of trees, and 
the like. 
PREENING, in natural history, the ac- 
tion of birds dressing their feathers, to en- 
able them to glide the more readily through 
tlie air, &c. For this purpose they have 
two peculiar glands on their rump, which 
secrete ap unctuous matter into a bag that 
is perforated, out of which the bird occa- 
sionally draws it with its bill. 
PIJEGN AN CY. See Midwifery. 
PREHNITE, in mineralogy, a species 
of the flint genus. Its colours are green in 
almost all its shades. It is sometimes mas- 
sive, sometimes crystallized. Externally 
PRE 
the crystals are smooth and shining; inter- 
nally they have a glistening pearly lustre. 
It is harder than glass, easily frangible : 
specific gravity 2.6 to 2.9. Before the blow- 
pipe it foams, and melts into a brownish 
enamel. This mineral has been compared 
with the zeolite, to which it bears some re- 
semblance ; but it does not, like that, be- 
come gelatinous with acids. According to 
Klaproth it consists of 
Silica 43.83 
Alumina 30.33 
Lime 18.33 
Oxide of iron 5.66 
Water L83 
99.98 
Loss 2 
100.00 
It occurs in Dauphiny, and in many parts of 
Scotland. 
PRELIMINARY, in general, denotes 
something to be examined and determined 
before an affair can be treated of to the 
purpose. The preliminaries of peace con- 
sist chiefly in settling the powers of ambas- 
sadors, and certain points in dispute, which 
must be determined previously to the treaty 
itself. 
PRELUDE, prceludium, in music, is 
usually a flourish or irregular air, which a 
musician plays off-hand, to try if his instru- 
ment be in tune, and so lead him into the 
piece to be played. Very often the whole 
band in the orchestra run a few divisions, 
to give J;he tune. 
PREMISES, in logic, an appellation 
given to the two first propositions of a syl- 
logism, as going before, or preceding the 
conclusion. Premises are the foundation or 
principles of our reasoning; which being 
either self evident or demonstrative propo- 
sitions, the truth of the eonclusion is equally 
evident. 
Premises, in law, from the Latin pre- 
missa (the foregoing), is applied to that 
part in the beginning of a deed which ex- 
presses the names of the grantor and gran- 
tee, and the land or thing granted ; but it 
is chiefly used to signify the thing granted 
only. 
PREMIUM, or PniEMiuivi, properly 
signifies a reward or recompense; but it is 
chiefly used in a mercantile sense for the 
sum of money given to an insurer, whether 
of ships, houses, lives, &c. See Insurance. 
The term premium is also applied to what 
is given for a thing above par, or prime 
