AMM 
rianthinm bell-shaped, oblong, erect, with 
eight streaks and folds, quadrangular, eight- 
toothed, teeth alternate, bent in, and per- 
manent; corolla none, or four-petalled, pe- 
tals vertically ovate, spreading, inserted 
into the calyx ; the stamina have filaments, 
(four or eight) bristly, the length of the 
calyx into which they are inserted, anthers 
twin, the pistillum is a germ subovate, 
large and superior, style simple, very short, 
and stigma headed; the pericarpium is a 
roundish, four- celled capsule (bury) cover- 
ed with the calyx; the seeds are numerous 
and small. 
AMMI, bishop’s weed, in botany, a dis- 
tinct genus of umbelliferous plants, belong- 
ing to the Pentandria Digynia class of Lin- 
naeus ; the flower of which is rosaceous, and 
composed of heart-like petals ; and its fruit 
is a small roundish and striated capsule, 
containing two striated seeds, convex on 
one side, and plane on the other. There 
are four species. 
AMM ODYTES, in natural history, the 
launce, a genus of fishes, of the order Apo- 
des : head compressed, narrower than the 
body: upper-lip doubled: lower jaw nar- 
row, pointed : teeth small and sharp. Gill 
membrane seven rayed : body long, round- 
ish, with very small scales: tail distinct. A. 
tobianus, or sand launce, so named from its 
shape. It inhabits the northern seas ; and 
is from 9 to 12 inches long. It buries itself 
on the recess of the tides a foot deep in the 
sand, and in fine weather rolls itself up and 
lifts its nose just above the sand ; it is the 
prey of other rapacious fish ; the flesh is 
tolerably good, but it is used in most cases 
as baits. The launce lives on worms, water- 
insects, and small fishqs, and even occasion- 
ally on those of its own species. The mac- 
karel is very partial to this fish as its own 
food. The launce spawns jn May, deposit- 
ing its eggs in the mud, near the edges of 
the coast. 
AMMONIA, in chemistry. Volatile al- 
kali, in its purest form, subsists in a state of 
gas, and was thought, till the late experi- 
ments of Mr. Davy, to be composed of azote 
and hydrogen. It may be obtained in 
the following maimer: put into a retort 
a mixture of three parts of quick-lime and 
one part of sal ammoniac in powder. Plunge 
the beak of the retort below the mouth of 
a glass jar filled with mercury, and stand- 
ing inverted in a bason of mercury. Apply 
the heat of a lamp to the retort: a gas 
comes over, which displaces the mercury 
and fills the jar. This gas is ammonia. It 
AMM 
was known by the name of volatile alkali,' 
it was also called hartshorn, because it was 
often obtained by distilling the horn of the 
hart ; spirit of urine, because it may be ob- 
tained by the same process from urine ; and 
spirit of sal ammoniac, because it may be 
obtained from that salt. Dr. Black first 
pointed out the difference between ammo- 
nia and carbonate of ammonia, or ammonia ' 
combined with carbonic acid; and Dr. 
Priestley discovered the method of obtain- 
ing it in a state of purity, by the process 
already described. Ammonia in the state 
of gaslit transparent and colourless like air; 
its taste is acrid and caustic like that of the 
fixed alkalies, but not nearly so strong, nor 
does it like them corrode those animal bo- 
dies to which it is applied : its smell is re- 
markably pungent, though not unpleasant 
when sufficiently diluted. Its use as a sti- 
mulant to prevent fainting is well known. 
Animals cannot breathe it without death. 
When a lighted candle is let down into this 
gas, it goes out three or four times succes- 
sively ; but at each time the flame is consi- 
derably enlarged by the addition of another 
flame of a pale yellow colour, and at last 
this flame descends from the top of the 
vessel to the bottom. Its specific gravity, 
according to the experiments, of Kir wan, 
is 0.60, that of air being 1.00 ; while Mr. 
Davy, whose gas was probably purer, found 
it 0.55. At the temperature of 60°, a hun- 
dred cubic inches of this gas weigh, accord- 
ing to Kirwan, 18.16 grains, according to 
Davy, 17.068. Hence it is to common air, 
nearly as 3 to 5. When exposed to a cold 
of — 45° it is condensed into a liquid, which 
again assumes the gaseous form when the 
temperature is raised. When passed through 
a red hot tube of porcelain or glass, it is 
totally decomposed and converted into hy- 
drogen and azotic gas. It combines very 
rapidly with water. When a bit of ice is 
brought into contact with this gas, it melts 
and absorbs the ammonia, while at the 
same time its temperature is diminished. 
Cold water absorbs this gas almost instan- 
taneously, and at the same time heat is 
evolved, and the specific gravity of the 
water is diminished. Water is capable of 
absorbing and condensing more than a third 
of its weight of ammoniacal gas. It is in 
this state that ammonia is usually employed 
by chemists. Tire term amriionia almost 
always means this liquid solution of ammo- 
nia in water. When heated to the tempe- 
rature of about 130°, the ammonia sepa- 
rates under the form of gas. When exposed 
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