SCH 
By heatinjjf it exhibits positive electricity at 
one end, and negative at tire other : as it 
cools, these electricities are reversed. It 
occurs in primitive rocks, cliiefly in quartz 
and granite ; with the former, it constitutes 
a peculiar mountain rock. It is found on 
many parts of the Continent, and in Scot- 
land. It differs from tourmaline in colour, 
degree of lustre, fracture, transparency, 
and distinct concretions ; also in geonostic 
situation ; tourmaline occurs almost always 
imbedded, and in single crystals ; but schorl 
is aggregated, and occurs in beds. 
Tourmaline, called also electricus tnrma- 
lin, is of a green or brown colour, passing 
into others even to the indigo blue. The 
colours are mostly dark. It occurs very 
seldom massive, oftener in rolled pieces, 
but most frequently crystallized. The crys- 
tals are generally three sided prisms ; tliey 
are usually imbedded ; the internal lustre is 
splendent and vitreous. It is hard and 
easily frangible. Specific gravity from 3.08 
to 3.36. Before the blowpipe it melts 
into a greyish-white vesicular enamel. It 
was found in Ceylon and the Brazils in the 
16th century; and since that in Madagascar 
and Ava, in many parts of the European 
continent, and in Scotland. Two speci- 
mens have been analysed by Bergman and 
Vanquelin, the former was brought from 
Ceylon, the latter from Brazil. 
Tourmaline of Ceylon. Of Brazil, 
Silica 
37.0 ... 
... 40.0 
Alumina 
39.0 ... 
Lime... 
, 15.0 ... 
... 3.84 
Oxide of iron 
. 9.0 ... 
.. 12.50 
manganese. 
100.8 97.34 
Loss 2. 66 
100 
Tourmaline has been long celebrated for 
its electrical effects, which are exhibited 
by friction, and also by heating; but if it is 
made very hot, as beyond 200“ of Fahren- 
heit, it is deprived of its electrical proper- 
ties. The more transparent the tourma- 
line the stronger its electrical properties. 
It is sometimes cut and polished, and worn 
as a jewel ; hut on account of its want of 
transparency it is not very highly esteemed. 
The green coloured tourmaline has been 
described as the emerald ; the blue, as the 
sapphire ; and the crimson-red variety first 
found in Siberia, and since in Ava and Cey- 
SCI 
Ion, has been called the daurite, siberite, 
and rubellite. Mr. Greville is in possession 
of the most magnificent specimen of the 
red variety, it is valued on account of its 
beauty and rarity at lOOOt. 
SCHOTIA, in botany, so named from 
Richard Vander Schot, a genus of the De- 
candria Monogynia class and order. Natu- 
ral order of Lomentacea:. Leguminosae, 
Jussieu. Essential character: calyx five- 
cleft ; petals five, inserted into the calyx, 
closed by the sides lying over each other ; 
legume pedicelled. There is but one spe- 
cies, viz. S. speciosa, lentiscus-leaved scho- 
tia. It is a native of Senegal and the Cape 
of Good Hope. 
SCHRADERA, in botany, so named in 
honour of Henr. Adolph. Schrader, a genus 
of the Hexandria Monogynia class and or- 
der. Essential character : calyx a superior 
rim, quite entire; corolla five or six-cleft; 
stigmas two; berry one-celled, many-seeded. 
There are two species, viz. S. capitata and 
S. cephalotes. 
SCHREBERA, in botany, a genus of the 
Diandria Monogynia class and order. Es- 
sential character : calyx two-lipped ; co- 
rolla from five to seven-cleft ; capsule pear- 
shaped, two-celled, two-valved ; seeds from 
eight to ten, membranaceous winged. There 
is but one species, viz. S. swietenioides. 
SCHIVALBEA, in botany, so named in 
honour of Schwalbe, a physician, a genus of 
the Didynamia Angiospermia class and or-, 
der. Natural order of Personat^p. Schro- 
phulariae, Jussieu. Essential character : ca- 
lyx four-cleft, the upper lobe very small ; 
the lowest very large and emarginate. There 
is but one species, uiz. S. Americana. 
SCHWENKFELDIA, in botany, so 
named in memory of Caspar Schenckfelt, 
a Silesian physician, a genus of the Pentan- 
dria Monogynia class and order. Natural 
/)rder of Rubiaceas. Essential character : 
involucre four-leaved ; corolla funnel-form ; 
Stigmas five ; berry five-celled, many-seeded. 
There are three species. 
SCHWENKIA, in botany, so named 
from Martin Welhelm Schwencke, professor 
of botany at the Hague, a genus of the Di- 
andria Monogynia class and order. Natural 
order of Luridae. Scrophulari®, Jussieu. 
Essential- character : corolla almost equal, 
with the throat plaited and glandular ; sta- 
mens three, barren; capsule two-celled, 
many-seeded. There is only one species, 
viz. S. Americana, Guinea Schwenkia. 
SCI-fflNA, in natural history, a genus of 
D 2 
